ARTA tweeter measurement problems - diyAudio
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Old 21st June 2009, 09:00 PM   #1
doug20 is offline doug20  United States
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Default ARTA tweeter measurement problems

Im having a hard time figuring out why I can not get Arta to give me a smooth response with running both tweeters in a test using pink noise.

Here is the FR Plot...

Click the image to open in full size.

It looks out of phase ( or something similar, Im no expert) but I have swaped wires and Im using a DCX so I have changed the phase on each tweeter, I have modified everything and nothing will change. I have no idea what Im doing wrong.

Here are the indidual tweeter measurements

Left tweeter
Click the image to open in full size.

Right tweeter
Click the image to open in full size.

The measurements are done center of my listening area in my HT room center point between the tweeters 8 feet back.

Im really stuck now as to why this is happening, I could have screwed something up but my DCX is identical for both drives, I have triple checked my wiring too.
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Old 21st June 2009, 09:19 PM   #2
breez is offline breez  Finland
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Looks like comb-filtering effect. Nulls at approximately 4 KHz apart means a time difference of 0.125 ms (180 degrees phase shift) or a multiple of that. In distance this is 4.3 cm or a multiple. Try to carefully measure the distance to the tweeters from the mic position.

Why do you need to measure with both tweeters running?
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Old 21st June 2009, 09:31 PM   #3
doug20 is offline doug20  United States
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Quote:
Originally posted by breez
Looks like comb-filtering effect. Nulls at approximately 4 KHz apart means a time difference of 0.125 ms (180 degrees phase shift) or a multiple of that. In distance this is 4.3 cm or a multiple. Try to carefully measure the distance to the tweeters from the mic position.

Why do you need to measure with both tweeters running?

Thanks, I will take that measurement.

Why? Im curious about my overall in room response and any Im curious to what Audyssey is EQing (before and after).

Originally I was just measuring individual drivers to setup my crossovers/EQ settings via my DCX.
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Old 21st June 2009, 09:37 PM   #4
doug20 is offline doug20  United States
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Mic is 88" (223.52cm) from the left speaker, 83" (210.82cm) from the right speaker, the Mic is 35" (88.9) high, my tweeter centers are 38" (96.52) high.
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Old 21st June 2009, 09:40 PM   #5
doug20 is offline doug20  United States
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Quote:
Originally posted by breez
Looks like comb-filtering effect. Nulls at approximately 4 KHz apart means a time difference of 0.125 ms (180 degrees phase shift) or a multiple of that. In distance this is 4.3 cm or a multiple. Try to carefully measure the distance to the tweeters from the mic position.

Why do you need to measure with both tweeters running?

IF this is true shouldn't I be able to tweek the time difference in my DCX to fix this. I have tried many, many values in the delay setting and I saw no change.

Or moving my speakers would work but again no change
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Old 21st June 2009, 09:53 PM   #6
doug20 is offline doug20  United States
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Update, thank you!!

I re-measured, set the exact distances and we have a better measurement no lobing.

THanks for the little lesson about lobing between speakers, I only thought of lobing with the CTC spacing on a single baffle.
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Old 21st June 2009, 10:03 PM   #7
breez is offline breez  Finland
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Quote:
Originally posted by doug20
Mic is 88" (223.52cm) from the left speaker, 83" (210.82cm) from the right speaker, the Mic is 35" (88.9) high, my tweeter centers are 38" (96.52) high.
Bingo! 223.52 - 210.82 = 12.7 cm. Approximately 3 times 4.3 cm. Disregarding the height difference, won't change the distance difference much.

Quote:
Originally posted by doug20
IF this is true shouldn't I be able to tweek the time difference in my DCX to fix this. I have tried many, many values in the delay setting and I saw no change.

Or moving my speakers would work but again no change
Moving speakers or electronic delay should change the pattern (different nulls or no nulls), but you really shouldn't use delay to 'fix' the interference. While listening your head will move and the distance to one ear from the speakers will continually change. This would happen with any speakers with or without delay!

I'm not familiar with Audyssey, but it should measure one speaker at a time.
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Old 21st June 2009, 10:14 PM   #8
doug20 is offline doug20  United States
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full system measurement mains/subs

Click the image to open in full size.

Couple of dips to work on if I can fix them at all.

and someday I need to figure out how to set Arta scales properly.

That measurement above was 80dB on my RS SPL meter.
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Old 22nd June 2009, 12:37 PM   #9
Henkjan is offline Henkjan  Netherlands
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if the dips are from the driver, you can (and should) fix them easily with the Behringer, but if they are in the low end and caused by room modes, you probably should do something in the room.. and remember to measure at different locations, and not optimise for 1 location
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Old 22nd June 2009, 01:38 PM   #10
doug20 is offline doug20  United States
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Quote:
Originally posted by Henkjan
if the dips are from the driver, you can (and should) fix them easily with the Behringer, but if they are in the low end and caused by room modes, you probably should do something in the room.. and remember to measure at different locations, and not optimise for 1 location
Thanks,

They are caused by room modes so Im not sure there is a fix for some of them, speaker placement is restricted a little bit so I will live with some of the dips.

I also agree to measure at different locations. My only goal with this exercise is to learn more about measuring speakers (Gated reponse, THD, Impulse), Measuring room decay and also learning more about Arta.

In the end Audyssey will do its thing (I even have the Pro version on order) so that I can tweak it too a specific curve I like.
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