Any math folks here for volume calculation?

[SHRED]

I am trying to figure out how to reduce air volume in a subwoofer enclosure.

I want to add some wood to displace my current internal box volume from 0.87 cu ft to 0.65 cu ft.

Is my math correct here?

---

1728 cu in (1 cu ft) times 0.87 cu ft = 1503 cu in (current box volume in cu inches)

0.87 minus 0.22 = .65 (ideal box volume in cu ft)

1728 times 0.65 = 1123 (ideal volume in cu in)

1503 (current box volume) minus 1123 (ideal box volume) = 380 (volume in cubic inches to be displaced)

Since "two by fours" measure out at 1.5" x 3.5" I figured about 72 inches worth cut and glued inside the box should work.
1.5 times 3.5 times 72 equals 378.

[kath]

1. Looks good to me!

[SwissTony]

3. Your maths (with an s where I come from) are good

but your presentation makes following the calculations a tad difficult. How about...

i cubic foot (cu ft) = 1728 cubic inches (cu in)

Current volume = 0.87 cu ft

Desired volume = 0.65 cu ft

Desired reduction = 0.87 - 0.65 = 0.22 cu ft = 0.22 x 1728 cu in = 388.16 cu in

Required length of 2by4 = 388.16/(1.5 x 3.5) = 72.41 in

Your calculation is correct (I doubt if the difference would make any difference in practice) but hopefully my layout will reassure of that fact.

[SHRED]

4. Thanks...

I added for speaker displacement of the air space.

Here's how it made sense to me although your layout is easier to read.


1728 cu in x 0.87 cu ft = 1503 (current box volume in cubic inches)
1728 cu in x 0.65 cu ft = 1123 (ideal box volume in cubic inches)

1503 minus 1123 = 380 cu inches needed to be displaced.

380 cubic inches minus speaker displacement 84.6 cubic inches = 295.6 cubic inches of displacement needed.



I used 2 by 6 wood. It actually measures out at 1.5" by 5.5".

So 1.5" x 5.5" x 36" = 297 cu inches. I didn't have to be exact of course but I wanted to be close.