Subwoofer science

Jaepheth · Post by **Jaepheth** » 2005-10-01 05:30pm

I guess this goes under science...

anyway, I was thinking about building a new box for my existing subwoofer or possibly for a larger one...

What I was wondering was, besides sealed/vented, what other aspects affect sound? Specifically, how does a box's mass and size affect the sound the subwoofer creates? Does material change sound much?

Post by **Darth Wong** » 2005-10-01 05:39pm

The box should either be so vast that its resonant frequency is very very low (ie- deeply subsonic) or it should be extremely rigid with good damping, otherwise you'll get a monster resonance out of the enclosure as its walls vibrate.

It is common practice to use a "tuned port" to extend the deep bass performance of the driver, but this has to be done carefully. What you want to do is make sure that the resonant frequency of this tuned port is below the point where the driver's frequency response starts to drop off naturally, so it boosts the SPL in that range and effectively extends the driver's bass response. Otherwise, if the resonant frequency is too high, you'll create a bulge in the mid-bass response that muddies the sound (note that rap afictionadoes and other half-sentients may actually like this kind of boomy, muddy mid-bass, and many systems are designed with that in mind).

Jaepheth · Post by **Jaepheth** » 2005-10-01 05:55pm

what I was planning:

Basically a subwoofer that doubles as a foot rest

I was asking how mass would affect it because I was planning on making it out of steel and maybe lining the inside with ply wood, and then covering it with foam/cloth to make it comfortable.

Is it a feasible design?

aerius · Post by **aerius** » 2005-10-01 07:12pm

Jaepheth wrote:I was asking how mass would affect it because I was planning on making it out of steel and maybe lining the inside with ply wood, and then covering it with foam/cloth to make it comfortable.

Is it a feasible design?

Bad idea. Metals go ring-a-ling unless it's pretty thick and thoroughly damped. Think bells. You can get around it by using the smallest possible enclosure and coating the inside with a thick layer of rubbery tar-like damping material. Problem then is sound quality will most likely be compromised and/or the sub will be exceedingly hard to power.

Plywood is not a good choice since its properties are inconsistent and more importantly, it's damn near impossible to get a good solid joint. This is why most speaker manufacturers now use MDF or HDF, consistent quality and they can take a router to the edges and make solid interlocking joints. Afterwards a nice vaneer or paintjob is applied.

As for making a sub and calculating the dimensions of the box, go here and download the subwoofer calculator program. Read the instructions, pull up the specs for the speaker you're using, punch them in, and let it do the work.

Post by **Beowulf** » 2005-10-02 12:15am

Jaepheth wrote:what I was planning:

http://img399.imageshack.us/img399/8585/design4sz.jpg

Basically a subwoofer that doubles as a foot rest

I was asking how mass would affect it because I was planning on making it out of steel and maybe lining the inside with ply wood, and then covering it with foam/cloth to make it comfortable.

Is it a feasible design?

A subwoofer that doubles as a foot rest is doable. Construction materials is wrong, as aerius has stated. You'll probably be wanting to use 3/4 to 1 inch think MDF for the box. Finish the sides, and put a cushion on top. Downside to this is that you have a reduced amount of room gain versus sticking the thing into the corner.

Another thing, it'll look kinda odd as a foot rest with a wire going to it, or pair of wires, if you're doing a powered sub. If you do do a powered sub, and decide to use a plate amp for it, it would be adviseable to have the section of the box holding the amp mostly sealed off. This will reduce air leakage from around the edge of the amp, which sounds fairly bad.