Matching driver output without resistors?

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Faizal Ali

Faizal Ali

Member
Joined 2004
#1
The following is from the website for Coherent Audio speakers:

The Coherent “XD crossover” is exclusive to our line. This unique system uses no resistors to pad down the compression driver to match the woofer section output. The woofer has one inductor in the signal path, and the compression driver has one capacitor and optional bypass caps on it. “Impedance Matching" is then used to make the two drivers act as one in the critical midrange 800hz to 2500hz frequency range.
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Does anyone know how this would work? To my (limited) knowledge, one could move the crossover point by varying the values of the inductor and capacitor in such a first order arrangement and in so doing find a point where the summed frequency response of the two drivers is closest to flat. But how would one overcome the differing sensitivities? Coherent uses Radian coaxial drivers and, for instance, the LF of the 5212B has a sensitivity of 96dB, while the HF is 107dB. How does one balance that out without using resistors?
 
#2
If by “Impedance Matching" they mean a zobel to pull the CDs impedance lower, that gives the lie to the claim of no resistors. Sure, there would be no resistors in series with the driver, but a zobel would still load down the CD branch of the xover, and destroy the illusion of a purely 1st order crossover which they seem to be giving.

It would be interesting to see actual measurements.
 
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#4
I have the same sort of crossover on speakers I built.
I realized I did not like sound of a midrange compression driver when it had a 6 DB L pad compared to non- padded.
I had a 2nd order crossover using ferrite cores and just wound extra onto the core for padding. Other nice thing is the capacitor drops in size. Basically, the autoformer can also be the crossover choke in this case.
 
#5
Scottmoose said:
I assume they're using autoformers. Which doesn't mean the page isn't riddled with marketing of course. 😉
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same idea spirit, as far this is not a resistor there is no false claims. Also a pot is strickly not called a resistor while dissipating heat towards the return path, could be a simple pot in zobel position ? If that, this is even more tricky claim than if they use autoformer ! Or did they found the worse ESR cap on Earth ?
 
#6
This next paragraph from their site gives you insight into their way of thinking...
In our opinion less is better .. some high end x-over designs have as many as 25 elements in their designs.

Early on, Frank noticed that each combination of capacitors and coils ” ring “ at a given frequency, and this phenomenon reflects radio filter theory . The more combinations, the more ringing .. and this makes its way through to the ear. Our XD x-over thus greatly reduces this ringing, and helps to produce clean and smooth mids and highs.
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