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Old 19th September 2008, 04:08 AM   #1
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Default Shelf bracing detrimental for SPL?

Would shelf bracing a la Creative Sound Solutions http://www.creativesound.ca/pdf/SubD...ans-290307.pdf

be detrmental to the SPL output from a sub, aka in competitions? This has been put forward to me, but my requests for substantiation of the statement has been lacking so far, I cannot come up with a single reason for that statement to be true. Can someone enlighten me please?
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Old 19th September 2008, 05:24 AM   #2
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Default Re: Shelf bracing detrimental for SPL?

Quote:
Originally posted by buggsson
I cannot come up with a single reason for that statement to be true. Can someone enlighten me please?
They would help keep the box panels from being uncontrolled passive radiators...

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Old 21st September 2008, 09:26 AM   #3
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In SPL you are going for tenths of a gain...flexing enclosure panels is wasted energy...I would think the more the bracing the better.

The owner of sundown is testing enclosure bracing by metering then adding a layer to the baffle...seems like its working.
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Old 29th September 2008, 12:19 AM   #4
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Yes, I would agree with you both, with the little knowledge I have, that bracing would be to an advantage. That is what I believe, but I was then contested by someone who claimed the opposite. I hope there will be some more replies here so I can answer him again on the subject. I don't think he knows exactly why it would be as he said, because he could not substantiate his claim in any way.
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Old 29th September 2008, 11:57 PM   #5
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Well while this would more than likely be a highly unlikely situation, if the "uncontrolled passive radiators" actually managed to resonate at a good frequency for the spl competition, i.e. around 50-60hz, then it actually could help, and a brace would be detrimental. However, this is highly unlikely and I doubt you would actually see much gain. Instead, the better answer is that bracing reduces panel flexing that could be creating destructive resonances.

Bracing is important to keep a box solid, it can help keep a box from being destroyed with some of the more ridiculous SPL woofers being created, but otherwise will have very little effect overall. Before growing up and moving on, I competed in IDBL competitions and was the number one ranked in New York State in my class and number 7 in the country in 1999 and 2000. I also competed in Iasca pro competitions and while never doing quite as well (I blame a lack of enthusiasm and being busy rather than being better at making things loud), I still did plenty of install work and enclosure experimentation. In homes and cars, rooms dominate the effects on bass far more than the subwoofer drivers or boxes, but that still doesn't mean they are worth ignoring. None the less, while I can find differences in the bass response of a poorly constructed subwoofer box in a home, I rarely did in a car. While I'll admit that I haven't built a car subwoofer box in over 5 years, and my measuring equipment is far more resolving today than then, I think my conclusion of the time is still true, the car environment dominates the response far more than the box.

In other words, while the person who told you that adding bracing will have a negative (detrimental) effect on total spl ability is incorrect, I also wouldn't go too crazy with it, especially if the box is less than 3 cubic feet. If its ported with a slot port, and designed correctly, the slot port will also act as bracing, and a minimum of extra bracing is all that is needed. I would not bother with double thickness baffles as it will add almost nothing to the dampening, however if you need the strength, its worth considering. However, if you need the strength, use high ply count baltic birch. To increase SPL in the car, I would spend more time bracing the car itself. We don't put bullet proof 1" thick lexan panels for windows because they don't blow out, we do it because they don't flex like uncontrolled passive radiators. Adding additional bracing to the inside of the car is a good idea as is seem welding. While I saw this only done in the top levels of competition, it can have a pretty huge overall impact on minimizing flexing. While this is very expensive to have done, and would seem like excess, as was already said, you win by tenths of a decibel. My competition record was 167.8 and I was beat by someone who was only 1/10th higher, and arguably may have only been 5/100th's higher.
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