Amplifier Power Requirements

There have been several references recently in other threads to amplifier power requirements, so I thought the following information might be of interest.

Unfortunately I cannot remember the website from which I obtained the data a couple of years ago otherwise I would give the appropriate credit.

Geoff

[IMGHTTPDEAD]http://www.gmweb.btinternet.co.uk/SPL.gif[/IMGHTTPDEAD]
 
I tried to post Friday, but my ISP suddenly decided that this site didn't exist for some reason.
Nice reference, Geoff. Seems that I recall that the 'average' living room has about 30-40 dB background noise, so you've got to get up above the noise floor before you can begin to hear anything.
On the other hand, I had to buy a house way out in the country before I could get anything like the quietness that I remember as a kid. I suspect that the 30-40 dB figure is out of date...

Grey
 
Hi all ...

Your right about some 30 to 40dB SPL background noise, but that doesn't mean that a moderate classical music is played back realisticly at 84dB + 30 to 40dB = 114dB or more. You can easlely hear throuhg some background noise.. I think people don't ussualy listen to music at 110dB.. why? It give you that peeeeeeeeeep after the music has gone.....
greetings..
Thijs
 
All very true and correct .... but note he differentiates between average and peak power requirements, whereas we are using W-RMS as our amp measure. Remember a 100W-RMS amp can produce far greater peak power - even before it clips.

If you build a power amp in W-RMS to handle the peaks at high volume you are gonna spend some big bucks (both in amplifiers and speakers).

cheers, mark
 
mefinnis said:
All very true and correct .... but note he differentiates between average and peak power requirements, whereas we are using W-RMS as our amp measure. Remember a 100W-RMS amp can produce far greater peak power - even before it clips.

Hi, correct me if I'm wrong, but IMHO the difference between RMS and peak power is usually not so big: if the signal reaches the power supply rails during a transient, it has no other choice than clipping ... At the same time, the RMS power can be measured ... just below clipping (OK, including some power supply rail sag during continuous operation at full power).

Regards, Dirk
 
Mark

Quote:

Remember a 100W-RMS amp can produce far greater peak power - even before it clips.

I think your comment needs clarification. The peak output power into the rated load impedance is twice the rms power. Higher peak power levels can only be achieved if the load impedance drops due to the speakers characteristics (which may or may not occur at the required frequency) and if the power supply is capable of delivering the additional current.

Also, this higher peak output is only applicable to push-pull output stages. A single-ended Class-A is current limited as well as voltage limited and the peak output power will be no greater than twice the rms power for which the quiescent current was set.

Geoff
 
I accept all comments above.

This sort of started when I tried to advise someone (with good and honest intent) that the real difference between a 60W Aleph5 and a 100W Aleph4 was not going to be very much at all, and the extra heat of the A4 was probably not worth the hastle/cost. (ie. double the heat and hardware for 2.2dB)

There seemed to be a firm misconception out there about how dB related to watts.

I'm not gonna argue for a nanosecond that to play really loud without distortion/clipping you need a lot of watts/headroom ..... just that going from 60 to 100W is not going to achieve this ........ which I would say the original post here clearly displays.

You are either like the masses and listen to music modestly loud at times, when anything above 20-40W is ample, or you like ear splitting perfect sound and you should be in the X1000 territory .....

I am concerned that some among us may interpret the table above as justifying small power increases, when I do not think it does, IMHO.

For the few who are chasing the "sonic boom", your money will be better spent in more efficient speakers .... read horns .... and Nelson may be about to help you here too ;)

cheers, mark

PS: How many dB is 1W of acoustic energy?