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Multi-Way Conventional loudspeakers with crossovers

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Old 21st March 2003, 04:06 AM   #1
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Lightbulb Just discovered stiff, dead material for cabinets

It's called Hardibacker board and is available at Home Depot for $10 per 3'x5' sheet (both 1/4" and 1/2" thicknesses)
This board is meant to be a base for ceramic tile but seems like it my work quite well on my next home speaker-building project. It consists of 90% cement and sand, 10% cellulose fiber. I will probably just use it on the baffle for it's hardness (also, it's very heavy). A 1/4" sheet glued to a 3/4" sheet of MDF is how I'll try it, I think. I won't use it on the rest of the cabinet because I'm going with two layers of 1/2" MDF with a slightly softer layer in between... Dynamat, asphalt paper, very thin foam or rubber, etc. I'm experimanting with sandwiching different soft materials in the walls of cabinets... doing two projects at once. These are my first attempts at home speaker-building, and I'm really enjoying it.
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Old 25th March 2003, 03:47 AM   #2
TheoM is offline TheoM  United States
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Default cab materials - foam sandwich.

I've used the thin concrete tile backing from Home Depot - The weight's good but I think its not that rigid - and rigidity is what you need most in a box. As for sanwich materials - I have done a lot of work in that area. Foam sandwich materials have the highest strength to weight ratio of anything known. You can buy 3 or 4" foam sandwich material cheap - they make houses with it - whole walls that need no studs. The strength is nonlinear with the thickness of the foam because of the way that stress impinges on the system. One wall goes into compression and the other into tension. ... The foam would damp low end well, I assume. I've always wanted to try this.
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Old 26th March 2003, 04:00 AM   #3
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Yes, I know it's not that rigid, but it is very hard... and if it used with another material, it might be good. The key is to use a stiff epoxy to adhere the two surfaces. I was planning on the hardibacker and mdf with a fiberglass epoxy resin joining the two.
As for the foam... I've been toying with that idea, myself. Years ago I met someone who built telescopes and he used foam and luan. Apparently, he needed it to be as light as possible and very stiff. The key to success, he said, was to get 100% coverage with the glue he was using to join the two materials. The foam-board combo seemed very stiff. One of these days I will try it myself.
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Old 26th March 2003, 05:59 PM   #4
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mcmaster-carr has some products that might be interesting. or at least could give some ideas:

http://www.mcmaster.com/catalog/109/html/3236.html

also check out the next 5 pages, 3236 through 3241. (just type over the number before 'html'....or alternatively, go to the home page and look for 'sound absorbers' under the 'raw materials and springs' heading.)

/andrew
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Old 27th March 2003, 04:19 PM   #5
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Default Maybee it's to hard

Well during collge some twenty years ago I was testing some houndred materials for speaker cabinetts.
Tested alot of hard materials like marble and so on. The hard ones was were stable and good but had one side effect that they spread high fs resonance between the drivers. So I would recomend you to have separate surface baffles for each driver with damping sandwish material behind.

Remember some of the strange results I got back when.

1" MDF was better than 1" birch plywood
2x1" MDF was better than 2x1" birch plywood
2x1" birch plywood with vinyl damping in between was alot better than 2x1" MDF with vinyl damping.
If I remeber right the best result weight we got from
1/2" Birchplywood, Epoxy glue, Alu foile, Epoxy glue, 1/2" HDF, standard wood glue, thin asfalt, standard wood glue, 1/2" birch plywood. If weight is not a matter were are alot better material.

Magnus

Yes my english is bad
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Old 27th March 2003, 04:48 PM   #6
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I'm redoing my bathroom and also just discovered Hardibacker. It is really dusty to cut. Much worse than MDF. Wear safety glasses as pieces do tend to fly with this material.
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Old 27th March 2003, 06:10 PM   #7
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Default You just found a DEAD STIFF?? He he.

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Old 27th March 2003, 10:02 PM   #8
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Default building materials - some more ideas

the hardie company also makes exterior siding products. the 'hardisoffit' might be a good ticket for a more finished look, if you want to use it exposed. it could be painted...heck you could even plaster it or tile over it. also it might be a little less dusty...still, it's cement board. you gotta expect some dust.

link to hardisoffit

has anyone ever tried using gypsum board (a.k.a Sheetrock) as cabinet walls?

how about Homasote?

how about layers of Masonite?

also, adhering (or stapling) lead flashing to the walls will add some significant weight.

seems to me, any multi-layer composite assemblage is going to perform better than any single-layer assemblage. the sound transmission is going to go way down due to the differing material properties.
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Old 27th March 2003, 10:21 PM   #9
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You all are great!

Being that this is my first home speaker building project, it's turning out to be quite the experiment...

... and a fun one at that!

I'm buying up all kinds of soft materials to sandwich between the hard layers of the cabinet, and to also use as damping material inside the cabinet. Some of the soft stuff includes tool box liner, two kinds of anti-slip carpet padding... one for hard floors and and the other for carpet (when you put a piece of carpet on top of wall-to-wall carpet... it's like a synthetic wool material), and a kind of shelf padding. I think these materials have potential. I can't wait to try them. In additon, I have egg-crate foam padding and Dynamat left over from other projects.

I've also decided to mix up the materials for the cabinet, itself... using MDF, hardibacker (only for the baffle), birch ply-wood, and particle board. I'm doing this in an effort to reduce the resonant frequency that each material might have. Any input on this idea is welcome. Thanks.

Thanks for all the responses.
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Old 27th March 2003, 11:31 PM   #10
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Default one more idea

...that i've heard of people doing, is to build a box-within-a-box, such that the space between the boxes is filled with sand, or sand + lead shot. i suppose you could even make some wild cement concoction, to really make it dense and heavy - maybe use a glue-sand-shot mixture. (yuck. ) however the vibration damping might not be as good as with dry sand.

(btw if you try this, sterilize the sand first in the oven.)

/andrew
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