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Date: Fri, 29 Apr 2005 00:29:48 +0100
From: Pooh Bear <rabbitsfriendsandrelationsnospamail.com>
Subject: Re: I think I blew my amp??!!


James Sweet wrote: > > > > 1. The amp's power rating will be at a certain, reasonable, distortion > > level - say 5%. That 5% distortion doesn't happen *at* the clipping > > point but some way before it. So you can drive the amp harder and get > > more power than it's rating, but it sounds crap so the manufacturer > > can't make any claims about this higher rating. > > > > 2. If you then continue to drive the amp harder still, and into real > > clipping, the resulting sharp edges on the output waveform mean the > > amp is generating much more power at high frequencies than it would > > normally. The tweeters in the speaker system would normally only > > expect to see a small fraction of the amp's output, so when the amp > > starts producing serious power in the tweeter's range, safety margins > > can get eaten into. > > > > Actually it's more the rating of the *speaker* that's the issue. A 140W > speaker will not handle 140W anywhere near continuously, that rating is > music power, which assumes that the average RMS power is much lower. When an > amplifier clips hard the output is much closer to DC at the *peak* power of > the amplifier which is substantially higher than the RMS. > > If you don't believe me, take a speaker rated at 140W, assuming it's 4 ohm, > connect it to a 24V DC source (which will cause it to draw about 140W) and > see how long it takes the voice coil to smoke. You probably won't get more > than 10-15 seconds out of it. Tweeters usually go first, but I've seen > *many* speakers damaged by an underpowered amp clipping, if you open one up > the voice coil is blackened. Actually that's not a fair test. Any modestly rated power speaker relies on the voice coil movement to help cool it. In some cases *very much so*. The magnetic assembly also helps provide cooling. You'll see fins on the back of some high power speakers - they're not just there to look good. ;-) I've even seen some high power rock concert systems that pump forced air cooling via 'plumbing' to cool the voice coils ! Graham ( audio genius )

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