Article

Tuesday, February 15, 2011

The Benefits Of Switch-Mode Power Amplifier Technology

How a switch-mode power supply actually works, how a switch-mode amplifier processes the signal, and more

It’s an answer to a sound company’s prayers: low-weight, cool-running power amplifiers with low current draw.

Look for switching power supplies in power amps, and switch-mode power amplifiers.

Compared to a standard amplifier power supply, the benefits of a switch-mode (switching) supply are lower size and weight. Compared to a standard analog power amplifier, a switching amp tends to run cooler and draw less current because it is so efficient.

In addition, the amp can be smaller and lighter because of compact circuits and less-massive heat sinks.

A switch-mode power supply creates DC from the AC mains power using transistor switches and other components. A switch-mode amplifier turns its output transistors on and off at an ultrasonic rate when it amplifies the audio signal.

A conventional amp with a switching power supply is often called a “switching” or “digital” power amplifier. But so is an amplifier that uses switching in its audio amplification.

It’s hard to tell what you’re getting, so you’ll need to check the product literature for details.

To sort out the differences, let’s explain how each system works.

Switch-Mode Power Supply
As we know from experience, amps of high power tend to be quite heavy. One of the main factors in that weight is the iron in the power transformer, which is part of the amp’s power supply.

To avoid core saturation at the 50 Hz or 60 Hz frequency of the AC mains, this transformer must be large and massive. That characteristic leads to minimal inductive reactance at those low frequencies.

It would be great if the mains frequency were a few hundred kilohertz. Then a smaller, lighter power transformer could handle the AC mains without saturating. That reduces the weight of the amp as well.

In a switching power supply, the 50 or 60 Hz line frequency is converted to about 100 kHz so that a junior-sized transformer can be used. The filter capacitors can be smaller too.

See Figure 1, below. From left to right in the diagram, this is the signal path:

1. The 60 Hz mains power is fed to the switching power supply.

2. The supply rectifies and filters the incoming AC power to convert it to DC. (This is the same principle used in any AC-to-DC power supply).

3. Connected to the DC output, transistor switches turn on and off at an ultrasonic rate. They chop the DC into pulses, which effectively creates a mains power supply at a high frequency. In other words, they convert DC to ultrasonic AC square waves.

4. Next in line is a low-weight isolation transformer. The square waves pass through it by magnetic induction.

5. Finally, another AC-to-DC circuit rectifies and filters the waveform to produce DC for the power amplifier circuitry.

A control circuit (not shown) senses the output voltage of the transformer and adjusts the switching circuit in real-time to regulate the final DC output voltage.

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As you can see, switching power supplies are more complicated than conventional supplies.

A benefit of this scheme is high efficiency. That is, the amplifier wastes very little power in the form of heat. Most of the incoming AC power is converted to amplifier output power.

How does that happen? Well, remember from Ohm’s Law that voltage times current equals power. When the voltage or current in a device is zero, so is the power.

The switching or “chopping” transistors produce no current when they are switched off, and produce no voltage when switched on, so they generate very little power as heat. This results in a highly efficient power supply.

Switching, Not Linear
So far we’ve examined the switch-mode power supply inside a power amplifier. Now let’s look at how a switch-mode power amp processes the signal.

Not too many years ago, all touring power amps were linear designs, not switching. You could call a linear power amp “analog” and switching power amp “digital,” although that usage is incorrect. In an analog amp, the output devices (power transistors) operate like a variable resistance, using the input signal to modulate a strong source of current from the AC mains.

That modulated current drives loudspeakers to make sound.

Now consider a switch-mode amp. Through a process called Pulse Width Modulation or PWM, the input signal modulates the width of ultrasonic rectangular waves that are generated in the output devices.

A low-pass circuit filters out the high frequencies in those analog rectangular waves, resulting in an analog, amplified signal that goes to the loudspeakers.

In one method (Figure 2), a high-speed comparator compares a high-frequency triangle wave with the audio input.

The output is a series of pulses whose width corresponds to the input signal’s amplitude and frequency.

From the comparitor, the signal goes to a switching controller. It drives a high-power switch, which generates an amplified version of the comparator’s PWM signal.

The amplified pulses are low-passed filtered to yield rounded, high-power waves to drive the load.

PWM varies the instantaneous duty cycle of ON states and OFF states. In contrast, an A-to-D converter using PCM (Pulse Code Modulation) generates a string of 1’s and 0’s thousands of times a second.

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Both approaches convert the “digital” signal back to analog at the output of the system.

We mentioned before that the output transistors are producing rectangular waves to be modulated by the input signal. These waves are generated by switching the power output transistors on and off at an ultrasonic fixed frequency, at the power-supply voltage of the amp.

Several pairs of transistors act as switches in push-pull mode – one transistor in a pair switches on while the other switches off, and vice versa. Class D amplifiers use that method, while Class I or BCA amplifiers operate with more sophisticated switching to generate the rectangular waves.

Class D amplifier designs have existed for about 50 years. But only in the last few years have these designs become affordable because of the enhanced power handling, efficiency and speed of modern output transistors.

As we said, the current or voltage in a transistor switch is zero when it is fully off or on. At those times, the current times voltage (power) is theoretically zero, and so is the power that is wasted as heat. In other words the efficiency of a switch-mode amp is near 100 percent.

Linear amps are a different story. Most of the time, current flows through the transistors and voltage drops across their terminals. The result is power dissipated as heat – energy that does not contribute to the signal feeding the loudspeakers.

A typical linear amp might have an efficiency of 30 percent. To prevent the amp from overheating, it uses fans and heat sinks. But a switch-mode amplifier requires less cooling and provides efficiency up to 80 or 90 percent.

No amp can be 100 percent efficient because some power is used by the input stage, so not all of the AC power from the wall outlet is used to drive a connected loudspeaker load.

Still, a switching amp can be considered “green” because it uses less energy than a conventional amp would for the same amount of output power.

Other schemes, such as making the power supply “track” the input signal, also improve efficiency.

Myth Vs. Reality
In referring to a switching power amp, the term “digital” is more of a buzzword than reality. The PWM signal in a switch-mode amp is actually an analog waveform that can be filtered. It’s digital only in the sense that it has two voltage states. It is NOT a sequence of numbers that represents the musical signal.

Many users are confused by the terminology. A “digital” amp is not an amplifier specially designed to reproduce digital sources such as CDs. It’s an amplifier that uses switching transistors in its power supply or in its audio output stages.

Products
Some power amps that include a switch-mode power supply are the QSC CX, DCA, OLX2, and Powerlight 3 series; Crown CDi, DSi, XTi, CTs, and I-Tech series, Lab.gruppen C and FP+ series, and the Yamaha P Series II. Some switch-mode (Class I) power amps are the Crown I-Tech HD Series.

Thanks to switching power supplies and switching power amps, we can roll in a rack of power without breaking our backs, and save energy too.

AES and Syn Aud Con member Bruce Bartlett is an audio engineer and audio journalist. He is the author of Practical Recording Techniques 5th Ed. and Recording Music On Location.

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TOA Promotes Bob Tamburri To Marketing Director

Tamburri brings over 25 years of industry experience to TOA.

TOA Electronics, Inc. has promoted Bob Tamburri to the position of Marketing Director.

Bob will be responsible overseeing product marketing, product management and marketing communications nationwide.

Bob has acquired over 25 years of experience in the audio industry. He has been involved in Product Marketing & Development for over 12 years, having served similar roles for other Professional & Consumer audio electronics manufacturers.

President & CEO, Mr. Masahiko Takao said, “TOA needs to strengthen and expand its product marketing activities in order to reach its goals.”

“Mr. Tamburri has been serving well in his role as Marketing & Product Manager and I believe that he can bring his experience and talent in that area to his new position.”

“He will be working to develop exciting new products for the US market, improve the visibility of TOA products and in communicating the “TOA Solution” advantage to the market.”

TOA Electronics Website

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The Bigger Picture On The Equalization Of Loudspeakers

Considering the off-axis as well as the on-axis response

The procedure often followed for equalizing a loudspeaker is to place the measurement microphone on-axis and adjust for the flattest frequency response.

This often involves boosting some filters when the axial response over a range of frequencies is lower than the average.

Those that are opposed to the use of boost filters may choose to arrive at the same resultant response by reducing (cutting) parts of the response to the lowest common denominator. This results in the same electrical curve, but without compromising headroom in the signal chain.

The whole procedure is initially performed looking at the direct field of the loudspeaker.

A Different Perspective
This article suggests a modification to this approach, by considering the off-axis as well as the on-axis response.

The goal of the equalization process is to produce a better sounding system for the audience. Yet a relatively small percentage of the audience sits in the on-axis position. It would therefore seem ill-advised to consider only the axial position when equalizing a system.

Another popular approach is to average the response of a number of seating positions to arrive at the best “common denominator” curve for the equalizer. This can also produce good results, but care must be taken to exclude artifacts due to room reflections from the measured data, as each movement of the mic places it in a different acoustic environment.

This makes it a challenge to limit the response measured at each test position to the direct field from the loudspeaker. Most contributions from the room will be random at different seating positions and not addressable by equalization. So, the spacial average is not a bad idea, it is just hard to implement.

Another Path, Same Destination
Another way to consider off-axis listener positions is to determine the base equalization curve for the loudspeaker by observing its 3-dimensional radiation balloon.

A properly gathered balloon will reveal the anechoic response of the loudspeaker at all listener angles.

Since the direct field of a loudspeaker is considered to be largely independent of the acoustic environment (at least at short wavelengths), direct field equalization based on balloon data has a strong theoretical basis.

Figure 1 shows the axial frequency response of a multi-way loudspeaker. The dip in response at 500 Hz is due to phase cancellation between multiple drivers in the box. A boost filter at this frequency center will restore the axial response to flat.

But observation of the entire radiation balloon at 500 Hz (Figure 2) shows that the devices come into phase at two off-axis positions, possibly producing a significant peak in the response for many of the audience members.

The “correction” made to the on-axis response will produce an even less ideal response off-axis where a greater number of listeners are located, or even worse at a microphone position causing a feedback problem.

Devices that have a destructive phase offset at one listener position are likely to have an in-phase relationship at another. The notch might better be addressed by the use of precision signal delay between the elements.

In general, for a single transducer equalization will inflate or deflate the balloon at a specified octave band. The same effect occurs at all angles around the device.

But what is often needed is a re-shaping of the balloon, which can be accomplished by using multiple elements and varying their physical spacing and relative delay.

This is the heart and soul of beam-steered loudspeakers. Boost and dip filters applied based on the axial response only can change the directivity of a multi-element device, since the phase shift introduced by the filter can cause a change in the way that the multiple elements interact.

It should be noted that psychoacoustics also plays a role in this.

Peaks in a frequency response are much more audible (and bothersome) to humans than dips in the response. We are more aware of “too much” than “too little.”

A safe approach to equalization that embodies the theories described herein is to avoid the use of boost filters when calibrating a sound system, since it is better to have “too little” than to have “too much.”

If a sound practitioner used the axial response for equalization, and cut-only filters to smooth the resonant peaks, acceptable results would likely be attained for most listeners since off-axis lobes will not be “inflated” by the process.

Conclusion
Loudspeaker balloon data is useful for direct field equalization of a loudspeaker. It is plausible that the complete equalization of the direct field can be determined from the axial frequency response and the spherical balloons.

The remaining equalization chores can be left to the installer or commissioner of the system. This can include compensation for boundary loading, device coupling, etc.

The possibility also exists based on the above for a manufacturer to provide an appropriate equalization curve in the form of a simple magnitude vs. frequency plot or as a setting that can be imported into popular digital signal processors.

Pat and Brenda Brown head up SynAudCon, the leading independent organization for in-depth, practical audio education.

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NewTek Releases TriCaster Virtual Set Editor

New application lets users personalize their HD production with customizable sets.

NewTek  has announced the release of NewTek TriCaster Virtual Set Editor (VSE), which allows TriCaster TCXD850 and TriCaster TCXD300 users to customize TriCaster high definition (HD) virtual sets to fit their production needs.

TriCaster Virtual Set Editor will be showcased on the main stage of NewTek booth E20 at the Broadcast Video Expo 2011, February 15-17, in London.

With TriCaster Virtual Set Editor, producers get exclusive TriCaster VSE Sets that produce real-time reflections and specular highlights, and have a wide variety of elements that can be edited.

TriCaster VSE users also have the option to create their own virtual sets by populating Layer Sets with their artwork, or composing layers in Adobe® Photoshop®, and then importing the layers into TriCaster VSE, which instantly transforms the PSD file into a Layer Set for use in VSE.

Once a TriCaster virtual set has been customized with Virtual Set Editor, users can easily export it for immediate use in their TriCaster live production.

Virtual Set Editor includes three TriCaster VSE-compatible virtual set content files, three Layer Sets and three PSD examples.

For a limited time, VSE will ship with three bonus sets, valued at over $1000, providing early buyers with a total of six VSE-compatible virtual set content files. Additional content may be sold separately.

“With the quantity of live shows being produced every day, both for broadcast and the Web, it’s crucial that producers are able to personalize their programming with a look that viewers will recognize,” said NewTek Executive Vice President of Engineering, Andrew Cross.

“TriCaster VSE lets users of TriCaster TCXD850 and TriCaster TCXD300, customize live virtual sets or create them from scratch. The intuitive interface allows for quick and easy navigation, and producers will find it a very affordable approach to designing a studio environment that is every bit as unique as their content.”

NewTek TriCaster Virtual Set Editor provides the ability to:
• Change the color and tone of set elements
• Apply custom logos and artwork to sets
• Replace background images with video or images of choice
• Show or hide select set furniture and fixtures
• Add custom backgrounds and frames to double-box effects
• Set start and end framing position of virtual zoom
• Adjust placement (position, scale and rotation) of live video inputs
• Add your own artwork to Layer Sets to create custom virtual sets
• Import layered Adobe® Photoshop® files to create original HD virtual sets from 2D images

With TriCaster, anyone can simultaneously produce, live stream, broadcast, project and record HD and SD network-style productions.

A single operator or small team can switch between multiple cameras, virtual inputs and live virtual sets, while inserting clips, titles and motion graphics with multi-channel effects.

TriCaster is used by broadcasters, sports organizations, schools, houses of worship, government agencies and others to provide a new level of extended programming and content to their audiences.

The NewTek TriCaster Virtual Set Editor is available now and retails for US$995.

NewTek Website

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Monday, February 14, 2011

Clear-Com Names Larry Estrin Strategic Technology Specialist

Will be leveraging his extensive knowledge and experience in the live sound and broadcast markets to help promote the Clear-Com brand to industry professionals

Clear-Com has named industry veteran Larry Estrin as its new strategic technology specialist. As a result of the merger of HME’s Pro Audio Division with Clear-Com, Estrin is now joining the Clear-Com team to promote the brand globally, build sales opportunities and assist with product development and marketing activities.

Estrin will be leveraging his extensive knowledge and experience in the live sound and broadcast markets to help promote the Clear-Com brand to industry professionals. His involvement in many landmark events, such as the first multi-satellite global broadcast of a major concert, live stereo broadcast of the Olympic Opening Ceremonies, stereo broadcasts of the Grammys and Academy Awards, as well as numerous other high-profile projects for the White House, NFL and Disney, has earned him the status of being an educational and informational resource. 

From his work in the trenches, he is able to easily identify the issues that current and potential customers are facing and help to design solutions that best meet their needs.  In addition to working with users, he will act as a resource to Clear-Com’s product management department, taking an active role in the development of products, solutions, specific workflows, and framing existing capabilities of the company’s award-winning products in ways to better solve the challenges of this industry.

To date both Clear-Com and HME have received Technology & Engineering Emmy Awards. Clear-Com was recognized for the creation of The Belt Pack: Distributed Amplifier Systems in Live Production, and HME was awarded for the Development of the Wireless Intercom System.

“I am very excited to have the opportunity to become part of a company that shares my philosophy of working with the client to determine what their needs and goals are and to develop solutions that help meet these needs,” says Estrin. “Clear-Com is constantly evolving its products as the industry changes, and continues to develop cost-effective solutions for our global partners. I believe this union of Clear-Com and the HME Pro Audio Division, the originators of wired and wireless communications, respectively, will lead to new horizons in global production communications.”
 
“We are happy to have someone with such extensive field and industry knowledge as Larry become a part of the Clear-Com team,” says Matt Danilowicz, president of Clear-Com. “Much in the spirit that drives Clear-Com, Larry has consistently been an innovator—constantly looking at new ways to deliver solutions to clients’ needs. We are very much looking forward to the ideas he will share with us and, in turn, that we will bring to our customers.”

Clear-Com Website

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A Vision Of Connectivity

Inside the systems for the Jones Convocation Center at Chicago State University.

When it opened in late 2007, the Emil and Patricia A. Jones Convocation Center (JCC) on the campus of Chicago State University (CSU) began what is sure to be a long tenure as the home of the men’s and women’s basketball teams, as well as a vital role as a sports, entertainment and community hub on the city’s south side.

Just one thing was missing - sound reinforcement up to the premium standards of the rest of the $47 million multi-purpose venue.

That facet has now been addressed, and then some, with the recent implementation of not one, but two specific-purpose systems capable of meeting and exceeding expectations for any event the facility hosts.

The JCC comprises more than 140,000 square feet, centered on an arena offering enough assembly space to seat up to 6,000 people, topped on one side by a sky box lounge with a capacity for 100 more.

Surrounding spaces host eight locker rooms, a weight room, a training room, academic study rooms, conference and receptions areas, offices, walkways with multiple concession areas, and much more.

Budget constraints impacted the sound reinforcement situation in the initial construction phase, so a temporary arena PA solution was put into place and other events requiring more dynamic support were served with rental systems.

While not ideal, the situation actually turned out to be somewhat of a blessing in disguise, affording university and venue staff the luxury of formulating plans to more precisely meet the real-world needs being observed and experienced on a regular basis.

So when funding became available in 2010, they were ready. After going through a thorough RFP and selection process, CSU began discussions with Sound of Authority (SOA), a leading Chicago sound and production company, about implementing specific solutions.

SOA, founded by president/ CEO Ernest (Ernie) Greene in 1978, has fostered and earned a long professional relationship with the university in supporting numerous events and projects stretching back more than a decade.

The team was further enhanced with the addition of Aaron Johnson, CTS. As the head of Chicago-based Johnson AV Engineering, he has successfully collaborated with SOA in the past and brings to the table a strong resume of designing systems and managing high-level projects.

Greene and Johnson interfaced with Yvette Warren, CSU director of the office of meetings and events, as well as Jerome Jackson, whose title is external manager for the office of meetings and events, but more accurately, he has a dedicated hands-on role with system and production issues at the venue.

Broader Goals
The arena system needed to meet two often disparate goals: meet public address requirements for sporting events and other general uses as well as deliver true full-range dynamic performance for concerts, convocations, theatrical productions, and so on. Further, it needed to be flexible – not just anchored to one position and also capable of being configured in multiple ways.

“The university staff was excellent in defining the broader goals to be achieved, and communicated well their ideas about flexibility and connectivity,” Johnson notes. “They’re great to work with and very open-minded about the concepts we suggested about where we wanted to take this.”

After some investigation, the sound team came to one inescapable conclusion: dual systems would be necessary to fully meet the vision for the project.

One would incorporate concert line arrays; the other, distributed loudspeakers to cover all seats in the arena bowl. Yet while this involved two complete sets of “racks and stacks” (amplifiers and loudspeakers), most of the rest could be accomplished with shared components and infrastructure.

It started with a digital backbone, and with audio distributed on a local area network where it could be accessed at multiple points not only in the arena, but also in the greater facility. Johnson has deployed CobraNet successfully on several projects in the past and felt it would be an optimum solution here as well.

“CobraNet is stable and proven, really almost a legacy technology at this point, which is a good thing when you want to guarantee success,” Johnson explains. “We also wanted to avoid copper wire for signal transport as much as possible, given the size of the venue, the expense it would incur, and to avoid the EMI (electromagnetic interference) problems that can happen with huge copper cable runs in venues and systems of this scope.”

Miles of cable trays running throughout the outlying areas of the facility accommodated Cat-5e cabling runs needed for this audio distribution system. In addition, going with Cat-5e made for an easier time in routing cable within the existing infrastructure.

There are two bundles on the Cobra- Net network. One is the drive line from the input of the front of house console to the system’s overall digital signal processing (also networked), and the other goes from the processing to Whirlwind CO2a 2-channel output modules in the sky box lounge and ticket booth, both of which receive a matrix mix stereo feed.

“As these types of applications go, this one is pretty light, but we have plenty of capacity in this network,” Johnson says.

“Plus it is expandable for any future need, so anywhere we want to add an audio or a submix feed, it’s essentially a matter of adding a Cat-5e cable and running it where it needs to go.”

Selecting A Route
Residing in a secured steel rack in one of the corners of the arena’s main floor is a BSS Soundweb London BLU-800, which is the “brains” of the entire system. It offers configurable I/O, configurable signal processing, CobraNet audio and a high-bandwidth, fault-tolerant digital audio bus.

BLU-800 also offers an open architecture that is fully configurable through a (Harman) HiQnet London Architect interface that offers a palette of processing and logic objects in a “drag and drop” method of configuration, providing a simple and familiar design environment.

It supplies all system processing, routing and preset configurations, and in essence, everything routes in and out of the BLU-800 via its digital audio bus, and it is broken out in 8-channel blocks via the BLU BOB break out boxes.

The onboard BLU-Link network transport, which can carry 256 channels of fault-tolerant, low-latency audio at 48k Hz/24-bit, or 128 channels at 96 kHz/24-bit across a standard Cat-5e connection, is the primary feed to both the power amplifiers for both sound reinforcement systems, which are rackmounted at the catwalk level. (Note that the amplifiers for the subwoofers are mounted with BLU on the floor level.)

“BLU is the primary feed to the catwalk equipment, and it’s a very efficient, cost-effective way to route signal up there and back down to the floor as needed,” Johnson states.

“This allowed us, for example, to have the amplifiers for the subwoofers on the floor level, meaning that a really long cable run from the catwalks was not necessary.

“This is the first time we’ve deployed the BLU platform. It’s extraordinarily flexible, yet stable, and with BLU-Link, BSS has really kind of changed the game with respect to audio networking and transport. One other important thing to point out is that latency of this network is negligible, having no impact at all.”

Custom panels are mounted on wall surfaces on each side of the arena to provide plenty of I/O capability. Each panel includes four line-level inputs, CobraNet and EtherSound patching, and eight channels for production intercom. The north end panel also provides four output channels for subwoofers and front fill loudspeakers.

Another panel at the north end, also housed in a secured steel box, includes a BSS 9015 interface for the BLU-800, providing easy selection of the desired system preset mode. A keyswitch included in this panel allows for turning on/off the entire system, with all electronic components on LynTec power sequencers.

Plenty Of Digital
The client stipulated a preference for Yamaha digital consoles based on familiarity, with a study of available models leading to the selection of two Yamaha MC7-48 models – one for the house and the other for monitors. Both are built into portable road cases (along with their respective stage boxes and mic preamps) so that they can be stored in an equipment room, as well as easily moved around wherever they’re needed in the arena, pending the system configuration.

“We determined that both the Yamaha PM5D and PM1D were a little bit of overkill for this application, so focused on the M7CL, which is a fine board with plenty of capability,” Johnson explains.

“And, Yamaha had just come out with the EtherSound stage box, which is an attractive option and one that we wanted for the house console. And, we also wanted to utilize a digital snake of some sort so that all of the mic preamps were as close to the stage as possible.”

Further, both house and monitor consoles are equipped with CobraNet output cards, so if, for example, the house console has a problem, the monitor console can be seamlessly swapped in, and vice versa. All of the monitor outputs are identical in their assignments, furthering the ubiquitous nature of the two consoles.

Another handy feature of the boards is that although the 48 analog inputs are replaced by EtherSound ports, the M7CL-48ES retains eight OMNI inputs and eight OMNI outputs that can be used for direct analog connection. These provide an ideal way to insert outboard processors and other equipment.

The sound team also put together a portable rack with components for basic stand-alone use and to provide some additional enhancement at the front of the house.

It includes a Rane MLM 65 6-channel analog mixer for low-channel- count, light-duty mixing, joined by a BSS FCS-960 graphic EQ inserted on left and right outputs, and a Denon DN-C550R dual CD player/recorder retained from the previous system.

The rack also incorporates a custom panel providing six microphone and two stereo inputs, as well as two line-level outputs. “We wanted a simple option, one that is easy to use and all of that good stuff,” Johnson notes. “So it works as a stand-alone solution for small applications, in addition to offering additional EQ and sound source input when patched in for larger productions.”

As with all other electronic system components on this project, rock-solid surge protection is provided by SurgeX SX Series units in the rack. “You just can’t beat SurgeX when you’re serious about protecting your gear,” Johnson adds.

Blanket Coverage
Johnson performed EASE modeling in determining loudspeaker layouts that would ensure optimum coverage when the system is in its distributed PA and concert modes. The arena is a “typical” configuration, with seating surrounding the main floor all the way around and split into upper and lower levels. Sightlines are excellent – there isn’t a bad seat in the house.

The PA system main loudspeakers are from Danley Sound Labs, all offering the company’s proprietary Synergy Horns.

Along the long sides of the arena, pairs of Danley SH 60 full-range loudspeakers (60-degree by 60-degree dispersion) are flown with cabinets in horizontal position to cover each zone, one handling the upper seating region and the other assigned the lower seating region.

Coverage to the corners and ends of the arena by single Danley SH 69 full-range loudspeakers (90-degree by 60-degree dispersion with rotatable horn) flown in the same grid pattern. Typically just one of these loudspeakers is needed to cover its respective zone from top to bottom.

“The client wanted true full-range audio even though this is a distributed approach, and that’s why we went with the Danley boxes - they are substantial,” Johnson says. “The pattern control of these boxes is excellent, which makes it really easy to lay it out in terms of coverage.”

All of the Danley loudspeakers are driven by Lab.gruppen C68:4 4-channel power amplifiers providing 1,700 watts at 4 ohms. The Danley units are 4-ohm cabinets, so each amp channel drives a single loudspeaker.

The arena floor covered with Electro-Voice QRX Series full-range loudspeakers retained from a previous system. These are mounted in the main, central scoreboard region, and are biamped (one channel each for LF and HF) by EV P2000 amplifiers in the main floor rack.

The Full System
Both Sound of Authority and the client sought L-Acoustics loudspeakers for the concert system, leading to the selection of larger format KUDO line arrays. As a result, arrays of up to eight KUDO modules can be flown in a stereo pair at one end of the arena or on one of the long sides. Flying infrastructure is provided at both locations for quick, convenient deployment.

KUDO features proprietary K-LOUVER variable directivity supplying 50-degree/110-degree symmetric coverage or 80-degree asymmetric coverage, perfect for an application demanding extra flexibility.

This is furthered by splay angles up to 10 degrees for increased vertical coverage when needed. The rigging system is ergonomic and fast, which aids in quick system transitions from one location to the other.

Four L-Acoustics SB28 dual-18 direct-radiating subwoofers extend response down to 25 Hz, and as an interesting side note, these are also used increasingly with the distributed PA system to add a bit more “oomph” during basketball games. All of the L-Acoustics loudspeakers are driven by companion LA8 amplified controllers that are rack-mounted with the Lab. gruppen amplifiers in the equipment rack on the catwalk level.

As noted, presets for both concert and distributed PA are provided by the BSS processing. Six presets are available, and some of them combine elements of both loudspeaker sets. Options include concert north (one end), concert north with rear fill, concert east (long side), concert east with rear fill, arena (full distributed), and arena with subwoofers.

Also available for any application are 12 proprietary 15-inch passive monitor wedges and four Bag End TA5000 passive wedges, as well as a Whirlwind passive splitter (48 by 10) with ground lift. Up to three more Yamaha EtherSound stagebox mic preamps can be added, under the control of the house console.

A nice assortment of Shure wired and wireless microphones are also on hand. The six channels of Shure UHF-R wireless have companion handheld transmitters as well as bodypacks that can be outfitted with Shure lavalier mics or Countryman E6 earset mics.

Wired mic choices include Shure SM Series dynamics and condensers, and there’s even Beta Series drum mics and Whirlwind Direct2-JT direct boxes. All portable system gear is stored in a secure equipment room right behind one of the main entrances to the main floor.

“What was envisioned has now been achieved,” Johnson concludes. “It’s a very flexible yet stable system, or perhaps more accurately, series of systems. Essentially all you have to do is plug everything in where you want it, select your preset and it’s a go.”

Take our extensive Photo Gallery tour of the installation. For those who are interested, the article is available for download (pdf) in its entirety.

Keith Clark is editor in chief of Live Sound International and ProSoundWeb

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Audio-Technica Introduces The U855QL Cardiod Dynamic Gooseneck Microphone

The unit is ruggedd and designed to provide excellent intelligibility in environments with excessive ambient noise.

Audio-Technica has announced the introduction of the U855QL Cardioid Dynamic Gooseneck Microphone.

Designed for use as a high-quality talk-back, paging and dispatch microphone in commercial, industrial and entertainment applications, the U855QL features a versatile gooseneck design that allows for flexible positioning and dependable performance.

Its tailored frequency response ensures excellent intelligibility in environments with excessive ambient noise.

The U855QL’s easily adjustable gooseneck permits quick positioning, and the quick-mount design includes an XLRM-type connector insert at the base, allowing the microphone to be plugged directly into an any standard XLRF-type surface or cable connector.

The unit features extremely rugged all-metal construction for long-lasting performance. The low-profile element provides a uniform cardioid polar pattern that reduces pickup of sounds from the sides and rear, improving isolation of the desired sound source.

The microphone’s protective screen reduces wind noise and “popping” when used close to the sound source.

U855QL Specifications:
Frequency Respons: 150-16,000 Hz
Open Circuit Sensitivity: -53 dB (2.2 mV) re 1V at 1 Pa
Impedance: 600 ohms
Weight: 9.8 oz (278 g)
Dimensions: 17.64” (448.0 mm) L, 1.18” (30 mm) head diameter, 0.75” (19 mm) base diameter
Output Connector: Integral 3-pin XLRM-type
Color/Appearance: Non-reflective black finish

The U855QL Cardioid Dynamic Gooseneck Microphone is now available with a U.S. MSRP of $130.00.

Audio-Technica Website

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Sierra Video Appoints Asia-Pacific Region Sales Manager

Pang-Hung Cheung is based in Hong Kong and has an extensive history in broadcast and post-production markets throughout Asia.

Sierra Video has announced the addition of Pang-Hung (PH) Cheung as its Regional Sales Manager for the Asia Pacific region. 

With this new position, Sierra Video establishes a dedicated presence in Asia to augment opportunities in the region’s aggressively expanding video markets.

Sierra Video is experiencing a rapid increase in business opportunities for its products and systems throughout Asia and the Pacific region. 

Mr. Cheung is charged with supporting the company’s existing distribution channels in key markets and expanding its reach to customers by establishing additional channels.

“Our products enjoy excellent reputation in the region, both in terms of functionality and reliability, as demonstrated by our steadily growing sales,” said Dr. Adel Ghanem, President of Sierra Video. 

“PH’s tremendous technical and sales experience in the Broadcast and Professional video markets will support and enhance Sierra’s growth in the region. “

Mr. Cheung is based in Hong Kong and has an extensive history in broadcast and post-production markets throughout Asia.  Focused on video system design and product sales over the last 20 years, he is uniquely qualified to provide real-world system expertise to Sierra Video customers. 

Mr. Cheung has worked in broadcast markets in the Asia Pacific region, and has served as a technology liaison with key manufacturers in the broadcast field.

Prior to his work in product sales and system design, Mr. Cheung served in an engineering capacity at a number of broadcast and production operations. 

He helped create the first full SD digital studio facilities in Hong Kong and the first SD digital studio for China Central Television.  Mr. Cheung received a MSc from UMIST in the UK and holds engineering certifications in the UK, Europe, Hong Kong and Australia.

Sierra Video Website

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Friday, February 11, 2011

Washington State Christian Life Center Selects Tannoy VQNET Full Range Speakers

VQNET 60s were selected due to the requirement of a loudspeaker that offered highly intelligible speech reinforcement and detailed and musical reinforcement of live and recorded music.

For over 80 years, the Christian Life Center (CLC) of Port Orchard has been a fixture on Washington’s Kitsap County.

Very much a multi-purpose worship space, in addition to their own services, praise concerts and old-fashioned hymn nights, CLC also functions as a center for community events.

They regularly host evangelical community outreach efforts such as their regular August Cruisin’ Sunday car show and food drive, local police awards ceremonies, as well as various pageants, dinners and guest speakers.

Over time, as their ministry has expanded and their worship has become ever more contemporary, CLC began to take stock of their existing A/V infrastructure with an eye to better serving their growing congregation by updating their systems. Initially their attention was centered primarily on their video infrastructure, said Chad Rose of Poulsbo A/V design/build firm, Rose Media.

Since Rose’s original discussions with CLC roughly three years ago, however, the church began to realize that it was their audio system that needed the most attention.

Part of one of the largest network of Pentecostal congregations in the world, CLC serves both the spiritual and worldly needs of its congregation by placing an emphasis on developing and maintaining strong relationships with God and members of the community at large.

In any relationship transparent communication is key and in a congregation that hovers between 700 and 800 people on any given weekend, maintaining that relationship can be difficult if people can’t make out what others are saying.

“Clarity of sound and not being able to hear was becoming an issue during services,” Rose says, “so audio quickly rose to the forefront as the priority when funds became available.”

Designed and installed by Rose and completed in September 2010, the systems specified for the CLC do include some video upgrades, but Rose’s primary focus was a comprehensive overhaul of the audio infrastructure in the CLC’s main auditorium, and the installation of a system featuring key components by Tannoy and Lab.gruppen.

One of the reasons Rose chose Tannoy VQNET 60s for the project was the requirement for a loudspeaker that offered both highly intelligible reinforcement of speech as well as clear, detailed and distinctly musical reinforcement of live and recorded music.

With a contemporary music program, often featuring various incarnations of full electric praise bands and an acoustically demanding environment, achieving that was not without its challenges.

“The room is a big rectangular box with lots of reflective surfaces,” Rose says, adding that no acoustic treatments were installed when it was first built.

“Even when you don’t have the sound on and you’re just talking to someone, the room is very live – so to find a speaker system that could perform well in there was challenging.” As was finding a place to put them, he adds.

“There aren’t many rigging points in the ceiling – it’s not designed to support external weight.” As a result Rose called in the structural engineer who had worked on the original construction to source out just where they could hang the speakers.

“We kind of knew what we wanted based on other churches,” puts in CLC media director, Larry Rubio, who has been volunteering at the church for the past 25 years. “We wanted to get away from the mono sound of the previous system and to reach the corners of the sanctuary.”

“To have good sound throughout, rather than in just one section.” Finding a way to achieve their vision, however, given both the lack of acoustic treatments and limited rigging points was unclear until Rose introduced the VQNET 60’s into the mix.

The CLC had other goals as well, Rose explains. Among them, making lower stage volumes possible for performers and enhancing their technician’s ability to reconfigure the system for different applications easily. But, first and foremost, they required dramatically improved intelligibility and coverage. “That’s why Tannoy was chosen. It had the most accurate coverage and was still intelligible at a high SPL.”

To meet their needs, Rose’s design departed from the pre-existing system’s configuration immediately. “The original system was a mono cluster and didn’t include any low end support,” he says. “Also, the side seating sections of the room weren’t covered by the system, so by putting in an expanded LCR system we were able to get more coverage on the sides and provide a little bit of a stereo field.”

The mains consist of four Tannoy VQNET 60s – two mounted in the center of the stage directly in front of the auditorium’s wooden proscenium, and one 15-feet to each side of that center cluster, just above the edges of the roughly 40-foot x 26-foot stage.

“For optimum coverage of the side seating sections the system is configured in stereo and utilizes cross matrixed, delayed feeds of the left and right channels in the center cluster,” Rose explains.

Low frequency reinforcement is provided by four OAP Audio TR-218 dual 18-inch subs flown to the left and right of the outer Tannoy VQNET 60s, placed just above the church’s two video screens. “Tannoy would have been our first choice,” says Rose, explaining that the choice of the OAP product was motivated purely by budget considerations.

Control over the mains and over eight Aviom personal monitor stations onstage is provided by a Yamaha M7CL 48 Channel Digital Console with an Aviom card installed. An additional Yamaha O1V console in the facility’s dedicated broadcast booth is also connected to the front of house console.

DSP is provided via the VQNET 60’s onboard signal processing. “The whole system is on VNET,” Rose says. “There’s a VNET controller for the subs and a VNET interface at front of house. So for ongoing maintenance you can just plug into the USB port, log on and change settings.”

One Lab.gruppen C Series C 88:4 amplifier is located in the same pre-existing forty-space rack as the VNET Controller and powers the passive subs. Because of the choice of Lab.gruppen, however, that rack looks far emptier than it once did. “The old system had a total of nine amps for the center cluster – so we went from nine amps to one that puts out 2100 Watts per sub. With the system being largely self-powered it worked well to have one single amplifier that can perform like two or three.”

“It also worked well to have the tight pattern of the VQ speakers,” he adds. While he’d heard good things about the boxes from friends prior to specifying them, before deciding on Tannoy Rose tried several other products in EASE models.

“We tried a couple of line array options, but line arrays wouldn’t have performed well in the space. Also I’d have to have a really wide array to cover the room, and then we’d be getting a lot of reflections off the side walls.”

Overall, the compact Tannoy VQNET 60s simply outpaced the competition, putting out more SPL with fewer boxes. “As far as modeling goes, they performed a lot better than the other options and the price point was also good compared to other products. They really perform like a line array in a box. It’s amazing how accurate and precise the coverage is.”

Beyond that, Rose says, “The system really fun to listen to music on. Once we got it in the air I dialed it in, sat and listened – just by myself – and they sound really nice, like studio monitors.”

High praise, but based on something Rose noticed while listening to a track on the system that he’d heard many times before, Lady Antebellum’s ‘Need You Now’.

“It was crazy. I’d never noticed that there’s this whole telephone conversation at the beginning. I’d just never heard it, but it goes through the whole introduction and it was like ‘wow, that’s actually there’. The same experience I’ve had with studio monitors.”

Most importantly, the church is more than satisfied with the system. While there was a lot to accomplish when they started, they’ve now got a lot to be happy about. “It’s a big difference from where we came from,” says Rubio.

Tannoy Website

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Thursday, February 10, 2011

Kramer Introduces Twisted Pair Transmitter/Receiver Pair With EMP Protection

The units can transmit computer graphics, stereo audio and RS-232 signals over long distances with advanced EDID handling

Kramer has announced the introduction of the TP-123-od/TP-124-od twisted pair transmitter/receiver pair.

The TP-123-od transmitter and TP-124-od receiver are a high-performance twisted pair solution for sending computer graphics video, unbalanced stereo analog audio and unidirectional RS-232 control command signals over long distances with advanced EDID handling capability and unique “Overvoltage Defense” EMP protection built-in.

The TP-123-od and TP-124-od offer a compact and inexpensive solution for multiple signal transmission over long distances.

The TP-123-od and TP-124-od are part of Kramer’s new “od” (Overvoltage Defense) family of twisted pair transmitters and receivers, specifically designed to include electromagnetic pulse (EMP) protection.

The EMP of nearby lightning strikes can damage sensitive electronic equipment by inducing a high momentary surge in voltage. Kramer’s “od” products, while manufactured for indoor use only, are designed to protect against such occurrences.

These models are HDTV compatible, and support computer graphics video resolutions up to WUXGA and HDTV resolutions up to 1080p.

The built-in EDID capture and emulation capability ensures that the correct signal resolution is output to any monitor connected without the need for an external EDID capture device.

The TP-123-od transmitter has one computer graphics video input on a 15-pin HD connector, one unbalanced stereo audio input on a 3.5mm mini jack, one RS-232 input on a terminal block connector and one twisted pair output on an RJ-45 connector to send the signals to the receiver.

The TP-124-od receiver has one twisted pair input on an RJ-45 connector for the incoming signals from the TP-123-od, one computer graphics video output on a 15-pin HD connector, one stereo audio S/PDIF RCA connector output, one unbalanced stereo audio output on a 3.5mm mini jack and one RS-232 output on a terminal block connector.

The TP-123-od and TP-124-od has a system range of more than 300ft (more than 100m), and employs Kramer’s Power Connect feature, where a single connection to the transmitter can power both the transmitter and receiver (for distances over 150 ft, high quality CAT 6/7 cable must be used for the Power Connect feature).

The required 12V DC is transmitted through the twisted pair cable, along with the other signals to the compatible receiver. The TP-124-od has trimmers to adjust the signal “Level” and “EQ” to ensure proper image quality.

The TP-123-od can store and recall a default EDID setting in non-volatile memory allowing convenient and accurate connection to any source. EDID (Extended Display Identification Data) is 128 bytes of data that a display provides to the graphics card of a connected computer source.

The EDID describes the display’s capabilities so that the source can output the best possible signal for that display. The source and the display exchange this information over the Display Data Channel 2 (DDC2) using pins 12 and 15 of a standard 15-pin HD computer graphics video signal connector.

The advanced EDID handling capability of the TP-123-od ensures that if a display is turned off, temporarily disconnected or is out of communication with the source, the source continues to output the best possible signal resolution.

The EDID emulation makes the source think that the display is still directly connected even when the EDID information is unavailable directly from the monitor.

Systems including matrix switchers, distribution amplifiers, 5-wire coax signal distribution and twisted pair range extenders, for example, are unable to pass EDID information since pins 12 and 15 from the monitor are not available to the source in these applications.

In all these instances the TP-123-od can be used to capture the EDID information from the display and provide that EDID communication to the source, assuming that a proper 15-pin HD VGA cable that passes all 15-pins is used between the source and TP-123-od. This allows the source to output the best possible signal for that display device.

The TP-123-od and TP-124-od are housed in the Compact Kramer TOOLS enclosure. They carry a list price of $465.00 per unit in the United States and are currently in stock and available from Kramer Electronics sales companies around the world.

Kramer Website

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Cable Anatomy 101: A Look At Six Key Factors To Keep In Mind

Like roads and highways, cables can be utilitarian by nature, but through making the right choice to arrive at our destination we can achieve clean, optimized audio.

Cable selection presents two primary challenges: myriad choices and overall quality.

I’ve explored these challenges and have defined six factors that can help point you in the right direction.

These factors include appearance, durability, flexibility, sonics, conductivity and shielding. Let’s have a look.

Appearance
Understand the difference between the look of quality - like shiny gold-plated connector housings - and actual quality construction and materials.

A primary problem arises when assumptions are made that the materials inside a cable housing are as fancy as those that can be easily seen in the connector.

For example, molded cable housings can hide poor construction, such as inadequate shielding.

Copper is the most widely used material cable component, offering high conductivity. (Silver is also highly conductive, but cost can make it impractical.)

It only makes sense that signal should travel through copper, tip to tip.

If possible, when evaluating cable, open the connector and check the soldering. Make sure there are no blobs (too much solder) and no contaminates from wire insulation or foreign particles.

The solder should have a smooth slightly shiny surface. A dull solder joint indicates poor workmanship and a poor or non-existent connection (termination).

Another termination method avoids foreign materials (like solder), which can increase the risk of interfering with signal flow.

One process is IDC (insulation displacement connection), done by creating a cradle for the wire in the shape of a “V.”

When the wire is inserted into the cradle, it’s pushed to the smallest point of the V, stripping away the cable insulation at the contact points. (This technique does require sturdy strain relief; more on this later.)

A more recent termination technique relies upon ultra-sonic welding, a process by which the center conductor and the connector are vibrated together at a high rate of speed while being compressed.

This causes them to intermingle and fuse together as one.

Durability & Flexibility
Exposure to temperature, humidity, chemicals, floor traffic and the like can wreak havoc on cables and connectors.

Dirt is an extreme abrasive, while foot (and wheel) traffic frequently shred many types of shielding, internal insulation and even the center conductor - sometimes without showing noticeable outer jacket damage.

Durability and flexibility may be opposing demands. One can come at the expense of the other.

Durability may come in the form of strain relief, termination, the outer jacket and the materials used inside the cable. The outer jacket surrounds the individual conductors and is intended to protect the shielding and conductors from the elements.

While outer jackets are commonly made of polyvinyl chloride, differing chemical compositions and blends can yield a similar look with vastly differing strengths and ranges of flexibility.

A cable that is thicker might look and feel more durable, and if that size is due to a double-thick outer jacket, flexibility can actually be increased.

Simply, the cable can be more impervious to damage, meaning it can be used in more applications.

The size of conductors, as well as the types of shielding, also impact durability and flexibility. Understand that everything comes at a price.

A more durable cable will (and should) cost more. You get what you pay for.

The term strain relief refers to the relief of strain at the point where a connector attaches to a cable - the termination point.

Strain can come from several different sources, such as pulling on the cable rather than grasping the connector to disconnect; stepping and pulling on the cable; repeated tight coiling, flexing and other common abuses.

Sonics
The sonics of a cable (or its “sound quality”) can be assessed in several ways. Like loudspeakers and amplifiers, cable can “color” sound - this can be good or bad depending on individual taste and desired effect. To each his/her own.

Colorization of sound by a cable is based on shielding and/or conductivity. Some combinations and proportions are potentially pleasing.

Capacitance and inductance affect frequency response the most. We tell people to look at the capacitance per foot figure to evaluate how the high frequency response may be affected over long runs. It’s usually measured in per foot (pF), so short lengths aren’t affected much.

The materials used as the inner conductor insulators also affect the capacitance and the signal propagation.

Beyond this, it’s vital to listen for noise and hum, both with and without signal present.

Any extraneous noise can be prime indicator of poor construction techniques or substandard materials.

It’s important to listen to a length of cable with it terminated properly at the source end.

An open-ended cable will have an extremely high impedance, making it act like an antenna - as soon as a mic is plugged in, the noise disappears.

Conductivity
While copper has a certain amount of resistance to signal flow, steel and aluminum have significantly more. This resistance dissipates in the form of heat. (It’s why steel and aluminum alloys are great for constructing toasters and space heaters but not so great for cables.)

Some cable conductors are made with a combination of aluminum (slightly better than steel) clad in copper.

This is a more cost-effective approach and can be effective in meeting conductivity needs, but the more copper (preferably high purity or oxygen-free), the better the conductivity.

The more electrons to move, the larger the conductors must be. This is the overriding reason that an instrument or patch cable shouldn’t be used in place of a loudspeaker cable.

According to the AWG (American Wire Gauge) system, conductor area doubles with each reduction of three in AWG.

For example, a 13 AWG conductor has twice the copper of a 16 AWG conductor, while a 10 AWG has twice the copper of a 13 AWG, and so on.

Unlike instrument and microphone cables, which typically carry currents of only a few milliamps (thousandths of an amp) or less, the current to drive a loudspeaker is much higher.

An 8-ohm speaker driven with a 100-watt amplifier will pull about 3.5 amps of current. By comparison, a 600-ohm input driven by a line-level output only pulls less than two milliamps. (0 dB = .775 volts / 600 Ohms = 1.29 mA) (For more about cable gauge, lengths, Ohms Law and more, see “Science or Snake Oil?”.)

Shielding
Cable conductors need to be shielded from noise, of which there are two common types. The first is handling noise, in the form of cracking, swishing, scratching, popping, buzzing or humming sounds.

Handling noise can be heard with the cable plugged in but no source audio present. This can be due to substandard electrical termination at the connectors, worn or partially broken center conductor, or inferior wiring in general.

The actual cable construction and the relationship between inner conductors, shielding and outer jacket also affect handling noise.

The second type of noise is interference, of which there are two common types: RFI (radio frequency interference) and EMI (electromagnetic interference).

RFI can be caused by very high radio band frequencies. (You might actually hear a radio station through your system, or high-pitched squeals or hiss.)

EMI can be caused by electromagnetic fields that can emit low frequencies. These fields can surround transformers, power lines and other devices that use or transport large amounts of electrical current. (It’s also often heard as hum or buzz.)

Three primary types of shielding are employed to combat these problems: braid, spiral and foil. In terms of cost, braid shielding is the most expensive, involving copper strands woven into a braided pattern around the center conductor’s inner jacket.

The braided approach works best with microphone cables because of their low inductance. (Inductance is the storage of magnetic energy. Magnetic energy is stored as long as current keeps flowing).

Spiral shielding is more flexible than braiding, and is commonly used in guitar cables. A drawback to spiral wrap is that, like a slinky in motion, one side compresses while the other separates. It’s through these separated strands that RFI can enter.

To compensate for the rejection loss of RFI, sometimes a secondary shield is added, using carbon as a semi-conductor. This is generally effective over very short distances.

The carbon is not a solid sheet, rather, microscopic bits of carbon mixed into another, more flexible material (usually a plastic composite). The bits of carbon conduct current from bit to bit.

Foil wrap shielding is the least expensive shielding method, and some provide full 100 percent coverage. It can be very effective against RFI.

A drain wire runs next to the foil, providing a way to terminate the foil at the connectors, and is a technique is most often used in the construction of snakes. (Note: The drain wire runs along the foil shield to provide a means to connect the foil shield to the connector. The drain wire itself doesn’t actually do much shielding at all.)

Journey’s End
It’s often true that the last thing on the system professionals mind is cable.

After all, like roads and highways, they can be utilitarian by nature.

But as with roads and highways, making the right choices is the optimum way to get to your destination, which is good, clean optimized audio.

All it takes is some attention to the basics combined with critical evaluation.

E. Victor Brown is a veteran pro audio journalist. And special thanks to Cable Factory and Gotham Audio contributing to this article.

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Symetrix Automix Matrix 780 The Choice Of Serbian Conference Room

The Matrix 780 handles speech reinforcement for the busy conference room in the municipality of Vracar, Belgrade, Serbia.

A recently completed conference room in the municipality of Vracar in Belgrade, Serbia serves the local government with a state-of-the-art audio/visual system.

In addition to supporting conferences and sophisticated multi-media presentations, the main stereo sound system (with a supporting subwoofer) also permits the user to hold special movie events.

The system, which is built around a Symetrix Automix Matrix 780 digital signal processor chosen for its power, simplicity, and very competitive price, delivers speech reinforcement, both for delegates and for visiting speakers or members of the public, as well as signal distribution, both for ENG journalists and for a large plasma monitor in the foyer of the building.

Based in Belgrade, Lola Audio designed and installed the new conference room’s A/V system. Zoran Kecojevic, former general manager and now owner of Lola Audio, led the effort, relying on his nearly four decades of experience to deliver a system that sounds and looks amazing and is flexible enough to accommodate a huge range of events, such as meetings of different political parties, training of municipality government staff, presentation of new town planning solutions and architectural projects, popular scientific lectures, celebrations, etc.

Despite its flexibility, Lola Audio designed a user interface that is intuitive and simple to use.

The inputs to the system are many. A well-chosen 48x2 bantam patch panel and two Extron stereo audio switchers feed and complement the twelve-input Symetrix Automix Matrix 780 in such a way that the routing controls supplied by the 780 deliver or suppress appropriate inputs for a variety of circumstances.

In addition to six Clockaudio gooseneck microphones for delegates, Lola Audio outfitted the building with a pair of Clockaudio wireless microphone systems for lecturers or audience questions.

The Extron switchers allow technicians to preview source material from a modern complement of audio and video input devices – iPod jack, DVD, BluRay, BR/HD recorder, PC, notebook, Flash Card audio recorder, etc.

The outputs consist of a speech-reinforcement system, a hi-fi media playback system, media output, and a recorder. For the speech-reinforcement component, a Symetrix 581E distribution amplifier sends signal to Lab.gruppen C-series amplifiers, which in turn feed a central HK Audio loudspeaker array.

Two Symetrix 780 outputs supply signal and corresponding mixes to Extron in-wall loudspeakers at the lectern and at the president’s desk for audience first row fill. Lab.gruppen C-series amplifiers also power a stereo pair of HK Audio twelve-inch two-way loudspeaker systems on either side of the projection screen. An HK Audio fifteen-inch subwoofer supplies the rumble, when needed.

Finally, a Tascam HD-R1 flash card audio recorder makes it easy to archive committee meetings and the like, also providing very useful LAN access for audio file transfer to municipality administration for transcription!

The Symetrix Automix Matrix 780 forms the heart and brain of the multi-limbed system. Input processing includes equalization, filtering, and dynamics, along with Symetrix’ well-regarded feedback suppression and auto-mixing algorithms, both in conference and presentation modes. Less glamorously but just as critically, the 780 easily accommodates a large number of pre-selected routing configurations, which turn off, turn on, and mix appropriate inputs for distribution to appropriate outputs. “The Symetrix Automix Matrix 780 is a perfect device for an installation like this,” said Kecojevic.

“The twelve inputs and eight outputs meet the system’s needs, and all of the processing capabilities and routing logic are powerful and easy to implement. On top of that, the unit occupies just one rack space and comes in at a price point that is very competitive.”

Users operate the system with a Crestron controller and/or an Axiomtek touch-panel PC. The Crestron six-inch touch-panel sits at the lecturer’s desk and allows for event-related preset selection, direct mute, volume control, and other commonly required tasks.

“It was very easy to use third-party controllers with the Automix Matrix 780,” said Kecojevic. “The Ethernet connection and protocol is simple and robust.”

For more demanding events, such as presentations with many talkers or celebration recitals, the Symetrix 780 control software can be used from a separate control PC.

Symetrix Website

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Wednesday, February 09, 2011

Don’t Bet Your Life: Get System AC Grounding Right

Although hum and other problems are often blamed on “improper grounding,” in most cases there is actually nothing improper at all.

After teaching seminars for more than 15 years now, it still amazes me how many otherwise competent professionals don’t understand the importance of proper equipment safety grounding.

Even more shocking (pun intended), many routinely and casually disconnect safety grounds to solve noise problems!

Generally speaking, the purpose of grounding is to electrically interconnect conductive objects, such as equipment, in order to minimize voltage differences between them.

National Electric Code (NEC) requires that 120-volt AC power distribution in homes and other buildings must be a three-wire system.

Figure 1 shows how AC power is typically delivered from the utility company to the load at an outlet. For simplicity, only two of the three main utility connections are shown in the drawing.

One of these incoming utility wires, which is often un-insulated, is the grounded or “neutral” conductor.

Note that both neutral (white) and line (black) wires are part of the normal load current circuit shown by the arrows.

Code requires that the neutral (white) and safety ground (green) wires of each branch circuit be tied or “bonded” to each other and to an earth ground rod at the service entrance.

Any AC line powered device with exposed conductive parts (that includes signal connectors) can become a shock or electrocution hazard if it develops certain internal defects.

Insulation is used in power transformers, switches, motors and other internal parts to keep electricity where it belongs.

However, for various reasons, the insulation can fail - effectively connecting “live” power to exposed metal as shown in Figure 2. Such a defect is called a fault.

For example, if the motor in a washing machine overheated and its insulation failed, the full line voltage could energize the housing of the machine!

Anyone who accidentally touched the machine and anything grounded, such as a water faucet, at the same time could be seriously shocked or electrocuted. 

Remember: current will always return to its source, whether the path is intentional or accidental. Electrons don’t care - they can’t read schematics! 

Trip The Breaker
To return this fault current directly to its source, many devices have a third wire connecting exposed metal to the safety ground pin of their plugs.

The outlet safety ground is routed, either via the green wire or metallic conduit, to the neutral conductor at the main breaker panel.

This low-impedance connection to neutral causes a high fault current to flow, quickly tripping the circuit breaker that removes power from the circuit. To function properly, the safety ground must return to neutral. (Note that the EARTH connection had nothing to do with this process!)

Never, ever use devices such as three- to two-prong AC plug adapters, a.k.a. “ground lifters,” to solve a noise problem! (Figure 3) Such an adapter is intended to provide a safety ground (see the fine print) in cases where three-prong plugs must be connected to two-prong receptacles.

If a proper safety ground isn’t available, always use a ground-fault circuit interrupter (GFCI). A GFCI works by sensing the difference in current between the line and neutral conductors.

This difference represents current in the live conductor that is not returning in the neutral - the assumption is that the missing current is flowing through a person.

If the difference reaches about 5 mA (milliamps), an internal circuit breaker is tripped, removing power from the circuit. The GFCI shown in Figure 3 is unusual because it has a retractable ground pin that allows it to be used with a two-prong outlet.

Also consider two devices connected by a signal cable, each device having a three-prong AC plug. One device has a ground “lifter” on its AC plug and the other doesn’t.

If a fault occurs in the “lifted” device, the fault current flows through the signal cable to get to the grounded device. It’s very likely that the cable will melt and burn. Defeating safety grounding not only is both dangerous and illegal, it also makes you legally liable!

In a typical recent year in the U.S., consumer audio and video equipment electrocuted nine people and started 1,900 residential fires that caused 20 deaths, 110 civilian injuries, and over $30 million in property damage.

Current determines the severity of electric shock. At 1 mA or less, it’s simply an unpleasant tingle. But at about 10 mA, involuntary muscle contractions can result in a “death grip” or suffocation if the current flows through the chest.

Currents of 50 mA to 100 mA through the chest usually induce ventricular fibrillation that leads to death.

The resistance of dry human skin is high enough to safely allow lightly touching a live 120-volt conductor, but normal skin moisture allows more current to flow as does increased contact area and pressure.

Lightning & Dirt
The earth itself is the return path for the current in a stroke of lightning. To protect people and equipment from lightning, we must make a connection to actual soil.

Overhead power lines are frequent targets of lightning. As a result, virtually all electric power distribution lines have one conductor connected to earth ground periodically along its length.

Before this was done, power lines effectively guided lightning inside buildings, starting fires and killing people.

The (NEC) code-required earth ground at the service entry panel serves to direct lightning to earth ground before it enters the building. For the same reason, the code requires telephone, CATV, and satellite TV cables to “arrest” lightning before it enters a building.

Because soil has resistance just like any other conductor, earth ground connections are not at zero volts with respect to each other or any other mystical or “absolute” reference point. Code allows the resistance of this earth connection to be as high as 25 Ω.

Since this is far too high to trip the circuit breaker under fault conditions, an earth ground should never be confused with a safety ground.

Safety ground must be connected to neutral at the main service entry panel. If more than one ground rod is used, Code requires that all must be bonded to the main utility power-grounding electrode. (Figure 4)

Facts Of Life
Most sound (or video) systems consist of at least two devices, which operate on utility AC power. Although hum and other problems are often blamed on “improper grounding,” in most cases there is actually nothing improper at all.

Any properly installed, fully code-compliant AC power distribution system will develop small, entirely safe voltage differences between the safety grounds of all outlets.

In general, the lowest voltage differences (a few millivolts) will exist between physically close outlets on the same branch circuit and the highest (up to several volts) will exist between physically distant outlets on different branch circuits.

These normally insignificant voltages cause problems only when they occur at a vulnerable signal interface - more unfortunate than improper.

What’s all of this have to do with hum and buzz? People have a strong tendency to blame “dirty” AC power for audio-video system noises.

But in fact, AC power is a utility much like a public highway - used by huge trucks as well as sports cars.

Eliminating noise problems by “purifying” the AC power is much like re-paving the highways to fix a car’s rough ride. A much more cost-effective and practical approach is to eliminate the problem that allows the power line to enter the signal path in the first place.

This is analogous to replacing bad shock absorbers in a car to isolate it from rough roads. Finding and eliminating these coupling points will be topics of upcoming columns. 

Always make electrical safety your top priority!

Additional installments of “Clear Path” by Bill Whitlock are available here.

Bill Whitlock has served as president of Jensen Transformers for 20 years and is recognized as one of the foremost technical writers in professional audio.

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Extron Receives UL Accreditation To Self-Certify Safety Tests

The UL Mark is recognized as a true indicator of product safety in the AV industry.

Extron Electronics is proud to announce that Underwriters Laboratories - UL has awarded our in-house regulatory compliance testing facility with two accreditations: Client Test Data Program - CTDP and Supervised Manufacturer˙s Testing - SMT.

CTDP was established by Underwriters Laboratories to allow manufacturers to use their own testing facilities to test and certify product samples in support of UL mark certification.

SMT accreditation certifies that a manufacturer’s testing laboratory meets ISO standards for operation and recognition of test results generated at that facility.

At Extron, we are continually enhancing our fully-equipped testing facility to qualify products under additional safety, reliability, and environmental standards. By testing and certifying devices in-house, product designs are refined continuously, allowing safe products to reach the market sooner.

“The UL Mark is recognized as a true indicator of product safety in the AV industry,” says Andrew Edwards, President and CEO of Extron.

“Receiving UL accreditation to test our products in-house eliminates the turnaround time associated with outside testing. This allows us to expedite product development and meet the needs of our customers.”

The two accreditations awarded to Extron cover standards for Audio Visual IEC/UL 60065 and Information Technology Equipment IEC/UL 60950-1.

Additionally, the SMT program entails strict adherence to all ISO 17025:2005 testing and calibration requirements. Extron is one of the very few manufacturers to have earned both CTDP and SMT accreditation for an in-house regulatory and compliance testing facility.

In addition to UL accreditation, the Extron regulatory compliance testing facility is accredited by the Federal Communications Commission - FCC and other regulatory bodies for compliance with various national and international standards.

Extron Electronics

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Sonnet Introduces RackMac Mini Solution For Mac Mini Servers

The RackMac mini Secures Two Mac mini Servers in a 1U Rack Space.

Sonnet Technologies has introduced its RackMac mini rackmount solution for the latest line of Mac mini servers and computers.

Intended for the office or for transportable rack use, the unit supports the installation of one or two Mac minis into a 1U rack space.

The RackMac mini manages airflow and provides a front-panel power switch and USB port for each Mac mini.

Constructed of rugged steel with a black powder-coat finish, the 11-inch-deep RackMac mini firmly secures the computers behind a smart front panel. For each Mac mini, the front panel includes DVD, IR sensor, and power indicator slots; a power switch; and a USB port. Pressing each computer’s power button, connecting a keyboard or mouse, or attaching a USB drive is simple.

A padded locking bar securely holds the Mac minis in place for transportable rack use. Convenient cable tie points allow all cables to be secured, as well. The RackMac mini comes preassembled.

Enclosed inside the RackMac mini, Mac minis keep ambient temperature chill for reliable operation.

The Sonnet rackmount solution’s design prevents recirculation of hot air around the Mac minis, ensuring that cool air goes in a one-way path through the front panel openings to the computers’ air intakes, exiting out the rear.

“The Mac mini server is a great server for most applications. The remaining challenges have been how to mount them securely, how to cool them reliably, and how to turn them on without pulling them out of the rack,” said Robert Farnsworth, CEO of Sonnet Technologies.

“The RackMac mini is the perfect solution. Just add Mac minis.”

RackMac mini (RACK-MIN-2X) is available now with a suggested retail price of $169.95.

More information on the RackMac mini is available on Sonnet’s website.

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