Cascade All Pass Filters

foxcob wrote:

   ...

> I've heard the arguments for minimum phase vs linear phase for audio
> filtering before because of the pre-ring, but I'm interested in why linear
> phase would not be ideal for a cross-over.  It seams that the cross-over
> could be complementary for the high / low pass sections and cancel out. 
> Theoretically it sounds good, but is a problem of the loudspeaker
> performing this way in reality?

Crossover design is tricky. The speakers for different ranges are 
physically separated, forming a directional array in the crossover 
region. In some installations, the woofer is at the front of the 
cabinet, while the driver for the horn tweeter can be some distance 
behind. There are interesting discussions of crossover networks at 
http://www.frazierspeakers.com/download/cross.pdf and particularly 
http://www.rane.com/note160.html. Avoiding interference effects is just 
as important as maintaining good stereo effect in different parts of the 
room.

Jerry
-- 
Engineering is the art of making what you want from things you can get.

>On Mon, 11 May 2009 13:18:26 -0500, "foxcob" <jacob.thefox@gmail.com>
>wrote:
>
>
>>I've heard the arguments for minimum phase vs linear phase for audio
>>filtering before because of the pre-ring, but I'm interested in why
linear
>>phase would not be ideal for a cross-over.  It seams that the
cross-over
>>could be complementary for the high / low pass sections and cancel out.

>>Theoretically it sounds good, but is a problem of the loudspeaker
>>performing this way in reality?
>
>Yes, it's a problem in reality.
>
>Consider that the lowpass and highpass sections of perfect
>reconstruction crossovers have frequency responses that sum to unity
>magnitude and impulse responses that sum to a (delayed) impulse.  This
>means that the pre-ring (and post-ring) of the highpass function is
>out-of-phase with the pre-ring (and post-ring) of the lowpass
>function.  If the outputs are summed arithmetically or electrically,
>the ring cancels perfectly.  But in reality the outputs are summed
>acoustically.  This means that there will be some locus of points in
>space where they cancel perfectly (or there would be if the
>transducers were identical), but at every other point in space they
>will not.
>
>Greg
>
That is what I suspected.  Thanks.

Jacob

On Mon, 11 May 2009 17:29:50 -0500, "foxcob" <jacob.thefox@gmail.com>
wrote:

>That is what I suspected.  Thanks.

You're welcome.  Some relevant info here:
http://www.aes.org/e-lib/browse.cfm?elib=8170

Available directly from me; just ask.

Greg