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Author Topic: Power amp specs and ratings....  (Read 11713 times)

Nathan Schwarzkopf

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Power amp specs and ratings....
« 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. 
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John Roberts {JR}

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Re: Power amp specs and ratings....
« Reply #1 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.
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TJ (Tom) Cornish

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Re: Power amp specs and ratings....
« Reply #2 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.
« Last Edit: March 11, 2015, 02:10:00 pm by TJ (Tom) Cornish »
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Chrysander 'C.R.' Young

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Re: Power amp specs and ratings....
« Reply #3 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.
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TJ (Tom) Cornish

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Re: Power amp specs and ratings....
« Reply #4 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.
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Scott Holtzman

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Re: Power amp specs and ratings....
« Reply #5 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!
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John Roberts {JR}

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Re: Power amp specs and ratings....
« Reply #6 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!
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David Sturzenbecher

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Power amp specs and ratings....
« Reply #7 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.


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David Hoover

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Re: Power amp specs and ratings....
« Reply #8 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

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John Roberts {JR}

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Re: Power amp specs and ratings....
« Reply #9 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.


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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???
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Re: Power amp specs and ratings....
« Reply #9 on: March 11, 2015, 08:40:45 pm »


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