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March 14, 2019 / consort3

Asymmetric crossovers

The Aug 99 issue of Electronics World had an asymmetric third order crossover in its letter page communicated by Van Dormael. This uses a difference amplifier giving V(high-pass)=V(in)- V(low-pass). This gives a flat frequency and phase response giving a perfect transient response. I had seen a similar idea in the 1980 National circuits manual but the other way around. I have modelled both circuits and they do indeed give the flat responses.  The second circuit is a Rauch or MFB filter mentioned in Ashley and Kaminskys 1971 paper  “Active and passive filters as loudspeaker crossover networks” , you can analyse the circuit here:

http://sim.okawa-denshi.jp/en/MultipleFB3Hikeisan.htm

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The asymmetric idea appears to originate from Ashleys 1962 paper Transient response of ideal crossover networks. It was taken further by Small of Thiele/Small fame, he wrote a paper in 1970 “Constant voltage crossover network design”. Contemporary criticism:

Augspurger-comments-constant-voltage

Renardson has a nice piece on asymetric crossovers:

http://www.renardson-audio.com/xovers.html

An interesting variant of the asymmetric crossover is the Harsch one. A 4th order Butterworth filter on the woofer and a 2nd order Bessel on the tweeter with a time delay give a practical solution.I feel I am retracing the footsteps of JMLC Jean Michel Le Cleach with this topic. More here:

http://jimbee.over-blog.com/page-4543655.html

I am also treading in the footsteps of Nelson Pass who wrote this in 1982!

https://www.passdiy.com/project/articles/phase-coherent-crossover-networks

Here are Uwe Beis’ thoughts on the matter:

https://www.beis.de/Elektronik/Linear_X-Over/LinearAmplAndPhaseXOver.html

In 1983 Lipshitz and Vanderkooy showed how to do the subtractive linear phase filter using a higher slope by incorporating a time delay. In September 1987 Elektor published an active version of the type. This shows how to configure and implement the delays

https://circuitsdiagramlab.blogspot.com/2017/10/simple-3-way-active-crossover.html

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