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Old 11th January 2019, 08:05 PM   #631
Juhazi is offline Juhazi  Finland
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Looks like woofer and mid are not at same cycle, timing issue. Play only WM and increase delay to mid gradually check also with inverted polarity of mid. This is a really painstaking stage and you might need more delay than you think.... When it looks and sounds ok, check MT timing too. Then all three.
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Old 11th January 2019, 08:21 PM   #632
BYRTT is offline BYRTT  Denmark
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Originally Posted by mbrennwa View Post
...The woofer output obviously interferes with the midrange between 900 Hz and 2 kHz. This is not good, and we need to fix this somehow. Is this the leakage of the elliptic low pass filter of the woofer?...

...I really think the woofer needs some work. It really shouldn't upset the midrange like it does. What are your thoughts about this?
Even using 100% clean slopes as the theoretical pure target shared by Paul show ripple summing spread over systems bandwidth and specific in that 1-2kHz area there is some interference for this particular filter setup, well even if all drivers had same center and AC as was it a perfect coxial there is still some small ripple but less than when they physical spaced apart as for Monkey Box. Thought is not much to do about it when 100% clean slopes is not perfect but in simulation it looks tweaked component version is little worse in that area than Pauls' original, other thought is guess many real world systems to be practical and cost effective have exactly same non ideal sum as compromise, other thought is above can be why many use symetrical LR filters because of non ripple smooth summing but will have to be simulated if works any good for physics of Monkey Box.

Last edited by BYRTT; 11th January 2019 at 08:23 PM.
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Old 11th January 2019, 08:36 PM   #633
mbrennwa is offline mbrennwa  Switzerland
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Quote:
Originally Posted by Juhazi View Post
Looks like woofer and mid are not at same cycle, timing issue. Play only WM and increase delay to mid gradually check also with inverted polarity of mid. This is a really painstaking stage and you might need more delay than you think.... When it looks and sounds ok, check MT timing too. Then all three.
Adding some artificial delays will most certainly change the interference -- but it will not remove the issue, and it would be difficult to implement in the analog x-over.

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Originally Posted by BYRTT View Post
Even using 100% clean slopes as the theoretical pure target shared by Paul show ripple summing spread over systems bandwidth and specific in that 1-2kHz area there is some interference for this particular filter setup, well even if all drivers had same center and AC as was it a perfect coxial there is still some small ripple but less than when they physical spaced apart as for Monkey Box. Thought is not much to do about it when 100% clean slopes is not perfect but in simulation it looks tweaked component version is little worse in that area than Pauls' original, other thought is guess many real world systems to be practical and cost effective have exactly same non ideal sum or compromise, other thought is above can be why many use symetrical LR filters because of non ripple smooth summing but will have to be simulated if works any good for physics of Monkey Box.
I don't think this issue is related to summing at the x-over frequency (about 400 to 500 Hz), which is much lower then the trouble area of about 1-2 kHz. Ideally, the woofer should be "silent" from 1 kHz and up.

I'd expect the woofer to be out of phase above the x-over frequency. Remember that the elliptic filters have "leaky" stop bands and the (unfiltered) woofer gets really loud between 1 and 3 kHz (about 100 dB-SPL or so). I wouldn't be surprised if the stop-band "leak" causes the midrange trouble at 1-2 kHz -- but I am not sure.

Would it make sense to try another filter function without "stop-band leakage" (Butterworth, Bessel, etc.) just to see if the issue goes away?

EDIT: take a look at the modelled acoustic output of the woofer at 1-2 kHz in post 619. It's only 24 dB below the midrange. Hmm.

Last edited by mbrennwa; 11th January 2019 at 09:01 PM.
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Old 11th January 2019, 09:06 PM   #634
BYRTT is offline BYRTT  Denmark
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Quote:
Originally Posted by mbrennwa View Post
...I don't think this issue is related to summing at the x-over frequency (about 400 to 500 Hz), which is much lower then the trouble area of about 1-2 kHz. Ideally, the woofer should be "silent" from 1 kHz and up.

I'd expect the woofer to be out of phase above the x-over frequency. Remember that the elliptic filters have "leaky" stop bands and the (unfiltered) woofer gets really loud between 1 and 3 kHz (about 100 dB-SPL or so). I wouldn't be surprised if the stop-band "leak" causes the midrange trouble at 1-2 kHz -- but I am not sure.

Would it make sense to try another filter function without "stop-band leakage" (Butterworth, Bessel, etc.) just to see if the issue goes away?
Below visuals show how the perfect text book slope would sum, the first one is using Monkey Box spacing of drivers and AC mismatch, the second one as a perfect coxial with same AC and no spacing. Guess mostly for other slopes symetrical or non symetrical than a pure symetrical LR we get some ripple interference here and there, if LR will work good for Monkey Box physicals and sum smooth as its theory is non known and has to be simulated.
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File Type: png 1000b.png (174.0 KB, 108 views)
File Type: png 1000a.PNG (170.4 KB, 104 views)

Last edited by BYRTT; 11th January 2019 at 09:09 PM.
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Old 11th January 2019, 09:40 PM   #635
KaffiMann is offline KaffiMann  Norway
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You guys can look at filters all you want, but the wiggles coincide pretty good with the expected internal resonances that come out through the port.
See that small spike on acoustic resonance at ca 250hz? often, but not always, that marks the beginning of trouble, it is the sole reason I suggested having the port further away from the woofer.
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Old 11th January 2019, 09:52 PM   #636
mbrennwa is offline mbrennwa  Switzerland
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Quote:
Originally Posted by BYRTT View Post
Below visuals show how the perfect text book slope would sum, the first one is using Monkey Box spacing of drivers and AC mismatch, the second one as a perfect coxial with same AC and no spacing. Guess mostly for other slopes symetrical or non symetrical than a pure symetrical LR we get some ripple interference here and there, if LR will work good for Monkey Box physicals and sum smooth as its theory is non known and has to be simulated.
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Originally Posted by KaffiMann View Post
You guys can look at filters all you want, but the wiggles coincide pretty good with the expected internal resonances that come out through the port.
See that small spike on acoustic resonance at ca 250hz? often, but not always, that marks the beginning of trouble, it is the sole reason I suggested having the port further away from the woofer.
Guys, I am with you. But I believe I wasn't clear enough about what I was talking about. I was NOT talking about any issues at 500 Hz or below.

Take another look at the SPL curves in the first attachment of post 629. The black curve was measured WITH the woofer, the red curve was measured WITHOUT the woofer. You can see that WITH the woofer, the SPL is LOWER between 1-2 kHz. This must be some interference resulting from the woofer output in the 1-2 kHz range, which, according to the modelled curves in post 619 is only 24 dB below the midrange output in the 1-2 kHz range.

Last edited by mbrennwa; 11th January 2019 at 09:55 PM.
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Old 11th January 2019, 09:56 PM   #637
Juhazi is offline Juhazi  Finland
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If this is timing issue, minidsp feeding 3 amplifiers will never behave exactly like a passive circuit driven from a single amp. We must also remember that some amps invert phase, some don't. So, I don't think same calculated delays work for both.

With minidsp 2x4HD you can change timing very delicately, by 0,01ms (10us, 3mm) steps. Above xo wavelength shortens and hickups come easier visible in measured response than below xo, where reflections mess up everything.

I am accustomed to LR symmetrical filters, I have tried duelund, first order, Bessel etc. and S.Harsch with minidsp and Hypex, but I just don't get them working and sounding right. Steep filters like LR48 are more forgiving to make response look right, but sound is eery instead of airy like with poor timing.

Kaffiman noticed perhaps the most obvious reason, reflex port resonances, have you measured the port mouth response? Backside port with 90¤ bend in the pipe might help. My Amphion Helium has backside port.
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Last edited by Juhazi; 11th January 2019 at 10:05 PM.
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Old 11th January 2019, 09:59 PM   #638
KaffiMann is offline KaffiMann  Norway
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... I see. What about 4th order BW for woof/mid?
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Old 11th January 2019, 10:35 PM   #639
Paul Vancluysen is offline Paul Vancluysen  Belgium
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Quote:
Originally Posted by mbrennwa View Post
This must be some interference resulting from the woofer output in the 1-2 kHz range, which, according to the modelled curves in post 619 is only 24 dB below the midrange output in the 1-2 kHz range.
Yes, but with the tweaked woofer filter the outband reduction between 1 and 2 kHz is 5 dB worse than the original targets.
In the plot the SPL of the modified filter and the original targets.
I did see it while making the digital version of the tweaked filter, but I thought it was your idea to do the modification like that.

Maybe it is better to reduce the woofer outband conform the targets.

Of course a low pass LR4 at 500 Hz has more outband reduction above 1.2 kHz and about 18 dB more at 2 kHz and in phase with the midrange. But it is not elliptical...
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Old 11th January 2019, 11:22 PM   #640
BYRTT is offline BYRTT  Denmark
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Can't stop thinking it has been there all the time simulation or not including if one use optimal textbook smooth responses and is inherent non ideal compromise to filter type even if we had not any AC timing plus spacing mismatch, some plot scales mask the fenomen but its there in all of them below.
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