power vs. sound

Posted by Shawn Harvey [IP: 206.31.111.18] on August 09, 1999 at 18:01:54
Using Mozilla/4.0 (compatible; MSIE 5.0; Windows NT; DigExt):

In Reply to: power vs. sound posted by SMR [WizOp] May 27, 1999 at 14:53:24

Stuart,

Not discussing all the claims that the 1000W amps have an "iron fist" on the bass or provide "endless power", there are instances where a lack of power can be a problem.

I just bought a pair of Joseph Audio RM22si's which are a pretty stable 7 Ohms but only 85db sensitivity. It's very easy for me to run my 80W Linn amp to clipping (a very ugly sound) at not terribly high sound levels. They don't sound that loud to me, at least.

Remember that power ratings are made at one frequency into a purely resisitive load -- totally useless information.

Your speakers are:
a) producing many, many frequencies (harmonics, distortion, IM effects, etc.) at any given time
b) dynamic, not steady-state
c) not a purely resistive load by any means

So power output is really an issue in some cases. I am looking for a deal on a Bryston or Pass 150W amp right now, actually.

The only problem is getting a real power rating from the manufacturers. Perhaps a frequency sweep graph into 8, 6 and 4 ohms as well as an impedance graph for each.

If you are running 100W into 8 resistive ohms at +/- 90 degrees you are *not* getting 100W of power (well, ok, 100W x the speaker's transducer function).

Footnote:
Actually, in truth, I was very surprised that my amps clipped so soon. They can double their power into 4 ohms. I think the issue is the very low sensitivity coupled with the fact that while the resistive impedance is rather flat, the reactive impedance may be all over the place.

I still like the speakers enough to replace the amp instead of the speakers, though. :)

Shawn Harvey

Follow Ups:

• power vs. sound - SMR [WizOp] 22:11:12 08/09/99 (0)

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