Best non-wood prototype material for cabinets?

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
 
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.
 
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.
 
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.
 
A different approach

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.
 
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
 
Sorry, Bill, I guess it does help to establish a baseline.

What tools do I own?

All of them, I guess. If I don't have it, I have friends that do. I suppose CNC machining and injection molding would not be feasible, but certainly everything needed to build speakers is no problem. I have a friend who has a complete metalworking shop. My personal shop is only 20' x 20', and sheet goods are problematic. I usually work with solid wood. My skill level is such that I can cut my own veneers.

My problem is lack of time and my age, so I thought a thread on lighter, quicker prototype materials would be helpful to this beginning speaker builder. I don't know how open baffles, or TL's, or horns, or quarter wave do-dads, or arrays, or whatever, sound at this point, and I don't want to spend the next five years wrestling MDF sheets around to find out, so I am very grateful for the replies so far. I love thinking outside the box :cool:

Doug
 
Two more things:

For smaller projects in MDF, I often buy MDF shelving rather then the 4x8 sheets. The shelves are 12" wode and 8' long with a bullnose on one edge (gets ripped off first). It's just a lot easier to deal with them than the sheets, as long as you don't need anything over 11.5" wide. Plus, they fit in my Honda.

For an adhesive for laminating, I use the 3M High-Strength 90 (stronger than 77). It's really contact cement in a spray can: you spray both pieces, let it dry for a couple minutes, then put them together. Very strong. I have been using it lately to laminate aluminum flashing to wood (walnut lately) for RFI shielded amp cabinets.


I like the idea of a fixed size box with replacable baffles, and known volume wood block that you can drop in to alter the box volume.
 
Taperwood:

At 65, I'm not fond of wrestling with sheets of 3/4 MDF either. I do manage though.

With a table saw, sabre saw, pin nailer, router, palm sander and glue I can cut the MDF, make the speaker cutouts, assemble, flush trim and roundover a box in less than 1 hour. I wind up with a quality, uncompromised product that is ready for primer. I'm sure you can do this too.

Why not have Home Depot cut up some MDF into third and quarter sheets which you then have on hand. That eliminates your major objection to prototyping in MDF.

I don't see how any of the alternate methods proposed here are going to be any faster. And, they are all going to sound terrrible.
 
I agree with Bill - It's probably not worth the trouble prototyping anything but an open baffle speaker in cardboard or foam.

I've also had luck getting Home Depot and Lowes to cut the panels to finished size for me. Some will, some won't, depends on the person you find to help you. At a minimum I can usally get a sheet cut into strips and those strips cut to fit in my car.

I've also bought precut quarter sheets on days when the store's "help" was nowhere to be found. It's more expensive, but at least I was spending my time building speakers instead of looking for someone to help me.
 
With MDF, you still need 3 to 4 cuts per panel and plenty of dust with glue particles in it.

I try to design around stock lumber sizes (1x4, 1x6, 1x10, etc.). My current project uses 1x4 and 1x10 pine panels at various lengths. The yard cut them on the miter, they were easy to transport on public transit and really, really cheap.

And I don't agree with Bill. I think it's possible to develop a new type of composite material. Okay, I suppose that's not prototyping a speaker, but the enclosure material.

:)ensen.
 
Well, if anyone is like me, I save every scrap of wood until I am buried up to my neck. So if I build prototypes out of chipboard or MDF, what do I do with the box when I'm done? Tearing it apart just makes a bigger mess.

I understand foam or cardboard will not sound the same, but I need to be able to build something without firing up the shop.

My thoughts on prototyping:

You have an idea or an existing design. You build something. It doesn't matter what materials you use or how shoddy it looks. This is your baseline. You look at it; you listen to it. You ask others (my wife) what's good, what's bad. If it stinks, you stop right there. If it shows promise, you build another prototype, deeper, taller, shorter, fatter, whatever you think will address the most glaring defects. If you then get acceptable improvement, you build something out of wood or whatever and start tweaking for your final design. With every change you always compare it to your previous prototype via A/B testing. It's time consuming but worth it.

The result I got following this method on my little computer speakers was astounding. You would not believe it was the same speaker.

Doug
 
Ok, that makes sense to me. Suppose I want to concentrate on full-range, single driver speakers at this point and supplement with a subwoofer. What would be considered low end bass? Anything below 100Hz? Would you think a well-built prototype would handle sound down to that level?

My musical tastes center on vocals, acoustic, folk, blues, old-country, jazz, etc. Occasionally some rock, but I'm not into bass-heavy music anymore.

Doug