Please, Help Find The Angles...

[Derek Arita]

:confused:I'm trying to build this subwoofer enclosure from a website drawing, but I can't figure out the angles on the box. Here's the site,

http://mobile.jlaudio.com/products_enclosures.php?menu=6&prod_id=308

At the bottom of the page, you'll see the box and it's dimensions. What are the angles and what's the length of the angled, unmarked piece? This is all too much for my little brain.
Also, these boxes require material that flexes as little as possible. Most boxes are made of MDF, but I've read that birch ply is better because it flexes less.....is this correct?
Thanks for the use of your superior brains.

[Dan Friedrichs]

Hi Derek,

The length of the unmarked piece is 346.3mm (or 13.63"). The top (obtuse) angle is 109.2degrees, and the lower (acute) angle is 70.8degrees.

For reference, this can easily be found using Google Sketchup - just draw the 3 known lines, then connect them with the fourth line. The "Tape measure" tool lets you measure that last line, and the "Protractor" tool lets you measure the angles.

A good-quality plywood will be stiffer and hold screws much better than MDF. I would avoid buying it from Lowes/HD, though, as their plywood is often twisty or full of voids (holes) on the inside. Plywood would be lighter than MDF, and likely more durable.

[Mark Oberreuter]

The angles are 109.27* and 70.73*
The unmarked piece is 13.64" long on the longest side.

Here's a link to a great calculator:
http://www.csgnetwork.com/righttricalc.html

[roman fedyk]

MDF is the material of choice for speakers as it is dead compared to plywood or any kind of wood for that matter. For speakers you want the most inert material you can get. Plywood would resonate and not give you the sound you need. For a car it may be fine, but for audiophile speakers MDF is the way to go.....In fact High Density MDF is the best. It weighs a lot but that is good, pick up any high end speaker and note how heavy it is.

[Eric DeSilva]

MDF is the material of choice for speakers as it is dead compared to plywood or any kind of wood for that matter. For speakers you want the most inert material you can get. Plywood would resonate and not give you the sound you need. For a car it may be fine, but for audiophile speakers MDF is the way to go.....

I've heard Wilson Audio uses Corian for their Watt/Puppy speakers. Always wanted to try using that stuff for speakers...

[Derek Arita]

MDF is the material of choice for speakers as it is dead compared to plywood or any kind of wood for that matter. For speakers you want the most inert material you can get. Plywood would resonate and not give you the sound you need. For a car it may be fine, but for audiophile speakers MDF is the way to go.....In fact High Density MDF is the best. It weighs a lot but that is good, pick up any high end speaker and note how heavy it is.

I know one must take all you read on the web with a grain of salt. That said, I've read on several sites that the key to a good sub enclosure is rigidity...flex is the enemy...that's why many prefer a good quality birch ply, with the added benefit of less weight in the vehicle.
Also, thanks for the calcs. I'll check out the websites.

[roman fedyk]

I've heard Wilson Audio uses Corian for their Watt/Puppy speakers. Always wanted to try using that stuff for speakers...

Yes in fact several years ago there were speakers made of cement. Talk about stiff...

[Peter Aeschliman]

Use MDF for sure. If you're worried about flexing, add some bracing to the interior of the box. If you want to get anal about it, you should add the volume of that bracing to the internal volume of the enclosure.

The problem with building this enclosure only using the outer dimensions is:

1) You don't know what the thickness of their material is. If you want to be precise about the internal volume of the box, and all you have is outer dimensions, you need to figure out the thickness of the material.

2) Many sealed enclosures with two drivers have separate sealed chambers for each sub. You don't know whether that's the case with this design.

Here's what I would recommend, having built a lot of car audio enclosures in the past. Design it however you want to. The subs you have should tell you how much internal volume you need, net of the displacement of the sub itself. Build it to fit your own car. The advantage is that you don't have to deal with bizarre angles (109.27 degrees??? screw that!!).

Just my $.02.

[Derek Arita]

My other consideration is a possible weight savings using plywood over MDF. How much lighter is birch ply over MDF?