Vandersteen 5A's Internal crossovers/batteries

Active biasing of capacitors in a loudspeaker crossover was invented by Gregg Timbers of JBL/Harman. It is used in the Everest D66000 for an example, applying batteries as mentioned above. In the newer Everest D67000 the bias voltage is achieved via diodes rectifying the incoming voltage from the amplifier which charges an electrolytic capacitor. The advantage to this approach is that the bias voltage always will be higher than the incoming voltage, and there no need to replace batteries.

JBL Everest D66000 XO schematic

Active biasing of capacitors places a bias voltage to a midpoint between two capacitors relative to ground. The voltage can be applied with a battery, or a series connection of batteries to achieve a higer bias voltage or as described above. Th sonic benefit form active biasing is only achieved as long as the bias voltage is higher than the incoming AC voltage from the amplifier, that being said 27VDC (3 ea 9V batteries in series) is certainly high enough for even very loud playback.

Good Listening

Peter

Peter...thanks for the very incisive explanation. I wonder why more manufacturers don't use this method? That's what threw me, I have never really heard of this being done in a crossover before.

MoFi,

Don't know why its not more widely used, one explanation could be that you'd need twice the capacitance otherwise required. For an example if your crossover design for the high-pass filter for the tweeter calls for a 5uF capacitor followed by a 15uF capacitor with a .3mH coil to ground from their midpoint (typical values).

To convert this to a actively biased crossover you would need two 10uF (replacing the 5uF) capacitors in series with their midpoint being the bias point followed by two 30uF (replacing the 15uF) capacitors in series with the bias point being their midpoint, so you can see the bill of materials stack up pretty quickly.

Good Listening

Peter

Thanks again for all the information regarding my post.