Volume versus effective volume?

[ramchip007]

Well I've been reading through the forms was inspired to start on a sono tube project. So I got the sonosub calculator and started playing some numbers and decided to get a 24 inch diameter tube 12 feet long and cut it in half for 6 foot per sub I guess. I thought The effective volume ment the total volume until I got the tube home cut it in half set it in place and just kept shaking my head saying to myself How in the world could this tube only be 7 1/2 cubic feet. So then I'd punched the numbers in a volume calculator and got over 18 ft.³ so now I'm realizing there's two different figures, volume and effective volume . Could somebody shed some light on this confusing situation. Does this sound like way too much volume for a 15? Here are some speaker parameters
3.95 ohm
Qts: 0.578
Qes: 0.673
Qms: 4.095
Fs: 24.5hz
mms: 130g
cms: .300mm/N
BL: 11
Vas: 284L
xmas 27 mm

[ramchip007]

Well I guess I made an error inputting information I think I put the width of the tube. When it wanted the width of the driver or something crazy. I'm a little worried that with 18 ft.³ I will reach over excursion may be I will try it sealed .

[Mike P.]

If your tube is 72 inches tall then you subtract .75 inch from each end for the end caps. Now this makes the internal length of the tube 70.5 inches. The volume of a tube 70.5 by 24 inches is 18.5 cubic feet. If the sub is going to be sealed then you subtract the volume of the driver from 18.5 feet to get the effective volume. If the sub is going to be ported then you subtract the volume of the driver plus the volume of the port to give you the effective volume. Effective volume is also known as net volume. That is a big sub you're planning on. What subwoofer are you going to use?

[ramchip007]

I have two Exodus XJ15 15 from DIY cable. Look like I might have to cut the tubes down to around 10 ft.³. But I'm not sure , maybe one of the gurus on the site will have an idea.

[Mike P.]

For recommended sub size read post 42 of this thread.
http://forum.carstereos.org/12-and-15-t66831p5.html