DESIGNERS’ BENCH Issue #4 - DIRECT DRIVE
Direct Drive means that each amplifier is directly connected by nothing but a short wire to its driver. No intervening components. This means getting rid of the old passive filters aka ‘crossovers’ by doing their work in the processor. During 30 some years of designing passive filter circuits I was constantly aware of their shortcomings.  The unavoidable cost was degradation of the signal.
Back in the 90s we demonstrated this quite starkly with our HOTROD series.  By merely upgrading the quality of the filter components in our standard models we achieved obviously superior results. But the underlying problems with those circuits remained - they are by definition resonant circuits that add ringing and delay. Worse: they decouple the driver from the amplifier.  When the amp is stiffly coupled to the driver it controls the driver's position moment by moment; when that coupling is degraded by intervening components the amp loses its grip and driver’s position begins to be dominated by its own moving mass and resonant system.  So it fails to track the signal. This is especially noticeable in the bass.  A well coupled woofer goes "WHACK WHACK WHACK!" Poorly coupled goes "BLUB, BLUB BLUB..." Blunt, again: this single advantage is, by itself, reason enough to ditch the old passive filters in favor of Direct Drive.  Just compare the two schematics:
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DESIGNERS’ BENCH Issue #4 - DIRECT DRIVE
Direct Drive means that each amplifier is directly connected by nothing but a short wire to its driver. No intervening components. This means getting rid of the old passive filters aka ‘crossovers’ by doing their work in the processor. During 30 some years of designing passive filter circuits I was constantly aware of their shortcomings.  The unavoidable cost was degradation of the signal.
Back in the 90s we demonstrated this quite starkly with our HOTROD series.  By merely upgrading the quality of the filter components in our standard models we achieved obviously superior results. But the underlying problems with those circuits remained - they are by definition resonant circuits that add ringing and delay. Worse: they decouple the driver from the amplifier.  When the amp is stiffly coupled to the driver it controls the driver's position moment by moment; when that coupling is degraded by intervening components the amp loses its grip and driver’s position begins to be dominated by its own moving mass and resonant system.  So it fails to track the signal. This is especially noticeable in the bass.  A well coupled woofer goes "WHACK WHACK WHACK!" Poorly coupled goes "BLUB, BLUB BLUB..." Blunt, again: this single advantage is, by itself, reason enough to ditch the old passive filters in favor of Direct Drive.  Just compare the two schematics:
Table of Contents