mix current drive with voltage drive at LF? - diyAudio
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Old 27th April 2006, 10:17 AM   #1
diyAudio Member
Join Date: Feb 2002
Location: Germany
Default mix current drive with voltage drive at LF?

Current drive has been discussed before here. The main advantages are reduced distortion through these mechanisms:

- force proportional to Bxl for current drive vs. (Bxl) for voltage drive
- Le and Le modulation are rendered irrelevant because they will always be small compared to the impedance of a current drive amp
- dito for VC resistance variation due to self heating

The main disadvantage is that Q_e -> infinity, i.e. you loose electrical damping, resulting in a huge FR hump at resonance and possible uncontrolled overexcursion.

A Linkwitz transform circuit could flatten the FR, but due to the high Q involved, the compensation would be very sensitive to parameter variations, say over temperature. The problem of overexcursion is also not effectively dealt with.

Increased mechanical damping comes to mind, but the usual methods (lossy suspension, increased conductivity of VC former, air flow resistances, oil or fat damping) are usually very nonlinear in excursion or velocity or will vary with temperature.

Have there been attempts to combine voltage and current drive so that there is voltage drive around and below resonance and current drive above? In the simplest case the driver is only used above resonance, i.e. a midrange or tweeter. In this case, it might suffice to connect an inductor in parallel to the driver which would shunt voltages generated by resonant motion of the driver.

The other question I have been wondering about is, for an unmodified driver (as for the approach outlined here or the LT approach), there is only a relatively low mechanical loss above resonance. Will there be a significant difference in decay times between voltage and current drive above resonance?
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