Enclosure Calculation help for two 15's

[Joelcanthearyou]

I am putting two 15 inch subwoofers in my 95 Honda Accord.
The system will be powered by about 3500 watts of continuous power up to 5000 watts.
I need help calculating box size.
I listen to pop music from the 80’s, modern eclectic music like stuff on KCRW.com 24 eclectic channel. Some rap, and some beasty boys, a little classic rock, Pink Floyd. Just about anything good, sorry no country.
I have had three 10s, two 12s, and now I want to blast my windows out with clean tight heart stopping bass!
Tried online calculators but no help on sealed box size.
Here are speaker specifications for a single subwoofer:
2X4 Ohms
2.5” KVS voice coil
200 oz magnet
Fs (Hz) 30
Qms 5.0
Qes .90
Qts .75
SPL (dB) 89
Vas (ft^3) 6.02
I will probably put some pillow batting in the box and cover the inside and outside with heavy coats of silicon paint. This has worked great in the past.
Just need a little help on box size.
Any suggestions would be great.
Thanks for the help, look forward to blasting out my hears and eyeballs, what did I say...

[Cal Weldon]

Maybe you'll get a response over here in Car Audio.

[jol50]

You can download WinISD and its pretty easy to punch in the numbers to model any sub. You don't need all the specs it asks for, just mostly what you listed. But, odds are those are not good subs for a small box with a high qts like that. Ported box subs are around .4-.5 roughly, sealed lower like .3, and the .6 and higher are best for infinite baffle or IB though lower ones can work with EQ. IB is no box or the whole trunk. Those numbers are not set in stone, but it tends to work that way. You can put them in the largest box you can make but in that car it will not be large enough to get good bottom. You will need at least Vas to get some bottom and that is 6cf each. Another sub would work better for you to use a small box, small relative to a big 15". Maybe not what you wanted to hear, but the way it works. In a small box those subs will play high bass like crazy, say 100Hz or something, but not much 30Hz. They will be hard to tune with way more output at 100 than even 40.

I mean, you will be way better off getting something that works right before you invest the time/effort to install them. If you are stuck with them the best you could do is make a giant box and run one. They would work pretty good IB, if you mounted them in a rear deck or into the rear seat with the whole trunk as a box. If you want pure loud, better to go with a box though it handles more power and with the right subs will shake your car no problem. If you can fit ported they put out the most. You may need a larger amp for smaller box subs they tend to be less efficient though they do put out more at low frequencies in a small box than another sub.

I have four 12s into my seat and figure pair of 15s there will give near the same output. Output is way more than I need right now, fun at times, but the setup is quite heavy. I'm looking for subs with near the same specs except 20Hz Fs which means they will have good output down to that.

[tsmith1315]

IMO, the entire trunk would be just about right for those woofers, but 3.5kW would be excessive.

I would consider around 3.5 cubic feet per woofer a minimum size without specific EQ to compensate. At 7 cubic ft for 2 woofers, chances are you'd have to build that in the trunk.

Even with compensation, I wouldn't go smaller than what would provide a Qtc around 1.6 or so unassisted. The power/excursion required to make up the lost octaves gets to be a real problem unless Fs is extremely low or you're not concerned with low bass.

[Flatlander]

Good call, tsmith. The total Q is way too high for an enclosure smaller than the sum of a Honda interior, "in my book."

Those drivers are better suited as open back drivers outside, than "sub-woof in an enclosed space" use.

You would have better sound if you chose a stronger set of twelve inch drivers in a sealed enclosure with that power amp.

[Joelcanthearyou]

Well maybe I could go with three 10's and one 15?
I also have two three 12's. But I want something that can play just about anything loud, hard, tight, and low...
If I need to put in different size subs with different size boxes I will do it. Thank you for the help.
I will upload my speakers and let you decide what I should put in my ride.

Thanks and I look forward to blasting down the highway when we are finished. Bye for now. Joel.