How do you determine what would be a good box size for a sub?

[Umbra]

I've got a pair of http://www.memphiscaraudio.com/products/subwoofers/power-reference-subwoofers/15prx12d4/ (Power Reference 12s [the previous version]). I've also got a minivan and originally I was going to put a single ported 8" in the front between the seats so I can carry people and cargo without having to take stuff out, but I've found it's rare I need seven seats or the entire space for stuff. So, new plan is to make a ported box for these two, strap it down to the metal bars that the seats usually snap into, then if I need to I can just drag the thing out.

I've got a lot of ways I can set this up. I can put it all the way back and fire it at the hatch, fire it up, fire it down, or fire to either side sliding door. I'm thinking down or up. I have an amp rack that I built to fit under the back seat that will limit the size in the back.

Anyway, Memphis doesn't list a recommended size. They do sell boxes though (like this one) that I'm guessing are meant to be paired with their subs. That one is 3.4 cubes. I can build the box. Would 4 cubes be good, tuned to 33Hz (a bit higher if I'm firing downwards)?

Is there a mathematical way to do this? I plugged it into this calculator:

Speaker Box Calculations

and it spit out 10 cubes for enclosure volume. Maybe I did something wrong.

Any help would be appreciated, thanks.

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[los33 10+ year member]

I've got a pair of 15PRX12D4 - Memphis Car Audio (Power Reference 12s [the previous version]). I've also got a minivan and originally I was going to put a single ported 8" in the front between the seats so I can carry people and cargo without having to take stuff out, but I've found it's rare I need seven seats or the entire space for stuff. So, new plan is to make a ported box for these two, strap it down to the metal bars that the seats usually snap into, then if I need to I can just drag the thing out.
I've got a lot of ways I can set this up. I can put it all the way back and fire it at the hatch, fire it up, fire it down, or fire to either side sliding door. I'm thinking down or up. I have an amp rack that I built to fit under the back seat that will limit the size in the back.

Anyway, Memphis doesn't list a recommended size. They do sell boxes though (like this one) that I'm guessing are meant to be paired with their subs. That one is 3.4 cubes. I can build the box. Would 4 cubes be good, tuned to 33Hz (a bit higher if I'm firing downwards)?

Is there a mathematical way to do this? I plugged it into this calculator:

Speaker Box Calculations

and it spit out 10 cubes for enclosure volume. Maybe I did something wrong.

Any help would be appreciated, thanks.

Those are recommended sizes so with multiple subs you would add each, but to get detailed sizes you would need apps like bass box pro, torres box calculator, winisd.

Others can produce a better answer towards this as im not to big on calculating enclosure sizes.

 

[hispls 5,000+ posts]

At a glance the subs' specs suggest they want large-ish sealed box to perform nicely.

 

[Umbra]

At a glance the subs' specs suggest they want large-ish sealed box to perform nicely.

I believe you.

In general though. Is there a formula or some way people or even the engineers designing the sub come up with recommendations or do they just stick them in a bunch of different sized boxes until they hit a sweet spot?

 

[big scott]

it goes by the sub specs.

some sub are good for sealed or ported.. ect..

 

[lew-e 10+ year member]

I think he's asking what specs determine what and in what combination.

Sent from my HTC One_M8 using Tapatalk

 

[hispls 5,000+ posts]

I believe you.
In general though. Is there a formula or some way people or even the engineers designing the sub come up with recommendations or do they just stick them in a bunch of different sized boxes until they hit a sweet spot?

There's plenty of graphically oriented software that predicts response in box based on Fs, Qts, and Vas. Google searching can dig up the math if you like to do it long-hand or build your own spreadsheet or graphing app.

In general high Q (around .7) and low Fs is a woofer that works well in "infinite baffle" which is essentially a huge sealed box.

 

[Umbra]

I've found a suitable formula, among others: Useful Formulas