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Old 23rd October 2012, 05:04 PM   #1
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Default Panel Bracing

When I was building a set of large BR's, I mounted the drivers in the unfinished boxes, put them face to face and fired them up out of phase. I wanted to break in the drivers a little bit. I was surprised at the amount of sound that was passing through the sides, even though the panels has a 2"x1/2" brace running the full length and the sides covered with 1" fiberglass. Since the boxes were already sealed, I didn't investigate at that time.

On to today. I am working on the prototypes for a more modest BR using the A10.2. I braced the sides of one box with a 1/4"x1 1/2" brace top to bottom. The panels in question are ~15"x8". I attached a 2" piece of rubber tubing to the tip of a microphone and sealed the end of the mic with tape. I then placed the rubber tip against the side of each box and got the following:

Click the image to open in full size.

The absolute dB scale is irrelevant. The Black trace is the braced panel and the red trace is the unbraced panel. The blue trace is the difference scaled up 60dB.

Interesting.

Bob
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Old 23rd October 2012, 05:37 PM   #2
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That it is. Should make for an audible difference in the noise floor & outright dynamic range (on some material -probably not much difference on Kiss or Motorhead )
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Old 24th October 2012, 05:14 PM   #3
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Thanx Bob. The differences are predominately <100 Hz. The blue difference curve doesn't seem to reflect this.

Should be significant with any music with bass content.

dave
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Old 24th October 2012, 08:22 PM   #4
Tom V is offline Tom V  United States
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Two different drivers: How do we know the difference is the bracing and not sample variation between the drivers?
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Old 24th October 2012, 09:00 PM   #5
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Quote:
Originally Posted by planet10 View Post
Thanx Bob. The differences are predominately <100 Hz. The blue difference curve doesn't seem to reflect this.
It's hard to compare traces that are so strongly sloped, but I think that the difference trace is correct. Doing one comparison raises more questions than answers. I need to tie the two longitudinal braces together to see if that further prevents the box from breathing. Also, both boxes were lined with 1" of Owens corning 701. Perhaps the fiberglass is responsible for the abrupt high end rolloff, perhaps not.

Quote:
Originally Posted by Tom V View Post
Two different drivers: How do we know the difference is the bracing and not sample variation between the drivers?
Because I'm telling you so. The driver was a MA A10.2, and even if they were different drivers, Mark's tolerances are pretty close.

Bob
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Old 24th October 2012, 09:10 PM   #6
sippy is offline sippy  United Kingdom
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Quote:
Originally Posted by Tom V
Two different drivers: How do we know the difference is the bracing and not sample variation between the drivers?
Quote:
Because I'm telling you so. The driver was a MA A10.2, and even if they were different drivers, Mark's tolerances are pretty close
It could be ANY single driver that fits in the hole, you would still see roughly the same things on the graph.
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Old 24th October 2012, 09:35 PM   #7
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Quote:
Originally Posted by Bob Brines View Post
1/4"x1 1/2" brace top to bottom
Hi Bob, would that be a .25" -wide- brace, or a .25" -deep- brace?
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Old 25th October 2012, 12:24 AM   #8
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Quote:
Originally Posted by rjbond3rd View Post
Hi Bob, would that be a .25" -wide- brace, or a .25" -deep- brace?
1 1/2" wide piece of 1/4" plywood.

Bob
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Old 25th October 2012, 01:35 AM   #9
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Thanks. What I was trying to visualize was which side of the brace (grain-wise) was glued to the panel, and it seems it must have been the end-grain, but I guess it doesn't matter as far as the general principle of quieting down the panel is concerned.
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