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Date: Wed, 27 Apr 2005 19:09:32 +0100
From: Colin Stamp <col.dustbinnospamp.plus.com>
Subject: Re: I think I blew my amp??!!


On Wed, 27 Apr 2005 02:44:35 GMT, "James Sweet" <jamessweetnospamail.com> wrote: >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. Absolutely. If an amp damages a speaker, it's virtually always because the speaker is under-rated compared to the amp. Not the other way round. >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. I guess what you mean here is that the output starts to approximate to a squarewave, which has it's RMS value equal to it's peak. If that's the case, then I'm not disagreeing. > >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. That's not a particularly good test - no cone movement means no airflow over the coil. You'd be better off using a squarewave within the speaker's operating range. Still, again, I don't disagree with the general idea that speaker power ratings are often stupidly misleading. >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. > But what is it about the blackening which makes you think it was always caused by clipping? Certainly it's possible for a surprisingly small amp to knacker a surprisingly "high power" speaker, but you seem to be suggesting that the same speaker would survive if driven to the same volume level by a bigger amp running cleanly. That's only very rarely the case. Cheers, Colin.

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