Cross-over filters

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Ampdog

R.I.P. 23 June 2022
Joined
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I have just noticed a simple low/high third order cross-over suggestion and wonder whether anybody has used it.

I still cannot put a diagram on (some day my scanner will co-operate), but the description is simple enough (it is a bi-amping device, i.e. electronic). A low pass third-order filter is composed in much the usual way: A second order op-amp circuit (much like the Sallen-Keys one) is followed by a normal series R and parallel C to give the third order, followed by a unity gain op-amp as a buffer to feed the l.f. channel.

The output of this is then 'summed' out of phase with the wide-band input in a unity gain inverter, to give the h.f. output. The result is a mirror-image cross-over with the vector sum of the two channels being a constant, both amplitude and phase-wise, without the need for close tolerance capacitors. (The same caps serving for both channels.)

It sounds very logical and enticingly simple. This does of course not take care of driver idiosyncrasies following the respective power amplifiers, but I believe those can be dealt with separately.

Any comments (or has this been known)?
 
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