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MTX ThunderForm Unloaded Enclosure

Holds a single 12" sub — fits 2005-2009 Ford Mustang (Black)

Item #: 236MUSB12U

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1 Review | 1 question - 1 answer

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Crinkled french fries, discarded receipts, old gum wrappers — you probably have everything in the hidden corners of your vehicle except great bass. ThunderForm enclosures fill the nooks and crannies of your vehicle with low tones that stand out, but their factory look blends right in.

MTX engineers evaluate the "sonic signatures" of top-selling vehicles so they can design ThunderForms as custom acoustic matches. Each ThunderForm fits and blends inconspicuously into your vehicle, so you get great bass without losing any space. They're made of high-density polyethylene resin to curb resonances — they deliver bass that's tight, hard-hitting, and way down low. The airtight enclosure provides the correct internal volume to yield optimum bass response.

This black enclosure comes without a speaker — you install your favorite 12" subwoofer. For best results, MTX strongly recommends using a speaker designed for an enclosure with a volume of 1.2 cubic feet. The enclosure mounts in the trunk on the passenger side of select 2005-2009 Ford Mustangs.

Please check with us before purchasing by using the vehicle selector on our site, or calling an Advisor at 1-888-955-6000 to verify fit information.

Product Highlights:

  • custom-fit black subwoofer enclosure for 12" sub
  • mounts in the trunk on the passenger side
  • fiberglass construction
  • volume: 1.2 cubic feet (sealed)
  • dimensions: 15-1/8"H x 27"W x 14"D
  • mounting depth: 8-3/4"
  • warranty: 5 years (free repair or replacement for 2 years, prorated replacement for years 3 through 5)
  • Our 60-day money-back guarantee

MTX ThunderForm Unloaded Enclosure Reviews

Average Customer Review:

1 Review

Great fit - big sound and still have most of trunk!

Written by: dnut from Ann Arbor, MI on June 14, 2014

Crutchfield Customer Review (What's this?)

This unit fits great in my 2014 Mustang GT. Love that I can get big bass and still get to the spare tire if I need to. I put in a Rockford Fosgate 12" P3 sub and it puts out some big bass. Note that the instructions say to screw the unit down through the floor of the trunk and then install the sub. I did not do this - I used some of the industrial velcro instead - so far, no movement. I may fasten it to the bolt that sits above it sometime later, not sure.

Pros: - As advertised, gives you a sub enclosure that fits your Stang without sacrificing the whole trunk. I can still lift up the spare tire cover and not brush against the sub - after I cut the carpet.

Cons: - It seemed kind of weird that the enclosure would not fit the MTX sub - at least the 500W one which was 1/8" too deep according to the specs. The Rockford Fosgate P3 fits just fine - but I had to screw the grille in separately as it would not fit into the inset. In the end, it all works and looks good though.

Hands-on research

What's in the box?

Download owner's manual

  • Custom-fit unloaded 12" subwoofer enclosure
  • Grille
  • Hardware
  • Installation instructions

Product Research



Vehicle Compatibility: This Bass Slammer custom-fit enclosure is designed specifically to fit the 2005-2009 Ford Mustang (coupe or convertible). Not compatible with Shaker 1000 Sound System.

Note: Please refer to the Crutchfield Vehicle Selector to confirm fit for your vehicle.

Mounting Location: The enclosure mounts in the trunk on the passenger side.

Enclosure Type: The sealed enclosure features fiberglass construction and fits one 12" woofer.

Tools For Installation:

  • Powered screwdriver
  • #2 Phillips head bit
  • 6" Bit holder extension
  • Wire cutters


5 Year Warranty Terms: This product carries a 5-Year Prorated Warranty with the following terms:

  • Years 1-2: Products found to be defective in materials or workmanship during the first two years will be, at Mitek's option, repaired or replaced by Mitek at no charge. The warranty period does not renew, but continues on from the original date of purchase.
  • Years 3-5: The purchase price of an item which becomes defective after the first two years and prior to the end of the warranty period will be prorated and credited toward the purchase of a new MTX product. The amount of proration is determined by dividing the original purchase price by the number of months in the warranty period (60), then multiplying the result by the number of months remaining in the warranty period.

Our Product Research Team

At Crutchfield, you'll get detailed, accurate information that's hard to find elsewhere. That's because we have our own in-house Product Research team. They verify what’s in the box, check the owner's manual, and record dimensions, features and specs. We stay on top of new products and technologies to help people make informed choices.

Customer Q&A

1 question already asked

We have not received any answers from other customers on your question. I would recommend reaching out to an Advisor by phone (1-800-324-9695) or online chat. They should be able to help answer your question. [ Jeff  Jul 20, 2015 ]  Staff