Article

Tuesday, June 28, 2011

OSA And SES Give Assist To “Oprah’s Surprise Spectacular” With Yamaha And NEXO Audio Support

The event aired May 23 and 24 bringing together some of the biggest names in movies, music and television in the one-time-only gathering to celebrate the 25-year legacy of "The Oprah Winfrey Show"

With joint production support from Special Event Services (SES) and On Stage Audio (OSA), “Oprah’s Surprise Spectacular” (Harpo Productions) aired May 23 and 24 bringing together some of the biggest names in movies, music and television in the one-time-only gathering to celebrate the 25-year legacy of “The Oprah Winfrey Show.”

As part of audio system, SES and OSA provided two 96-input Yamaha PM1Ds (cascaded together for 200+ inputs), an M7CL-32 digital console, DME64N digital mix engine, and MSP101 reference monitors.

Monitor world consisted of dual 96-input Yamaha PM1Ds, seven NEXO NXAMP 4x4s, and 12 of the new NEXO 45 N-12 line monitors.

“The Yamaha PM1Ds at both FOH and Monitors were chosen by Harpo’s mixers due mostly to familiarity with the control surface,” states Jim Risgin, OSA Vice President.

“In conjunction with our Audio Director, JR Chappell, FOH mixers Jimmy Ostrom and Scott Ragsdale, and Monitor Engineers Brad Galvin and Ian Kuhn, we all decided early on that the Yamaha PM1D platform was by far the best choice for this event,” states Gerry Formicola, Audio Production Manager, Harpo Studios.

“Its ultimate reliability and versatility allowed for us to make changes on the fly as the ‘oh by the ways’ came up in our tremendously tight time frame from load in to load out.” Harpo Productions also has a Yamaha PM1D installed in their primary studio.

isgin said the Yamaha M7CL was used as an on-line backup console fed with splits on all production mics, and full mixes from the broadcast trucks.

“We took advantage of the MY card platform implementing Rocknet MY141 cards for all signals to and from the M7CL,” says Risgin.

The Rocknet 100 series stage racks fed all inputs, and all the outputs were routed to the Yamaha DME64N matrix device (“chosen for its rock solid design and ability to take multiple sources via its MY slots” Risgin added) through the same MY141 cards.

The DME64 was outfitted with MY16AES cards to receive all signals for the main PA and then used as the system processing for all PA zones. These zones were fed out of the DME via Rocknet keeping all signals native to Rocket for the long haul up to the catwalks for distribution.

All consoles, DME and Rocknet were fed Master Word Clock from an Apogee Big Ben, keeping all signals synchronized. The DME was the matrix for combining all signals and allowing redundant console operation.

Harpo’s audio production team chose NEXO 45 N-12 line monitors for two reasons: audio quality and sensible industrial design.

“Yamaha District Manager Mike Eiseman had been talking to me about the 45 N-12s for months,” says Formicola. “When this event came up, it seemed a natural fit to take advantage of its low profile for television as well as the exceptional sound of the units.”

Risgin said he found the NEXO wedges stable and more than able to handle all the requests from the various artists using them during show taping. They were able to scale coverage by adding more segments without making significant tonal changes, and not having to chase EQ’s regardless of the quantity of cabinets deployed at any position.

Some of the guests that appeared on the broadcast and received the added benefit of the new NEXO line monitors included Rascal Flatts, Kristin Chenoweth, Rosie O’Donnell, Dr. Phil McGraw, Dr. Mehmet Oz, Nate Berkus, Alicia Keys, Aretha Franklin, Patti LaBelle, Josh Groban, Jackie Evancho, Jamie Foxx and Stevie Wonder.

The United Center, which hosts over 200 events per year and is home to the Chicago Blackhawks and Bulls, welcomed 13,000 Oprah fans for the taping.

Yamaha Commercial Audio
Nexo

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Tuesday, March 22, 2011

Anton / Bauer To Present At NAB 2011

The company will offer presentations from leading industry professionals in the Vitec Group’s live event area.

Anton/Bauer has announced they will feature several presentations from industry experts discussing on-location shooting and proper battery care and maintenance in The Vitec Group’s Live Event Area during the 2011 NAB Show in Las Vegas.

“Each year, NAB provides Anton/Bauer with an opportunity to not only share our expertise with the industry, but to gain insight from other highly skilled professionals who will be in attendance,” says Shin Minowa, vice president of marketing and business development.

“We are pleased to be presenting on such relevant topics regarding batteries and power and look forward to a productive and enlightening show.”

The following is a list of Anton/Bauer presentations, along with the dates and times:

Monday, April 11, 11:30 am – 12:00 pm, “Shooting on Location with Buck McNeely”

Buck McNeely, host and producer of the Outdoor Adventure TV series “The Outdoorsman with Buck McNeely,” has been using Anton/Bauer batteries exclusively for more than 20 years. The largest syndicated outdoor adventure series in the world,

“The Outdoorsman” is broadcast on over 500 TV stations in the U.S. and on many networks worldwide. McNeely has been working as a cameraman, producer and director in the TV and film industry for more than 30 years and will be on hand to discuss shooting on location with Anton/Bauer.

More information on McNeely and “The Outdoorsman,” on their website.

Tuesday, April 12, 2:00 pm – 2:30 pm, “Battery Master Class – Proper Care and Feeding for Your Batteries” (this session will recur on April 13 from 3:00 pm – 3:30 pm)

Batteries are a part of our everyday lives, from cell phones to laptops to cameras, and can be the cause of great irritation when they don’t work properly. But most people are unaware of the basics – How long do your batteries typically last and why? How do batteries work? Why don’t they work sometimes?

As the experts in battery innovation and technology, Anton/Bauer will present the Battery Master Class. Aimed at educating NAB attendees about batteries and power supplies, the Battery Master Class will focus on the many different types of battery chemistries and the advantages/disadvantages of each, charging routines and voltage, getting the longest life from your battery and will conclude with a question and answer session.

Throughout the NAB Show, various Vitec Group brands will share the same Live Event Area stage and feature presentations from leading industry professionals, including Vincent Laforet (Monday, April 11, 12:00 pm – 12:30 pm), Vincent Laforet and Phillip Bloom (Monday, April 11, 3:30 pm – 4:00 pm), Phillip Bloom (Tuesday, April 12, 12:00 pm – 12:30 pm) and Michael Huss (Wednesday, April 13, 12:00 pm – 12:30 pm).

The agenda and guest speakers at the events may be subject to change.

For up to the minute information about this exclusive event, and to register for any of the sessions, please visit the Vitec Group’s website.

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Monday, March 07, 2011

In Profile: Ted Leamy - System Engineer & Businessman

On the edge of the audience experience.

“You know,” Ted Leamy says, “I’m always troubled when people ask me to write or be on panels, telling me, ‘we want to hear what you have to say,’ because I don’t know much of the math.”

“I just know you’re supposed to point the loud part toward the audience and turn it up.”

As understatements go, that’s a big one. Over the course of his career Leamy has optimized sound systems for a who’s who of important acts and venues of the past 30 years.

In every case, however, the experience of both those aiming the “loud part” and those on the receiving end of it have always been a major preoccupation for him; guiding his hand as both a systems engineer and businessman.

Consequently, when he talks about career highlights, he often focuses on people - the mentors, friends and acquaintances who have challenged him to excel and shown a path forward in good times and bad.

His experiences with Robert Scovill on the Rush and Def Leppard tours serve as a prime example.

“They were a technical highlight and a triumph,” he says. “Robert and I found a way to work together taking advantage of each other’s skills to blend the science of system design/optimization with the art of mixing. I learned to listen critically during those shows and rely little on instrumentation once the performance began.”

Born and raised in Union, NJ, Leamy started working in audio as a teenager. And while he cites a love of music as a major factor in his choice to do so, underlying that was a childhood attraction to science and technology.

“I was a geeky little kid. I had all my amateur radio licenses when I was seven or eight years old.”

Once he began working he saw no reason to interrupt his busy schedule by going to college. “While everybody else was attending shows, I was unloading trucks and rigging loudspeakers. Everything for me was practical. I think I was a bright young man; it’s just that liquor, women and music seemed a far better choice than an electrical engineering degree.”

By age 20, however, after a two-year stint with Teddy Pendergrass in the mid 1970s, Leamy began questioning his career choice. At the time he’d landed a regular gig at NYC’s infamous Great Gildersleeves, occasionally working at nearby CBGB to augment his pay.

“It sounds romantic, but those were terrible times. I wasn’t making any money. I was sleeping in a flophouse. It was dreadful.

“Still, there’s something to be said for keeping at it,” he continues, adding that if he’s remembered for any single trait in his career it would be perseverance, a “stick-at-it-untilit’s- done-right” theme driven, in part, by some of the more difficult experiences in his personal life. Experiences, by the way, he wouldn’t trade away for an easier journey.

Audience Experience
His perseverance paid off when Electrosound’s Mick Whelan came through Great Gildersleeves on an Elvis Costello tour in 1977. Whelan, who would become one of Leamy’s earliest mentors, was impressed the young house tech.

“He said, ‘I gotta take you with me’,” Leamy laughs. “And I said, ‘sure, sure, now get the hell out of the club and don’t steal anything’.” But less than a week later, Leamy was working a Cheap Trick tour with Whelan.

“In the late 1970s, if you were sober, had a strong back and showed up on time; those were pretty good qualifications for a starting position.”

But Leamy brought far more to the table than that. Fascinated by music and how it could sound so different from venue to venue, he consumed technical information voraciously, taking full advantage of his senior compatriots’ willingness to share their knowledge.

“I gotta tell you, after I was at Electrosound for about six months I thought to myself; if I stay sober, if I don’t do drugs, if I pay attention and learn, I could run this place.”

And he did just that, working his way up from “just a guy slinging loudspeakers” to become the company’s president. “Now some people would say, that’s not something to be proud of, it took you 23 years!”

Throughout his career, Leamy’s approach to system optimization has always centered on the audience experience. “That’s the ultimate arbiter of whether you’ve succeeded or not. I may not have time to be a civilian, but I am able to turn off my technical side and just listen, and I think that’s brought me a lot of success. But paranoia helps, too,” he adds, “and a certain level of low self esteem.”

Clearly, beyond versatile critical listening abilities, he also possesses an often self-deprecating sense of humor, which he says is integral to his leadership style.

“It can be disarming in difficult situations. Laughing while pushing a ‘giant boulder up a hill’ is a good way to motivate others to join in and help.”

That, and his fanatical dedication to getting things done on time and correctly won him the respect of his peers on high profile outings like the Bob Dylan/Tom Petty and the Heartbreakers and Grateful Dead stadium tours in the mid 80s. His work ethic also earned him the nickname of “sergeant major” from Electrosound’s owners.

Practical Things
When it comes to system optimization, Leamy cautions against being overly reliant on instrumentation. “It can be hypnotizing,” he offers, and can distract from serving up what both the audience and the crew want and expect – namely, a great show.

“A bad design is a bad design,” he adds, with the mastery of the mandatory keystrokes of any given technical platform only part of the equation. “That’s why it’s important to look at the practical things. When you’re optimizing a system a lot of people look at the instrumentation and say, ‘well, it tells us this, so that’s the answer.”

“And I reply, ‘well, that doesn’t make any sense. So let’s look at what we did wrong with the test rig.’ I joked earlier that it’s good to be paranoid, to have low selfesteem, but I’m always questioning if it’s really the answer, or if it’s just the first answer that came by.”

To Leamy, good sound is about exceeding expectations, a passion that enabled him to develop leadership qualities that the shy little kid with the amateur radio licenses couldn’t have imagined possessing. These qualities informed his role on many tours, including 1995’s Nine Inch Nails/David Bowie “During the Dissonance” tour.

“It was a great tour, but both acts were on at the same time during the set change - a unique and exciting challenge. So two mixing consoles were live at the same time and they thought for sure there was going to be fistfights among the band’s mixers. So I would go out on the tour as something of a statesmen to keep ‘the peace’ - there were no fistfights on my watch.”

Leamy refers to the leadership roles he’s played at Electrosound, JBL and now Pro Media/UltraSound as “a set of overalls” he puts on, but adds, “I think I have a way of breaking a problem down to its base parts; developing a plan, helping everyone involved understand where the finish line is, and never being afraid to roll up my sleeves and push to get there.”

This also requires an abiding patience - “patience for people,” as he puts it. “Everybody’s got something to offer, and you’ve got to listen as much as you talk.”

Moving Farther Away
That said, Leamy also admits to “an impatience for incompetence and crappy sound” that has played a key part in his professional advancement.

The ethic served him well when he departed Electrosound in 2000 to work with JBL Professional, where he held a number of positions - some he was instrumental in creating - before becoming vice president of installed sound.

During his tenure at JBL, he added some impressive projects to his portfolio, among them a system retrofit of the Grand Ole Opry, as well as installations like the Walt Disney Concert Hall and dozens of high-profile sporting venues, including Chicago’s iconic Soldier Field. Working on permanent installations for very large venues was a logical next step in his career.

“The whole nature of modern music has matured, so the whole concept of installations has matured,” he explains.

“There’s good audio all around us - in our cars, in our homes. People’s expectations, whether they’re going to a cinema, a sporting event, or to worship, are higher than ever.”

Ultimately, however, he felt he was moving farther away from the front line of the audience experience, and, frankly, missed it. Not that the front line had always been pleasant: “The cold showers, the crappy food; you’re not living the life of glamour.”

Another complication, he says, was one of the personal experiences he spoke of earlier - the ongoing effects of a childhood illness that had once evolved into a life-threatening situation in the early 1980s.

“Still, the problem is that getting off the road was the first step away from where the excitement is. A concert, or a sporting event is a tribal experience.

“To go to the new Meadowlands and stand in the middle of that crowd and do some critical listening is incredible in the context of the event. What you’ve done is an additive element to that tribal experience.

That’s excitement. That’s a measure of success. To be able to affect a change on that front line and see a positive difference, it’s awesome.”

Coming Back Home
Inevitably, that conviction prompted his move to Pro Media/UltraSound in 2007. A homecoming, he says, both professionally and personally. “At JBL I didn’t do the installations, but here I do, and I’m running a business that I absolutely adore.”

“When I was with Electrosound and we did the Grateful Dead, Tom Petty and Bob Dylan stadium tours, Don Pearson (co-founder of UltraSound) and I became such good friends. And UltraSound and Electrosound, gosh, you could hardly tell the companies apart, we worked so well together.”

Leamy also counts Pro Media founder Drew Serb and Pro Media/UltraSound’s Derek Featherstone among his close friends and business associates. “These are folks that have known me for ages. It was just a good life decision for me.”

“About every three or four years, even during my tenure at JBL, they’d call me up and say, ‘c’mon, come and work here.’ My only regret is that I come here after my dear friend Don passed away and that he and I never had the opportunity to sit in the building together as comrades in arms.”

In Leamy’s world, it comes down to the people - “Mick Whelan, Jim Douglas, Sam Berkow, Mark Gander at JBL, and many others,” he says, that informs his enduring conviction that, as an audio professional, businessman, and human, it’s important to look ahead as well as behind you.

“A lot of people have helped me, which is why I say that if you achieve some level of success, you’ve got to turn around, see who’s behind you and help them.”

Coolest Place To Be
It’s a philosophy he puts in practice by sharing his own perspective and experiences with others. He’s a contributing editor and writer for various pro audio publications, and also serves as associate director of the Zappa Institute of Technology - now an officially accredited academy in the Los Angeles Unified School District that teaches at-risk students about job opportunities in production.

Looking behind him and lending a hand to help others move forward is something Leamy intends to continue to do as long as he continues to work at making good sound, which he intends to keep doing. Period.

“For me there’s something about audio that inspires the concepts of God and creation. These are the laws of physics, the laws of the universe, the foundation underlying what music and audio technology are.”

“It’s really the optimization of a loudspeaker system that has inspired and excited me the most, and continues to. And now I’m back to the edge of the audience experience, to the nexus of art and science, and it’s the coolest place in the universe to be.”

Fast Facts
Job Title: Chief operating officer at Pro Media/UltraSound
Location: Hercules, CA
Years in the Business: 30-plus
Favorite Tools: Practical common sense
Worked With: Pro Media/UltraSound with various touring artists and on installs including Dallas Cowboys and New Meadowlands Stadiums, JBL Professional on installations including Walt Disney Concert Hall, Soldier Field, the Grand Ole Opry and multiple NBA, NFL and major league baseball venues; and Electrosound as system engineer for Rod Stewart, Tom Petty and the Heartbreakers, Bob Dylan, Rush, Lenny Kravitz, Def Leppard, Foreigner, Cheap Trick, Billy Idol, Bob Marley, Ted Nugent and others

Based in Toronto, Kevin Young is a freelance music and tech writer, professional musician and composer.

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Tuesday, October 19, 2010

Tech Tip Of The Day: Battery Shelf Life

How long can I store batteries? Do they lose power?

 
Q: Like lots of readers here, I help out at my church on Sunday with the Audio.

Recently I was reading ProSoundWeb and saw a TechTip where someone asked if storing used batteries in a refrigerator really makes them last longer.

Now, I can’t for the life of me believe that this can remotely work, even if science is slightly on the Tech Director’s side.

However, after reading all that I got to thinking about the batteries we use at church.

How long can I store batteries (the normal way, thank you)? Do they lose power?

A: Most battery types lose up to 8-20% of their charge per year, depending on the temperature they are stored at and the battery type.

This is due to non-electricity producing chemical “side” reactions that take place within the battery’s cells over time.

As you mentioned, it is possible to extend the life of alkaline batteries by up to 5% through an alternative storage method.

However, no matter how you chose to store your batteries, it might be wise to take the advice of church blogger Gary Zandstra and invest in a battery tester which can help you prevent the preventable.

As always, we welcome input from the PSW community and would love to know your thoughts on battery storage and life. Feel free to let us know in the comments below.

 
For more tech tips go to Sweetwater.com

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Sunday, December 30, 2007

Transcript: Smaart Impulse & Phase Measurement

A thoughtful forum exchange sheds light on the issues of Smaart Impulse & Phase Measurement.

Question posted by Patrik Arnekvist on September 17, 2001
I know there’s a lot of Smaart experts here so here goes a thought. When using the delay locator, Smaart assumes that the right delay setting is at the highest peak of the waveform. At low frequencies - is that really the right thing to do, I mean the “waveform” starts at a zero energy level..or? At 40 hz, there is some time between zero and top of the impulse. (Does Smaart use the same peak as the reference?) I experimented with it, and did a measurement of a 2 way crossover going directly into Smaart with no delay applied. Smaart wanted to delay the low output. Why? I also couldn’t get a coherent phase response with no delay on the low output. How does smaart analyse the phase response? I also wonder what the difference is between 0 deg and 360 deg, is it only time dependent?

Reply posted by Paul Tucci on September 17, 2001
- “When using the delay locator, Smaart assumes that the right delay setting is at the highest peak of the waveform.” For an Impulse Alignment, yes, the peak is the right thing to use. For a smooth phase through acoustic crossover area alignment, it may NOT be the right timing. There are choices to be made about what to do with the info Smaart gives us.

- “At low frequencies, is that really the right thing to do? I mean the “waveform” starts at a zero energy level..or?” At 40 hz there is some time between zero and top of the impulse.” Correct, and insightful.

- “I experimented with it, and did a measurement of a 2 way crossover going directly into Smaart with no delay applied. Smaart wanted to delay the low output. Why?” I did this same experiment and scratched my head for months. Its called group delay. The low pass filter in the crossover causes some things to happen. Higher frequencies are rolled off at a chosen db/octave at a certain frequency. That’s the understandable part. The PHASE shift caused by the crossover, and this is just a fact of life one cannot avoid, is problematic. Yes, it is in fact delaying the low frequency output. That’s why you measured it that way and that’s why Smaart’s phase trace was incoherent until you added the proper delay to synchronize your measurement. Smaart gives you some good clues to tell you when measurements are bad. I am parent on duty this Am so I must run. I’m glad to see all these Smaart questions coming up now. I suggest to the powers that be that a Smaart-centered live chat is in order. I’ll elaborate more later.

Reply posted by Patrik Arnekvist on September 17, 2001
Thanks for your response. The thing is also, when I delayed the low output , I got a deep cancellation at the crossover point, if it all were in phase, why would that happen?

Reply posted by Paul Tucci on September 18, 2001
“The thing is also, when I delayed the low output , I got a deep cancellation at the crossover point, if it all were in phase, why would that happen?” Your choice of wording is curious. You say Smaart wanted to delay the low end. Do you mean to say Smaart measured a time difference between the reference side of your equation and the output of your xover? That would be normal. The delay would go on the reference side because you want to have compare the two when they are synchronous. “Row, row, row, your boat” vs “gently down the stream” does not a valid comparison make. Understand the analogy?

If you introduced delay onto the measurement side of the equation, ie, the low xover out, you made an even more invalid comparison. This would explain your lack of coherence. You may have created the transversal equalizer responsible for the notch described by comparing the same signal to itself, though one is offset in time at twice the wave period of your notch frequency. That’s a mouthful. Then again, if you didn’t include the throughput delay of the digital (?) xover (approximately one millisecond)in your measurement, a 500 hz notch (1/2 of 1000hz or one millisecond of time) would appear. Could go either way.

Reply posted by Earl Driggers on September 17, 2001
Keeping in mind that phase is time and time is phase, by delaying the low output the relative phase between the two outputs is probably 180^( or close ) now. Another thing to keep in mind is that phase/time misallignment will only effect the frequencies common to both outputs. Now that the delay time is correct on the outputs, having to invert the phase on one of the outputs is a common occurance.

Reply posted by Chip on September 18, 2001
Earl, I’d take some degree of exception to the phrase “phase is time, time is phase”. While this is essentially true, I submit that there can be differences. For example, It’s entirely possible to have two completely time coherant signals. It’s just as possible to adjust the phase of one of those signals, without adjusting it’s time. Agreed?

I’m still trying to completely get my head around this one. But to the best of my understanding, the real trick seems to be realizing the difference. Here’s what I’ve found to be the marker between the two .... phase angle. If the time is correct, the phase angle of the two sources will be parallel. if the phase angle is leaning forward, or backward, it would indicate early or late arrival. In the case where the phase angle is parallel but they don’t overlap, phase adjustment would be the appropriate tool to slide the phase angle without changing the angle. Is this making sense? Any input would be helpful.

Reply posted by Phill Graham on September 18, 2001
Alright Chip, see if this helps. For a wave to be a wave, it has to propagate in both space and time, otherwise it is simply a vibration. Math people wanted to be able describe things that change in a periodic manner. It turns out that trigonometric functions fit the bill nicely. However, you need a conversion factor that takes real world wave position and time, and translates it into the mathematical notion of “angles”.

Hidden in the equations for the wave propagation are two basic parameters. One basically says “swallow up” 30deg. of angle for every foot of travel in the air, and the other says “swallow up” 30 deg. of angle for ever .5sec of time elapsed (or whatever). The combination of these describes the wave’s movent in space and time. “Phase” lumps these two together.

It is important to realize that pure delay is not a flat (zero slope) phase plot, but rather a linear one with a slope proportional to the delay through whatever the device in question is. That is where the term “group delay” (-1st derivative [slope] of the phase) derives from, as the the group delay curve will be completely flat for an device with pure delay.

When Meyer sound talks about their phase correction through the spectrum, it is important to remember the small print at the bottom “phase vs. pure delay.” They are not correcting the phase to represent a flat (zero slope) line, but rather trying to get it to match the straight (but sloped) line of the pure delay between the speaker and the measurement system. Let me know if this makes sense, I wrote it in a hurry.

Reply posted by P.Tucci on September 18, 2001
“I’d take some degree of exception to the phrase “phase is time, time is phase.” Me too. While limiting your discussion to sine waves, I believe that to be true. A 90 degree phase shift of an 1120 hz tone is a quarter mSec of time. A 180 degree phase shift of the same frequency would be half of a wavelength, or half a mSec of time. At other frequencies, the same time displacement does not create a similar degree of phase shift as other have pointed out. It could be argued that phase is time on a specific frequency by frequency basis only.

The longer the wavelength, (lower frequency) the more time is needed to create that degree of phase shift when compared to an equal phase shift of a shorter wavelength (higher frequency. With that in mind, it makes sense that an offset delay introduced at the crossover’s low output will cause a phase shift that affects the upper end of the bandwidth more so than the lower end of the bandwidth. An equal phase shift across that entire bandwidth would have to be differing delay times for differing frequencies. If I got my money’s worth from Jamie, Sam, Don, and Mr. McCarthy, that would be an all pass filter.

Reply posted by Tom Danley on September 18, 2001
“An equal phase shift across that entire bandwidth would have to be differing delay times for differing frequencies. If I got my money’s worth from Jamie, Sam, Don, and Mr. McCarthy, that would be an all pass filter.” This is the behavior of a point source (one who’s diameter is small compared to the wavelength it is producing) with “flat” response. As defined by its electrical equivalent circuit and as measured ala Heyser, a typical woofer, to have flat frequency response, must (mid band) have an acceleration response to the VC force. This is accomplished by the motor force acting on the drivers moving mass which ends up reflecting an RC filter (C being mass). This 1 pole roll off of the radiator velocity counter acts the improving radiation efficiency (an acoustic/dimension related slope with no phase shift associated with because it is a changing resistance), producing flat response but at about a -90 degree acoustic phase shift (input Voltage with respect to output pressure after all fixed time delays are accounted for). At the low end, even in a sealed box or infinite baffle, cabinet tuning will cause a large amount of acoustic phase change, going through zero degrees at resonance (Z max where mass and spring are equal but opposite) to a positive value as the system is dominated by compliance stiffness.

Going up, the phase is also zero at the R min point in the impedance, this is where the series L in the VC is equal but opposite the mass reactance (C) and these two terms cancel out leaving the Rdc in series with the acoustic load and losses (a small R). So you see, you all ready have a “thing” which has a different delay for each frequency, a woofer and most speakers. At low frequencies, unwrapping the acoustic phase back to nominally zero degrees can be done without dsp and when done makes a wonderful sounding subwoofer. Unlike conventional woofers, the zero phase and flat response yields a system which CAN reproduce a complex waveshape.

The normal, non zero acoustic phase is the main thing which has stopped many attempts at active sound cancellation in its simplest form. I have spent a great deal of time working on speakers which had as little acoustic phase change over the widest frequency range possible as well and would also say that makes a significant audible difference.

On the other hand, I do everything with drivers, crossovers and horns and physical placement, partly because I want to actually attack the real problem but also because I am not to hip actually working with dsp. I know it is possible to correct all the phase stuff this way too and there is at least one hifi dsp correction product which claims to do this, at least at the microphone location.This is one area where an efficient horn can have an edge, to the extent they are dominated by the acoustic load, a resistance, there acoustic phase is resistive about zero degrees (output pressure and input voltage coincide over a wide range of frequencies).

Reply posted by Chip on September 19, 2001
Tom, Two questions:
1) would you consider preparing a “idiots guide to LF phase”? I’m very interested in the phase artifacts caused by different types of boxes and venting / porting methods. I never realy considered this as such a huge factor in the differing performance of different types of boxes.
2) How would you best describe an all-pass filter, and it’s effects?
David, et all, please respond as well. This type of shared information is why we are here.

Reply posted by Nathan Butler on September 18, 2001
Whenever I think of this, I like to reference some simple mathematics. Bear with me… A pure tone can be described by:
1) cos(wt) where w = frequency, t = time

With a phase shift (1) becomes:
2) cos(wt + p) where p = phase in degrees

With a time delay, (1) becomes:
3) cos(w(t + td)) where td = time delay

As an example, let’s say w = 100, p = 90, and td = 0.9
(2) becomes cos(100t + 90)
(3) also becomes cos(100t + 90)

Now let’s make the frequency, w = 200
(2) becomes cos(200t + 90)
(3) becomes cos(200t + 180)

Essentially, a time delay yields similar results to a phase shift, except that a time delay increases the phase shift with frequency. Hope this helps.

Reply posted by Patrik Arnekvist on September 18, 2001
I gotta go and try if changing phase angle on my omnidrive to, say 90 deg changes the delay, I guess it will. but how does one come to the conclusion that here I need to shift the phase angle 90 deg? I can’t really inderstand why one would need to do that. But changing the delay must be different, cause the time of 90 deg at 5kHz is quite different than 90deg at 100 Hz..right? I’m getting a headache here, excuse me for thinking out loud.

Reply posted by Chip on September 18, 2001
Patrik, If I understand the electronics correctly, the phase adjustment in the DSP simply “rolls” the phase without adjusting time. If I’m correct, changing the phase would not change the result of an impulse time measurement. To the best I can understand it, at this point, the differentiating factor between the requirement for a phase adjustment VS. a time adjustment would be the phase angle relationship AT the crossover frequency. If the angles are not parallel, some time adjustment is required.
Once the phase angles are parallel, if necessary, you can adjust the phase to make the phase angles lay one on top of the other while remaining parallel. If you were to continue to adjust the time, you would loose the coherance of the phase angles and have a less phase coherant area above, and below, the crossover point.

Reply posted by David Gunness on September 18, 2001
Everything you’ve said is true - so I think you’ve got it. Let’s see if I can clarify it. If the arrival times are the same, the phase response curves will be parallel. If the two signal paths are “in phase” at crossover, the phase response curves will have the same value at the crossover frequency. The ideal situation is for both of these conditions to be true, but occasionally you can’t achieve both by only adjusting delay.

Reply posted by Chip on September 18, 2001
David, This is exactly what I was getting at. You were able to deliver it in a much more understandable way than I was. Can you think of any other way to differentiate between the two?

Reply posted by David Gunness on September 18, 2001
Delay always produces phase shift, but the phase response can be shifted without producing delay.

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