Loop delay error - Home Theater Forum and Systems - HomeTheaterShack.com

 
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post #1 of 6 Old 12-22-18, 02:41 PM Thread Starter
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niklasmagnus
 
Join Date: Oct 2007
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Loop delay error

Hi,

I have made a lot of measurement and have been struggling to properly measure the delay between Right and Left subs. Since I have a Behringer UMC22 soundcard Dayton mic I have the option to both run Acoustic reference and Loopback reference. I use a minidsp 2x4 balanced between a Marantz AVR and a Crown amp. When running acoustic reference i have connected the center main speaker to the left AVR channel. Connections are: UMC22 line out1 -> AVR CD R. AVR preout FR - > minidsp line in 1 -> line out 1 and 2 -> Crown line 1 and 2. So when change the sub I mute/ unmute in minidsp software.
Mic in center of the room with almost perfect triangle to the subs. Room is perfect rectangle.

Problem is that with using the loopback reference the delay is off big time according to info. But looking at the impulse graphics it looks good. So how to trust the result and what is wrong? I also tried to switch channel in between Minidsp and amp to see if the problem would follow but no, it stays with the physical sub. Cable length is the same. But with acoustic ref is look god.
I plan to do a MSO when adding 2 more subs but if loopback is an issue it may become a problem.

Please look at the attached REW file, measurement 1, 2, 10 and 11 are with Loopback refn and switched channels.

Thanks for helping me clearing out this
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post #2 of 6 Old 12-23-18, 05:50 AM
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Re: Loop delay error

You should update to 5.19, which has changes to the way delays are calculated for subwoofer/limited range measurements.

From the impulse responses L and R look well aligned, you are getting different figures for loopback because it is comparing peak locations and the peaks are in very different positions relative to the IR start.

More concerning is that the responses are different between acoustic and loopback reference, the choice of timing reference should not have any effect on the measured response. The acoustic ref impulse responses look odd, with ringing ahead of the start of the IR.

There is also a spike in distortion for your R+L measurements at the 44 Hz peak, you may be clipping the mic input on those.
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post #3 of 6 Old 12-23-18, 08:18 AM Thread Starter
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niklasmagnus
 
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Re: Loop delay error

Thanks John. I just left home for Christmas celebration a few days. Will take actions on your input when I get back.
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post #4 of 6 Old 12-26-18, 05:35 PM Thread Starter
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Re: Loop delay error

Hi,

Have had some problem last days with setting the delay in my Marantz SR5006. I tried so many different thing not understanding why the Distance function want come in to play. Finally I got a advice to try activate the EQ in the AVR. So I have set MultiEQ XT to manaul and all EQ to 0db, so the EQ want affect the baseline. Now suddenly I can set delay using the Distance future.

So I hope to address Johns input tomorrow.

But a question: Is it like this on all Marantz or just my old one? Maybe this is common sense, but was new to me.
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post #5 of 6 Old 12-31-18, 03:34 AM Thread Starter
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niklasmagnus
 
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Re: Loop delay error

What can be the reason for this pre ringing? I have taken a lot of measurements now and LCR show pre ringing on the impulse response but not for the subs.
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post #6 of 6 Old 12-31-18, 04:24 PM
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Re: Loop delay error

I don't know. The response is also significantly different though, so something seems to be changing besides the type of timing reference.
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