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"passive" vs "active"

Posted by Christine Tham (R) on November 21, 2006 at 13:50:38

In Reply to: Oh yes, of course. posted by Presto on November 21, 2006 at 09:09:09:

There's actually some research on this in the 70s, and the general conclusion seems to be it's better to apply filtering post amplification (or "passive" as you call it) vs before amplification.

The main advantage of bi-amplification is that multi-driver speakers present a complex impedance load on the amp. Amplifying each driver separately greatly simplifies the "load" being presented to the amp, and hence allow the amp to more precisely control each driver, achieving higher damping factors for the woofer and better preserving the delicate high frequencies of the tweeter.

If you accept the above explanation, then filtering post amplification simplifies the load further, thus even better results. However, filtering prior to the amp is not necessarily an improvement, since it's not the complexity of the input signal that challenges an amp, it's the complexity of the output load.

There is a counter argument that says filtering the amp used to drive the tweeter achieves better transparency. So I guess the optimal result is probably (using your terminology) "active" filtering the tweeter, and "passive" filtering the woofer. I don't know anyone who does that, except perhaps embedded in a powered monitor.

The reason I don't like digital filtering (and DSPs in general) is that in my experience they seem to add a veil or a "haze" to the sound. I first noticed this when I realised my system sounded much better without digital bass management than with (at the expense of slightly less deep bass). Then I noticed everytime I put a processing step between the music and my ears I always seem to lose some "life" from the music. So now I run everything unprocessed - even though as you know I have more than enough hardware to do lots of processing if I wanted to.

I even listen to Dolby Digital 2.0 soundtracks without applying Pro Logic II/IIx (for concerts and anything that's not surround encoded, they sound better that way). And I've given up on equalization, convolution, bass management, upsampling.

I know, it's heresy on this forum, but hey, at the end of the day it's the music that matters.

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