Newbie question, how to figure SQ. feet from custom sizes?
 

I was never good at math so forgive me about the simple question. When ever I look at crazy fiberglass designs I wonder how they get the correct SQ. feet from the enclosure? Do they guess at a estimate size or do you measure the enclosure with water?

Thanks
Rob

I still calculate enclosure volumes when working with fiberglass to within 10%. Sometimes the subs can be in a flat box with a fiberglass trim or cover like in the Mercedes posted here a while back that I built.

For SQ competitions cars its trial and error. When doing exotic fiberglass enclosures, sometimes the angles or any other factors change the sound. In my high profile competition cars, Ive built several enclosures over and over for each vehicle. Then we do RTA and LEAP analysis and measurements inside the vehicle. We also run test tones to find resonant frequencies of the vehicle for SPL competition vehicles. Analyze the data from different enclosures and pick the best or keep building and experimenting until we get as close to perfection as time will allow.

Thanks for the reply,

I never knew how much time it takes to complete a enclosure. The reason why I asked is I was going to make a simple box that fits in my spare tire area but didn't know how to measure the air space.

Thanks
Rob

Depending on the sub specs and size you can take rough measurements. I think the full spare tire well in a 5th gen Civic is a little over 3 cu ft.

Or you can get packing peanuts and fill up the spare tire well. Get a mailing box that is exactly 1 cu. ft. and measure how many boxes of peanuts you scoop out of the well. Thats a very simple and easy way to do it.

Do you suggest this method for boxes as well? I was thinking about building a sealed box just behind the rear seats, with a angle wall. The speakers I would use are either 2 JL 10W3 or IDQ 10's. It's nothing special but I never build a box to fit the car, it's always vise versa.

Thanks
Rob

Square footage of boxes should be simple to calculate. Even square ones with an angle. You calculate the square box seperately LxWxH, then the angle seperately. Add them together and you have the cubic volume of the box. Dont forget to calculate for wood thickness and or any internal bracing.

and the structure of the speaker itself.

Woofer displacement specs come with the speaker's documentation as well.