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-   -   LPF function dependent on phase? (http://www.diyaudio.com/forums/solid-state/21229-lpf-function-dependent-phase.html)

Lusso5 7th October 2003 06:30 PM

LPF function dependent on phase?
 
I was testing a Dynaudio sub last night, and could hear higher frequencies making it past the LPF. They were very insignificant, and very "distant" sounding. Couldn't hear them without putting my ear right up to the driver (at low volume of course).

The upper-bass sounded a bit muddy, so I checked my settings, LPF: 80hz, OK that is where I wanted it. Phase: REV, ahh I was running the driver out of phase. Switched it back, much better.

Here is the wierd part - when I switched the driver back in phase, those freq. were gone, and it seemed the LPF was working properly.

Do x-overs usually allow a little residual freq. to make it through, at very low levels? If so, what would the phase of the driver have to do with cutting that out?

PMA 7th October 2003 07:41 PM

It depends on the order of the LPF.
1st order -6dB/octave, 2nd order -12dB/octave, 3rd order -18dB/octave. The lower order the more frequencies above cut-off pass through.
Phase: 1st order LPF has phase angle of -45 at cut-off frequency etc.


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