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Power
Thursday, February 02, 2012
Powersoft Joins Crestron Integrated Partner Program
Powersoft is now a member of Crestron Integrated Partner Program with the full permanent installations catalog, which is a plug-in, developed by Crestron for Powersoft, that includes the entire range of products.
The catalog allows seamless integration of Powersoft amplifiers in Crestron-controlled environments, including video, security, evacuation and other remotely accessible devices.
The feature set includes full alarm monitoring, mute and volume control, preset selection, power on/off, and real time metering for Duecanali, M Series and K Series. In addition, Ottocanali is currently undergoing tests to be included in the list.
“This important development is yet another step in our plan to expand our presence in the permanent Installation market,” says Luca Giorgi, Powersoft pro audio business unit manager. “The future of this market will be increasingly characterized by the integration of various subsystems into a single complex environment, where the key concept is easy accessibility. We believe that we could not miss the opportunity of being part of it.”
“This is a significant step into that direction because it will greatly expand the interoperability of our products in that market, where we have already set the bar in terms of power consumption, energy efficiency and environmentally sustainable products,” adds Luca Baldi, the newly appointed permanent installation account manager.
PSAV Deploys Crown Audio VRack Amplification System For Hotel Events
PSAV Presentation Services, the world’s largest A/V rental supplier with more than 800 offices worldwide, many located on-site at major hotels, specializes in providing in-house audio-visual services to the hospitality industry for meetings and events, and maintains one of the largest, most up to date equipment inventories in the industry.
Since its introduction, PSAV has been using Crown Audio VRack, a turnkey amplifier rack system that includes three I-Tech HD I-T12000 power amplifiers, a versatile input panel with analog and digital connections, and a globally universal power distribution system that can be set to meet U.S. and international power standards.
All of the components are housed in a wheeled rack that can be flown in the same manner as a line array loudspeaker system.
“Typically, a hotel sells the meeting space and we work with the end client to provide the equipment and labor required to manage the event,” notes Jacob Ingle, audio product manager for PSAV. “Since we own all of our equipment, we have to select products that are cost-effective, efficient and reliable in order to maintain a profitable bottom line.”
“We have been using Harman products for quite a long time and even discussed building pre-configured amp racks with Crown before VRack was introduced. When they introduced the VRack, it was the perfect solution for a number of our amplification needs,” continues Ingle.
“One of our goals is to standardize gear as much as possible so our technicians can move from location to location and be familiar with the equipment they’re going to use,” says Ingle. “Having a unified amplifier package like VRack makes this a lot easier. We have many locations large and small, and VRack is adaptable to different situations because it allows multiple configurations for analog and digital inputs, for different types of speakers and for system networking.”
“Crown’s VRack is the perfect solution for the audio rental supplier because of its benefits as a plug-and-play solution for customers like Jacob who face an ever-changing set of challenges based on each event,” states Brian Pickowitz, marketing manager for Crown.
“Another major advantage is that VRack interfaces with Harman’s HiQnet Performance Manager system design and setup software and is specifically designed to work with JBL VerTec loudspeakers. Because we use a lot of JBL, Soundcraft and other Harman gear in addition to Crown, VRack becomes part of an all-in-one solution where all components ‘talk to each other’ using HiQnet. This makes system setup and operation much easier and a great deal more efficient,” adds Ingle.
Technomad Upgrades Audio Presence at Club Med Sandpiper
Systems integration firm Axxentos of Fort Lauderdale, Florida turned to Technomad upon evaluating the outdoor audio needs of Club Med Sandpiper in nearby Port St. Lucie. The new outdoor audio systems, featuring 14 Technomad weatherproof loudspeakers, comprise part of a property-wide renovation alongside indoor AV upgrades and general construction projects.
Club Med Sandpiper’s 400-square-mile resort property exists in southern Florida’s sweltering climate, requiring durable outdoor audio systems that can withstand the year-round heat, humidity and moisture. The resort also required high-quality loudspeakers that could power full-range, high-volume audio over long distances, and reproduce soothing background music at clearly audible levels.
“I’ve learned what gear can survive in harsh environments over the years, and from all the outdoor installations I have done, only one company reliably endures the elements — and that is Technomad,” said Olivier De Kegel, owner and president of Axxentos. “They also produce great sounding audio.”
The external pool system proved the biggest challenge as De Kegel had little guidance from the resort, other than that management wanted a nice-sounding background music system during the afternoon and a louder system in the evenings. He installed two Technomad Berlin loudspeakers, the largest loudspeaker in the company’s range, to handle both requests with one system. The Berlins accommodate every activity from Bingo to full-blown nightclub-style events.
Axxentos installed a 70-volt infrastructure to accommodate long cable runs from a new central audio headend to various areas, including the bar. Ten Technomad Vernal 70-volt loudspeakers power the bar zone, delivering music and entertainment to guests enjoying daytime activities and the nightlife.
Two Technomad Noho loudspeakers also welcome guests with high-energy music audio at the entrance as they check in, with lower-volume background music playing in between arrivals.
“The resort wanted a system they could easily manipulate at the welcome area to balance loud and soft audio, and the Nohos offer power that is closer to the Berlin but compact enough for installation at the entrance,” said De Kegel.
Elsewhere, Axxentos installed AV systems in new conference rooms, built a mobile DJ unit and renovated a large theater system, merging existing equipment with some new components. But the outdoor audio systems remain the crown jewel of the resort upgrades.
“This was my largest installation to date, with some interesting upgrades and unique challenges,” said De Kegel. “They went from being fully analog to a more digital, centralized model. There won’t be any dull nights with the high-quality audio systems they have, and the durability of the Technomads ensure they won’t have to replace the outdoor systems every two years.”
Rich Trombitas of Cardone Solomon & Associates and Vic Palmer from Quest Marketing were presented with “Outstanding Service” awards at the annual Powersoft rep meeting held at the 2012 NAMM show.
“Rich and Vic have gone above and beyond for our customers during 2011,” explains Ken Blecher, EVP of Powersoft Advanced Technologies Corp. “It was only appropriate that we acknowledge their efforts and our appreciation with the Outstanding Service awards.”
During the meeting Blecher also announced the addition of Jonathan Garner to the Powersoft team. Garner will provide inside sales and logistics support for the company.
“We continue to experience tremendous growth in the U.S. market,” adds Blecher. “With our powerful team of sales reps and expanded infrastructure in California, we are well prepared for continued growth in 2012.”
Extron Introduces 800-Watt ENERGY STAR Qualified Power Amplifier
Extron Electronics has introduced the new XTRA Series XPA 4002 two-channel power amplifier, a compact 1U, convection cooled amplifier that delivers 400 watts RMS per channel, also available in low impedance and 70-volt versions.
The XPA 4002 is an ENERGY STAR qualified amplifier with an Extron exclusive, highly efficient, advanced Class D amplifier design.
It also features patented CDRS - Class D Ripple Suppression technology that provides a smooth, clean audio waveform and an improvement in signal fidelity over conventional Class D amplifiers.
The XPA 4002 is half the size of comparable amplifiers, conserving rack space and weighing only 9 lbs (4 kg). The Extron exclusive, high efficiency design generates very little heat and allows the amplifier to be convection cooled.
“The XPA 4002 is our newest ENERGY STAR qualified amplifier that delivers a unique combination of high power output and very efficient operation,” says Casey Hall, vice president of sales and marketing for Extron. “It is ideal for driving high powered speaker cabinets or a large quantity of distributed speakers in large spaces such as auditoriums and houses of worship, while consuming less energy, running cooler, and taking up less space than competitive models.”
The XPA 4002 features an auto power-down feature that automatically places the amplifier into standby after a period of inactivity, and consumes 30 watts or less when idle and less than 1 watt in standby mode.
It also has an ultra low inrush current draw to prevent power circuit overload that occurs when multiple amplifiers are switched on simultaneously. This feature eliminates the need for power sequencing in systems with multiple amplifiers in large centralized equipment racks, and prevents other equipment from experiencing power interruption from associated power surges.
Additionally, the XPA 4002 amplifier features very low thermal dissipation under full load, which keeps racks and equipment cabinets cool.
Meyer Sound Expands Low-Voltage Line With Three New Loudspeakers (Includes Video)
The Meyer Sound line of self-powered, low-voltage audio products has grown with the addition of three new 48-volt, DC-powered loudspeakers that offer the same performance as their AC-powered counterparts.
The new UPM-1XP 48 V DC ultracompact wide-coverage loudspeaker is the low-voltage version of the UPM-1P ultracompact three-way loudspeaker. The UPM-1XP is capable of 123 dB peak SPL over an operating frequency range of 75 Hz to 20 kHz.
The new UPJunior-XP 48 V DC ultracompact VariO loudspeaker combines the distinct advantages of the low-voltage, self-powered concept with the versatility of the VariO constant directivity horn. Its 80 x 50-degree dispersion pattern can be changed from horizontal to vertical orientation. Power output is 126 dB peak over a 70 Hz to 20 kHz operating range.
The new UMS-1XP 48 V DC ultracompact subwoofer extends low-voltage system response to an operating frequency range of 25 Hz – 160 Hz and a peak SPL of 127 dB at 1 meter. Visceral impact is provided by dual 10-inch cone drivers.
“Ourlow-voltage systems are the answer to installations where AC cannot be run to loudspeaker positions yet the low-distortion audio quality and power in Meyer Sound self-powered products are essential,” states Luke Jenks, Meyer Sound product manager for loudspeaker products. “These new products can provide a level of sonic bandwidth and speech intelligibility to raise the bar for discreet, easy-to-install systems for environments that include museums, restaurants, bars, and convention centers.”
Meyer Sound self-powered low-voltage systems incorporate on-board amplifiers and signal processing. Unlike their AC-powered cousins, the UPM-1XP, UPJunior-XP, and UMS-1XP draw DC power from a remote rack-mount power supply. The loudspeakers receive 48-volt DC power and balanced audio via a five-pin connector.
These loudspeakers can be installed using Class 2 wiring without using conduit, resulting in reduced installation time and cost. Amplifier circuits are specifically designed to store power for peak demands, allowing the flexibility of lengthy cable runs while still preserving the advantages of self-powered systems.
Proprietary RMS remote monitoring system is available for comprehensive monitoring of all critical loudspeaker and amplifier parameters as well as individual loudspeaker muting.
In addition to the newly announced systems, which will begin shipping in April 2012, Meyer Sound’s low-voltage, DC-powered product line also includes the UP-4XP ultracompact loudspeaker, MM-4XP miniature self-powered loudspeaker, MM-4XPD directional miniature loudspeaker, and the MM-10 miniature subwoofer. All of these products can be ordered with custom colors to match any decor.
Switchcraft Announces New AudioStix Line Of Adapters
Switchcraft has introduced the new AudioStix line of adapters, the newest additions to the company’s expanding line of premium pro audio products.
AudioStix can be used as stand-alone adapters, rear mounted into modular Switchcraft QGPK Series rack panels, or permanently installed into any number of custom racks and wall plates.
Four versions are available now:
—#318 Mini AudioStix is an 1/8-inch mini to XLR adapter with volume control and ground lift —#319 is an 1/8-inch mini to terminal block adapter with ground lift and pad switch —#366R is an XLR female to BNC (110 to 75 Ohm) adapter —#367R is a BNC to XLR male (75 to 110 Ohm) adapter
Note that all AudioStix versions are outfitted with transformer isolation.
Joe Manning Of International Sales Named Panamax/Furman Asia-Pacific Manufacturer’s Rep
Panamax/Furman has named Joe Manning of International Sales as its new manufacturer’s representative for the Asia-Pacific region.
Under the agreement, Manning will help Panamax/Furman expand its presence in the Asia-Pacific market by establishing distribution networks and managing sustained growth for the company’s consumer and pro A/V lines of power and energy management solutions.
Manning founded International Sales in 1993 to provide a bridge between U.S. manufacturers and professional distributors and dealers around the world.
For the last 18 years, the company has sold high-quality home theater and commercial A/V systems from high-profile manufacturers through its international distribution networks. As the company’s owner and president, Manning has been recognized as a “CEDIA Manufacturer’s Representative of the Year.”
“It’s an honor to be selected by Panamax/Furman to represent its innovative products in the Asia-Pacific region,” says Manning. “The company has continued to lead the pack in power and energy management, and offers a wide portfolio of solutions to meet the needs of customers in all the major electronic markets. I look forward to working with Panamax/Furman as we develop new distribution networks and further penetrate the Asia-Pacific market.”
“Joe Manning is an accomplished leader who has garnered respect throughout the A/V industry for his sales and distribution expertise in both the commercial and home theater markets,” adds Dave Keller, senior vice president of sales and marketing, Panamax/Furman. “His experience is a perfect match for Panamax/Furman and will be instrumental in increasing our market share in the Asia-Pacific region. We look forward to a long and mutually beneficial relationship with him and International Sales.”
Pascal Launches New Ultra-Compact 1000-Watt Amplifier Module
Pascal A/S, a manufacturer of high-power OEM amplifier modules, has launched the new, ultra-compact S-PRO2 amplifier module, designed to power a wide range of loudspeakers, line arrays and subwoofers.
The new S-PRO2 is a complete power pack offering 2 x 500 watts (RMS) at 4 ohms, and 1,000 watts in bridge mode. The integrated universal power supply including power factor correction (PFC). It measures only 2 x 3.1 x 8.5 inches (5.1 x 8.0 x 21.5 cm).
It incorporates proprietary Pascal UMAC class-D technology, as well as Pascal UREC power supply technology and PFC functionality that provides universal mains and regulation for worldwide AC mains compatibility and consistent power performance.
“Our new S-PRO2 is our response to client demand for an ultra cost effective 2 x 500 watts, all-in-one amplifier module with an unprecedented price per watt ratio,” states Pascal sales manager Peter Frentz. “Yet it delivers extremely audiophile sonic performance.”
The S-PRO2 includes a wide range of protection features as well as auxiliary power for DSP cards.
All amplifier channels are over-current protected on outputs. Current clipping is engaged when the amplifier channels exceed its specified peak current output.
A built-in DC protection circuit will attenuate any DC signals on the amplifier inputs, produced by an input signal containing a DC signal.
Power supply over- and under-voltage protection is implemented, which means that the power supply will enter a protection mode when the operational off-line voltage exceeds or drops below the specified upper and lower operational off-line AC voltages.
Temperature protection of power-stages and heat-sinks is implemented to secure the amplifier module from overload.
The S-PRO2 is also has Energy Star Compliance, particularly handy in installations. When the amplifier is put into Sleep Mode, major circuitry parts are powered down, which leads to low AC
mains power input specification of less than 0.5 watt. In sleep mode the +7.5-volt and +/- 15-volt rails are still active, which enables a possible network/DSP to remotely power up the amplifier again.
A high frequency protection is implemented in order to protect filter components from overload, protecting the amplifier from excessive HF signals on the outputs.
Bringing Clarity To Loudspeaker Power Ratings & Their Relationship To Performance
It’s unfortunate that misunderstandings about power ratings have precipitated an arms race to provide large numbers
One of the most confusing subjects in audio? Loudspeaker power ratings.
It’s generally accepted that a large loudspeaker power rating is a sign of quality and something to be desired.
And it’s the performance metric that probably has the greatest influence on the consumer’s buying decision.
But a closer look reveals that power rating is far less significant than other metrics regarding the performance of the loudspeaker.
The term “power rating” requires further explanation to avoid misunderstanding. It’s tempting to associate it with the acoustic output of the transducer, or even the recommended amplifier size.
But it has little to do with either.
First, let’s expand the term to make it more meaningful.
How about “maximum input power dissipation?” The term “input power” is appropriate because the loudspeaker presents a load to an amplifier.
Assuming negligible effects from the cable (a safe assumption if the correct wire selection criteria are used), the output power of the amplifier becomes the input power to the loudspeaker.
And because bigger amplifier power ratings are accepted as better (i.e., a sport utility vehicle versus an economy car), it’s assumed that larger loudspeaker power ratings indicate a better product.
Figure 1: How the power “thing” (amplifier to loudspeaker) works. (click to enlarge)
Amplifiers that connect directly to loudspeakers are called power amplifiers, because their output is a higher voltage and current facsimile of the input voltage to the amplifier. (Figure 1)
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Power amplifiers are rated for power generation. A bigger number is generally better as it indicates the potential for the amplifier to do more work.
Loudspeakers are rated for power dissipation. Their power rating describes the amount of continuous power that can be dissipated in the form of heat without damage to the loudspeaker.
While at first glance it may appear that more power dissipation is better, this is only true if the method used to achieve it does not compromise the efficiency of the loudspeaker.
Modern power amplifiers act as constant voltage sources to the loudspeaker. This means that the output voltage of the amplifier is essentially independent of the load placed on it by the loudspeaker.
If you drive an amplifier with a signal and measure its output voltage with no load connected to the output terminals, and then connect a loudspeaker to the terminals, there is no significant change in the reading on the voltmeter.
The difference between the no load and loaded case is that with the load present current will flow from the amplifier terminals through the loudspeaker.
Lower load impedances (more loudspeakers in parallel) draw more current from the amplifier, increasing the total power transfer from source to load. (Figure 2)
Figure 2: Lower impedances (loudspeakers in parallel) draw more current. (click to enlarge)
This is why the total output power of the amplifier generally increases when driving more loudspeakers. Note that the output power of the amplifier increases, but the power is distributed among the connected loudspeakers.
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So, if one loudspeaker is connected in parallel with another, the total power output of the amplifier increases but the power per loudspeaker does not.
In fact, it probably drops a little. It is best to keep amplifier loads above 4 ohms to minimize cable effects and avoid excess current demands on the amplifier.
The Arms Race
The power drawn by the loudspeaker from the amplifier is found by multiplying the voltage times the current.
Conservation of energy says that all of the power from an amplifier must be accounted for. Part of the power produces the mechanical movement of the loudspeaker, and the rest of it becomes heat.
The mechanical movement of the cone produces the sound from the loudspeaker. The heat is a waste by-product, and like any waste quantity, it must be disposed of.
Unfortunately the conversion of electrical power to acoustical power is an inefficient process (less than 10 percent is typical) so most of the amplifier power is wasted (heat) and must be dissipated.
The power rating of the loudspeaker describes the capacity of the loudspeaker to dispose of the heat produced by the inefficiencies of the conversion process – so back to our expanded definition of “maximum input power dissipation.”
As such, it’s a mistake to associate the power rating of the loudspeaker with its sonic performance. Higher power dissipation ratings simply mean that the loudspeaker is better at cooling itself.
But power ratings by themselves give no indication of efficiency in producing acoustic power, which is the purpose of the loudspeaker.
It’s possible to increase the power dissipation rating of the loudspeaker by reducing its efficiency. One could simply add some resistive elements internally.
The result is a very large power rating but very little sound – not what we’re after!
The sound pressure level (SPL) produced by a loudspeaker is more closely related to the applied voltage than the applied power.
This can be seen by plotting the on-axis SPL against both. (Figure 3)
Figure 3: On-axis SPL against applied voltage and applied power. (click to enlarge)
The power drawn by the transducer varies with frequency, and while the SPL is often referenced to the input power, it actually tracks the input voltage quite closely.
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It’s desirable for the loudspeaker to have a flat voltage response, so that equal drive voltage per frequency produces a flat magnitude response on-axis.
The ideal loudspeaker could produce the desired sound pressure level using as little power as possible. There would be less heating due to the higher efficiency.
So there is nothing impressive or inherently beneficial to driving lots of power into a loudspeaker.
It’s more impressive to get lots of sound with less applied power. Think of mileage ratings for automobiles, and you have the right idea. It’s more about efficiency than consumption.
Horn loading and boundary placements are methods of increasing loudspeaker efficiency, allowing more sound per applied electrical watt.
Proper Perspective
The same misconceptions about power ratings in loudspeakers occur when we choose a light bulb. The wattage rating is often associated with the light output – more watts, more light.
Bulbs have a luminosity rating that describes their light output, but few consumers ever consider it.
So, if we need more light in a room we buy a “bigger” bulb (higher wattage rating).
It’s only natural to apply this assumption to loudspeakers. Next time, shop for the highest lumens output for a given power input and you’ll get the best value.
A very high power rating on a loudspeaker doesn’t mean that it will be very loud.
Rather than saying “Wow, the Killsound 5K loudspeaker handles 5,000 watts!” it would be better to ask “Why do I have to feed 5,000 watts to the Killsound 5K to get 100 dB SPL in the audience? On the hand, the Efficienator 1 loudspeaker can produce that level and only have to dissipate 100 watts!”
A more meaningful loudspeaker rating would be that of maximum SPL. This rating can be found by scaling the loudspeaker’s sensitivity rating by the maximum input power rating.
It allows a loudspeaker with a lower power rating – but higher sensitivity – to compare favorably with a loudspeaker with a higher power rating but lower sensitivity.
It’s unfortunate that misunderstandings about power ratings have precipitated an arms race among manufacturers to provide large numbers.
Big power ratings are an easy sell, but high efficiency is a better goal.
Power Test
Many methods exist for determining the maximum input power to a loudspeaker. All of them have their merits, and all have similar attributes.
A meaningful power test must include:
- A broadband noise stimulus that is band-limited for the device-under-test.
- A method of determining the power transfer between the amplifier and the device-under-test.
- A time metric that describes how long the loudspeaker can dissipate the applied power.
- And (ideally) a measurement of SPL from the loudspeaker.
Figure 4 shows a useful way of plotting the results of the test. The noise stimulus is often pink noise (equal energy per 1/n-octaves).
Figure 4: A good way to plot power test results. (click to enlarge)
Some methods use flat pink noise and others use a weighting scale to simulate the spectral content of music.
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The latter type can produce higher power ratings since more of the electrical energy is shifted toward the lower frequency bands where a transducer can usually dissipate more heat due to its heavier construction.
To determine power transfer, both the voltage and the current applied to the device-under-test must be monitored.
It’s not sufficient to calculate the power transfer from the applied RMS voltage and the nominal impedance of the load.
The load impedance will increase when the device-under-test heats up, reducing the power drawn by the load (power compression).
When a loudspeaker is operated near its power dissipation limits it is not unusual to increase the power applied to the load by turning up the amplifier, but with the result of no additional sound pressure level and even a reduction in power transfer.
It’s best to consider power ratings on a decibel (proportional) rating scale. Wattage ratings can be extremely misleading with regard to the performance of a device.
Consider the fact that a loudspeaker with a 500 watt continuous power rating will only be slightly louder than one with a 250 watt rating (+3 dB), assuming that the efficiency of both are the same.
This means that there is little practical difference between the two, even though there is an apparent large difference in their ratings.
Most power tests modify the pink noise stimulus to have a lower crest factor – the peaks in the program material are reduced by a clipping circuit.
The practical reason for clipping the waveform is to allow the amplifier to deliver more power to the load.
The maximum output power for unclipped pink noise is about 1/10th of the amplifier’s sine wave rated power. Clipped pink noise can produce about 1/2 of the amplifier’s sine wave power rating, allowing power testing with reasonable amplifier sizes.
The clipping artifacts do not contribute significantly to the heating of the loudspeaker, but the lower crest factor produces more power (higher RMS voltage) into the load.
A continuous power test feeds 6 dB crest factor pink noise to the loudspeaker for a specified period of time (i.e. two hours). This is a demanding test for the loudspeaker, since there are no breaks in the program material to allow cooling.
Program power ratings attempt to simulate music or speech by reducing the duty cycle of the waveform. If the noise is pulsed, some cooling can occur between bursts and more short term power can be applied prior to failure.
Many manufacturers estimate the program power rating by doubling the continuous power rating (+3 dB or 2x is a reasonable assumption).
The actual recommended amplifier size will be larger than either of these ratings. A reasonable estimate is the continuous power rating +6 dB (4x).
Given these definitions, a complete and meaningful power rating for a loudspeaker might be: Maximum Input Power – 200W/400W/800W (continuous, program, recommended amplifier size)
Apples To Apples
Once can easily see the problem with comparing loudspeaker power ratings.
It takes a lot of research to assure an “apples to apples” comparison, and many specs simply don’t include enough background information to allow this. Feeding a loudspeaker with less than its rated power presents no danger.
In fact, it will have a longer, happier life with less power. I recommend limiting the input power to no more than one-half (-3 dB) of the continuous rating for reliable operation.
In the preceding example, this would mean using an 800-watt amplifier, feeding it typical program material (10 dB to 14 dB crest factor) and driving it just to the brink of clipping as a maximum.
Under these conditions, the amplifier will be producing about 80 watts or less into the loudspeaker, which is safely below the continuous rating.
Since the amplifier has a potentially large output, care must be taken to assure that low crest factor program material is not turned up too loud as it could damage the loudspeaker.
Finally, it’s important to realize when the point of diminishing returns is being reached when turning up the volume on a sound system.
Each 40 percent increase in applied voltage to the loudspeaker produces twice the input power, and a slight (+3 dB) increase in sound level.
Remember that with audio it is the proportional chance that matters. As the volume of the system is increased in 3 dB steps, eventually the limits of heat dissipation are reached and the next 3 dB “breaks the camel’s back.”
A loudspeaker is very near its maximum loudness at one-half of its rated power. There is nothing to be gained by going further and the loudspeaker will likely suffer permanent damage.
Advancements in automotive technology have produced vehicles with greater efficiency and lower operating cost due to reduced waste.
The audio industry should have a similar goal – achieving the desired SPL using less amplifier power.
As efficiencies increase, the need to dissipate lots of power should diminish – as should our fascination with high power ratings.
Pat & Brenda Brown lead Syn-Aud-Con, conducting audio seminars and workshops around the world. Synergetic Audio Concepts (Syn-Aud-Con) has been a leader in audio education since 1973. With nearly 15,000 “graduates” worldwide, Syn-Aud-Con is dedicated to teaching the basics of audio and acoustics. For more information, go to http://www.synaudcon.com
Accidental Electrician: Eliminating Dreaded Sound System Hum & Buzz
An epic tale of finding and eliminating a system's long-time and ongoing hum and buzz issues. Just who was the culprit?
There’s no better feeling than when you’ve setup your system and turned it on to find it lacking any noise.
This is no major feat when you have control of the electrical distribution, but when you don’t, things can be a bit more dicey.
The classic scenario when the system powers up with a hum is for the operator to declare “ground loop!” followed by muttering and cursing while digging in the accessories box to locate the power cord cheaters.
I find it funny how a device that’s supposed to be used to provide an electrical ground connection on older two-prong outlets is most often employed to lift the ground instead.
In such situations, you gotta do what you gotta do to safely eliminate these nuisances if possible. But I often see that the whole ethereal concept of a “ground loop” is a distraction from one big fact: not every hum comes from a ground loop.
What seems to be nearly universal is that a lot of folks don’t understand that the existence of a ground loop is not actually the cause of a ground loop hum. A ground loop is only a condition that is exploited by the true problem, which is an electrical current flowing through the loop.
Carefully designing a system to not have ground loops is a noble engineering endeavor. But in my book, there’s no real reason to do so if you take the time to eliminate the actual hum sources and potentials.
Treat the cause, not the symptom.
One job I worked in the past was on a sound system with a noise problem that historically couldn’t be solved.
This system was in a mid-sized church in a community known as the “Home of the Hardheaded Dutch.”
(You may accuse me of racial stereotyping, but believe me, this is how they referred to themselves. And they were proud of it.)
When we first walked into the sanctuary, the system was on and I immediately heard a significant buzz. The contractor turned to me and said, “Oh by the way, we’re going to solve their noise problem too.” Which was to say, “You need to fix this because I can’t.”
I hemmed and hawed about how the problem could be from the transformer on the pole, but was actually just making stuff up out of thin air, aggravated about having been surprised with this additional time-consuming task being added to my already conservatively budgeted schedule.
The church elder and de facto tech director we were working with was a retired Master Chief named Dave. He knew diddly-squat about sound systems, but possessed a good nose for BS. I could tell he wasn’t buying mine.
Pocketful Of Cash
I got on with acquainting myself with the system. Much of it had been obtained as surplus from the 1986 World’s Fair in Vancouver. I was surprised to find a rack filled with Bryston amps, still with a few years of warranty left and working just fine!
What disturbed me was that everything at the amp rack was plugged into cheaters and Radio Shack power-line RF filters. Someone wasted a pocketful of cash to buy those.
I removed them and the molesto mucho buzz was transformed into a simple hum. A step in the right direction…
After eliminating the lighting dimmers as the noise source, there were no other obvious conditions that I could immediately identify as contributing to the problem.
So I went home and whined to my wife about how I had been abused by having this additional issue dumped in my lap. She didn’t buy my BS either.
Three days later, we were back, doing the first thing these projects always require: taking everything apart. As we slowly updated and re-assembled the system, I got to a place where I could examine the power distribution.
I strung an extension cord from one of the sockets at the amp rack to the front of house position, and then used my trusty old Wiggins to check between the hot on the extension cord and the hot at the front of house outlets.
As feared, it measured 208 volts, meaning that the two different power circuits were on differing phases. It was time to root around in the breaker box.
The building had a modern electrical system, which is fortunate. I’ve run across some problems in systems that were on legacy electrical distribution, and short of violating code, there’s sometimes not a whole lot that can be done to fix a problem.
Well-Meaning Electrician
Suffice to say that a dedicated electrical ground and a modern distribution system is imperative for safe, noise-free sound.
Four circuits in the breaker panel were dedicated to the sound system, and sure enough, they were grouped together all in a column. This was a typical commercial 3-phase box with the phase alternating for every row.
The shame was that I could tell by reading the written-over labels that originally the sound system circuits had been on every third row (i.e., a common phase).
So the original system installer (OI) had specified that the circuits needed to be all on the same phase. My guess is that some well-meaning electrician had thought it would be smart to group the circuits together during one of the church expansion projects. I returned the circuits to their original spacing.
Having all the power circuits on an identical phase is important for minimizing the possibility of an inter-chassis current in a ground loop.
Power supplies leak small amounts of AC to ground. If there happens to be enough leakage from gear in the ground loop, and it’s of differing phases, an inter-chassis current will flow through the loop great enough to induce a hum.
By establishing a common system power phase I minimized the ground loop hum potential.
Elsewhere though, the OI committed a serious faux pas. The original installation included a remote power switch for the amp rack, which consisted of a key-switch on a panel at FOH that fed AC from a transformer to the coil on a relay at the amp rack. Turn the switch, the relay closes and the amps have power.
The problem was that the OI appropriated one of the shielded balanced lines running through the FOH to stage conduit for the remote power switch. For 90 feet, there was a line carrying 60 Hz AC in cramped proximity with all of the system audio wiring!
Removing the remote power switch eliminated this hum potential. We could have run an alternate line for it, but Dave didn’t care for the attitude exhibited by those who had keys (control) towards those who didn’t so he decided to just do away with it.
Sudden Problems
Next, the system was gotten to the point where the console was re-patched and turned on. There was a hum.
Examining the console, I began to see that there were some channels and sends marked “Bad” and “Don’t Use.” I began to grow suspicious. Dave said that one day they came in and the console was suddenly having these problems. My gut said the console had taken a surge during a lightning storm.
They had continued using it not realizing that there was more to the console problem than just non-working channels and sends.
Replacing faulty gear (and a lecture about surge protection) was the solution for this hum source. We snagged the console from the church’s youth room and patched it in. Ahhhh, schweet silence! I declared, “This house is clean!”
Too bad it wasn’t so.
It was the afternoon of the project’s last day and there was a sound check scheduled with the worship team that evening. We had patched in numerous mics for vocals, piano, drums, guitar cab and DIs for acoustic guitar, bass and keys.
When I opened the channels and pushed up the faders, there was a hum. My heart sank and Dave now began to give me “the eye.”
It wasn’t on just one channel, but on almost every channel from the stage. Pull the faders down or mute the channels and the hum would go away.
So the problem wasn’t ground related because it was controllable. Phantom on or off made no difference. Dynamic mic, condenser mic, or DI also made no difference.
I hit the stage and started taking a closer look at things. I picked up one of the mic cables and was disgusted to find that I recognized the writing on the jacket. I had seen it once before.
This cable had a certain respected pro audio name on it that had no business being there. I don’t know if this cable was a manufacturing screw-up or possibly a counterfeit, but it had no valid use anywhere in a sound system. It wasn’t even shielded twisted pair.
I looked across the stage and counted upwards of two-dozen of these demon-possessed cables from hell.
Luckily, there was a decent pro audio store about 20 miles away. We bought out their stock and I cut up the old cables so no one would be tempted to salvage them from the dumpster and put them back into service.
The final fix was replacing the bad cables with good ones. For the first time ever, the system was noise-free and there wasn’t a single lifted ground or shield anywhere.
I suspect that the original issue was with the remote power switch, and as the other issues occurred, they contributed to the complexity of solving the problem.
It’s a shame that out of hardheadedness they put up with it for as long as they did. But I can well understand the lack of trust when it came to parting with their money over a seemingly unfixable problem that shouldn’t have been there in the first place.
BS comes in many forms. Sometimes as talk, sometimes as a bogus feature in an install.
Not many weeks later, the church decided to expand the project by replacing the ailing console, adding a personal monitoring system and investing in some surge protection.
I guess we’d earned the respect of the Master Chief. Hooyah!
Since his start 30 years ago on a Shure Vocalmaster system, James Cadwallader remains in love with live sound. Based in the western U.S., he’s held a wide range of professional audio positions, performing mixing, recording, and technician duties.
The REAL question is not what is the power handling, but what is the OPTIMUM size power amplifier to use on a loudspeaker?
“So how many watts can this loudspeaker take?” The technical answer is that it depends on the thermal and mechanical limits of the drivers and crossover components.
The practical answer is that it depends on the program material played: its peak/average ratio or transient content and spectral (frequency) content.
The REAL question is not what is the power handling, but what is the OPTIMUM size power amplifier to use on a loudspeaker?
Rule of Thumb
For a rule of thumb the best answer is found using what is commonly called the loudspeaker’s RMS (root mean square) power rating. Use an amplifier that is twice the RMS rating. If you can’t find an amplifier with that exact rating, multiply this power rating by 0.8 and also by 1.25 to find a range of acceptable power.
Example: A loudspeaker has a 250-watt RMS rating. Twice this is 500 watts. Therefore the acceptable range for the power amplifier to use is from 400 watts (0.8 x 500) to 625 watts (1.25 x 500). Anything larger is potentially excessive power. Anything smaller can cause damage from the amplifier clipping. Remember that the power amplifier output you select must be rated for the nominal impedance of the loudspeaker (i.e., 16, 8, 4 or 2 Ohms).
The RMS rating represents the thermal power limit for the loudspeaker. It is also a good number to use for comparing products. Twice the RMS rating represents a realistic scenario for most actual audio signals. This is 3 dB more power than the RMS rating. An amplifier’s RMS rating is based on a sine wave measurement. The peak power in a sine wave is 3 dB more than the RMS power. Therefore using twice the RMS power rating for the loudspeaker provides 6 dB more power for short term power peaks.
A good loudspeaker can easily handle this. Why? The RMS rating for professional loudspeakers is almost always measured using pink noise for a test signal. The content of this test signal is an RMS level with peaks that are 6 dB above the RMS level. Thus testing a loudspeaker with pink noise requires an amplifier that can produce power peaks of 6 dB above RMS level of the input signal to the loudspeaker without clipping. The rule of thumb provides an amplifier with this capability.
Real World Audio Signals
Real audio signals usually have peaks at least 10 dB peaks their RMS level. Therefore, with a properly sized amplifier just below clipping on those peaks, the RMS value of typical audio signals will be at least 3 dB below or half of the loudspeaker’s RMS rating. This provides a margin of safety.
Still Possible to Damage a Loudspeaker
Having said this, it is entirely possible damage a loudspeaker with an amplifier that is in the “rule of thumb” power range. Why? Because power handling depends on the type of input signal and the user - not the manufacturer - controls the input signal in actual use.
For example, the RMS and peak levels can be about equal on compressed audio signals and for certain signals from instruments like synthesizers or highly processed electric guitars. This means any amplifier power capability above the loudspeaker’s RMS rating can damage it!
Also, no matter what size the amplifier is, clipped signals are death to loudspeakers, even if the clipping occurs in the mixer, equalizer or other signal processor.
There is not a perfect answer to the power handling question. This rule of thumb is a realistic guide for the optimum size power amplifier to use on a loudspeaker for MOST live audio signals. It allows the loudspeaker to be used to its maximum specified power rating.
Caveat About Distortion
Almost no loudspeakers are rated for their distortion at maximum power. For this reason there is nothing implied by the manufacturer in the maximum power rating that says a loudspeaker will still sound good at its maximum power rating. If you find that a loudspeaker “sounds bad” when run near its maximum rating, then the maximum distortion that you find tolerable will be the limiting factor rather than the maximum power rating.
Note: This applies to professional loudspeakers from reputable manufacturers, and includes drivers as well as complete loudspeaker systems.
Knowing Cone Drivers: How They Work, Understanding Key Data & Specs
What's really going on with woofers, and what are the important factors in how they perform as well as how they impact the performance of loudspeaker systems
(Editor’s Note: Eminence Speaker LLC contributed to this report.)
Cone drivers (also referred to as woofers and transducers in this article) are not overly complex. When an electrical current passes through a wire coil (the voice coil) in a magnetic field, it produces a force that varies with the current applied.
The cone, connected to the voice coil, moves in and out, creating waves of high and low air pressure. The coil and magnet assembly are the “motor structure” of the loudspeaker.
The movement is controlled by the loudspeaker’s suspension, which comprises the cone surround and the “spider”.
The surround and spider allow the coil to move freely along the axis of the magnet’s core (or “pole”) without touching the sides of the magnetic gap.
More important than knowing the details of how cone drivers work is the understanding of key data and what it means. Prior to 1970, there were no easy or affordable methods accepted as standard in the industry for obtaining comparative data about loudspeaker performance.
Recognized laboratory tests were expensive and unrealistic for the thousands of individuals needing performance information.
Standard measurement criteria were required to enable manufacturers to publish consistent data for customers to make comparisons between various loudspeakers.
Things began changing in the early 1970s, however, when several technical papers were presented to the Audio Engineering Society (AES) that resulted in the development of what we know today as Thiele-Small Parameters.
The authors of the papers – A.N. Thiele and Richard H. Small – devoted considerable effort to showing how the following parameters define the relationship between a cone driver and a particular enclosure.
The key working components of a loudspeaker and how they fit.
These parameters can be invaluable in making choices because they can tell you far more about the transducer’s real performance than the basic benchmarks of size, maximum power rating or average sensitivity.
Let’s have a look at the parameters defined by Mr. Small and Mr. Thiele. (And note that we listed Mr. Small first this time – bet he doesn’t get that very often!)
Fs: The free-air resonant frequency of a cone driver. Simply stated, it’s the point at which the weight of the moving parts of the speaker becomes balanced with the force of the driver suspension when in motion.
If you’ve ever seen a piece of string start humming uncontrollably in the wind, you have seen the effect of reaching a resonant frequency. It’s important to know this information so that you can prevent your enclosure from ‘ringing’.
With a cone driver, the mass of the moving parts, and the stiffness of the suspension (surround and spider), are the key elements that affect the resonant frequency.
As a general rule of thumb, a lower Fs indicates a woofer that would be better for low-frequency reproduction than a woofer with a higher Fs. This is not always the case though, because other parameters affect the ultimate performance as well.
Re: DC resistance of the driver measured with an ohm meter, and often referred to as the “DCR.” This measurement will almost always be less than the driver’s nominal impedance.
Some users sometimes get concerned the Re is less than the published impedance and fear that amplifiers will be overloaded. Due to the fact that the inductance of a speaker rises with a rise in frequency, it is unlikely that the amplifier will often see the DC resistance as its load.
Le: Voice coil inductance measured in millihenries (mH). The industry standard is to measure inductance at 1 kHz. As frequencies get higher, there will be a rise in impedance above Re, because the voice coil is acting as an inductor.
Consequently, the impedance of a cone driver is not a fixed resistance, but can be represented as a curve that changes as the input frequency changes. Maximum impedance (Zmax) occurs at Fs.
Q Parameters: Qms, Qes, and Qts are measurements related to the control of a transducer’s suspension when it reaches the resonant frequency (Fs). The suspension must prevent any lateral motion that might allow the voice coil and pole to touch (this would destroy the driver). The suspension must also act like a shock absorber.
Qms is a measurement of the control coming from the driver’s mechanical suspension system (the surround and spider). View these components like springs.
Qes is a measurement of the control coming from the driver’s electrical suspension system (the voice coil and magnet). Opposing forces from the mechanical and electrical suspensions act to absorb shock.
Qts is called the “Total Q” of the driver and is derived from an equation where Qes is multiplied by Qms and the result is divided by the sum of the same.
As a general guideline, Qts of 0.4 or below indicates a transducer well suited to a vented enclosure. Qts between 0.4 and 0.7 indicates suitability for a sealed enclosure, and Qts of 0.7 or above indicates suitability for free-air or infinite baffle applications.
Vas/Cms: Vas represents the volume of air that when compressed to one cubic meter exerts the same force as the compliance (Cms) of the suspension in a particular speaker.
Vas is one of the trickiest parameters to measure because air pressure changes relative to humidity and temperature – a precisely controlled lab environment is essential.
Cms is measured in meters per Newton, and is the force exerted by the mechanical suspension of the speaker. It is simply a measurement of its stiffness.
Considering stiffness (Cms), in conjunction with the Q parameters, gives rise to the kind of subjective decisions made by car manufacturers when tuning cars between comfort to carry a family and precision to go racing.
Think of the peaks and valleys of audio signals like a road surface, then consider that the ideal driver suspension is like car suspension that can traverse the rockiest terrain with race-car precision and sensitivity at the speed of a jet plane.
Vd: Peak Diaphragm Displacement Volume – in other words, the volume of air the cone will move. It is calculated by multiplying Xmax (voice coil overhang of the driver) by Sd (Surface area of the cone). Vd is noted in cc, and the highest Vd figure is desirable for a sub-bass transducer.
BL: Expressed in Tesla meters, this is a measurement of the motor strength of a driver. Think of this in terms of how good a “weightlifter” the transducer can be. A measured mass is applied to the cone, forcing it back, while the current required for the motor to force the mass back is measured.
The formula is mass in grams divided by the current in amperes. A high BL figure indicates a very strong transducer that moves the cone with authority.
Mms: The combination of the weight of the cone assembly plus the “driver radiation mass load.” The weight of the cone assembly is easy: it’s just the sum of the weight of the cone assembly components.
The driver radiation mass load is the confusing part. In simple terminology, it is the weight of the air (the amount calculated in Vd) that the cone will have to push.
Rms: Represents the mechanical resistance of a driver’s suspension losses. It is a measurement of the absorption qualities of the driver suspension and is stated in N*sec/m.
EBP: Calculated by dividing Fs by Qes. The EBP figure is used in many enclosure design formulas to determine if a driver is more suitable for a closed or vented design.
An EBP close to 100 usually indicates a driver that is best suited for a vented enclosure. On the contrary, an EBP closer to 50 usually indicates a speaker best suited for a closed box design.
This is merely a starting point. Many well-designed loudspeaker systems have violated this rule of thumb! Qts should also be considered.
Xmax/Xmech: Short for “maximum linear excursion.” Driver output becomes non-linear when the voice coil begins to leave the magnetic gap.
Although suspensions can create non-linearity in output, the point at which the number of turns in the gap (see BL) begins to decrease is when distortion starts to increase.
Xmax is voice coil height minus top plate thickness, divided by two, while Xmech (as expressed by Eminence) is the lowest of four potential failure condition measurements times two: Spider crashing on top plate, and/or voice coil bottoming on back plate. Voice coil coming out of gap above core; physical limitation of cone.
Take the lowest of these measurements and then multiply it by two. This gives a distance that describes the maximum mechanical movement of the cone. (For Eminence transducers, half the Xmech value represents the one-way excursion limit that if exceeded would cause permanent damage.)
Sd: This is the actual surface area of the cone, normally given in square centimeters.
Zmax: Represents the driver’s impedance at resonance.
Usable frequency range: Manufacturers use different techniques for determining this, and most are recognized as acceptable in the industry. However, they can arrive at
different results.
Technically, many drivers are used to produce frequencies in ranges where they would theoretically be of little use. As frequencies increase, the off-axis coverage of a transducer decreases relative to its diameter.
At a certain point, the coverage becomes ‘beamy’ or narrow like the beam of a flashlight.
See the chart at left – it demonstrates at what frequency this phenomenon occurs relative to the size of the transducer. If you’ve ever stood in front of a guitar amplifier or loudspeaker cabinet, then moved slightly to one side or the other and noticed a different sound, you have experienced this phenomenon.
Clearly, most two-way loudspeaker systems ignore the theory and still perform quite well.
Power handling: A transducer needs to be capable of handling the input power it’s provided. The general rule of thumb is that a power amplifier, when reproducing any program source, “provides” long term- thermal power that is approximately 1/8 its maximum rated output before clipping (rap music excluded).
This is why even UL testing for power amps is done, and listed for on the back of the amp, at 1/8 the rated output power of the amp.
Typically, a loudspeaker will handle somewhere between 6 dB to 10 dB higher peaks than its long-term-average power rating, particularly in the case of the conservative EIA-426A standard used by several manufacturers.
This means that if a loudspeaker is rated for 100 watts long-term-average power, the amp driving it should be rated between 400 and 1000 watts – if the user does not compress the source signal. Once compression is used, all bets are off.
Generally speaking, the number one contributor to a transducer’s power rating is its ability to release thermal energy. This is affected by several design choices, but most notably voice coil size, magnet size, venting, and the adhesives used in voice coil construction.
Larger coil and magnet sizes provide more area for heat to dissipate, while venting allows thermal energy to escape and cooler air to enter the motor structure. Equally important is the ability of the voice coil to handle thermal energy.
Mechanical factors must also be considered when determining power handling. A transducer might be able to handle 1000 watts from a thermal perspective, but would fail long before that level was reached from a mechanical issue such as the coil hitting the back plate, the coil coming out of the gap, the cone buckling from too much outward movement, or the
spider bottoming on the top plate.
The most common cause of such a failure would be asking the speaker to produce more low frequencies than it could mechanically produce at the rated power. Be sure to consider the suggested usable frequency range and the Xmech parameter in conjunction with the power rating to avoid such failures.
Sensitivity: One of the most useful specifications published for any transducer, it’s a representation of the efficiency and volume you can expect from a device relative to the input power.
Manufacturers follow different rules when obtaining this information – there is not an exact standard accepted by the industry. As a result, it is often the case that loudspeaker users are unable to accurately compare the sensitivities of different products.
Eminence Speaker LLC and Live Sound/ProSoundWeb Senior Technical Editor John Murray contributed this article.
Higher voltage? Longer life? Bringing some facts to the process
9V Transmitter
For the 9V transmitter I used the Shure SC1-TA. It has a relatively low current drain (50mA) that remains relatively constant with increasing time until the battery voltage is insufficient (6.5V) to keep the unit on. This is a VHF system.
AA Transmitter
For the AA testing I used the Lectrosonics SM. It is an ultra-miniature digital hybrid UHF transmitter than runs from a single AA cell. The current draw is voltage-dependent. The transmitter turns off when the battery voltage drops to 0.9VDC.
The Test Setup
To test the batteries I drove the wireless transmitters with a balanced aux level signal from an iPod interfaced to each belt pack via a passive summing/balancing interface (Figure 1). Each was driven with program to produce a full-scale receive signal level on its receiver for the duration of the test.
The turn-off voltage and current draw for each transmitter was determined with a variable DC supply (with on-board ammeter) and an oscilloscope. The battery voltage was monitored with a programmable USB data logger, chosen for its very high impedance and minimal loading of the battery.
Figure 1: The test rig. (click to enlarge)
Voltage samples were gathered at 1-minute intervals and the test duration extended well beyond the transmitter turn-off time. The results were plotted using a graphing program.
Figure 2 shows the results of the tests. I included a plot of cost vs. time, as well as an estimate of how many charges would be required for the rechargeable batteries to become cheaper than the disposables (not counting the cost of the charger).
The 500mA Lithium Polymer 9V battery (www.ipower.com) is a relatively new development and was suggested by Gordon Moore of Lectrosonics (the 400mAh unit from the same vendor should be avoided for high current drain applications).
Figure 2: Test results.
Specifications
The two major specifications given for batteries are the voltage (in volts DC) and the available current (in ampere hours).
If a battery can provide one ampere (1 A) of current (flow) for one hour, it has a capacity of 1 A·h. If it can provide 1 A for 100 hours, its capacity is 100 A·h. Most small batteries are rated in mAh.
As with audio gear, “one number” specs can be deceiving.
For example, the NiMH 9V had the highest voltage when fully charged (about 9.5VDC). Yet, it had the shortest life. The Li-Polymer 9V had the lowest full-charge voltage (about 8.2VDC) but lasted the longest.
So, higher voltage is not necessarily better.
The mAh rating of a battery should only be used as a rough estimate of its suitability for an application. For example, the Li-Polymer 9V has a mAh rating that is about three times the NiMH 9V, yet it lasted about six times longer in the endurance test.
Also the disposable AA batteries have higher mAh ratings than the rechargeables, but did not last nearly as long.
Test 123DC
So what can you do with a box of exhausted batteries?
You can test the battery tester! In the run down tests I often let the test rig run overnight to exhaust the battery-under-test. The data downloaded from the data logger showed what the voltage did as a function of time. Most batteries returned to near their full charge voltage once the transmitter shut off. Figure 3 shows the time record for one of the batteries.
Figure 3: The time record for one of the batteries.
If the exhausted battery were tested with a simple DC voltmeter, one could conclude that it was fresh. This is because a voltmeter has an extremely high input impedance to minimize loading on the circuit being tested. A good battery tester will load the battery prior to reading the voltage.
Larry Pajakowski turned the SynAudCon listserv on to an excellent battery tester, the ZTS Pulse Load battery tester (www.ztsinc.com, shown in Figure 4).
Figure 4: The ZTS Pulse Load battery tester. (click to enlarge)
After a fully automatic test cycle, percentage of remaining battery capacity is indicated on the LED bar display.
There are several models available and all are relatively low cost (less than $50 USD). Unlike my DC voltmeter, the ZTS correctly indicated the depleted state of each battery after the run down test.
Pat and Brenda Brown own and operate SynAudCon, conducting training seminars around the world in addition to providing in-depth web-based training.
If all else fails, don a bee bonnet, and convince your audience that the sound they’re hearing is a recent insect infestation
If you’ve been in the live sound business for any time at all, or working in any field related to sound, you’re quite likely to agree that the most maddening technical anomaly of all is the elusive “hum” or “buzz.”
These two terms can be related or separate, but they’re both nasty business just the same.
We’ve all set systems - large and small - only to power up and discover the beast within. Is it 60 Hz? 120? 240? A combination? Is it mains? Monitors? Backline? Lights?
First, do no harm! (Yep, this applies to us too.) Don’t start undoing your stage work in a panic. Try to discern what frequency(ies) are the problem. A Real-Time Analyzer can come in quite handy - even a rudimentary online RTA app is worth the investment.
Let’s focus on the common 60 Hz hum. Hopefully you’ve taken the time to verify the integrity of the house power. This is a must. A simple line checker from the hardware store is a cheap way to make sure the house is “keeping it clean” and feeding the proper line voltage – and with the hot, cold and ground in the right order.
Make sure (especially in small/medium house applications) to connect all PA power feeds, as well as backline, to the same source. Don’t mix and match! It’s a sure-fire ground loop headache waiting to happen.
Invest (wisely) in proper power conditioning and sequencing devices. These protect and catch big voltage issues long before they reach your gear. Also be sure to reduce any capacitive coupling by keeping parallel runs of audio and AC power separated as far as possible from one another. Do a little homework on parasitic coupling. It’s a fascinating subject and very important to us sound people who are prone to running lots of wire.
I know, I know, some of you are saying “go digital and clear up a lot of these issues.” True, some of this applies more to us old (and young) “analog dogs,” but digital offers its own sets of problems. I also don’t think I’m speaking out of turn in either case when I say that you’re only as good as what you’re being fed from the house.
Maybe you’ll get lucky and be able to isolate the problem to one or two input channels. And don’t forget the backline. Sometimes a bad filter capacitor in a backline amp can wreak havoc on your system and the stage audio as well. Use those DI ground lifts as needed. Keep XLR cables in mint condition. A few hours of work in the shop can save lots of headaches in the field.
There’s nothing wrong with older power amplifiers, but you might want to have a look inside. Change those old filter caps, or if you’re not budget-challenged, get some new amps. (They’re lighter weight too!)
Watch out for older small-venue fluorescent lighting or newer compact fluorescents. They and their respective ballasts have a way of getting into your wired (and wireless) systems. Most of the time the problem is a poorly grounded “main,” but nothing substitutes for a clean, stable and well-grounded source. (Not always possible, I well know.)
If all else fails, don a bee bonnet. (I always keep one handy in the gear box.) Convince your audience that the sound they’re hearing is a recent insect infestation, smile, and (try) to have a great show anyway!
Greg Stone has worked in live sound since 1976 and is the owner of Hill Country Ears Sound Company in South Texas.
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