Andres Cabrera wrote:
>I think the main problem that can occur from DC offset is overheating of
>the amp, and then heat protection turns the amp of....
>
>
Overheating of the amp is nonsense. Most amplifiers operate in class A
or AB anyway, and maybe in class D. Heat dissipation is independant of
the input signal for these amps. The types that might build up a problem
with heat (e.g. class H) aren't used in PA enviroments. And before the
amp overheats, your speakers will be dead.
The biggest problem regarding DC offset (and clipping) is the fact that
speakers are not made to cope with DC signals. They heat up very quickly
under DC load, and on top of that there is no air movement in the
speaker itself to cool it somehow (athough this last effect isn't that
important).
the following links provide quite some info regarding distortion,
clipping and DC offsets:
http://sound.westhost.com/clipping.htm
http://sound.westhost.com/tweeters.htm
The remark regarding the dynamic range is right though: the only time I
ever seen a blown up PA speaker was due to the dynamic range of the
music involved. It started with a very silent intro of a minute or so,
but then it contained a full-scale bassdrum. Nice to get a 'surprise'
effect, and probably nice in a silent studio enviroment with moderate
listening levels. But in a live situation there is a lot of enviroment
noise, which tempts the PA engineer to crank up the volume on silent
intro's so that the people are able to hear them. You can guess what
happens once the bass drum kicks in. Even when using a limiter this can
destroy speakers, because of its attack time. It's also not very healthy
for the public.
My recommendations:
- Be sure to do a decent sound-check: have a full-scale piece of music
ready for the PA engineer to set the PA desk incoming level, and be sure
not to change your volume when soundcheck is done.
- Adapt the dynamic range of your music to the live enviroment, e.g. by
using a compressor plugin just before the soundcard output.
Greets,
Pieter
Received on Mon Apr 4 20:15:09 2005
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