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I was wondering if anyone has ever tried fiberglass layers over a wooden cabnet to stiffen it,what are your thoughts?:dunno:
 

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Welcome to the Shack Bryan!!

No I haven't, but I don't think it would really stiffen it. Maybe someone else would have an opposite opinion...
 

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Thats something I have also been wondering about. I suspect you would want to look at carbon fiber or Kevlar as they are much stiffer than fiberglass.

Here is an article on gliders that gives some tables on strength/stiffness of various materials. I wonder if you would need to know the resonant properties of a material before using it for a sub?
 

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Thanks for the link,I work with cabon fiber and fiberglass building drag cars.CF is so expensive,I was thinking that with enough layers of glass you could get the desired stiffness.
 

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Cool. You have a big advantage knowing how to work with the material. You can probably find a similar table showing the stiffness properties of fiberglass.

Another quick search shows that glass and MDF construction is used in car woofer enclosures.

Edit: if you go ahead with this, let us know what you find out and post lots of pics.
 

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I would do a quick test where you compare how easy it is to bend wood and fiberglass of the same thickness.

I'm trying to remember what we used on the race car we built in college....there was balsa in the middle sandwiched between either fiberglass or carbon fiber. I'm starting to think it was carbon fiber, but whatever it was, it was super rigid as all get out. It was 1/4" thick and made up the floor of the cockpit. I think 1/4" might even be thick enough for a speaker - and it would be super light. I'm surprised I've not seen this is the pro industry yet - they're always willing to pay top dollar for lighter gear (cheaper and easier to transport and way faster to setup).
 

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I would say that it cant hurt and chances are it will help out. any change in material will limit the direct transfer of vibrations. you could put some foam (like maybe 1/4" thick) around the whole box then glass over that. Would be a very interesting project just to see what happens.

I cant see anything bad happening other then it just getting heavier. and if it dosent work out you could just leave it or slice and peel it off easily.
 

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Merry Christmas!


My opinion, carbon fiber would be an overkill and very expensive.

I do not beleive that adding fiberglass would add that much stiffness to the side walls.

I would suggest, using 3/4" x 3/4 " wood, build a cross and attach it to the inside walls of the speaker.

Using 3-4" fiberglass tape, fiberglass over the 3/4" cross and all the inside seams of the box. This should increase the stiffness of the walls.

Another idea, attached a foam core to all the inside walls. Find some foam from home depot (careful, some resin will melt the foam) and cut it to the inside dimensions of the box. Apply epoxy to the inside walls and attached the foam. Attach a layer of fiberglass to the foam. No idea concerning acoustics but you can build a strong and light weight sailboat using foam cores.


Epoxy is very expensive, $60-90 gallon, Polyester resin would work quite well for this application and it cost around $20-35 a gallon. Nasty stuff, wear a mask.

http://www.boatbuilder.org/mascart/index.htm

http://www.fiberglasssupply.com/Product_Catalog/Polyester_Resins/polyester_resins.html
 

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I would do a quick test where you compare how easy it is to bend wood and fiberglass of the same thickness.

I'm trying to remember what we used on the race car we built in college....there was balsa in the middle sandwiched between either fiberglass or carbon fiber. I'm starting to think it was carbon fiber, but whatever it was, it was super rigid as all get out.
Same with core boats (foam or balsa), very stiff.

When a boat hits a big waves, there are strong stress forces on the surface. The forces on the inside of the surface are directional 180 degrees different than the outside surface ie: one force is to the right, the other is to the left.

What the core material does, isolated these forces from each other. On soild hulls ie: all fiberglass, stress crack will form.

Having said that, bashing thru 5' waves made of water may be alot different than a 15 Hz sound waves.
 

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I wonder if there is anyone out there with an engineering/materials background that could interpret some of the materials properties for us.

From what I have read in a couple of quick searches, a material's strength is measured in several different ways, so when someone writes that fiberglass has twice the strength of aluminum (a comment I found on one car audio site), it is not clear what that means.

Is it just stiffness we are concerned with?

From what I have read, the type of resin used affects the composites stiffness as well and epoxy is recommended for applications where stiffness is important.

If we could find the appropriate explanation of the various measures of strength, and get measures for various materials available, it would probably not be too hard to figure out what thickness of figerglass/kevlar/carbon fiber would be required to replace say 3/4" mdf.
 

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If we could find the appropriate explanation of the various measures of strength, and get measures for various materials available, it would probably not be too hard to figure out what thickness of figerglass/kevlar/carbon fiber would be required to replace say 3/4" mdf.
Sorry, no engineering data for you but the strongest resin by far is epoxy, the second greatest invention for us boaters (Gin & Tonics being #1).

Next would be Vinyl Ester Resin, nasty stuff to work with and very finicky concerning ambient factors while setting. I would not touch this stuff.

Last of course is Polyester.

While this is a interesting discussion, I could not justify building a 100% fiberglass box. To get that "fiberglass look", you will need a mold and apply gelcoat first then layer it with fiberglass. Then you will still have to attach the front baffle to it, no clue how to do this.

The ability of epoxy to bond to a surface is it's greatest asset. Someone mentioned, "if it doesn't work, just scrape it off". Don't even think that you can easily remove the stuff once set.

Use it to strength wood joints such as corners. If you have an odd shape design and cannot cut precision angles, fill in the gaps with an epoxy filler and then tape over the seams. Even for a waterproof box, I would still use wood and epoxy over it.

If bored, check out this link to see what is possible with wood and epoxy construction.

http://www.devlinboat.com/sockeye42.htm
 

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Paydirt! This article talks about the properties of various materials as it relates to audio and even gives a formula to calculate equivelant thicknesses of material. It turns out fiberglass (e-glass) is about the same as baltic birch (for a flat surface), so no gain there.

You can use the formula to calculate the equivelant thickness for other materials like carbon fiber though.
 

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Why exactly are you trying to make the cabinet more stiff? Typical bracing methods are more than sufficient to prevent any audible resonances and/or cabinet flex within the normal passband for a subwoofer.

If you are looking for a more efficient solution to minimize resonances or flex a viscoelastic constraint layer coupled with typical bracing will be approximately 8 times more effective than just bracing alone.
 

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If that is the case then fiberglass won't do much to stiffen a cabinet alone, but if applying fiberglass directly to the wood it is possible for a constraint layer to be created. If the two materials have sufficiently different physical impedance characteristics when coupled together these mismatched impedance can actually act to minimize resonances. The efficiency of this constraint layer will be dependant on application as well as materials used.
 

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Would a product like Damplifier be considered a viscoelastic constraint layer?

http://www.secondskinaudio.com/vibration-mat/damplifier.php?category=70
It is hard to tell with the minimal information provided on the website. I typically recommend use of Peel & Seal for use as a viscoelastic constraint layer. During the application process it is imperative that a heat gun is used to achieve better adhesion with the material. If for some reason the material will be subject to high heat Dynamat is a superior, but more expensive, choice as it is designed to withstand such conditions.

An example of a high efficiency constraint layer suitable for a midrange enclosure would be: 3/4" exterior cabinet grade ply - 1/8" peel & seal - 1/2" hardibacker brand cement board. This used in conjunction with dense bracing will result in a cabinet that has attenuation of resonances 20-30dB below average. Such attenuation will result in completely inaudible resonances in virtually all circumstances.
 

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The one reason to consider a composite is if it has characteristics that allow you to use considerably less material to give you the same acoustic properties. It appears that fiberglass does not.

Carbon fiber looks like an interesting material though. It is very stiff, but does not flex much before failure (very high compressive/tensile strength).

Out of curiosity, do you have reference material on cabinet design/bracing/constraint layer materials?

How one would use a material for construction or bracing or damping would depend very much on the physical characteristics of that material, but its not something I have seen discussed in any of the design discussions I have read.
 

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Out of curiosity, do you have reference material on cabinet design/bracing/constraint layer materials?
The best source I can recommend is finding material engineering texts used by a local university. I personally do not own any such books and am not aware of any 'best'. I just borrowed some books from an engineering friend a few years ago.
 
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