How do amplifier manufacturers come up with their wattage ratings? - diyAudio
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Old 14th December 2012, 12:17 AM   #1
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Default How do amplifier manufacturers come up with their wattage ratings?

Hi. I didn't find a better place to put this thread so I'm giving it a go here

I have allways wondered about the wattage ratings of different amplifiers. Some are giving off huge ratings, like 7x200W while others advertise "real watts" and then put out a more modest number. How do they find these wattage ratings? When IE. NAD talks about "real watts", are they talking about an avarage wattage into a 8Ohm load for an indefinite amount of time? Or are they still talking about some peak wattage that lasts for 1ms? The reason I'm asking is because I wan't to try and sell amplifiers in the future. It will be hard to compete with manufacturers that just picks a number out of thin air, puts a "W" at the end of it and paints on their amps. I wouldn't feel comfortable doing that :P
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Old 14th December 2012, 12:24 AM   #2
cotdt is offline cotdt  United States
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As long as the public accepts your amplifiers and it gets good reviews, the wattage rating doesn't matter. Just look at SET amps and their tiny power ratings. That said, those amps are typically rated based on the onset of clipping driving an 8 ohm load.

On the other hand, a lot of commercial amps use power ratings based on 10% THD, and then proceed to add the power output of each channel together into a single wattage figure.

If you tap into the lucrative audiophile market, you can sell your 2W amps for $2000 (people have commissioned me to build such amps). I don't think low power ratings are an issue. It can even be used as a marketing tactic.

Last edited by cotdt; 14th December 2012 at 12:27 AM.
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Old 14th December 2012, 12:42 AM   #3
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I would just show it in True R.M.S power. But most of companies show it at peak power, since it sounds like it is more powerful and people "think" they are getting more power
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Old 14th December 2012, 12:45 AM   #4
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That's what I would do. Scope the output and then find the point before it clips, note it and calculate the wattage. I have ordered a scope and I would like to do this to my amplifiers I have in my basement. I have a rather expensive 2x70W class A amp, I wonder how much that can actually output. This reminds me of a tiny car amplifier I bought a while back. It cost me something like 20usd but had a wattage rating of 800W!
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Old 14th December 2012, 12:52 AM   #5
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Quote:
Originally Posted by Plecto View Post
That's what I would do. Scope the output and then find the point before it clips, note it and calculate the wattage. I have ordered a scope and I would like to do this to my amplifiers I have in my basement. I have a rather expensive 2x70W class A amp, I wonder how much that can actually output. This reminds me of a tiny car amplifier I bought a while back. It cost me something like 20usd but had a wattage rating of 800W!
Sure, you can do that, but a speaker isn't a constant 8 ohm impedance. There is typically an impedance spike that can go past 100 ohms. How much power into an 100 ohm load would be more "honest"
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Old 14th December 2012, 12:53 AM   #6
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Typical ad might say that an amp was capable of 100 Watts RMS at 0.05% thd, both channels driven. To advertize it as such, it had to do so under FTC-defined conditions. This may have been superseded by now but the FTC mandated test when I was in audio retail (late 70s-early 90s) was that the amp was to be warmed up for an hour at 1/3 power and then had to meet rated output at or below rated distortion into advertised load. of course then the question arose about whether this amount of performance info adequately described an amplifier's sound. It's not but the FTC gave it a shot and required compliance.
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Old 14th December 2012, 01:12 AM   #7
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~it's always the same thing !overpower the thing let's say your loudspeaker needs 100 watts take than a 200 wat amplifier if the the crosover holds it?
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Old 14th December 2012, 01:21 AM   #8
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CEA-490-A R-2008 is what you are looking for. You have to buy the PDF of the standards, but here is the basic idea:
CEA-2006 Amplifier Power Standards
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Old 14th December 2012, 01:24 AM   #9
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There is several methods of telling the customer of how many watts an amplifier is capable of delivering.

There is the PMPO, Peak Maximum Power Output.
Here we have the high numbers from small devices.
Worst example I have ever seen was from SONY.
They had a surroundsoundreceiver with a PMPO of 1000W
5X200Watts that was.
When looking at the power rating near the power cord as it enters the receiver it clearly tells us: Power consumption: 50 Watts.
This is a perpetum mobile folks. Put in 50 watts, get a kilowatt back.
Well, the 5 amplifiers are possible to deliver a 20uSek pulse into 1 Ohm, wich probably meassures 200Watts in exactly that period of time, then it's over.
Obviously the distortion is infinite.

Music Power is also seen. More realible than the one mentioned first, but still a very "nonmusical" way to tell us of how many watts. Often about the double of the next cathegory:

RMS watts, or Root Mean Square, is a more reliable form of watts in an amplifier.
The equation for this is like this. Lets take a 100% effective amplifier fed with 12VDC.
Speakers 4 Ohms.
Let the amplifier be mounted with a similar amplifier in brigded mode and we find this:
(12V)
2(4)
This gives us roughly 20W RMS. (Ever wondered how they get 50Watt in a caramp?)

Then comes the more sofisticated ways to meassure an amps power.
I will not go in to different manufacturers own "specs" but since there is some standards there is to select from wich is more non-manufacturer-dependent I select the FTC-norm

Here we have a way of meassuring the power where one can be sure that the amp delivers what it is declared to do.
The FTC-norm clearly states that both (all) amps in the device is to be driven simontaniously (different from all the above) continously over a period of time no shorter than 5 minutes.
There is also demands to the AC power (120 or 230VAC) Ambient temperature, the total frequency range shall be 20-20000Hz, and so on.
Unfortunately the manufacturer has the possibility to set what distorsion theese meassurements should be made at. BUT often this one is set to about 0,02% or less.
And here we see the lowest numbers compared to weight and price of the products.
And perhaps the only one truly to believe in?

There is many many other standards too, DIN45500 is the one where the term HiFi is implemented. Dont ask. The figures to obtain this honour of being a HiFi device is terrible. Just terrible.
JIS and other standards are there too.

So What is watts in an amplifier?
Depends strongly of who you ask.
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Old 14th December 2012, 01:29 AM   #10
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Ask the Consumer Electronics Association (CEA) See above.
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