Just discovered stiff, dead material for cabinets

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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. :)
 
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.
 
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.
 
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
 
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.
 
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. :nod:
 
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. :dead: ) 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
 
Magnus

Can you tell us more about how you tested the various materials? ie were you using accelerometer testing?

I'm interested in your comment that with hard materials you found high frequency spreading to other drivers.

Its interesting to note on the high end JM Lab speakers (eg Utopia) they have separate looking baffles. I had assumed that this was for looks, but maybe not...

Would this be a problem in exciting the other drivers or some other problem?

If you use separate hard baffles, then are you suggesting that they are connected to the main enclosure only by damping material, or is there a hard connection as well?

Mick
 
Well some more information

Faustin bargin

About layers masonite, works well and have really good damping, but do gets heavy bacuase of al layers needed, and it's recommended to use 2"x1" oak piece for stiffining the box up.

About double boxes with sand in between as damping super good, but really hard in practic, because somethere you have to join the boxes, holes for drivers and so on. How with what material?

Kanga
1. First we tested mechanical stiffness, don't have the documentation for the setup anymore but if you have intresst and I get some time over I could try to write/draw it up again.

2. Yes we used accelometers first some different types of piezo type but were not satisfied with them because it was difficult to attach them equal. So instaed we build an unbalanced motor with a pretty serious speed control. That we attached dead stiff to our test boards. Al testes were measured 500mm from vibration source with a laser picup. (wrote some of my old friends erlier to se if they could dig up the results somethere in sweden).
Will post them here as soon as I get them. With the hard materials you always get a hf (in this case over 2kHz) resonance/microphoni and it is most often over a wide spectra, but man made materials like cement and akrylat is alot better than marble,iron and so on.

3. Messurments in speakers 3way systems. We were able to see (hear in some cases) the resonance fs in hard surface materials in the test. Glass, marble and other really hard materials were really bad and not recommended at al because they also had some strange microphoni bump in low frequency 100-250Hz an area really critical for human voice. We were able to get rip of it with alot of damping and baffle splitting. But it is alot easier to use a material with better damping from the begining. Well I don't know why JM labs have splitt there baffles, but I'm not sure they know that either. *smile* an other thing about utopia look on the hard edges between the baffles, doesn't diffraction exist any more. Don't really belive in there designs and they don't sound that good. But I do love the power flower isn't that a sexy driver, I guess even my wife would allow me to buy drivers looking that good.

Sch3matic
Cast iron read above, to much microphoni..

Ones again sorry for my bad english, nylon boards are have but do sound wonderful.

Magnus
 
would a large mouse pad work?

for the inside of speakers??

http://sciplus.com/singleItem.cfm?terms=11262&cartLogFrom=Search

that hardware site had somthing like them for about 20bux. these guys have it for 3ish. ive always thought of them,buit i have no idea if they would be thick enough. this site has lots of stuff that might be used for other than intended purposes. i bought a bunch of rubber balls when i buil;t my speaks,,10 months ago?? i dunno. but i cut the balls in half,and used one set for under the cd player. worked as far as stopping the cd from skipping. when i get a real ent center for the equipment,,id like to use them under all of the electronics.i read somewhere that that is helpfull in some way,,it cant hurt.

roy
 
Re: Well some more information

svensken said:
Cast iron read above, to much microphoni..

Have you tried cast aluminium with some sort of resonance damping coating and/or wool felt (norwegian: "ull filt", dunno in swedish) ?

Aluminium does ring, but supposedly outside the audible range.

I'm considering using a cast aluminium chassis for a dipole speaker using the Bohlender-Graebner ribbons with 3 pcs Seas Excel 10" woofers. Would be nice to know if that's a stupid idea before I do it :xeye:
 
Re: Well some more information

svensken said:
Ones again sorry for my bad english,...
.. not particulary. I think most people understand you and that's what counts.

If you want to improve your spelling you may use this excellent dictionary which has both greek, svenska, english, german etc etc.
http://www.websters-online-dictionary.org/

Just found out what swedish means :) :att'n: Check the explantion at the end.
 
The cement board would be poor. It's high weight and low stiffness mean it will have low resonant freq.

"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. "

I don't know why you'd want to do that. The soft material essentially gives two unconnected sheets - the huge stiffness benefit normally given by spaced aheets is lost.

And its softness won't absorb sound because its trapped between the hard barriers.

What you want is light and stiff to give high resonant freq, and damp it. When it's light, it's easier to damp - damping material is most effective when sililar in mass to what it's damping.

The high freq means x number of damped cycles happens in a short time.

Surfboard type construction would be ideal - rigid styrofoam panels with fiberglass, or better yet carbon fiber.

While you're at it, make the panels curved for greatly increased stiffness.

There's lots of good info on fiberglassing at

http://www.tapplastics.com

In fact, I think I've just realized how I'm going to build my next speakers - carbon fiber sandwhich in a lute shape, with a bronze finish; Tap has bronze powder you mix into the finish coat.
 
noah katz said:

Surfboard type construction would be ideal - rigid styrofoam panels with fiberglass, or better yet carbon fiber.


Interesting idea. Most surfboards are made with urethane foam blanks and "glassed" with fiberglass cloth and polyester resin. Easy to work with and relatively cheap. Don't know where you'd get polyurethane foam sheets. However, a small fraction of boards are made with various styrene foams and glassed with glass cloth and epoxy resins (polyesters will dissolve styrene foams). Various styrene foam (styrofoam) sheets are commonly available for building insulation uses.

The "glassing" process is messy, but making whatever shape you want would be easy. I'm gonna keep this in mind for down the road.

Sheldn
 
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