Alignment @ the x-over point using 2nd order ALL-Pass filters   Leave a comment

So this is the last measurement job i did . Just the first day though . Screenshots are made with the SIM3 set-up and data viewer .


Start Mid-high no processing (red) vs. Mid-high processed (blue) . Sorry no trace with the lows added to the Mid-highs . Forgot to save that during the measurement but if the lows would be in play you can add about +/- 6db to the level of the low-mid range up to about 500Hz .

Mid high nop vs proc

High transfer traces all .

*So in the screenshot below You see the high’s with no processing (red) at really low level to prevent them from burning up . @ the processor window red gives a flat line on amplitude and phase indicating nothing’s happening at all .      

*The blue trace are the high drivers with a 24dB Linkwitz-Riley high-pass filter showing the typical signature of that filter . A 180° phase shift @ the x-overpoint @ 2400Hz and @ that same point a 6db reduction in amplitude . Also a 24db reduction a octave lower @1200hz . Also a 360° phase shift on the pass band of the high-driver .

*The green trace is the same as the blue but reduced in level to match the level of the Mid-driver in the next screen shot . The small bump in the processor phase trace indicates a eq point and further up the frequency scale i did put in a high-shelving eq to get a more flat response on the high-drivers .

High nop vs hp vs hp eq and proc all edits

Mid vs. High transfer traces .

*So the red trace are the high drivers with the 24dB Linkwitz-Riley high-pass filter applied to them and the eq filters .

*The blue trace is the Mid-driver with no processing applied yet as you can see @ the processor window (both traces being flat) . In the result phase window you can see the the trace having a up worth angle from about 300Hz up the frequency scale indicating from that point the frequencies are ahead in time compared to the synchronization point of SIM3 .

mid nop vs high processed result proc edit

Mid no processing vs. Mid with High & Low-pass filters applied .

*So here you see the response of the Mid-driver with no processing applied (blue) .

*And the same driver with a 24dB Linkwitz-riley high-pass filter @125Hz + a 12dB Linkwitz-riley low-pass filter @2400Hz (purple trace) . Again the clear signature of the Linkwitz-Riley filters can be seen . A 6db reduction at the x-over points and a 180° phase shift @ the 4rt order high-pass and a 90° phase shift @ the 2nd order low-pass (so @ the x-over point a 45° of phase shift per filter order) . Although the filters applied to the driver cause group-delay the phase trace still has a up worth angle from 1000Hz up the scale . If i apply electronic delay on the mid driver all frequencies produced by that driver will be delayed and i only have to delay the frequencies from 1000Hz going higher up the scale .

To do this I’m going to apply 2nd order all-pass filters to that driver only delaying a selected part of the frequencies (so it changes the phase response at the selected area since phase=time over frequency) .

Mid nop vs Mid hp lp

Mid alignment with high using 2nd order All-pass filters .

*So red is again the high-drivers with high-pass and eq filters applied to them .

*Blue is the Mid-driver with a 4rt order Linkwitz-Riley hp @ 125Hz and a 2nd order Linkwitz-Riley lp filter @ 2400Hz .

*The purple & green traces are the same as the blue trace but with the 1st and the 2nd second order All-pass filters applied to it and again some eq to get the frequency response a bit more flat . You can see the green trace aligning with the red trace over a large area (from about 1000Hz up to 4000Hz) . Both All-pass filters together have about the same response that a 8th order low-pass filter would have in the phase response but not the steep roll-off in the amplitude response (8th order would reduce the level by 48db/oct. past the x-over point) . The level only reduces with 12db/oct. because of the 2nd order Linkwitz-Riley low-pass @2400Hz .

Mid vs high ap2 alignment result proc edit

Mid vs. High aligned sum of both .

*Red are the high-drivers with processing applied (high-pass and eq filters) .

*Blue is the Mid-driver with processing applied (high/low/all-pass and eq filters) .

*Purple is the sum of the mid and highs . You can see they are aligned properly because there’s addition @ the x-over overpoint with about 6db . The reason for me to choose the 2nd order low-pass filter on the mid driver is simple . It will give a large overlap area between the high and mid-driver and if properly aligned creates more headroom @ the x-over area .

Mid vs High and sum all edit

Mid vs low .

*The low driver (purple & green) is the same driver as the mid driver in the screen shot below . Purple no processing applied yet .

*Green gives the response with a 4rt order Linkwitz-Riley high-pass @ 125Hz and a 2nd order Linkwitz-Riley high-pass @ 600Hz . The phase trace all ready aligns with the mid driver with a difference of about 30° in the overlap area between the mid and low driver so the addition in the overlap area is 5,7db instead of 6db .    

Mids vs lows edit

On the end of the second day the system looked like this (subs included). All drivers had a maximum delay of 0,25ms added to them and some more 2nd order all-pass filters to correct the phase response (a description of the technique used for this is explained in a other post @ this blog) . 

S L M H done

Tuning 01

IMAG0577  IMAG0579

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