Alignment with All-pass filters and the effect it has on the Impulse Response   Leave a comment

So i wondered about this . I’m spending a lot of time correcting or better to adjust the phase response of a loudspeaker system but never investigated the influence it has on the Impulse Response of a system .

So for now I’m posting without a explanation but as i expected the Impulse Response gets tighter in a “phase flat system” . As i keep writing on this post I’ll probably have to do some more measuring and the frequency response might vary a bit as well on the phase response . Has to do with available time and me needing the measurement mic for other jobs .

The system being measured is a 12-2 way loudspeaker cabinet build in the Netherlands , a APEX processor 4in/8out , Meyer sound’s SIM3 FFT analyzer and 1 DPA4007 microphone .

For now I’ll stick with the screen shots .

Impulse response @ the start of the measurement (no processing applied yet) .

001 IR strt xvr alignment via ap2 filters

Result window @ the start of the measurement .

002strt nop

Low & High pre all-pass alignment @ the x-over point .

Low : Linkwitz-Riley 12db/oct high-pass @ 80Hz and Linkwitz-Riley 12db/oct low-pass @ 2200Hz .

High : Linkwitz-Riley 24db/oct high-pass @ 2200Hz . Both drivers have a bit of EQ on it and the high driver needed to be reduced .

003result pre ap2 allignment xvr

Impulse Response of the above trace (not aligned yet) .

004 IR xvr alignment pre ap2 filters not phase aligned yet

First 2nd order All-pass filter on low @ 1500Hz bandwidth 1 oct. to align the low driver with the high driver @ the x-over point .

006 result xvr alignment 1st ap2 filter

Impulse Response changes because of the All-pass filter .

005IR xvr alignment 1st ap2 filter

Second 2nd order All-pass filter on low @ 3234Hz bandwidth 1 oct. to align the low driver with the high driver @ the x-over point .

008 result xvr alignment 2nd ap2 filter

Again the Impulse Response changes because of the 2nd All-pass filter .

007 IR xvr alignment 2nd ap2 filter

And the system aligned without delay but with all-pass filters (i did put in 1ms of delay on both the high and low driver but that’s for the following part of this post).

12-2 delayed system sim3

So that’s it for now . The following 3 screen shots are the system after phase correction . First with SIM3 (the system i like best) . Second 1 is from SAT-live and the 3rt 1 is from SMAART5.4 . Just to show that you can use whatever FFT analyzer that suits you or your budget . The data is the same as you can see .

SIM3 result window . 

12-2 phase corrected system sim3

SAT-live (thanx tommy great program) .

12-2 phase corrected system sat live

SMAART-live (Thanx to the people from Rational acoustics . I’m still thinking about buying a MAC and version 7 but have to make due for now).

12-2 phase corrected system smaart

I will update as soon as i have the time for it .

Posted 10/05/2012 by timobeckmangeluid in Geen categorie

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