High Efficiency Speaker Asylum: RE: JBL charge coupled capacitor network in crossover?? by Steve Schell Need speakers that can rock with just one watt? You found da place.

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Posted by Steve Schell (M ) on March 8, 2009 at 13:36:53

In Reply to: JBL charge coupled capacitor network in crossover?? posted by limono on March 4, 2009 at 19:56:15:

I have been fortunate to meet Greg Timbers of JBL on several occasions. He has mentioned the battery biasing of capacitors more than once, but just as with RCAfan mentioning conical horns it took a while for the importance of the information to make it through my thick skull. As with the conicals, when I finally experimented I was delighted with the results of this "charge coupling" technique.

Greg describes the technique creating a class A situation. I think this is correct. I have long thought that the remarkable retrieval of fine detail possible with single ended tube circuits is due to the avoidance of a zero crossing point with zero signal, i.e. the transformer(s) are biased up to some point between cutoff and saturation by plate current. Instead of tiny microvolt signals (reverberant tails, etc.) being distorted by nonlinearities in the crossover region where magnetic fields are collapsing and reforming in opposite polarity with every audio half cycle, these tiny signals sail on through the most linear operating region of a biased transformer as just a tiny modulation of the quiescent bias point.

So now it seems we have the same situation with capacitors. In the usual passive crossover, to pass the audio signal the electrostatic fields have to collapse and reform with every half cycle, and the smallest signals live in the most "dirty" nonlinear region of the device. Biasing the capacitors involves extra cost and expense, as one needs to two capacitors of double the value of the unbiased circuit (four times total capacitance) to achieve the same filtering. Rich and I have found that with the high pass crossover to our midrange / high frequency driver the improvement in sound is not subtle, more of a "Wow" experience.

Greg Timbers discusses the technique in the third post of the Lansing Heritage thread linked to below.

• Charge coupling thread   (Open in New Window)

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