How would I go about building a dual 12 inch Sub enclosure with deep heavy hitting Bass ?
August 25, 2011 9:29 PM   Subscribe

How would I go about building a dual 12 inch Sub enclosure with deep heavy hitting Bass ?

I am planning on setting a friend up with a car audio system ( 460 Watt Dual amp / new radio / two Dual 12 inch 4 Ohm 550 watt subs and a few replacement mid speakers for the front of the car ) I have wired up sound systems for fun (un tuned pretty much just subs on plywood setups ) but I really wanted this to be as hard hitting/heavy as I can make it with what I have ... I am good with power tools so I shouldn't have any problem with building an enclosure to fit in the trunk of his car, I just can't grok how tuning works *brain melts* what would be a good size/port size for my setup ? his car is a 2001 ford taurus and the enclosure will be placed right behind the rear seats in the trunk if that helps at all .

Thanks !
posted by 70klicks to Travel & Transportation (7 answers total) 2 users marked this as a favorite
Well, you'll need the spec sheet with all the Theile/Small parameters. There are several enclosure design programs out there that can calculate box volume, optimal sizing, etc., for you.

Usually there's a small range of volume that is acceptable for a speaker. You'll want to err on the bigger side for deeper bass. I tended to shy away from ported systems, since they accentuate one frequency a lot of the time. YMMV, of course.

Our shop built a 3 time state champion IASCA SQC vehicle with all sealed enclosures. I'm very confident that we wouldn't have done as well with ported because of the frequency bump.

As far as building tips, seal all seams with caulk. If you can create a trunk to cabin port in the back dash, do so. You *might* need polyfill to even out the frequency response (you'll need an RTA to test this), but don't just cram it full without reason.
posted by chrisfromthelc at 9:36 PM on August 25, 2011

Do you know of any programs that are browser based or work on mac OSX? winisd was recommended but it won't work for me :/ also it shouldn't be a problem to cut a port between the trunk and cabin , about how big should it be ?
posted by 70klicks at 9:47 PM on August 25, 2011

We used to remove the rear deck speakers and use that as ports. In theory, there would be nothing in the way of the sub to the passenger cabin, but obviously that's not feasible. It's just one of those things you'll have to judge for yourself.

I've only used WinISD, but you should be able to run it using a VirtualBox instance on OSX.
posted by chrisfromthelc at 9:57 PM on August 25, 2011

Thank you for all your help !
I don't actually have a copy of windows (virtual box needs it to create an instance ) would it be possible for you to run my speakers through winisd and give me an idea of the optimum volume/sizing ect ?
posted by 70klicks at 10:25 PM on August 25, 2011

Sure. Just email my username at with your parameters.
posted by chrisfromthelc at 11:17 PM on August 25, 2011

I'm not a car audio person, but have been involved in sub design & audio / acoustic engineering. I'd argue a (little!) bit with crisfromthelc about ported vs sealed enclosures, since which is best does depend a lot on the particular speaker parameters, box dimensions & shape, port size & location, etc. If those don't fall right, ported enclosures can be a peaky boomy mess; it it does work out, then you can gain a few dB of low-end response with a port.

I'd guess, however, that ported box in cars are likely different - since you've also got fixed & largely sealed boot & cabin volumes, they'd behave more like a bandpass box design? In which case, yeah, ported boxes could be peaky as hell, so sealed would be much simpler.

2nd'ing WinISD, but the calculations from given Thiele-Small parameters are actually pretty simple for sealed boxes, so online calculators (e.g. this) are as good as anything for calculating volume.

Personally I'm not as enamoured of polyfill etc as the manufacturers are, but not as dismissive as others can be. I'd use it, but not to account for a smaller-than-optimal box size. Don't overfill, but don't use too little - just a single layer, cut into a single piece shaped to line the enclosure, and stuffed loosely in place (i.e. not glued or stapled) so that it won't contact the cone. This will also allow you some leeway to tune the box if necessary.

Box shape can be a bit of a dark art, but if you remember the golden ratio (0.62:1:1.62), use polyfill to minimise standing waves inside the box, and follow the usual box-building tips (e.g. this FAQ) you can't go far wrong. Remember to account for the volume taken by the speaker itself, as well as any damping material you may use! Don't place the driver in the centre of a panel; offset it along the long dimension to minimise the chance of end<->end standing waves. And use proper non-hardening caulk to seal the box, not a bead of glue or silicone.

Oh, and for 2 drivers, add the Vas values together for your calculations.
posted by Pinback at 11:17 PM on August 25, 2011

@Pinback: You're exactly right about the the difference in open air versus a vehicle in regards to ported versus sealed. Unless you're going to great lengths to treat the entire vehicle, sealed has ALWAYS been easiest to make sound right.

There's a WinISD online version here:

I haven't really tried it, so, YMMV.
posted by chrisfromthelc at 11:24 PM on August 25, 2011

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