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Title: Power amp specs and ratings....
Post by: Nathan Schwarzkopf on March 11, 2015, 11:42:23 am
Its been a long time so hello all...

I know this has been beat to death.... because I have read and searched and read some more. 

If some one can give me a straight run down on what is what on these spec sheets.  Every manufacture seems to do testing a different way.  I know thats to get the numbers in the sweet spot for marketing.  The closest to a standard seems to be  the 20ms burst.  Powersoft uses a 25% duty cycle (8ms on 24ms off).  Others dont say like Lab.  If you read that paper they meyer put out it says that anything shorter than a half second test is not a real world application.  On a similar note it doesnt appear that manufactures post data like slew rate and damping anymore.  Its been a while since I had to compare and contrast like this. 

If anyone can help it would truly be appreciated.... if you are all sick of the discussion and tell me to go fly a kite i understand as I am sick of beating my head against the wall trying to line the numbers all up and find the best fit. 
Title: Re: Power amp specs and ratings....
Post by: John Roberts {JR} on March 11, 2015, 12:14:46 pm
This has been beat to death but the answer is there is no simple answer. Since music playback or performance involves a dynamic widely changing signal, simple single number tests do not reveal the complete story.

This is very similar to the problem with characterizing speaker power handling. They actually go hand in hand since the dynamic power output of amplifiers needs to be similar to dynamic power handling of speakers.

I do not accept the popular rant that manufacturers are trying to obscure the performance of their amplifiers, while marketers are paid to make them appear better than the next guy. 

My old advice remains the same, listen to reports from end users of different amp models. preferably with the same speakers as you use. The bottom line is how do the products work in actual use. This market acceptance (or not) has been the corrective feedback loop to filter out the weak sisters from the capable performers.

JR

PS Damping factor and slew rate are no longer audibly different between modern amps so making purchase decisions based on inaudible differences is not a good use to time or money.
Title: Re: Power amp specs and ratings....
Post by: TJ (Tom) Cornish on March 11, 2015, 12:54:40 pm
Its been a long time so hello all...

I know this has been beat to death.... because I have read and searched and read some more. 

If some one can give me a straight run down on what is what on these spec sheets.  Every manufacture seems to do testing a different way.  I know thats to get the numbers in the sweet spot for marketing.  The closest to a standard seems to be  the 20ms burst.  Powersoft uses a 25% duty cycle (8ms on 24ms off).  Others dont say like Lab.  If you read that paper they meyer put out it says that anything shorter than a half second test is not a real world application.  On a similar note it doesnt appear that manufactures post data like slew rate and damping anymore.  Its been a while since I had to compare and contrast like this. 

If anyone can help it would truly be appreciated.... if you are all sick of the discussion and tell me to go fly a kite i understand as I am sick of beating my head against the wall trying to line the numbers all up and find the best fit.
Nathan, here's my Cliff's Notes version of amplifier picking:

Step 1 - If the manufacturer of your speakers recommends a particular amp, buy it.  Even if it is more expensive, seems less of something on paper, etc.  Doesn't matter - buy the manufacturer's recommended amps and processing so you have a complete system rather than a buffet.  GOTO Step 4.

Step 2 - Buy an amp from a reliable manufacturer - QSC, Crown, Crest, Powersoft, etc.

Step 3 - Buy an amp that can produce your speakers' program power rating at the impedance you will be using them at.  For example, if you intend to run two 8Ω speakers rated at 800w program power, get an amp that can deliver 1600w into 4Ω.

Step 4 - Use recommended processor settings for your speakers - especially high-pass settings

Step 5 - Don't ever drive your amp into clipping for any reason.

Step 6 - Use your senses to determine if your speakers are stressed - ears, nose, etc.  If you sense trouble, TURN IT DOWN.

Step 7 - Enjoy the reasonable maximum performance of your system with minimal risk of blowing stuff up.
Title: Re: Power amp specs and ratings....
Post by: Chrysander 'C.R.' Young on March 11, 2015, 01:52:16 pm
Nathan, here's my Cliff's Notes version of amplifier picking:

Step 1 - if the manufacturer of your speakers recommends a particular amp, buy it.  Even if it is more expensive, seems less of something on paper, etc.  Doesn't matter - buy the manufacturer's recommended amps and processing so you have a complete system rather than a buffet.

Step 2 - Buy an amp from a reliable manufacturer - QSC, Crown, Crest, Powersoft, etc.

Step 3 - Buy an amp that can produce your speakers' program power rating at the impedance you will be using them at.  For example, if you intend to run two 8Ω speakers rated at 800w program power, get an amp that can deliver 1600w into 4Ω.

Step 4 - Use recommended processor settings for your speakers - especially high-pass settings

Step 5 - Don't ever drive your amp into clipping for any reason.

Step 6 - Use your senses to determine if your speakers are stressed - ears, nose, etc.  If you sense trouble, TURN IT DOWN.

Step 7 - Enjoy the reasonable maximum performance of your system with minimal risk of blowing stuff up.

I nominate this post as an early candidate for "post of the year."  With your permission, I would like to send this to any of my clients who ask this same question.
Title: Re: Power amp specs and ratings....
Post by: TJ (Tom) Cornish on March 11, 2015, 02:10:36 pm
I nominate this post as an early candidate for "post of the year."  With your permission, I would like to send this to any of my clients who ask this same question.
Sure thing.
Title: Re: Power amp specs and ratings....
Post by: Scott Holtzman on March 11, 2015, 05:29:46 pm
Sure thing.

This is very well said, and a subject, thanks to the vendors, that is clear as mud to sound folks of all experience.  From your first buying experience to the first time your write a check for an amplifier that cost more than your first house.  It's still more of an art than a science.

The sad thing is the vendors could fix this.  But then the differences would be clear to see and not easily obfuscated.

I also have seen folks talk about "single metric comparison".  Just comparing watts, like HP or any other term describing power is not looking at the whole picture.

Awesome job TJ - Communicating these concepts well is a gift!
Title: Re: Power amp specs and ratings....
Post by: John Roberts {JR} on March 11, 2015, 06:10:47 pm
This is very well said, and a subject, thanks to the vendors, that is clear as mud to sound folks of all experience.  From your first buying experience to the first time your write a check for an amplifier that cost more than your first house.  It's still more of an art than a science.

The sad thing is the vendors could fix this. But then the differences would be clear to see and not easily obfuscated.
Statements like this make me angry. I have worked in these trenches for decades, and no it is not that simple.

Please describe how to easily clear this up....    >:( >:( >:(

JR
Quote
I also have seen folks talk about "single metric comparison".  Just comparing watts, like HP or any other term describing power is not looking at the whole picture.

Awesome job TJ - Communicating these concepts well is a gift!
Title: Power amp specs and ratings....
Post by: David Sturzenbecher on March 11, 2015, 06:23:13 pm
I would recommend that everyone read up and support CAF.

cafgroup.org

This is an effort to standardize amplifier measurements by the best in the biz. If customers demand this, manufactures will buy in.


Sent from my iPhone using Tapatalk
Title: Re: Power amp specs and ratings....
Post by: David Hoover on March 11, 2015, 07:19:49 pm
It takes so much digging to find those specs you are talking about.  Therefore the checklist above is great as a guideline!

Just as a cool fact, the Danley EDA12000 amplifier can maintain it's 6000W a channel for 4 seconds.  Crown amps on their white paper says they can peak at 2dB above what their power rating is.  QSC gives you burst and RMS.  So reputable companies don't hide it further enforcing...stay with a good brand and use the above list.

Regards,
David

Sent from my Samsung Galaxy Note II
Title: Re: Power amp specs and ratings....
Post by: John Roberts {JR} on March 11, 2015, 08:40:45 pm
I would recommend that everyone read up and support CAF.

cafgroup.org

This is an effort to standardize amplifier measurements by the best in the biz. If customers demand this, manufactures will buy in.


Sent from my iPhone using Tapatalk
Well if the best in the biz are working on it, no problemo.  8)

As I have tried to communicate the "problem" is that music does not have one specific dynamic character but different genres have different relative duty cycles.

CAFgroup for "burst" or dynamic power testing use the old 20 cycles of 1kHz*** on at full volume, with 480 cycles at 10% (for the power supply to recharge). This is one benchmark for transient power and I recall the IHF promoting this back in the '70s as being meaningful for comparing the performance of power amps reproducing classical music transients (like the cannon shot in 1812 overture).

This burst test is better than nothing but not completely representative for how well amplifier XYZ will handle all different musical genre's. If this becomes the defacto power amp standard, amp designers will game their amps to excel at this one specific burst test, just like they gamed the 1/3 power FTC requirement in class G/H designs. Again not the worst thing that could happen, but any single burst standard that customers embrace in large numbers will become the default that engineers design amps to. I doubt that this hifi burst test from the '70s for classical music is widely representative for modern live sound reinforcement.

In my experience most successful big dog power amp designers have their own personal burst test stimulus that they use to vet amp designs, in combination with difficult customers who are hard to please, they use for beta testing.   

Sorry I don't mean to be so argumentative. If I believed there was a single comprehensive test that would work for all customers and genres I would embrace it with both arms. I would like to apologize to the OP for making this seem more complicated than it should be.

I will repeat my primary advice to buy powered speakers because actual design engineers have already made the difficult decisions for you. If you decide to stick with separate amps and speakers there have been a wealth of threads here over the years about sizing power amps to match speakers (and vice versa). Finally I repeat my advice to search here for first hand reports from sound professionals who have used the specific amps you are looking at in similar applications to yours. 

JR

****CAF also has a version of the burst test at 50 Hz which will discharge the reservoir cap a little harder than 1 kHz but an even lower frequency burst would reveal that mechanism even better. While I do not suggest that is an issue. If anything these should be a vigorous debate about 20mSec on/480 mSec off burst standard???
Title: Re: Power amp specs and ratings....
Post by: Scott Holtzman on March 12, 2015, 02:41:35 am
Statements like this make me angry. I have worked in these trenches for decades, and no it is not that simple.

Please describe how to easily clear this up....    >:( >:( >:(

JR
What made you angry?  I have been reading specs and trying to make equipment comparisons since I was a wide eyed teenager in the stereo store to today 40 years later.

I wasn't praising or damning any vendor.  How to find common denominators and how to weight different values to develop a completely objective comparison.

My intent was to praise TJ not offend anyone.  My apologies.
Title: Re: Power amp specs and ratings....
Post by: TJ (Tom) Cornish on March 12, 2015, 08:27:42 am
What made you angry?  I have been reading specs and trying to make equipment comparisons since I was a wide eyed teenager in the stereo store to today 40 years later.

I wasn't praising or damning any vendor.  How to find common denominators and how to weight different values to develop a completely objective comparison.

My intent was to praise TJ not offend anyone.  My apologies.
Scott, reading between the lines of JR's posts (and many years of doing so), I think some of JR's frustration comes from his experiences that engineers who do the "right thing" end up being actually penalized for doing so; either because they have to compete against other companies that are doing "questionable things" - overstating specs, tweaking their product to be good at the test but not necessarily good in real life, etc., and/or because customers are really good at wanting the wrong things: based on snake oil beliefs (slew rate/damping factor), wanting the cheapest possible product (which leads to more gaming by some mfrs to hit a test point), or otherwise being hung up on funny premises (Peavey gear sucks because bands who suck use Peavey). 

In the case of amplifiers this is doubly silly, as in the grand scheme of things, the amp doesn't make a huge difference these days.  Most of the weaker designs have left the market, and even moderately low-end amps are reliable and sound good.  Keep in mind that it also takes a doubling of amplifier power to get just a 3dB level gain; therefore a couple hundred watts these days makes virtually no difference.

I agree with JR that probably the best solution for the world is self-powered speakers, or passive speakers sold together with matching amplifiers - JBL+ITech, Nexo+NXAmp, etc.  This will accomplish two things - 1. As JR said, customers no longer have to care about inscrutable and/or irrelevant specs, and 2 - the manufacturer-tuned "system" will sound much better than most users' ability to roll their own tunings.  Modern DSP techniques like FIR processing only widen the gap between what manufacturers can do vs. the typical customer.

Thanks for the kudos. Looking back, I've been there/done that with a lot of these questions myself over the years.  Now I own only powered speakers and passive+matching amp systems.  I'll never go back to a la carte - my current stuff just works and I don't have to think about it.
Title: Re: Power amp specs and ratings....
Post by: Brian Jojade on March 12, 2015, 12:27:26 pm
If you're using spec sheets to make your purchasing decision, you're going to be easily misled.  Spec sheets are marketing materials, plain and simple.  This is true for speakers, mics, amplifiers, etc.

Real world use is what is key.  How YOU plan to use the gear is what matters.  Learning from people that have actually used the gear in question in the real world will give you far more usable information.  I really don't care how many watts a system claims to have, it's how it sounds in the end that really matters.

Heck, when I'm doing shows, I get asked ALL the time how many watts the system is.  I love on my iTech amps that it shows the current watts rating.  When I look at the display and tell people that ask that this is 8 watts right now, but the amp is capable of 5000 watts, they are always amazed.  Yeah, that's a spec, but out of context, it's meaningless.
Title: Re: Power amp specs and ratings....
Post by: Andrew Klingensmith on March 12, 2015, 01:21:00 pm
Well then, here is an "off the spec sheet" question ...maybe if I am lucky someone has, or had prior, both the Marco Tech and the RMX amps, that has actual use out there

I was wondering if going from the QSC RMX line to the Crown Macro Tech would be seen as a step up now days, and how efficient are these. I have had QSC RMX for some years, and other then the crazy volume pot issues they all seem to get, they have been good. However, maybe in my mind, I always saw or thought of the old school MA  (1200, 2400, 3600, 5000 & 5002) as a "Cadillac". Sure technology marches on, but I was always impressed but in fairness, the boys that had the MA's also had the coin for good speakers too. But I suppose like a pimped out Caddy, maybe some is just prestige

Question: I hear the Crown are power piggies and must be fed LOTS of power for them to do their magic. But would not the QSC RMX be just as bad as well? Or, as a direct compare, would the MA5002VZ be any worse to feed per watt of output then the RMX5050?

THANKS!!!!
Title: Re: Power amp specs and ratings....
Post by: John Roberts {JR} on March 12, 2015, 01:25:55 pm
Thanks for not dismissing my rant.

It is human nature when making major purchase decisions to strive to evaluate competitors products based on factual differences. The publication of specifications started originally to satisfy professional customers who have a better grasp on understanding them, "and" very importantly, decades ago there used to be measurable differences between model and brands that these specifications revealed. Amplifiers used to vary widely in frequency response, distortion, slew rate, damping factor etc.

The technology had improved to the point that there are no longer significant differences between similar models. As expected at the extreme high power points there will be differences due to different engineering design trade-offs to deal with limitations of mains current/power available but these are too complex to quantify from a simple metric, or fair to claim more or less is better. They can be different and all good.

If somebody tries to tell you that only they are telling you the truth and everybody else is lying, firmly grasp your wallet with both hands and back away.

JR
Title: Re: Power amp specs and ratings....
Post by: Scott Holtzman on March 12, 2015, 05:25:35 pm

In the case of amplifiers this is doubly silly, as in the grand scheme of things, the amp doesn't make a huge difference these days.  Most of the weaker designs have left the market, and even moderately low-end amps are reliable and sound good.  Keep in mind that it also takes a doubling of amplifier power to get just a 3dB level gain; therefore a couple hundred watts these days makes virtually no difference.



TJ, to jump on the technical first.  I agree on the amps, especially the 3db part, though that is very challenging with customers and even some engineers that insist I underpower our subs and tell them if that last 1.5db is critical you need to bring/buy more or larger subs.   I don't run anything at 98% power all the time.  I can also take all the power draw measurements and show them how low the average current usage is and they still don't care.

Where I can't get a grip is vendor created terms such as peak power (ok how long a peak and how long a rest between peaks for the energy storage in the amp to recharge).  My electrical side has a real problem that we can plug 2 Crown XTi4002 in a 15 amp outlet at a bar with stereo 4 ohm loads (subs) and not blow the breaker. 

What's more important the ability to cover the peaks or the ability to produce constant power?

The XTi's were a recent purchase, I had a real struggle as I didn't even know what class they were in compared to the QSC line I am operationally familiar with.  I made chart after chart of specs and price points and in the end I bought the 4002's because I got a great deal on them.  They seem to power the B&C loaded sub cabinets just fine (I thing 4"VC PS100's) but I still don't feel I made as informed a decision.

With all that in mind I tend to buy stuff that is widely used, respected and looked upon favorably by people I trust.  I could not imagine doing this alone and in a vacuum. 

As far as vendor bias.  I don't bash gear from any vendor.  For the most part, gear is pretty honest these days.  You can look at it, see the construction and know what it can and can't be used for.  If you ask more of something that it was designed or put it in the hands of a clueless operator you are not going to get results.  A true tech can wring the best out of any given setup. 

We all have buttons that are easy to push, I now think I understand a little bit more.  Thanks
Title: Re: Power amp specs and ratings....
Post by: TJ (Tom) Cornish on March 13, 2015, 09:12:29 am
TJ, to jump on the technical first.  I agree on the amps, especially the 3db part, though that is very challenging with customers and even some engineers that insist I underpower our subs and tell them if that last 1.5db is critical you need to bring/buy more or larger subs.   I don't run anything at 98% power all the time.  I can also take all the power draw measurements and show them how low the average current usage is and they still don't care.

Where I can't get a grip is vendor created terms such as peak power (ok how long a peak and how long a rest between peaks for the energy storage in the amp to recharge).  My electrical side has a real problem that we can plug 2 Crown XTi4002 in a 15 amp outlet at a bar with stereo 4 ohm loads (subs) and not blow the breaker. 
As you say, amps have energy storage, which provides burst capacity at the cost of increased average draw.  This coupled with the fact that a 20A circuit breaker will actually supply quite a bit more than 20A instantaneously before blowing allows this to happen.

What's more important the ability to cover the peaks or the ability to produce constant power?
The answer is "yes".  :)  All music has a crest factor - some moments in a song are loud, while most are significantly quieter.  Some genres have a different ratio, but this has been researched for years, and the 1/8 power rating  of modern amps is a good real-world reflection of current usage.  Most modern amps don't have a particular problem with either peaks or constant power, as the amplifier's ability to deliver power roughly corresponds to the driver's ability to sink that power.  A 4000w program woofer is probably only capable of a couple hundred watts of DC "toaster mode".

I honestly don't think there's a big smoking gun here in the pro world.  Car audio - probably.  Pro audio - not so much, as there are enough smart people in our industry to keep things reasonably honest.

I researched this and wrote up a little article about power consumption here (http://www.tjcornish.com/articles/understanding-power-consump.html).

Bennett Prescott wrote a great article on loudspeaker damage (http://bennettprescott.com/downloads/LoudspeakerFundamentals.pdf) that's worth a read as well.
Title: Re: Power amp specs and ratings....
Post by: Scott Holtzman on March 14, 2015, 01:12:59 am

I researched this and wrote up a little article about power consumption here (http://www.tjcornish.com/articles/understanding-power-consump.html).

Bennett Prescott wrote a great article on loudspeaker damage (http://bennettprescott.com/downloads/LoudspeakerFundamentals.pdf) that's worth a read as well.

Good points and thanks for the links I will read them this weekend.

Title: Re: Power amp specs and ratings....
Post by: paul bell on March 14, 2015, 05:55:41 pm
Just as a cool fact, the Danley EDA12000 amplifier can maintain it's 6000W a channel for 4 seconds.

Yes, this is the SpeakerPower SP2-12000. A few speaker companies are wisely using this and a few of their other units. I have some in use here and there. It's a pretty stompin unit.
Title: Re: Power amp specs and ratings....
Post by: Ross Neptune on August 03, 2015, 10:55:00 pm
Nathan, here's my Cliff's Notes version of amplifier picking:

Step 1 - If the manufacturer of your speakers recommends a particular amp, buy it.  Even if it is more expensive, seems less of something on paper, etc.  Doesn't matter - buy the manufacturer's recommended amps and processing so you have a complete system rather than a buffet.  GOTO Step 4.

Step 2 - Buy an amp from a reliable manufacturer - QSC, Crown, Crest, Powersoft, etc.

Step 3 - Buy an amp that can produce your speakers' program power rating at the impedance you will be using them at.  For example, if you intend to run two 8Ω speakers rated at 800w program power, get an amp that can deliver 1600w into 4Ω.

Step 4 - Use recommended processor settings for your speakers - especially high-pass settings

Step 5 - Don't ever drive your amp into clipping for any reason.

Step 6 - Use your senses to determine if your speakers are stressed - ears, nose, etc.  If you sense trouble, TURN IT DOWN.

Step 7 - Enjoy the reasonable maximum performance of your system with minimal risk of blowing stuff up.

Serious question, with so many speaker manufacturers ALSO making amps, would you still recommend their "opinion" on amp selection? IE, should I use a QSC amp that is slightly under the "program" rating for their own speaker rather than a powersoft amp that provides plenty (based on their own mystery tests). 

While I'm on that subject, anyone compare some of the powersoft m series with the newer QSC PLD, CXD amps?

This is the ultimate decision I'm deciding between.  Well, those or just going with the Ashly nXp which includes an amp (was already going with an Ashly Protea processor).
Title: Re: Power amp specs and ratings....
Post by: Ivan Beaver on August 04, 2015, 07:35:29 am
Serious question, with so many speaker manufacturers ALSO making amps, would you still recommend their "opinion" on amp selection? IE, should I use a QSC amp that is slightly under the "program" rating for their own speaker rather than a powersoft amp that provides plenty (based on their own mystery tests). 

While I'm on that subject, anyone compare some of the powersoft m series with the newer QSC PLD, CXD amps?


It has less to do with the brand and the power and more to do with exactly how YOU are using it.

For some styles of music that have a limited dynamic crest fact (low dynamic range), a smaller amp (and not let it clip) is better.

FOr music with a wider dynamic range, a larger amp will allow you to get more "life" and impact out of the loudspeaker.

There is no "correct" answer.  Only answer that vary depending on the situation.

Just like setting limiters.  Different situations require different setups-in order to get "the most" out of a system without blowing it up.

One size DOES NOT fit all.
Title: Re: Power amp specs and ratings....
Post by: Keith Broughton on August 04, 2015, 08:39:23 am
Quote
my primary advice to buy powered speakers because actual design engineers have already made the difficult decisions for you
Or systems that are speaker and amp packages.
As stated, the "hard" decisions are made for you with the added benefit of having a better chance of vendor support in the case of problems with the equipment.

Someone mentioned HP ratings for cars and as someone who has done a bit of racing and custom tuning of engines, I can say that the HP ratings can also be skewed in favour of a particular outcome.

That said, it would be reasonable to expect a manufacturer could tell you how long a "burst" recovery would take.
Consider the Behringer 12000 amp at 6000w/ch into 2 on a 15A plug. REALLY!?!?!?!
12000 watts for how long and what is the restore time?



Title: Re: Power amp specs and ratings....
Post by: TJ (Tom) Cornish on August 04, 2015, 09:32:54 am
Serious question, with so many speaker manufacturers ALSO making amps, would you still recommend their "opinion" on amp selection? IE, should I use a QSC amp that is slightly under the "program" rating for their own speaker rather than a powersoft amp that provides plenty (based on their own mystery tests). 

While I'm on that subject, anyone compare some of the powersoft m series with the newer QSC PLD, CXD amps?

This is the ultimate decision I'm deciding between.  Well, those or just going with the Ashly nXp which includes an amp (was already going with an Ashly Protea processor).
Ross, my original reply stands.  If the manufacturer recommends or requires a specific amp for their product, you should use it.  More amp power is not necessarily a good thing - that just gives you the potential to kill your drivers faster.

If the model of speaker you are using doesn't come with tuning and limiting data for a recommended amp system, then you have more flexibility to use 3rd party amps, but that probably indicates you are using either an old design speaker or a low end speaker, and if it were me, I would pick a different product to get the benefit of the manufacturer doing the heavy lifting on the programming.
Title: Re: Power amp specs and ratings....
Post by: John Roberts {JR} on August 04, 2015, 09:49:54 am
Serious question, with so many speaker manufacturers ALSO making amps, would you still recommend their "opinion" on amp selection? IE, should I use a QSC amp that is slightly under the "program" rating for their own speaker rather than a powersoft amp that provides plenty (based on their own mystery tests). 
Pretty much yes always take the manufacturer's advice, except with the caveat that you are using official published recommendations (approved by engineering) and not what some janitor who answered the phone at work told you (or worse, a salesman).

Back decades ago when I was working at Peavey I asked the speaker design engineers to fill out a matrix of which Peavey amps to pair with which Peavey speakers. That was a last century thing, now I say just use a powered cabinet.

JR
Quote
While I'm on that subject, anyone compare some of the powersoft m series with the newer QSC PLD, CXD amps?

This is the ultimate decision I'm deciding between.  Well, those or just going with the Ashly nXp which includes an amp (was already going with an Ashly Protea processor).
Title: Re: Power amp specs and ratings....
Post by: Art Welter on August 04, 2015, 12:29:43 pm
That said, it would be reasonable to expect a manufacturer could tell you how long a "burst" recovery would take.
Consider the Behringer 12000 amp at 6000w/ch into 2 on a 15A plug. REALLY!?!?!?!
12000 watts for how long and what is the restore time?
Keith,

Just before the last Christmas holidays I conducted a battery of tests on some old amplifiers and a new Behringer NU4-6000 four channel amplifier. To my surprise, the  NU4-6000 performed as well on low frequencies as on mid/high frequencies, and is capable of near full power sine wave output with all four channels driven to rated output at two ohms, or two bridged mono pairs driving four ohm loads each. The  $350 NU4-6000 appears to be within 3 dB of the $5500 Powersoft K10 rating on sustained (more than 1 second) output.

The NU4-6000 with two bridged mono pairs each driving four ohm loads just below the illumination of the clip/limit light each put out 85.5 volts at 60 Hz (1828 watts), 84.6 volts at 30 Hz (1789 watts), dropping the mains voltage on a 100' 10AWG 120V line from 118.1 volts down to 107.2 volts, drawing 31 amperes.

Using just one bridged mono pair, the amp ran for 40+ seconds before I terminated the test, as the amp was drawing 19.8 amperes, and the "tired" 20 amp mains breaker had popped several times in various tests already. The amp would have put out more power given a full 120 volts, but the test represents "real world" situation, we don't generally plug our amplifiers in to an outlet two feet from the mains transformer.

I also tested my old "heavy iron"  bass favorite, a Crest CA9, bridged into a 4 ohm load it dropped the mains to 99.6 volts, drew 37.8 amps but only put out 80 volts (1600 watts). The NU4-6000 put out more power, and drew only 50% of the power from the mains compared to the CA9.

My back (and bank account) are very pleased with the NU4-6000, after the testing I purchased another pair. The amps have run with no shutdowns in direct sunlight at 100 F temperatures. With only two shows so far, don't have any long term experience, but as cool as they run I expect longevity.

Art
Title: Re: Power amp specs and ratings....
Post by: Keith Broughton on August 04, 2015, 12:53:02 pm
Keith,

Just before the last Christmas holidays I conducted a battery of tests on some old amplifiers and a new Behringer NU4-6000 four channel amplifier. To my surprise, the  NU4-6000 performed as well on low frequencies as on mid/high frequencies, and is capable of near full power sine wave output with all four channels driven to rated output at two ohms, or two bridged mono pairs driving four ohm loads each. The  $350 NU4-6000 appears to be within 3 dB of the $5500 Powersoft K10 rating on sustained (more than 1 second) output.

The NU4-6000 with two bridged mono pairs each driving four ohm loads just below the illumination of the clip/limit light each put out 85.5 volts at 60 Hz (1828 watts), 84.6 volts at 30 Hz (1789 watts), dropping the mains voltage on a 100' 10AWG 120V line from 118.1 volts down to 107.2 volts, drawing 31 amperes.

Using just one bridged mono pair, the amp ran for 40+ seconds before I terminated the test, as the amp was drawing 19.8 amperes, and the "tired" 20 amp mains breaker had popped several times in various tests already. The amp would have put out more power given a full 120 volts, but the test represents "real world" situation, we don't generally plug our amplifiers in to an outlet two feet from the mains transformer.

I also tested my old "heavy iron"  bass favorite, a Crest CA9, bridged into a 4 ohm load it dropped the mains to 99.6 volts, drew 37.8 amps but only put out 80 volts (1600 watts). The NU4-6000 put out more power, and drew only 50% of the power from the mains compared to the CA9.

My back (and bank account) are very pleased with the NU4-6000, after the testing I purchased another pair. The amps have run with no shutdowns in direct sunlight at 100 F temperatures. With only two shows so far, don't have any long term experience, but as cool as they run I expect longevity.

Art
Now that you mention it, I seem to recal reading something about that.
Even though the Behringer amps don't quite put out the "advertised" power, the cost / watt ratio is still very good.
I suggested one of my equipment suppliers buy 4 DSP12000 amps and at $800 CDN/ea, a great deal.
So far, they seem to work just fine, although I did use a 2 pole 30 amp (L14/30) distro panel to power the rack.
As for the back, these 12000s are quite weighty so no benefit there. :(
This guy has been running a bunch of the first gen Powersoft Digam amps and we don't see all that much of a difference in average performance and for the lower cost, it's hard not to buy the Behringers.
Still, it would be nice to have some burst recovery specs.
As Ivan says, many times, it's the application that has to be the determining factor in amp choice.
I would probably not use Behringers for EDM but for straight up rock and roll, no problem!
Title: Re: Power amp specs and ratings....
Post by: Scott Holtzman on August 06, 2015, 04:36:09 pm
Now that you mention it, I seem to recal reading something about that.
Even though the Behringer amps don't quite put out the "advertised" power, the cost / watt ratio is still very good.
I suggested one of my equipment suppliers buy 4 DSP12000 amps and at $800 CDN/ea, a great deal.
So far, they seem to work just fine, although I did use a 2 pole 30 amp (L14/30) distro panel to power the rack.
As for the back, these 12000s are quite weighty so no benefit there. :(
This guy has been running a bunch of the first gen Powersoft Digam amps and we don't see all that much of a difference in average performance and for the lower cost, it's hard not to buy the Behringers.
Still, it would be nice to have some burst recovery specs.
As Ivan says, many times, it's the application that has to be the determining factor in amp choice.
I would probably not use Behringers for EDM but for straight up rock and roll, no problem!

I have to agree, against everyone's advice I picked up one of the four channel 'nukes and put that ugly bitch in a rolling case with an x32 rack.  I got an open box on flea bay for $349 shipped and have had no complaints.

What I am still trying to quantify is the original assertion of the thread.  Even if you get down to a common denominator (power for x # minutes with x load from x to x @ x% THD) you still end up with some amps with balls and some amps with no balls.  I have not heard the iTech's but I can tell you that the Xti's don't have something that the Macro Tech's do.  It always leave you with something in your gut that you left something on the table and made the wrong compromise.

Title: Re: Power amp specs and ratings....
Post by: John Roberts {JR} on August 06, 2015, 06:40:11 pm
I have to agree, against everyone's advice I picked up one of the four channel 'nukes and put that ugly bitch in a rolling case with an x32 rack.  I got an open box on flea bay for $349 shipped and have had no complaints.

What I am still trying to quantify is the original assertion of the thread.  Even if you get down to a common denominator (power for x # minutes with x load from x to x @ x% THD) you still end up with some amps with balls and some amps with no balls.  I have not heard the iTech's but I can tell you that the Xti's don't have something that the Macro Tech's do.  It always leave you with something in your gut that you left something on the table and made the wrong compromise.

Hello again Scott...  8)  "Balls" is not a technical term. You probably mean "duty-cycle". Amplifiers have not delivered 100% duty-cycle for a very long time, because customers decline to pay for 100% duty-cycle. 

Which leaves us with a fairly subjective, if the amp has enough duty cycle for your application it has balls, if not enough, no balls.  :P

As i said several months ago, listen to anecdotal posts from other professionals doing similar genres of music using similar speaker loads. First to identify weak sisters, and/or amps with "balls".  ;D ;D

I continue to be impressed with the modern generation(s)*** of light weight (light iron?) high power amps that  make decent power while wasting less as heat (yes even Behringer). The tree huggers have to love that.

I could have given you a duty-cycle spec back when I was still a power amp product manager (last century) but in my judgement you customers would have misused it, just like slew rate and damping factor before that.  (By "you" I don't mean you Scott, but you customers in general, while that probably includes Scott.).

JR 

*** We're probably at least two amp technology generations beyond what I had to work with. Peavey was pedaling as hard as they could to make class D kick class, but now it is delivering on those very old promises (light weight and lower cost). In my judgement the high voltage power switching devices just weren't up to the task back decades ago. 
Title: Re: Power amp specs and ratings....
Post by: Scott Holtzman on August 07, 2015, 05:27:18 pm
Hello again Scott...  8)  "Balls" is not a technical term. You probably mean "duty-cycle". Amplifiers have not delivered 100% duty-cycle for a very long time, because customers decline to pay for 100% duty-cycle. 

Which leaves us with a fairly subjective, if the amp has enough duty cycle for your application it has balls, if not enough, no balls.  :P

As i said several months ago, listen to anecdotal posts from other professionals doing similar genres of music using similar speaker loads. First to identify weak sisters, and/or amps with "balls".  ;D ;D

I continue to be impressed with the modern generation(s)*** of light weight (light iron?) high power amps that  make decent power while wasting less as heat (yes even Behringer). The tree huggers have to love that.

I could have given you a duty-cycle spec back when I was still a power amp product manager (last century) but in my judgement you customers would have misused it, just like slew rate and damping factor before that.  (By "you" I don't mean you Scott, but you customers in general, while that probably includes Scott.).

JR 

*** We're probably at least two amp technology generations beyond what I had to work with. Peavey was pedaling as hard as they could to make class D kick class, but now it is delivering on those very old promises (light weight and lower cost). In my judgement the high voltage power switching devices just weren't up to the task back decades ago.

John, I think duty cycle is the missing variable, it goes hand in hand with crest factor.  The new PLD amps from QSC have a 20ms spec.  I find that useful.

I know older amps had more energy storage, if you unplugged them playing you could still listen for a minute at some volumes.  That is somewhat invalid as I am sure control circuitry when the +5 rail goes down mutes outputs.

I do like the Peavey Class D's.  The price is not too pad and they are very aesthetically pleasing. 

Lastly, your statement on subjective reviews is interesting.  I have had cases where someone reports that the xxx product blows away the yyy.  When I have both products side by side the delta is not that great.

I think quality equipment at various price points, none of it is going to be widely disparate in performance.  Case in point the QSC KW-181, the JBL PRX-718xlf, the EV ETX18p.  They can all be interchanged without any problem form a client perspective and very little change even with trained ears.  To get a better sub (or amp, processor, mixer etc) than any of these ~$1000 or so boxes requires you to at least double in price, maybe more.  It continues to rise logarythmically and places significant barriers for small operators to move up to the next level.  You have to either capatalize or finance the equipment and be ready for a lower ROI until you actually sell it. 

It gets worse because now that you have updated your amp as this thread is about, now you need to upgrade both tops and subs, more amps, then your board is no longer relevant at the new level, you may need new lifts, it never seems to stop. 

Thanks for distilling down my chaotic thoughts into something digestible.  Oh look squirrel...... ::)
Title: Re: Power amp specs and ratings....
Post by: TJ (Tom) Cornish on August 07, 2015, 06:17:11 pm
It gets worse because now that you have updated your amp as this thread is about, now you need to upgrade both tops and subs, more amps, then your board is no longer relevant at the new level, you may need new lifts, it never seems to stop. 
Tim Mc's $3dB principle is an unfortunate reality of this industry.  The next stop after spending $10K is spending $20K, then $40K, then $80K...

I may sound like a broken record here, but I really wish people would stop caring about amps (and passive speakers in general), and start caring about systems - whether the amp is inside the speaker, or the amp is external, but a matched component with the speakers.  At this point in time, there's no benefit for consumers in having to care about all of this ridiculous minutae.

Step 1 - Buy a speaker system.  While shopping, evaluate the performance of the whole system, and make an appropriate purchasing decision. 

Step 2 - Do basic system alignment and room tuning to make the system fit the room. 

Step 3 - enjoy far better sound quality by leveraging the manufacturer's engineering efforts than what the average touring system tech is able to roll from a pile of mismatched bits and inadequate time and/or skill.

The only reason not to buy a matched system is maybe if you are trying to stretch old inventory as long as possible and want to reuse some old boxes, which is hopefully a temporary situation.  Other than that, a matched system is the way to go - both at the big-dog level and the lounge level.
Title: Re: Power amp specs and ratings....
Post by: John Roberts {JR} on August 07, 2015, 06:42:03 pm
John, I think duty cycle is the missing variable, it goes hand in hand with crest factor.  The new PLD amps from QSC have a 20ms spec.  I find that useful.
Thats only part of a spec. Sounds like maybe burst power, back in the '70s the IHF had a similar transient power (dynamic headroom) spec. The 20mSec stands for how long the amp makes the burst power. The legacy headroom spec also quantified a rep rate or recharge time. So 20 mSec of full burst power and 480 mSec for the PS to recharge. Obviously the faster the rep rate the less burst power. Yes this gets a little complicated. 

FWIW the duty-cycle for that 20/480 mSec burst is something like 4%.  (Caveat I'm just guessing I looked and didn't find complete details on the QSC burst power, just 20mSec of 1kHz on time, no rep rate or off time. )
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I know older amps had more energy storage, if you unplugged them playing you could still listen for a minute at some volumes.  That is somewhat invalid as I am sure control circuitry when the +5 rail goes down mutes outputs.
An arbitrary data point that means nothing. Modern high power amps turn off before the PS collapses to prevent awkward situations like the output trying to pull up and down at the same time. Old school analog amps will play for several seconds until the PS discharges and fuzzes out the sound.
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I do like the Peavey Class D's.  The price is not too pad and they are very aesthetically pleasing. 
The recent PV class D are after my time... I am still trying to forget the old PV class Ds.  :o
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Lastly, your statement on subjective reviews is interesting.  I have had cases where someone reports that the xxx product blows away the yyy.  When I have both products side by side the delta is not that great.
Whenever somebody reports a night and day audible difference, put both hands over your wallet and slowly back away.  8) Back in the '70/80s my informal rule for audibly significant is can you hear the difference through a screen door out in the yard.
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I think quality equipment at various price points, none of it is going to be widely disparate in performance.  Case in point the QSC KW-181, the JBL PRX-718xlf, the EV ETX18p.  They can all be interchanged without any problem form a client perspective and very little change even with trained ears.  To get a better sub (or amp, processor, mixer etc) than any of these ~$1000 or so boxes requires you to at least double in price, maybe more.  It continues to rise logarythmically and places significant barriers for small operators to move up to the next level.  You have to either capatalize or finance the equipment and be ready for a lower ROI until you actually sell it. 

It gets worse because now that you have updated your amp as this thread is about, now you need to upgrade both tops and subs, more amps, then your board is no longer relevant at the new level, you may need new lifts, it never seems to stop. 

Thanks for distilling down my chaotic thoughts into something digestible.  Oh look squirrel...... ::)

Amplifiers are a mature technology these days, while I would stick to names I recognize. I still advocate letting speaker engineers choose your amps for you.

JR
Title: Re: Power amp specs and ratings....
Post by: Scott Holtzman on August 08, 2015, 12:59:55 am

Amplifiers are a mature technology these days, while I would stick to names I recognize. I still advocate letting speaker engineers choose your amps for you.

JR

Clarification (I agree with the points you made).  I drifter when I made this comment.  My original intent is if one amplifier can drive a specific speaker to better audible performance than another similarly spec'd amp then we are missing a spec.  It appears that spec is duty cycle.  For all I know it could be transient intermodulation distortion.  A spec I haven't heard quoted in 20 years.

However when I made this comment I had broadened beyond the original scope to include speakers (both powered and unpowered).  I completely agree.  If a powered speaker exists at the performance point sought then I lean towards it.  People far smarter than I tuned the processing.  Next preferred would be an integrated system like the Vue AL4.  Last would be a processor by the speaker vendor such as EAW and QSC.  The Driverack to me is a processor that happens to have tunings for some JBL speakers.  A different Harmon division.

Lastly, I am stunned when a sound tech comes up to me extolling the virtue of their "tweaks".  Clearly this person is not in charge of a team of engineers.  If the tweeks extend outside the realm of environmental tuning or interfacing then IMHO they are nuts. 

One of Scott's rules to manage technician.  When asked to look at a problem start with what the technician last touched or was in proximity of (as they may lie about touching it).
Title: Re: Power amp specs and ratings....
Post by: John Roberts {JR} on August 08, 2015, 09:15:24 am
Clarification (I agree with the points you made).  I drifter when I made this comment.  My original intent is if one amplifier can drive a specific speaker to better audible performance than another similarly spec'd amp then we are missing a spec.
If you can reliably hear a difference, we can measure that difference and quantify it.
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It appears that spec is duty cycle.
Duty cycle is a possible difference but in my judgement would not track with different speakers, but more likely track with musical genre.
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For all I know it could be transient intermodulation distortion.  A spec I haven't heard quoted in 20 years.
Shhh there's a good reason TIM has dropped from the popular vocabulary, it was a spec searching for a problem, and not useful for differentiating between properly designed amps.

A subtle interaction that tracks with speakers is current limiting. More likely to be audible when speakers are paralleled or bridged (i.e. amps run near their current limit). Amp designers try to be generous with extra current output. Customers (and speaker designers) keep consuming the headroom that designers try to provide. Passive crossovers could be a critical variable creating unexpected impedance loads. Large companies that sell both speakers and amps, are less likely to screw up a crossover than a speaker only company, but again large well known companies should be safer. 
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However when I made this comment I had broadened beyond the original scope to include speakers (both powered and unpowered).  I completely agree.  If a powered speaker exists at the performance point sought then I lean towards it.  People far smarter than I tuned the processing.  Next preferred would be an integrated system like the Vue AL4.  Last would be a processor by the speaker vendor such as EAW and QSC.  The Driverack to me is a processor that happens to have tunings for some JBL speakers.  A different Harmon division.

Lastly, I am stunned when a sound tech comes up to me extolling the virtue of their "tweaks".  Clearly this person is not in charge of a team of engineers.  If the tweeks extend outside the realm of environmental tuning or interfacing then IMHO they are nuts. 

One of Scott's rules to manage technician.  When asked to look at a problem start with what the technician last touched or was in proximity of (as they may lie about touching it).
yup..

JR
Title: Re: Power amp specs and ratings....
Post by: Gordon Waters on August 08, 2015, 09:27:54 am
.Shhh there's a good reason TIM has dropped from the popular vocabulary, it was a spec searching for a problem, and not useful for differentiating between properly designed amps.


More accurately, it could be said that it was a problem that was very specifically related to the limitations on the transistors used in early solid-state designs, back in the 1960s and 1970s. These transistors had very slow slew rates compared to modern designs (and by that, I mean pretty much any transistor designed after 1980), and to compound the problem, designers were producing amp topologies that pretty much ignored the slew rate- making no real effort to compensate for it.

After the seminal papers by Matti Otala and Dr. William Marshall Leach in the early 1970s exposing the problem and offering several avenues for correcting it, there was a rapid advancement in design- to where, after about the mid 1970s, there were no real further instances of significant problems related to transient intermodulation distortion in amplifiers. I can't think of a design from any significant manufacturer made since then, that had any sort of significant issue with this.

In essence, it's a problem that has, fortunately, been laid to rest in the sands of time, so to speak. As such, it's really not a spec that warrants any real concern, now. 

BTW: I am not an EE by trade, but I studied under the late Dr. William Marshall Leach, back at the Georgia Institute of Technology, so I am somewhat familiar with this topic on a first-hand basis...

Regards,
Gordon.
Title: Re: Power amp specs and ratings....
Post by: John Roberts {JR} on August 08, 2015, 10:33:17 am
More accurately, it could be said that it was a problem that was very specifically related to the limitations on the transistors used in early solid-state designs, back in the 1960s and 1970s. These transistors had very slow slew rates compared to modern designs (and by that, I mean pretty much any transistor designed after 1980), and to compound the problem, designers were producing amp topologies that pretty much ignored the slew rate- making no real effort to compensate for it.
Not to quibble but you may be referring to gain-bandwidth product. Transistors do not have slew rates, while circuits using them could*** .  Many early transistor amp designs just dropped transistors into old tube circuits with little appreciation for the differences.
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After the seminal papers by Matti Otala and Dr. William Marshall Leach in the early 1970s exposing the problem and offering several avenues for correcting it, there was a rapid advancement in design- to where, after about the mid 1970s, there were no real further instances of significant problems related to transient intermodulation distortion in amplifiers. I can't think of a design from any significant manufacturer made since then, that had any sort of significant issue with this.
I recall seeing an interview of the older Peter Baxandall before he died, when they asked him about TIM (and I seem to recall a few similar proposed new classes of distortion.. SID?). He shrugged it all off as already well known to designers skilled in the art. (Baxandall was involved in HF radar circuit design during WWII so understood rate of change considerations).
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In essence, it's a problem that has, fortunately, been laid to rest in the sands of time, so to speak. As such, it's really not a spec that warrants any real concern, now. 
Kind of what I said... while at the time proponents of the sundry new distortions had high hopes for their significance. Coincidentally there have been many products designed over the years by engineers who were IMO NOT skilled in the art.  8)
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BTW: I am not an EE by trade, but I studied under the late Dr. William Marshall Leach, back at the Georgia Institute of Technology, so I am somewhat familiar with this topic on a first-hand basis...

Regards,
Gordon.

**** Slew rate. If you studied under Leach (RIP) you should be familiar with his classic paper describing how to rise-time limit an amplifier circuit such that it can never slew-rate limit. Unfortunately customers (who are always right) didn't get that memo, so major amp makers would literally defeat their rise-time limiting, so they could force slew rate limiting to have a number to publish. Try to explain rise-time to audio-phools and their eyes glaze over. ???

I considered Leach's contribution to the art positive, Otala and his fan boys, struck me as much ado about nothing (or very little). The same crowd made hyperbolic claims about known capacitor metrics (dielectric absorption), etc. For some reason audio attracts a population that still believes the available measurements do not completely describe the technology. I consider audio technology mature so I discourage mystical searches for some unknown missing specification. More often esoteric specs get hyperbolically inflated by marketers trying to differentiate their product where little real difference actually exists (like damping factor, etc).   

JR

PS If you studied at Ga tech did you know Dr Patronis? He was another solid citizen for the audio community (IMO).
Title: Re: Power amp specs and ratings....
Post by: Gordon Waters on August 08, 2015, 03:28:48 pm

PS If you studied at Ga tech did you know Dr Patronis? He was another solid citizen for the audio community (IMO).

Yes indeed. Learned a lot from him. He, at that time, was THE MAN in terms of distributed delay speaker configuration (taking advantage of the Haas Effect).

He oversaw the system setup when the Fox Theater in Atlanta was refurbed back in the 80s- and a LOT of the basic principles he put in place in that system, are STILL being used. The equipment has been upgraded several times, but the basic setup has remained a lot the same, in terms of the delay parameters and such that he specified. And it still sounds good, IMHO...

Regards,
Gordon
Title: Re: Power amp specs and ratings....
Post by: John Roberts {JR} on August 08, 2015, 05:14:53 pm
Yes indeed. Learned a lot from him. He, at that time, was THE MAN in terms of distributed delay speaker configuration (taking advantage of the Haas Effect).
Yup, Dr Patronis was the man for lots of stuff, and IIRC he also felt like he needed to oversee sound for the Ga Tech basketball games.  ;D
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He oversaw the system setup when the Fox Theater in Atlanta was refurbed back in the 80s- and a LOT of the basic principles he put in place in that system, are STILL being used. The equipment has been upgraded several times, but the basic setup has remained a lot the same, in terms of the delay parameters and such that he specified. And it still sounds good, IMHO...

Regards,
Gordon
If the room hasn't changed, the basic sound system design shouldn't change, but yes he was on top of the physics (and psycho-acoutics).

Dr Patronis patented a feedback killer decades before the electronic technology advanced enough to make them cost effective. I brought him into Peavey in the mid-80s to investigate licensing his invention, but it was legally complicated by the first company he licensed it to, so we never reached an agreement. Too bad, I would have loved working with him to bring that technology to a wider market (very hip technology for 30+ years ago).   

JR
Title: Re: Power amp specs and ratings....
Post by: Ivan Beaver on August 08, 2015, 06:02:13 pm
Yes indeed. Learned a lot from him. He, at that time, was THE MAN in terms of distributed delay speaker configuration (taking advantage of the Haas Effect).

He oversaw the system setup when the Fox Theater in Atlanta was refurbed back in the 80s- and a LOT of the basic principles he put in place in that system, are STILL being used. The equipment has been upgraded several times, but the basic setup has remained a lot the same, in terms of the delay parameters and such that he specified. And it still sounds good, IMHO...

Regards,
Gordon
Dr.P is a great guy, and very entertaining and informative to listen to.

What I love about him is that he can talk on whatever level you want to and go as deep or shallow as you want.

And he has no problem speaking his mind-whether you like it or not.

I have the unique distinction of the only person who has been shoot by one of his guns.

It was a 45 with a hair trigger and long barrel.

And I shot myself-we won't go into the details.