Let's talk about bracing... - AVS Forum
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Old 09-02-2010, 07:51 PM - Thread Starter
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As most folks know, Ricci has some pretty bad arse ported subs in the making. While reviewing the bracing, a question came to mind about how one might "optimally" brace a cab. Sure, anybody can line the walls with 3" of concrete and be done with panel resonance concerns, but in the world of practicality, where weight matters, I'm wondering if you guys could post some thoughts on optimal bracing designs.

This is an engineering question, so input from all the engineers would be particularly appreciated.

Challenge: minimize panel resonances for a given weight in a 2 x 2 x 3 feet sub enclosure constructed of 18 mm baltic birch.

I'm wondering if something simple like this (18 mm x 50mm strips glued on edge or perhaps 2 strips glued together and mounted across the enclosure as one would do with a dowell rod) would work as well as full internal panels for all practical purposes.


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Old 09-02-2010, 07:58 PM
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Originally Posted by LTD02 View Post

I'm wondering if something simple like this (18 mm x 50mm strips glued on edge or perhaps 2 strips glued together and mounted across the enclosure as one would do with a dowell rod) would work as well as full internal panels for all practical purposes.

I'm pretty sure a circular object has more vertical rigidity than a square object of the same mass?
Rectangular would be different for one width.

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Old 09-02-2010, 08:20 PM - Thread Starter
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so, you are saying a "half moon" type bracing would be better?

i'm digg'n that as it would be thickest at the point where the cab would want to flex the most.

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Old 09-02-2010, 08:35 PM
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Another thought is not to have equal width sections on the panel. For example, a 2ft wide section with a brace down the middle turns into 2, 1ft sections, each with the same resonance. If the brace was instead, 1 or 1.5" off center, you will now have two different width sections with two different resonances.

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Old 09-02-2010, 08:55 PM - Thread Starter
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bomber, your posts always make me think...thanks for weighing in.

"Another thought is not to have equal width sections on the panel."

that sounds right. so maybe we start at something like the golden ratio and work backward?

the first pair are around 61%, the next one to the left is 61% again, and again for the third. the one to the right of the double is 61% again from the edge.


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Old 09-02-2010, 09:06 PM
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the most efficient way to kill panel resonances is not to excite them in the first place.

BAM !

were you ready for such astonishing brilliance ?

now i would be glad to tell you how to do this if you paid me a million billion dollarz !

since you don't have that you are going to have to use your brain and figure out how panel resonances are excited.

also pliz note ! that killing resonance is not the only goal of bracing, in fact it is a SECONDARY goal. by simply building enclosure out of GOO you would avoid all resonances automatically. the primary function of bracing is ...

well now i am telling you too much already. you figure it out
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Old 09-02-2010, 09:56 PM
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Quote:
Originally Posted by LTD02 View Post

Challenge: minimize panel resonances for a given weight in a 2 x 2 x 3 feet sub enclosure constructed of 18 mm baltic birch.

Subs of the sort of dimensions you mention are fairly easy, as panel resonances will be out of band or easily raised in frequency by using well positioned bracing. Some minor (B&W) matrix style bracing would be all I'd use here.

For midbass and up, matrix eveywhere. Sand in between an inner and outer box is also extremely effective.
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Old 09-02-2010, 09:58 PM - Thread Starter
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"Some minor (B&W) matrix style bracing would be all I'd use here."

i'm unfamiliar with that bracing. got a link? post a pic?

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Old 09-02-2010, 10:02 PM
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Hire a stonemason to carve big marble stone into a sub cabinet.
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Old 09-02-2010, 10:07 PM - Thread Starter
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Quote:
Originally Posted by vasyachkin View Post

the most efficient way to kill panel resonances is not to excite them in the first place.

BAM !

were you ready for such astonishing brilliance ?

now i would be glad to tell you how to do this if you paid me a million billion dollarz !

since you don't have that you are going to have to use your brain and figure out how panel resonances are excited.

also pliz note ! that killing resonance is not the only goal of bracing, in fact it is a SECONDARY goal. by simply building enclosure out of GOO you would avoid all resonances automatically. the primary function of bracing is ...

well now i am telling you too much already. you figure it out

"the primary function of bracing is ..."

vas, you have some good stuff to offer. hey man, you were the guy who suggested the bracing scheme that ricci used in his ported design. i remember and give you props!

you were too proud to say your answer because you may be proven wrong. all your comments about how much of a genius you are and that nobody knows anything are toxic and poisonous in most readers' minds. we find it difficult to support you if all you do is poison the threads. just a heads up from all of us short bus riders. ;-)
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Old 09-02-2010, 10:07 PM
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Quote:
Originally Posted by LTD02 View Post

"Some minor (B&W) matrix style bracing would be all I'd use here."

i'm unfamiliar with that bracing. got a link? post a pic?

B&W Matrix. However, I tend to break up the long horizontal sections with sub braces too. The internals of the cabinet shown there has curved sides so doesn't need it a much as a rectangular box.

Here's another example pic from Tony Gee's Serious Sub.
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Old 09-02-2010, 10:08 PM - Thread Starter
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"Hire a stonemason to carve big marble stone into a sub cabinet."

must have missed sentence two of the op.

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Old 09-02-2010, 10:09 PM - Thread Starter
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that is a lot of bracing alpha niner. i can't believe that is weight efficient. it may be and i'm open to that, just would like to see some math or measurements in place of marketing.

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Old 09-02-2010, 10:16 PM
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Use birch or exterior grade plywood for bracing instead of MDF. It's stiffer IMO. And lighter.
MDF is better for shells, and plywood is better for bracing. Again, IMO.

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Old 09-02-2010, 10:22 PM
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Quote:
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i can't believe that is weight efficient.

Who cares? It's not like I'm going to move mine any further than from the garage to the living room and I see no need for all the bracing to be BB, so less expensive ply can save cost. Works well with MDF too.

Consider a box like you mentioned in the OP. The corners and edges are glued and are the strongest part of the structure. Each panel can flex either way from the edges depending upon the length and nodes will be set up depending upon the dimensions. Shorter panels or distances between rigid braces (these effectively sub divide the panel into smaller panels) will have resonant modes at higher frequencies. These are easier to damp, whether from the internal damping of the material itself or from an external method and as you go higher in frequency in the audible spectrum there is less energy in the program, so less available to excite the resonances in the first place.
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Old 09-02-2010, 10:28 PM - Thread Starter
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"Who cares?"

i was just curious about what the optimal bracing would be for a given weight. mentioned in the op. 4" concreate should be pretty resonant free, but heavy.

i was thinking more about optimizing the other end. how light can it be made without resonances.

maybe the answer is a creative application of 1/2" dowell rods. mounted at resonant points, tied off and glued at intersections. i don't know.

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Old 09-02-2010, 10:43 PM
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i was thinking more about optimizing the other end. how light can it be made without resonances.

Aircraft aluminium or carbon fibre skins over an extruded honeycomb core. Very light and rigid.
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Old 09-02-2010, 10:49 PM - Thread Starter
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that is kind of what i was thinking!!, but let's throw "reasonable cost" into the mix.

any thoughts on how thick a carbon fiber monocoque chassis would have to be for a subwoofer not to resonante it?

and how might this compare $ for $ against a baltic birch sub with dowell bracing?

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Old 09-02-2010, 10:55 PM
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you were too proud to say your answer because you may be proven wrong.

you're off by a mile.

i am not afraid of being proven wrong. in fact i am not afraid of admitting that my whole life is a failure. i think about killing myself every day. i wish i was never born.

i just don't want somebody else to capitalize on my ideas the way Edison capitalized on Tesla's ideas.

as time goes by i hope i will develop the will power to stop posting completely and keep all of my thoughts to myself. unfortunately it is human nature to want to share your ideas with others.

the primary function of bracing is to help the enclosure perform its primary function. HINT: not vibrating is not the primary function of enclosure ! ! !
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Old 09-02-2010, 11:06 PM
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i like the idea of a carbon fiber chassis.


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Old 09-02-2010, 11:07 PM - Thread Starter
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crazy talk vas...i've given you props for the bracing in ricci's massive ported subs. you just get carried away oftentimes with your comments. you have a role to play, stick around man. your comments about getting back into shape by feeding your body healthy foods have inspired me a bit. ;-)

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Old 09-02-2010, 11:08 PM - Thread Starter
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"i like the idea of a carbon fiber chassis."

it sure sounds cool, but the cost is outrageous. we'll have to wait in order to see if it can be made cost effective.

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Old 09-02-2010, 11:09 PM
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that is a lot of bracing alpha niner. i can't believe that is weight efficient. it may be and i'm open to that, just would like to see some math or measurements in place of marketing.

i think its quite weight efficient. certainly about 100 times more efficient than your proposed strips.

one brilliant idea i had as far as bracing is to fill the entire enclosure with open cell foam. the foam itself would be the bracing. however pulling that off would take some serious know-how in the foam business which i don't have and cannot be bothered to acquire.

you can pimp this idea to Geddes i bet he will have an orgasm the second he hears about it.
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Old 09-02-2010, 11:12 PM - Thread Starter
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"certainly about 100 times more efficient than your proposed strips."

$20 and my dignity says that you don't have the math to prove that point.

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Old 09-02-2010, 11:18 PM
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that is kind of what i was thinking!!, but let's throw "reasonable cost" into the mix.

any thoughts on how thick a carbon fiber monocoque chassis would have to be for a subwoofer not to resonante it?

and how might this compare $ for $ against a baltic birch sub with dowell bracing?

carbon fiber is a bad material for sub enclosure. it is fragile. i broke my Shimano carbon fiber bike shoes the very first day i put them on. i managed to exchange them for Sidi shoes without the store staff noticing the crack. a light tap with a hammer on your carbon fiber subwoofer box and it would be a gonner - that couldn't be good for your company's image.

i would maybe go with some sort of kevlar loaded foamed polypropylene faced with titanium if i wanted to waste money for no good reason.
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Old 09-02-2010, 11:21 PM
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Quote:
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"certainly about 100 times more efficient than your proposed strips."

$20 and my dignity says that you don't have the math to prove that point.

hm ... well there are finite element analysis programs for mechanical stuff you know ? you should just load both up in there and see. i don't have such programs nor do i know how to use them.

B&W matrix is quite similar to what Ricci is going with on his ported box. What i have done is simplified it to save the unnecessary work and wasted material.
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Old 09-02-2010, 11:27 PM
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Not my area, but I would think CF would cost lots compared to conventional wood construction, especially for a DIYer.
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Old 09-02-2010, 11:30 PM
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Not my area, but I would think CF would cost lots compared to conventional wood construction, especially for a DIYer.

it makes up for it by the unbeatable bling factor !
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Old 09-02-2010, 11:30 PM
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There is a nightmare of a thread going on over a DIYaudio about this for a while now.

In the end the only way to get the info you seek is for someone to do the testing, and then post the results. As the real question isn't what is the best way to do it, but how much is really enough? At what point does it stop showing up in measurements?
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Old 09-02-2010, 11:32 PM
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if you want to understand why B&W bracing is superior to yours you need to think of a diamond:

http://images.google.com/images?hl=e...=&oq=&gs_rfai=

and see how much more the B&W matrix resembles it than does your "design"

lol this looks like a subwoofer already:

http://www.halcyon.com/nanojbl/Image...ondLattice.gif

now diamond is not the best geometry possible. not all geometries are possible on molecular level and not all bonds are equally strong. this means that just because diamond is the strongest crystal doesn't mean diamond lattice is optimal for engineering.

just about any lattice is going to better than "strips" though.
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