Best non-wood prototype material for cabinets?

[Taperwood]

I did do a search and found nothing on material for prototyping speakers.

Ok, so after 30 years I decided to start building speakers again. My first project was cabinets for some Yamaha 3" drivers that I have used for many years on my computer. The improvement in sound was tremendous. But I had to build two prototypes and experiment with stuffing for what seemed like forever to get them to sound their best, and after wrestling a full sheet of MDF around, I don't think I want to do that again unless it's really going to count.

My question is what can I use to build quick and dirty prototypes of enclosures? Something light and easy to cut; something I can put together in a couple of hours. I saw some foam board at Home Depot for $10 a sheet. It's quite dense and had foil on one side. It is light and easy to cut, and I suppose I could use hot melt glue to put it together. Would something like this work?

I would not expect any material to sound exactly like a MDF or plywood, but I'm hoping I can build something quickly that will at least let me know how something will sound, generally.

So I ask, what is your best easy-to-work, non-wood protoptype material and why? Or is this wishful thinking? Thanks for your input

Doug

[simon5]

Thick cardboard should do the trick, unless you're prototyping a subwoofer, where you'll need at least MDF.

[Nuuk]

Polystyrene foam can sound a lot better than wood/MDF/ply etc!

[purplepeople]

Cardboard is cheap and easy but will sound boxy if not modified slightly. (Pun intended)

As I see it, the problem lies with the resonance and flex in the material, hence the popularity of MDF. When using thin or low-density material, one way to dampen the resonances and increase rigidity is to use composite construction.

First, make sure the cardboard has two outer layers sandwiching the corrugation. Some have only one which makes them easy to contour into curves but reduces their overall strength a lot. (Of course, this makes for some interesting acoustics if used on the inside surface, but that's another thing)

Anyway, once the first layer of card is cut, add a second layer using a grid of hot glue lines put down 30deg to the corrugations. The second layer goes on 30deg to the hot glue or 60 deg to the previous cardboard layer. Do a third layer that is 60 deg to the previous two.

If you've been using fairly common cardboard (as from moving boxes) you will have built up around 10mm of material. If you make a big sheet of this, it can be cut on a table saw. Or, if you are really handy with a ruler, you can cut each layer with a knife at the the correct angles and glue together each panel separately.

Hmmm. Maybe this is more like a new enclosure material than a prototype method.

[Euphase]

There is a poster board which is a sandwich of foam between two layers of carton paper. I used it to do makeshift baffles and measure baffle diffraction effects on this. It is a lot more sturdy than cardboard, even holds screws to some degree. I had used two or three layers of this to reach a thickness I wanted, then had cut out driver recesses for flush mounting them. An xacto knife worked great.

A box made out of these won't be good to do any low, mid-low frequency modelling, but for higher frequencies it will work as an early cheap prototype. At low frequencies it flexes and air pressure leakes to outside. I had once meaured the impedance of a woofer I had put in a box made out of this poster board material. The impedance graph was way out of wack below 500Hz, all kinds of dips and peaks.

[Bill Fitzpatrick]

I'm far from a hot glue expert but as far as I know the stuff cools and sets so rapidly you will not have time to lay down beads in a grid as suggested.

[purplepeople]

You're right Bill.

I normally work with PSA (tapes) so I was only thinking about how to do it with easily available stuff. In this case, maybe a spray adhesive would be good... like 3M Super 77 in an well ventilated area.

The foam core stuff is also good, but not as cheap or free. It does come in black, so even the protos will look halfway good. For this I would not use the thicker stuff, but use multiple thin layers. It's the layers glued up that make for the rigidity to keep bass notes from going through the walls.

:)ensen.

[DC Dave]

I tried the cardboard method before, but then I switched to using an adjustible MDF enclosure and got better results.

I built a test enclosure out of MDF with removable baffles and rear panels. I designed it for testing drivers 3-5 inches. When I want to test a new driver sometimes I have to make a new baffle, but now I have accumulated baffles cut for most sized drivers. I can add or subtract volume by securing premade sections to the box, or inserting wood blocks inside it. I can put a port on the baffle or seal it up. It works great, and is very universal.

[Taperwood]

Great input so far. Lots of neat ideas are swirling around in my head.

It sounds like just about anything will work. I agree that hot melt glue will probably not work most of the time, due to the fast set time. I figure duct tape or strapping tape will do the trick, and I do use Super 77 for other stuff. Maybe a bead of caulking at the seams and then some tape to hold it together. Should be pretty airtight.

To deal with box resonances below 500 Hz, will blankets or something soft taped to the outer surfaces help deaden the sound? I admit I know very little about acoustics.


After reading so far, some more prototyping ideas have popped into my head:

using paper from a paper shredder for stuffing? I have heard of using styrofoam peanuts. What about feathers?

corner bass traps and wall panels made out of layered or rolled cardboard or layered newspaper (yes, I am dealing with serious room issues in my little computer room with my new speakers).

This is great, keep em coming.

Doug

[Bill Fitzpatrick]

Taperwood:

You forgot to tell us what tools you have available.