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Using sound absorption to reduce standing waves
Using sound absorption to reduce standing waves
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Old 29th June 2020, 10:31 PM   #91
33Polkhigh is offline 33Polkhigh  United States
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Originally Posted by PB2 View Post
You could have built the box with 2 independent woofer chambers for the top and bottom,
then the longest dimension is 1/2 re how it is now. The top to bottom standing wave frequency would double and be easier to damp for that reason.
I eventually used clumps of stuffing in that cabinet. I do believe there was a bit of a standing wave problem in that cabinet. Additionally there was a +6db hump from when the 4 drivers are within a quater wave. Flaws in the design.
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Old 30th June 2020, 12:52 PM   #92
33Polkhigh is offline 33Polkhigh  United States
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I REALLY like the burrito approach myself; my current boxes won't allow that configuration exactly but that was almost the EXACT thing I was going to try first.

Where are papers and discussions on the pressure minimums and maximums again? I'd like to read up on that in more detail.

Thanks!
Putting sound absorption in the middle seems intuitive to me but I'm also curious about the reasons. One thing it does is naturally divide up the cabinet into smaller sections with non parallel surfaces.
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Old 30th June 2020, 01:11 PM   #93
oldspkrguy is offline oldspkrguy  United States
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Well, it seems perfectly logical but I would like to read up on pressure, velocity, etc. minimums and maximums as relating to size, shape, volume, surface area, etc. I have heard under-stuffed and over-stuffed speaker boxes both. They both sound bad compared to the "ideal"...too much is a bad thing, not enough is also a bad thing; happy medium, middle compromise (middle pun intended!!!).
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Old 30th June 2020, 01:26 PM   #94
AllenB is offline AllenB  Australia
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Using sound absorption to reduce standing waves
By using two woofers across the cabinet it is being naturally divided. The length mode is invalidated without the need for a partition. Eg, the wave from the other woofer is identical to what the reflection from a single woofer would have been in a half sized section of the box.
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Old 30th June 2020, 06:15 PM   #95
keithj01 is offline keithj01  United Kingdom
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There are 2 things in play here. Worst is resonant modes. Fix by graded stuffing (sparse in the middle, robust at the extremities).

Then there are reflections. Soften the boundaries between air and the sidewalls.

The two are not mutually exclusive...
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Old 2nd July 2020, 02:36 AM   #96
PB2 is offline PB2  United States
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Originally Posted by oldspkrguy View Post
Well, it seems perfectly logical but I would like to read up on pressure, velocity, etc. minimums and maximums as relating to size, shape, volume, surface area, etc. I have heard under-stuffed and over-stuffed speaker boxes both. They both sound bad compared to the "ideal"...too much is a bad thing, not enough is also a bad thing; happy medium, middle compromise (middle pun intended!!!).
You can do something that is analogous to a VSWR measurement in a microwave waveguide,
by using a small (1/4") mic to probe inside the box to find high velocity points, that is where
you want to put damping to reduce a particular standing wave.
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Old 2nd July 2020, 03:16 AM   #97
oon_the_kid is offline oon_the_kid  Malaysia
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BTW, I had a thought. If you are doing the burrito approach, do you still need to line the sidewalks with something?

Oon
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Old 2nd July 2020, 07:09 AM   #98
keithj01 is offline keithj01  United Kingdom
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Originally Posted by oon_the_kid View Post
BTW, I had a thought. If you are doing the burrito approach, do you still need to line the sidewalks with something?

Oon
Yes - for the reasons I've been suggesting.
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Old Yesterday, 02:55 AM   #99
33Polkhigh is offline 33Polkhigh  United States
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Originally Posted by keithj01 View Post
Yes - for the reasons I've been suggesting.
I didn't line the walls, but I suppose you could. I have so much bracing its not worth it. I personally like a little bit of a woody sound to the cabinet and don't want to get to carried away.
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Old Yesterday, 03:09 AM   #100
454Casull is offline 454Casull  Canada
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Originally Posted by 33Polkhigh View Post
I didn't line the walls, but I suppose you could. I have so much bracing its not worth it. I personally like a little bit of a woody sound to the cabinet and don't want to get to carried away.
What does the woodiness sound like and do you like it with all kinds of music?
 

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