Modern HiFi amplifiers are Direct Coupled, and can easily send a DC signal (or
a VLF one) to a speaker. The speaker coil cannot usually handle the high
current level for very long - especially if the speaker cone is pushed anywhere
close to its limit.

Problems can also arise at the other end of the spectrum - it is possible with
digital synthesis to generate VHF signals at high amplitude. Again, amplifiers
will pass this happily to the speakers (some amplifiers have an HF response
ascending above 30KHz) - the tweeters are, again not usually able to withstand
sustained attack in this way, and the low-mid drivers will not be too happy
either, if the crossover circuitry is less than ideal. Some amplifiers will
cut-out automatically, when they detect a high current drain, to protect both
the speakers and the output transistors, but not all amplifiers have this
facility, of course . It is a well-known technique for damaging speakers to
overdrive a low-powered amplifier so that it goes into hard clipping. A rough
rule-of-thumb is that the power rating of the amplifier should be about twice
that of the speakers - just don't turn the volume up full!

Whenever I generate a sound which I am not fully confident about (eg when
developing a new program), I always view the file first - I do not relish
putting full-amplitude DC or clipping either into my speakers, or (perhaps even
more unpleasant!) into my headphones. Alternatively, I turn the volume right
down, just in case.

I can't see drivers attempting to detect data errors such as swapped bytes -
that really isn't their job, and quite how one might do it isn't at all
obvious, at least to me. It is so easy to view a file and tell instantly if
there is a problem.



Richard Dobson



Larry Troxler wrote:

> On Sat, 18 Apr 1998, tolve wrote:
> > concerned that subsonic sideband frequencies that result from fm might
> > damage speakers. tried to check out some files with sndinfo, but base Frq
> > doesn't show up in the report on ppc running csound 3.48. how do i
> > ascertain lowest frequency?
>
> Hi, although I don't have a specific answer to this question, the general
> question of avoiding speaker/headphone/ear damage is one that has always
> been on my mind, and surprisingly I haven't seen this obvious
> high-priority topic discussed much.
>
> First, regarding subsonic frequencies; is it really true that these are
> bad for speakers? Aren't they blocked by the amplifier? If not, what is
> the mechanism by whitch they are damaging?
>
> Diverging to the more general topic of avoiding speaker damage, I think it
> would be interesting to hear what techniques people on the list tend to
> use. I'm speaking of the harzards involved when generating sound-files, as
> computer-music composer do, and not general techniques for avoiding
> damage from known-good sound sources.
>
> Currently, I use the "first listen with cheap headphones" technique.
>
> Along these lines, I've always thought it would be neat to have some way
> do detect mismatches sound formats (like littl/big endian mixups) at the
> back end, for example in the sound driver itself. I suppose things like
> this, and simlar problems like amplitude overflow, are the things I most
> worry about.
>
> Looking forward to comments.
>
> Larry
>
>  --  Larry Troxler  --
> lt@westnet.com -- Patterson, NY USA --