Playing the modular through my home stereo

[Magnus Danielson]

From: Martin Czech <czech at Micronas.Com>
Subject: Re: Playing the modular through my home stereo
Date: Thu, 2 Mar 2000 10:14:54 +0100 (MET)

> So I think the danger is too much "low" frequency energy for a particular
> driver, that is e.g. 40 Hz for a woofer, 200 Hz for a midrange and 2000
> Hz for a tweeter.
> 
> That's why large PA systems use sharp cutoff filters for the out of
> range frequencys.

Yes, that is part of the story, but also, if your bas for instance is emitting
too much energy above the cutoff you will get terrible summation problems
together with your mid driver. I've seen this. Its ugly. On the other hand,
there are troubles with using 48 dB/oct filters too, not only from the obvious
implementational problems, those can be solved, but with such sharp cut offs
causes the trouble of jumping accoustical center as a instrument or voice
glides over the cross over point. This makes it be comprehention to be an
unnatural behaviour.

You really have to watch out for energies on both side of the usable frequency
range.

> The problem gets worse with synths, because they can produce sine shaped
> waves, i.e. all the energy collapses into a very sharp frequnemcy line.
> 
> A speaker will have some membrane amplitude with white or pink noise,
> i.e. a noise power it can tolerate. This limitation is more on the heat
> side then (coils). With sine waves the tolerable power is usually much
> lower, because of membrane amplitude limits.

A sine surely causes you to run into Xmax limit, the noise causes you to run
into the power rating limit.

Actually, when AES has specified the power limit to be the power that a driver
can widthstand for 1 hour without chaning any property constantly with more
than 10 %. But, 1 hour is way too short time! It should more like 6 hours or
maybe even up to 12 or 24 hours, in order to properly cover the real life
problems. Consider, a techno rig pumping highly compressed audio at high levels
for a full nigth of a rave - your magnetic assembly will be virtually saturated
with energy - that is really hot!

> Good midrange drivers and tweeters with a properly dimensioned passive frequency 
> splitter and suitable max amp power are not easily blown away, it is the woofer
> that suffers, because there is no low end cutoff and because woofers are very
> inefficient, they should be called "heaters".
> 
> I'd suggest a sharp cutoff hp filter (like 24dB Bessel) at a frequency where the 
> woofer will drop out anyway (i.e. 70-50 Hz for most cheap speakers).

24 dB is not a sharp cut off, not in PA systems, 48 dB is. I'd say that 24 dB
is more like the norm these days.

Cheers,
Magnus