Date: Fri, 29 Apr 2005 00:40:46 +0100
From: Pooh Bear <rabbitsfriendsandrelationsnospamail.com>
Subject: Re: I think I blew my amp??!!


Colin Stamp wrote: > 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. You'll be amused to know that 'does clipping cause tweeter burn out?' is a commonly recurring and much discussed topic in the pro-audio groups. Considering they *ought* to know - there's still much debate. In the end it boils down to the long term power rating of the tweeter versus the crossover frequency. Graham

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