What do you gents think about building a box with this material? - diyAudio
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Old 28th October 2008, 02:10 AM   #1
tf1216 is offline tf1216  United States
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Default What do you gents think about building a box with this material?

http://www.signfoam.com/product.php?mode=sf3

I have a friend who may use his CNC machine to build me speaker boxes. He asked if I would be willing to try this foam instead of MDF.

There are other websites where even a more dense material can be purchased. Any opinions out there?
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Old 28th October 2008, 02:43 AM   #2
pjpoes is offline pjpoes  United States
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It's not nearly as strong as MDF in pretty much any area. It's less dense, which will mean that it will have less energy absorption and will be virtually transparent acoustically at lower frequencies. It has a lower tensile, compressive, and flexure strength. I would also guess that it would be considerably more expensive.

Now if the material is free or you are getting it at a reduced cost, it's not horrible. I would want to feel it in person, as its tensile is so much lower it worries me. None the less, I would say its ok, it could actually have some advantages, but mostly it just won't be as strong.

Consider using plywood or solidwood for the internal braces. This is good practice no matter what you use, but is especially true if using this foam material.

Consider laminating the foam with something to increase strength. While good for every panel, I would argue the front and rear need it most. Consider something like a phenolic plastic, thin plywood (1/8" 3 ply), or even solid wood.
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Old 28th October 2008, 02:56 AM   #3
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Even at it's most dense (18 lbs/cu. ft), it's only .29 g/cc, - less than have of a good box material like 15 ply baltic birch plywood or MDF which are in the area of .7 g/cc.
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Old 28th October 2008, 03:40 AM   #4
Pano is offline Pano  United States
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I've done it. As well as foam core and other related materials. It was just "OK." Seemed be transparent at low frequencies. But shootz! I didn't have any of the 12" thick stuff. (Did try sand filled, tho)

But what the heck, try it and tell us what you think!
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Old 28th October 2008, 12:14 PM   #5
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I believe these guys use something like foamboard for the enclosure: have a look through the technology pages. I've heard these breifly and was instantly impressed, they are very good in many areas.

Rountree Acoustics

The cunning bit is coupling the driver to the floor directly. Any compliance in the mounting of the driver is bad news in my opinion. The reaction forces of the driver in motion means you will be moving the baffle as well as the air. This method sidesteps it nicely. If you are looking at a conventional driver layout you have some thinking to do, a foamboard baffle just won't be stiff enough.

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Old 28th October 2008, 02:42 PM   #6
tf1216 is offline tf1216  United States
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Thanks for the replies gentlemen! I have not decided what I want to do yet.

I was also given this website:

http://www.precisionboard.com/Ind/products.htm

These guys seem to make more bulky foam. Does anyone think this product would work better?
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Old 28th October 2008, 03:24 PM   #7
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Quote:
Originally posted by tf1216
Thanks for the replies gentlemen! I have not decided what I want to do yet.

I was also given this website:

http://www.precisionboard.com/Ind/products.htm

These guys seem to make more bulky foam. Does anyone think this product would work better?
Well, their 40 lbs/cu. ft stuff come close (.64 g/cc) to the BB plywood and MDF. Wonder what it costs?

If it costs more and is = or < the standard box materials don't waste your time. Your best bet is to contact them and talk to a tech person about what you want to do and see what they say.
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Old 28th October 2008, 05:50 PM   #8
gedlee is offline gedlee  United States
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Polyurethane board is what I use to make my molds and prototypes. I find it great as a material, but what I use is outrageously expensive, about 10 times the cost of MDF. But MDF is not dimensionally stable and is no good for molds that you hope to use for years.

I have to say that the idea that it is density that is important is wrong. To me the lowest density with the highest stiffness is the best material. The poly boards that I use are ideal in this regard. And the poly is better damped than plywood (which is terrible in this regard) and MDF (which is pretty good). The poly boards cut great and glue great with two-part Urethane glues (the joint is stronger than the boards) - its a wonderfull material to work with. I suspect it would make a great speaker cabinet, but I'd never use it because of its cost. A good MDF box gets as good as it needs to be and is very very cost effective (although I do hate working with MDF - cutting dust, painting, its a real pain!).
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Old 28th October 2008, 06:36 PM   #9
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I had considered such a material for speaker once, but never built it. The difference and an important one I think, is that I had planned to cover (using vacuum bagging techniques) with several layers of carbon fiber fabric, and in between foam and outer plies, use viscoelastic dampening materials like used in soundproofing. This would likely be much more resistant to flexure than MDF or BB ply, but not sure about overall suitability.
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Old 28th October 2008, 06:59 PM   #10
sreten is offline sreten  United Kingdom
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Hi,

You could consider making a laminate and machining that.
The foam as the core and a high modulus outer layer.

Read up on the Celestion SL600.

Wharfedales me-too clone used a building section 1" or so
thick which was essentially a lightweight foam cored laminate.
The box had low internal volume for its size.

Really only make sense for small boxes, e.g. satellites, small
speakers or seperate mid treble enclosures due to economy.

/sreten.
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