Revision as of 17:14, 8 February 2008

This page briefly describes a simple methodology for selecting a subwoofer and building a small enclosure suitable to placement in the trunk of a Mazda Miata. While the reasons for using a trunk-mounted sub vary from person-to-person and are not universally accepted as a "good solution", I will leave that debate to message boards and present a simplified cookbook version here.

I've taken into account the acoustic environment present in the miata (specifically the trunk) and its interaction with low frequency reproduction. In short: this design will have smooth bass response and not rattle your trunk to pieces. I stress that last point.

Miata Trunk Sub

Preface: I've only done the math and selection for 10" woofers. I'm going to assume if you want something bigger and badder that you dont care about small trunk subs. I think 10 inches is about the sweet spot for size and output when given the constraints of the Miata's trunk.

Woofer Choices (to get you started)

Here are a few subs you can use in various price ranges.

• Tang Band WT-1427B 10" Neo Subwoofer ($59 on special at partsexpress, normally $87)
  You will get decent sound out of this for the money but it probably wont be eardrum crushing loud.
• Dayton RSS265HO-4 10" Reference HO Subwoofer 4 Ohm ($126)
  This will be pretty loud.
• Want it even louder? Build two of each!

Easy box size for the above woofers

Due to the flexibility of the design, all dimensions are +/- an inch or so but if you decrease some, increase others ok? OK. All use 3/4" MDF--the standard.

• Smallest Length and Width: 11" x 11" x 8-1/4" outside dimensions
• Thinnest for the Tang Band): 14" x 14" x 5-3/8" outside dimensions
• Thinnest for the Dayton HO): 12" x 12" x 7" outside dimensions
• Whatever you want: Just make sure the total volume is between 600-650 cubic inches. You can take the outside dimensions and subtract 1.5 from each (two .75" thick walls) and multiply them all together.

Example 11x11x8 box:

11 - 1.5 = 9.5
8.25 - 1.5 = 6.75
9.5 x 9.5 x 6.75 = 609.2in^3

Tuning your trunk sub box

Pick up a bag of pillow filling from either your mom or the local Michael's, Yardage store, or wherever you can find it. Before mounting the woofer, stuff the pillow stuffing in moderately loosely and make sure it doesn't rest on the back of the woofer cone. You can glue or staple it in if you like. This will smooth out the response and allow you to fine tune how it sounds:

• If it's rattly but doesn't have punch, remove the stuffing to decrease the apparent volume of the box.
• If it's too punchy/chesty and makes your hair twitch but doesn't have any deep sound, it's too small. Add a bit more stuffing to increase the apparent volume.

What else should I be aware of??

• It may be easier to find non-car subs with these numbers.
• As far as the CAR is concerned, I did nothing to the tunnels or parcel shelf. Just threw a box and big amp in the trunk. Works like a dream.

Warning about using other subs!

Not *every* sub will work for this. Some will be close and some will not. Some good starting points for Thiele-Small Parameters are: Fs: between 20-28 Hz Qts: between .25-.35 Xmax: bigger is better if you want it loud.