Hi!

I Am now thinking of building a subwoofer fpr my car. I am thinking of building a 2 chamber box (ported) with 2*10" speakers. The thing is that I am thinking of using plexiglas on the top of the box. So that I will be able to see the beauties inside. Maybe using plexiglass for the angled side to.

My question is, is there a problem with using plexiglas in the box or should I consider the box as it is, unregarding of material? And should I think of putting in foam into the bottom chamber (where the port is), and if so how much foam should I put in there?

Acrylic or Plexiglas (same thing) should work for your enclosure provided you use thick enough material and are able to seal all the joints fully, which can be tough. Velodyne makes sub enclosures out of the stuff. I believe sheets come at least 1 1/4 inch thick. You probably would want to use at least 3/4 inch, but it's rather expensive. ~$450 for a 4'x8' sheet, double for 1 1/4" material.

Stu

You probably would want to use at least 3/4 inch, but it's rather expensive. ~$450 for a 4'x8' sheet, double for 1 1/4" material.

Yes, with 1/2", seems like you could get some flex. FWIW, when I needed some 1/2" for an application on my boat, I went to the local Laird Plastics and they sold me a quarter sheet (2'x4'). Still very expensive, but much less so. Not sure where you are located, but smaller plastics resellers may not sell partial sheets if they have to special order the material. Laird is a national chain and they didn't seem to have a problem selling quarter and half sheets. If you have a small plastics shop locally that does custom fabrication, go see if they have any remnants that will do the job. If so, you can probably get it at less than half price.

they sold me a quarter sheet (2'x4').


A quarter sheet won't be enough to build the entire box out of plexiglas.

If the box were 24" wide by 12" tall by 12" deep, you'd have about .8 cubic feet per speaker (after you subract the volume taken up by the speakers themselves and the thickness of the plexiglas) which is in the ball park for most 10" speakers.

You could build the box out of one 2' by 4' sheet -- except for the two 12" x 12" end pieces. The box wouldn't really have to be 12" deep -- depending on the speakers you use, you could get by with as little as eight or nine inches -- but the plexiglas you save that way won't be in any useful shape or size.

Now if you want to just build a conventional box out of 3/4" MDF, with a plexiglas top in it -- then you can get by with a single 2' x 1' piece, which would probably be more fiscally sensible, and many glass and plastic shops will sell you 1/4 or in this case 1/16 of a sheet.

tanstaafl.

Or you could just buy one of the pre-made subwoofer boxes at Crutchfield that come with the plexiglass window already built-in with the gasket and cinching screws. Heck, in the new catalog, they even have them with neon and strobe lights if you want.

I am just using plexiglass for the top, wich is about 650*350 (mm) roughly.... I did some research and found a plastic reseller here in my town. So I mailed them about doing the entire piece for me. Then I dont have to worry about cutting it properly. Allthough I havent goten any answer from them yet.

I want to build my own box, since I already have made my own design that fits pretty good in my car.

The ports on the box will be facing the backseat (placed in the trunk) And the speakers are facing upwards. Is that so good with the ports almost jammed into a 'wall'? Maybe the air circulation will get a little tougher? Because I want the angled side to face outwards, towards the trunk opening. Any thought about that?

Is this a sedan or a wagon you are building the cabinet for ? Facing the ports towards the back of the seats will hinder performance, since it will make port tuning unpredictable (assuming you are mathematically calculating your box/port). Is the stereo system built for show or go ? I would consider an infinite baffle design for a sedan, placing the subs in the rear deck (theoretically) and only a ported or sealed enclosure for a wagon (no rear deck to acoustically isolate the woofer's front and backside).

Its a sedan. A renault 19. I have the box design already finished. Worked out with probox2000. A 2 chamber ported box. So the ports are calculated. Allthough I will leave room, say about 10 cm from the port exit to the backseat.

Acrylic and plexi aren't the same thing, plexi is much more brittle. If you bend both, the plexi will crack, the acrylic will develop a crease but stay together. If price is equal, I would get acrylic. However, at 3/4" thickness or so, I think either would be plenty, so - go with the cheaper one if there's a price difference.

Might talk to the seller as well, if they know a lot about plastic, one of them may be easier to work with down the road as far as fixing scratches, cloudiness, things like that go.

What drivers are you using ? Did you consider an infinite baffle design ? Basically the drivers "see" the cabin on one side of the cone and the trunk on the other side. Undoubtedly the most neutral sounding bass with the fastest attach, at a cost of efficiency and low end extension. Extension is rarely ever a problem in a sedan with two 10's. The bass reinforcement of the small environment makes good for the earlier bass roll-off. Efficiency can be made up for with amplifier power (as long as the drivers can handle it). My suggestion would be infinite baffle with an ajustable Q active highpass filter section in the bass chain (pre amplifier) to provide bass equalization. Easy to build, too (no cabinet). You just need to find a slick way to mount the drivers.
Good luck whatever you do !

Acrylic and plexi aren't the same thing

Um, sorry, but WRONG! Ever looked at a piece of Plexiglas? It even says it's acrylic on the label. Plexiglas is simply one of many brands of acrylic forms actually made of polymethylmethacrylate resin. Other brands include Perspex and Lucite. Acrylics are available in two forms, extruded and cast. Extruded acrylics tend to be more flexible, have tighter thickness tolerances, but have less clarity than a cast acrylic.

Stu

Gads, yes you're right. When I said acrylic, I had Lexan in my mind.

Plexiglass is a brand name of acrylic, kind of like how we use Q-tip to mean cotton swab. I stand corrected, there's no real difference.

IIRC it's Lexan, a polycarbonate, that is much more durable. You can actually bend it, cut it (it will melt from the heat but not shatter), and you can drill into it (again my experience with plexi is that it chips and cracks).

I'd like to rephrase my suggestion to "consider Lexan".

IIRC it's Lexan, a polycarbonate, that is much more durable. You can actually bend it, (...)

I'd like to rephrase my suggestion to "consider Lexan".

May I take this opportunity to remind everyone that rigidity is a critical factor in building any speaker enclosure, especially subwoofer boxes. Building the box out of flexible materials might not be the best idea.

Tony - Rigid? You couldn't have said that earlier? Now what am I going to do with my 50 lbs of coral putty and my new 14" Jamma Mamma Steet Noizz sub? Jeez.


-Zeke

Right, but we're talking about 3/4" thick, and a window. I don't see a problem, you think there would be one? It's a lot thicker than many off-the-shelf boxes have built into them. Sealing the sucker is the bigger problem in my mind.

IIRC it's Lexan, a polycarbonate, that is much more durable. You can actually bend it, cut it (it will melt from the heat but not shatter), and you can drill into it

Yes those are some of polycarbonate's properties. It also stops bullets in 1"+ thicknesses. It's what is used for "bulletproof glass." Polycarbonate has a bit of a gray cast to it, especially in the thicker sheets. It's also a little tougher to polish up, but is less sensitive to the blades used to cut it than is acrylic. It is also more costly than acrylic. Personally, I wouldn't recommend it for this application.

Stu

It is also more costly than acrylic. Personally, I wouldn't recommend it for this application.

Here's a thought... there is probably some perfectly good reason not to do this, and I'm just not smart enough to figure it out.

But how about instead of usiing plexiglas/lexan/acrylic/whatever, you use glass? It's inexpensive, it's scratch-resistant, and if it's over a quarter of an inch thick, it is pretty unlikely to break.

tanstaafl.

Two disadvantages I can think of immediately - weight, and it's tough to work with. If you can sketch and dimension exactly what you need then you'll probably be able to find somewhere to produce it for you, but by that time the cost may be creeping up again.

I see myself now, breaking out the vacuum cleaner.
shooooooommmmmmmm