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Author Topic: Power amp specs and ratings....  (Read 11617 times)

Scott Holtzman

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Re: Power amp specs and ratings....
« Reply #10 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.
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Scott AKA "Skyking" Holtzman
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TJ (Tom) Cornish

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Re: Power amp specs and ratings....
« Reply #11 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.
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Brian Jojade

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Re: Power amp specs and ratings....
« Reply #12 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.
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Andrew Klingensmith

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Re: Power amp specs and ratings....
« Reply #13 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!!!!
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John Roberts {JR}

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Re: Power amp specs and ratings....
« Reply #14 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
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Scott Holtzman

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Re: Power amp specs and ratings....
« Reply #15 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
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Scott AKA "Skyking" Holtzman
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TJ (Tom) Cornish

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Re: Power amp specs and ratings....
« Reply #16 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.

Bennett Prescott wrote a great article on loudspeaker damage that's worth a read as well.
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Scott Holtzman

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Re: Power amp specs and ratings....
« Reply #17 on: March 14, 2015, 01:12:59 am »


I researched this and wrote up a little article about power consumption here.

Bennett Prescott wrote a great article on loudspeaker damage that's worth a read as well.

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

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Scott AKA "Skyking" Holtzman
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paul bell

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Re: Power amp specs and ratings....
« Reply #18 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.
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Ross Neptune

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Re: Power amp specs and ratings....
« Reply #19 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).
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Re: Power amp specs and ratings....
« Reply #19 on: August 03, 2015, 10:55:00 pm »


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