Subwoofer Design Questions

[Dr Trina]

Hello,

I am looking to gain information on subwoofer design to build a custom sealed box in the corner of my theater. I will be using the EP2500 for power and the DEQ2496 for EQ. The box will be approximately 4' X 4' X 7' tall. I will plan to fill the box with as much insullation as possible leaving just enough room for the drivers. Any light you can shed on my questions below would be much appreciated.

1) Would it be better to use 4 X 12" woofers or 2 X 18" woofers?

2) Any suggestions for woofer company and model that provides great quality with a great price?

3) I understand how to properly brace the box, but is there any special considerations for box design?

[bemis23]

The pair of 18's will have much more bass radiating area than the 12" woofers. 4x 15" cones would provide the more than either configuration you mentioned. I would think that in a 100 cu ft box (asssuming 1" MDF on all sides for construction) you could probably fit 4 full 18" woofers.

[Deward Hastings]

A pair of 12" will typically have a (combined) surface of around 960 cm^2, a single 18" typically around 1200 cm^2. You multiply those areas by driver x-max to get swept volume (which determines output), so it depends on which 12" and which 18" you are comparing. Equally or more important is driver harmonic distortion . . . again it depends on the driver, but a pair of 12" can be mounted push-pull to cancel even order distortion. 12" may give more flexibility in mounting/enclosure shape . . . they'll fit between wall studs, for example (but if you're cutting holes for wall mounting it's probably not that much trouble to add headers).

With proper design (and choice of drivers) either will work just fine . . .

[---k---]

Sounds like you have done some reading, but not necessarily the right sources. The size of your box is quite large, and likely not needed - You'll need a forklift to move it if it is properly built. Also, that much stuffing, is likely too much. You should model your options in Unibox (preferred) or WinISD. Unibox will show you the differences between two 18" or 4 12"s.

I would wait for Kevin at DIYcable.com to get the Maelstrom 18" or the Tempest 15" back in stock. Then build one or two of those using Kevin's application's notes. He give box size and stuffing recommendations. Or try a pair of PE RS 15"HF.

[fbov]

Good points all, about the relative radiated energy of 12's vs. 18's. Let me add that the location of radiation will matter greatly if you plan on a large listening area. In many cases, the only way to smooth bass response is with multiple subs. Two 4x4x3.5' boxes give you flexibility a single corner sub does not. You clearly have plenty of power and EQ, but neither is effective in combatting low frequency interference effects from a single source.

Tell us more about your application as it's possible someone's already done something similar.

For subs, I'll also recommend Kevin Haskins at DIYCable, if only for his application notes.

http://www.diycable.com/main/default.php?cPath=24_93_150&Cid=912d6f2ac9dfbdcf47cf7c02c9ae3aa2

HAve fun,
Frank

PS Mal-X is back on the site.

[ThomasW]

Travis,

What's the budget for this build?

[Dr Trina]

I was planning to spend around $600 for the woofers total. I have enough materials for the box and already have the electronic components. Do you have something in mind and will that price range work or do I need to go up a little?

[ThomasW]

The box size you have is too small for IB drivers and too big for standard drivers.

If you want to go modular you could start with a couple smaller boxes that eventually stack to the 7' height.

Understand there aren't low cost 15"s or 18"s for box subs like there are for IB use.

[Dr Trina]

So when I posted the dimensions I was trying to maximize space because i was hoping to reach the area necessary for an IB. That said, I can certainly build a smaller box. From what I was checking into, the Malestrom X 18" drivers are $400 each. That would only be $800 for the two of them.

First, are these a good choice in that price point?

Second, If I chose to use two of them, what amount of Cubic Ft would be the maximum I would want to build to house them in the same box both facing forward?

[Dr Trina]

Dose anyone know about quality / comparisons between the Maelstrom X 18" woofers and the non-IB drivers produced by FiCar audio?

[ThomasW]

The Mael-X has a more sophisticated motor structure (XBL^2) technology.

The Fi's have a standard motor design. They're custom made to your order in Las Vegas. If anything goes wrong with the driver or they're damaged, they can be reconed for a fraction the cost of buying a new driver.

I don't think reconing is an option with the Mael-X

[Dr Trina]

In gathering information from Kevin at DIY Cable, it sounds like the Maelstrom X 18" drivers work comfortably in up to 10 Cu Ft per driver. I will re-calcualte some dimensions and see if I can slim down to a 20 Cu Ft box to house 2 drivers. More to come...