Panel Bracing

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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:

Panel_Noise.jpg


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
 
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.

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
 
Originally Posted by Tom V
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

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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