Miata Mailing List: April 1995, Message #139
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   From: Andy Poling 
Subject: How to blow speakers :-) (was Re: SPEAKERS)
   Date: Tue, 4 Apr 1995 10:55:18 -0400

This has probably been beat to death, but I figure it's worth a few more
bytes to expound further since this seems to be one of the world's most
mis-understood phenomenon (low-powered amps "blowing" speakers)... 

Taylor sez:
> With all due respect, I must dissagree with you. An underpowered amplifier
> can definitely "blow" a speaker.  When an amplifier runs out of power we say
> it is "clipping". This means the maximum ouput level at the speaker wires is
> equal to the amplfier's power supply voltage. What this means is the amp no
> longer is reproducing AC signals (music) it starts to become a DC generator.
> The music's peaks are cutoff and the signal starts to resemble a square wave.
> Because the amp is no longer reproducing peaks, there is no longer a cooling
> down period for the speaker's voice-coil. This causes overheating and
> possible failure. 

This is true.  It is also true that the square-ish wave produced by an 
amplifier driven to clipping also has very large harmonic components (a 
square wave is a sine wave plus an infinite collection of odd harmonics, 
which swquare off the waveform).

These harmonics are necessarily of higher frequency than the fundamental 
frequency.  This means that the tweeter(s) (and, if present, midrange(s)) 
have to handle reproduction of the harmonics.

Thus, you are likely to blow your tweeter(s) (and midrange(s)) by 
over-driving a low-powered amp.

-Andy

Andy Poling                              Internet: Andy.Poling@jhu.edu
UNIX Systems Programmer                  URL: http://jhunix.hcf.jhu.edu/~andy/
Homewood Academic Computing              Voice: (410)516-8096    
Johns Hopkins University (Balto, MD)     UUCP: uunet!mimsy!jhunix!andy