The following link answers the query in my earlier post ...

http://www.sengpielaudio.com/calculator-soundlevel.htm

It comes from a comprehensive listing of audio calculations which folk might find of interest.

http://www.sengpielaudio.com/Calculations03.htm

 

Great big thanks. I have always tried to avoid those Pascal calculations but this will make it easy.

 

(Agreeing with bountyhunter) Most music contains peaks of about 10x the average level. When your stereo is making music that is undistorted, you can usually assume you are running at about a tenth of its power rating...like, in the 5% to 20% range.

for vk6...The usual method is measure the RMS voltage and use the speakers' rated impedance to calculate RMS watts.*

Just a note on Fender brand musical instrument amplifiers. The last time I figured one out, they were using 3 stacked lies to arrive at their power rating. Still, (4) 6L6 tubes driving (4) 12 inch speakers produces some pretty good results. It just isn't what the label says it is. (Other Mfg's probably use the same kind of math.)

*It may well be "the usual method",but the term "RMS power" is still nonsense,what you are measuring is effective power!

"RMS" values for voltage & current were derived in the early days of Electrical theory,so that the normal Ohm's law & power calculation formulas could be used.

For instance,if an AC current flowing through a resistive element could do the same amount of work as,say a 10A DC current,the AC current was regarded as 10A RMS.

The "root of the mean of the squares" calculation was the mathematical relationship which backed up this concept.

At no time was the power called RMS power,the fact that the power was not constant gave rise to the term"effective power".

"RMS" power is a rather silly term which has gathered currency among audio people.
Electrical power generation people don't use it!

 

At no time was the power called RMS power,the fact that the power was not constant gave rise to the term"effective power".

"RMS" power is a rather silly term which has gathered currency among audio people.
Electrical power generation people don't use it!

Maybe it has something to do with where one was educated in electrical engineering - I was taught average power but have no problem with effective power. Curiously [in the context of your point] I always thought of RF engineers as being enamored of the term effective power. I recollect once being so annoyed by the term RMS power I sat down and started writing a didactic tome on the topic. I soon realized I would be wasting my time & sweat and got on with my real work.

As to whether electrical [power] engineers are purists with regard to their terminology, I wouldn't be surprised if a good number of them / us were lured to the "dark side" and make [erroneous] reference to RMS power.

 

Maybe it has something to do with where one was educated in electrical engineering - I was taught average power but have no problem with effective power. Curiously [in the context of your point] I always thought of RF engineers as being enamored of the term effective power. I recollect once being so annoyed by the term RMS power I sat down and started writing a didactic tome on the topic. I soon realized I would be wasting my time & sweat and got on with my real work.

As to whether electrical [power] engineers are purists with regard to their terminology, I wouldn't be surprised if a good number of them / us were lured to the "dark side" and make [erroneous] reference to RMS power.

Actually,I am an RF person,& back in the "Dreamtime",I was taught "Average Power".

In latter times,"Effective Power" has been more common in most of the stuff I have read,so I guess I have picked it up.

Maybe it isn't such a good choice,as it may be confused in some cases with "ERP"or more correctly "EIRP" as used with antennas.

I used Electrical(power) Engineers as an example of those who don't use the incorrect term,as I'm not sure that RF people have a lot of "street cred" on this forum!

 

http://www.meyersound.com/support/papers/amp_power.htm

"When an amplifier is rated in RMS watts, this is a shorthand way of saying “average watts obtained by the RMS method.”

http://www.caraudiohelp.com/newsletter/amplifier_power_ratings.htm

"The only true specification, if it is followed, is the RMS power rating (preferably using the CEA-2006 testing procedures)."

The regulatory agencies that write the standards need to hear from you. They still don't have it right.

 

http://www.meyersound.com/support/papers/amp_power.htm

"When an amplifier is rated in RMS watts, this is a shorthand way of saying “average watts obtained by the RMS method.”

http://www.caraudiohelp.com/newsletter/amplifier_power_ratings.htm

"The only true specification, if it is followed, is the RMS power rating (preferably using the CEA-2006 testing procedures)."

The regulatory agencies that write the standards need to hear from you. They still don't have it right.

I think you will find that they are Industry Associations,not regulatory agencies.
Such Associations often produce absolute twaddle!

After all,I can say that "cat"is a shorthand way of saying "duck",but that doesn't make it so!

 

OK. "Industry Associations". They need to hear from you. The EIA did this wrong for decades, now the CEA standard is wrong. They desperately need to know that there is no such thing as an RMS watt. Everything electronic that makes sound, from MP3 players to the Crown brand bridgable 3000 watt amplifiers are in need of a standard.

Even if you don't want to tell the Industry Associations what they have been doing wrong for decades, you can tell us, here at allaboutcircuits. How should the output power of audio amplifiers be measured?

 

OK. "Industry Associations". They need to hear from you. The EIA did this wrong for decades, now the CEA standard is wrong. They desperately need to know that there is no such thing as an RMS watt. Everything electronic that makes sound, from MP3 players to the Crown brand bridgable 3000 watt amplifiers are in need of a standard.

Even if you don't want to tell the Industry Associations what they have been doing wrong for decades, you can tell us, here at allaboutcircuits. How should the output power of audio amplifiers be measured?

Use this:

"When an amplifier is rated in RMS watts, this is a shorthand way of saying “average watts obtained by the RMS method.”

Because everybody understands what it means and what it is. Whether the use of terminology is perfectly accurate is not important if the information is communicated correctly.

In the game of golf, for many centuries they had only two kinds of clubs: irons and woods. Then they started making the woods out of aluminum. So, people called them "metal woods". Of course they are not both metal and wood, so the term is not accurate. But everybody knows exactly what it means so they use it.

 

The output power spec must include the amount of distortion (or else the output could be a horrible-sounding saturated square wave producing double the power of the amplifier that is barely clipping with low distortion).

The signal should be continuous so the duration of the signal must be stated or it else it is a lie about "instantaneous power" (it used to be called music power which is before the power supply voltage sags).

 

OK. "Industry Associations". They need to hear from you. The EIA did this wrong for decades, now the CEA standard is wrong. They desperately need to know that there is no such thing as an RMS watt. Everything electronic that makes sound, from MP3 players to the Crown brand bridgable 3000 watt amplifiers are in need of a standard.

Even if you don't want to tell the Industry Associations what they have been doing wrong for decades, you can tell us, here at allaboutcircuits. How should the output power of audio amplifiers be measured?

The "Steady State" ,or "Effective" or "Average" power of an amplifier should be measured in exactly the way you say,but the term "RMS Power" is incorrect.

The power you calculate from the RMS voltage & RMS current is the product of the two RMS values & cannot be the "Root of the mean of the squares" of the peak power.
0,7071x 0.7071 = (near as dammit!) 0.5.so that it is 0.5 P(pk).

There is no "RMS watt",it is only the voltage & current which need to have a correction factor, so that they can be used in the DC originated power formula.

Other countries,namely Australia & the UK ,& probably European countries as well,use the term "steady state power" to describe the power output derived from the standard single tone test.

 

A few comments from others:

http://www.hifi-writer.com/he/misc/rmspower.htm


http://www.n4lcd.com/RMS.pd


http://en.wikipedia.org/wiki/Audio_power


http://www.melbourneaudioclub.org.au/news7.htm


http://en.allexperts.com/q/Electrical-Engineering-1356/2011/1/f/FM-Stereo-power-output.htm


http://www.audioholics.com/education/amplifier-technology/amplifier-power-ratings

 

The output power spec must include the amount of distortion (or else the output could be a horrible-sounding saturated square wave producing double the power of the amplifier that is barely clipping with low distortion).

I recall for all the power audio IC's it was specified at some ridiculous value like 10% THD which is basically clipping the sine wave into a square wave. Marketing always gets their way in the game of specsmanship.

The signal should be continuous so the duration of the signal must be stated or it else it is a lie about "instantaneous power" (it used to be called music power which is before the power supply voltage sags).

yup, I remember music power. I think Radio Shack uses it exclusively.

 

I recall for all the power audio IC's it was specified at some ridiculous value like 10% THD which is basically clipping the sine wave into a square wave. Marketing always gets their way in the game of specsmanship.

yup, I remember music power. I think Radio Shack uses it exclusively.

Many years ago in the Sears catalog it said, "This 120W PMPO stereo console has an output of 4W RMS continuously per channel at low distortion".

Hmmm, stereo has two channels so the "120W" system is actually only 8W.
I am glad they were truthful.