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-   -   Mounting Subs in Plexiglass (http://www.diyaudio.com/forums/car-audio/42715-mounting-subs-plexiglass.html)

Ky_0686 17th October 2004 03:35 AM

Mounting Subs in Plexiglass
 
Hey,
I obviousely have a question. Has anyone tried or thought about mounting subs into plexiglass? Plexiglass is pretty strong, shatterproof. And I would imagine that if it was thick enough it could hold the weight of the subs. I mean they use the stuff in aquarium tanks that have several hundred gallons of water in them. I guess what I'm trying to find out is if the air movement inside the box is strong enough to either crack the plexiglass at the edge of the box where it would be screwed down, or around where the subs are set into place. Would reinforcing the edges with say a ring of aluminum help brace the plexiglass to prevent cracking? Or am I just asking too many questions? :D Thanks for any suggestions, or statements. ~Kyle

SupraGuy 17th October 2004 09:28 PM

I've used plexiglass as part of a sub enclosure, but not as the mounting surface for the subs. I can't see any reason why not, but I'd recommend that you use at least 3/4" (19mm) plexi for this task.

A large part of the reason why I've never done this is that it seems to me to be a terrible waste to cut a 9-11" hole out of a chunk of plexiglass that thick and just throw it away. (I suppose that it could be used for a round window in a different enclosure...)

You would need to take a lot of care around the bolt holes for the woofer, too much stress would crack the plexi. I'd suggest using a "T" nut, and heating it to sink into the plexi. You'd also need to be careful with the hole for the woofer, as it would be visible, as would the mounting hardware.

Tricky, but possible. It would also look very cool to have mirrored back and sides to the enclosure and/or an EL tube.

Ky_0686 18th October 2004 02:21 PM

Thanks for replying. I figured that it would have to be pretty thick to support the weight. I had been thinking 1/2" but I think that 3/4" would be better. I would think that the thicker plexi would be harder to crack too I had never thought about putting mirrors in it though, and it does sound really cool. I think I"m gunna try it. How would you suggest to cut the circles? I am not extremely worried about the edge on them because my subs will cover the edge, but they do need to be circular. I have read that a lot of people suggest a rotozip but they're around 50 bucks and I don't know if it is worth that kind of money. But if that is the only way I can do a good job then that is the way that I will do it. I was also planning on doing a little practice that way I don't mess it up. Anyway thanks again.

maxw 18th October 2004 07:08 PM

I looked into this at one point and it would work but acrylic that is 19mm or thicker is VERY expensive but I guess it depends on how big your sub is and how big and thick the cabinet needs to be.

If you use Lexan it wont crack, lexan is far less brittle than normal acrylic. Use T-nuts and proper acrylic glue. Dont use a jigsaw unless you want to file or sand the edges when you are done. I would ask a shop to cut it properly. The problem with jigsaws is that after cutting about 3cm the blade gets hot and melts through the acrylic instead of cutting it and it give a really ugly edge and sticks back to gether when it cools again.

Good luck!:)

SupraGuy 18th October 2004 10:05 PM

Here's how I'd do it:

To cut the circular hole, I'd use a plunge router with a circle jig. You might be able to make do with a dremmel tool or the like, but y ou'd have to be careful to keep it CUTTING instead of melting the plexi.

Once you have the hole cut, you can use a torch (lightly) around the hole to remove the tool marks. This will make the frosted surface clear (Provided that you don't overheat it and make it bubble) Remember, even though the woofer lip will cover the tool marks, you will still be able to see them because of the clear nature of the material.

You'll have to drill holes for the screws to hold in the woofer. You don't want to take the chance that the screws will crack the material. (It will be expensive stuff!) Use T nuts on the back side to secure the screws. You'll use machine thread screws. You can torch the screw holes as well to make them look nicer too.

Fitting the T nuts is a bit of a problem. They need to bite into the plexi in order to work correctly, but that's not really easy to do without damaging the material. I'd probably sit the T nut on the back of the plastic and heat it with the torch until the cleats melt their way into the plastic, then leave it to cool. This would be tricky not to scorch the plastic, but it could be done.

For the mirrored box, make sure that the mirror material is well bonded to the indide of the box. Contact cement should do an adequate job.

19mm would be the thinnest material that I'd consider for this job. 1" (25mm) would be better, but very expensive. This also depends on what kind of power that you're planning on putting through it.

A general note on plexiglass: It's very strong, and shatterproof. This is because the material flexes under force. This is a good thing when the material gets hit with a hammer, and you don't want it to break, but it's not so good when you want to make a woofer enclosure out of it. Byt making the material thicker, we are decreasing the amount that the material can flex (At least without applying more force.) making its properties more desirable for an enclosure. 1/4" (6.5mm) material is more than strong enough to support a woofer, but with the amount that the material would flex when the woofer is powered up, would make a very poor enclosure. This is why a large fish tank can be made using relatively thin material, and be very strong, even thoguh such an enclosure would not be suitable for a woofer cabinet.


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