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MTX Amplified ThunderForms

Custom-fit powered subwoofer for 2007-up Chevy Silverado and GMC Sierra Extended Cab

Item #: 23615XATTN

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2 Reviews | 1 question - 2 answers

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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 amplified ThunderForm fits under the rear seat of your 2007-up Chevy Silverado or GMC Sierra Extended Cab truck. It houses a Terminator 10" sub and a cool-running 200-watt amp that's custom designed to provide optimal power without straining your vehicle's electrical system. MTX's Electronic Bass Control (EBC) lets you adjust the bass level from the driver's seat. A variety of inputs allow easy integration into your vehicle's sound system, and the included 20' power harness simplifies supplying power to the amp.

Product Highlights:

  • custom-fit powered subwoofer with Terminator 10" sub
  • enclosure fits under the rear seat
  • built-in 200-watt RMS Class-D amplifier
  • high-density polyethylene enclosure
  • variable low-pass filter (50-150 Hz at 12 dB per octave)
  • preamp- and speaker-level inputs
  • 20' power harness included
  • dimensions: 36-1/5"L x 9"H x 16-2/5"D
  • warranty: 5 years (free repair or replacement for 2 years, prorated replacement for years 3 through 5)
  • Our 60-day money-back guarantee

Vehicle-specific enclosures with subs? Say what?

Instead of the usual sub in a box, the manufacturer creates a molded enclosure that fits perfectly into a convenient spot in your specific vehicle, housing a high-quality sub. Some enclosures even include a built-in amp, for the ultimate in stealth bass. The advantages? You don't lose much space (if any), your sub is perfectly matched to its enclosure, and your enclosure has a factory look that won't tell potential thieves you have an awesome sound system. Doesn't get better than that.

MTX Amplified ThunderForms Reviews

Average Customer Review:

2 Reviews

Nice sub.

Written by: Todd A from IL on September 7, 2015

Crutchfield Customer Review (What's this?)

3 might seem like a low rating but its average. Don't get me wrong, I love this sub but for the price and more for a LOC so I don't have to splice wires, it is kinda expensive. Not only that but MTX doesn't supply instructions on connecting this. They claim that they don't know what vehicle its going into so they can't supply instructions. I reminded them that this is a VEHICLE SPECIFIC enclosure so you know EXACTLY what vehicle its going in to. Anyway, I got tired of messing with them and ordered a PAC line out converter that plugs into the factory harness. Now about the SQ. That's a mixed bag. On some songs this thing hits good and sounds awesome. On other songs the bass is either muddhbor over lowering. It is absolutely necessary to connect and use the remote gain control or EBC as MTX calls it. I never had that issue with other amps. Gain was a set it and forget it deal. Probably has something to do with the factory head unit and its proprietary EQ curve. That being said, if you just want to compliment your factory system or just round out a mild aftermarket system, this is what you need.

Pros: Good SQ. Small size. Ease of mounting.

Cons: Non existent wiring instructions from MTX (Crutchfield to the rescue). Need to constantly adjust the gain as if it were a bass control.

MTX Amplified ThunderForms

Written by: Anonymous from Anchorage AK on July 13, 2012

Crutchfield Customer Review (What's this?)

Nice fits perfect in my 2007 GMC Siera Ext Cab and sounds pretty good.

Pros: Already amplified and has a remote gain that mounts in an easy to reach place for quick adjustment

Cons: The instructions are terrible There aren't any wiring instructions at all so if you've never installed amplifiers and subs before ya might need some help. The remote gain rheostat is a universal length and has the male end already installed so in my truck I had a ton of excess wiring that I had to roll up, zip tie and hide under the rear seat. Also, the speaker wire it's comes with only has RCA jacks on one end.

Hands-on research

What's in the box?

Download owner's manual

  • Custom-fit pre-loaded amplified enclosure
  • Wiring harness (20' power lead/3' ground lead and 3' remote turn-on lead)
  • Speaker-level to RCA harness
  • External bass control
  • Mounting hardware
  • Installation Instructions

Product Research



Vehicle Compatibility: This MTX ThunderForm custom-fit, amplified, pre-loaded enclosure is designed specifically to fit select 2007 and later Chevrolet and GMC Extended Cab Trucks.

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

Mounting Location: The ThunderForm amplified, loaded enclosure mounts under the rear passenger seat. (install hardware supplied). There is no loss of leg room.

Molded Enclosure: The molded, fiberglass enclosure resists flexing and dampens resonance.

10" Terminator Subwoofer: This enclosure comes loaded with a single 10" MTX Terminator woofer.

Class D Amplifier: The enclosure contains a built-in 200-watt Class D (digital) amplifier that allows RCA or speaker-level input. The amplifier is highly efficient and designed specifically for use with the subwoofer in the enclosure.

Built-in Low-pass Filter: The low-pass filter frequency can be varied from 50 to 150 Hz for a seamless transition between the output of this unit and that of the other speakers in the vehicle.

External Bass Control: The external bass control allows you to adjust the bass level from anywhere in the vehicle.

Auto Turn-On Feature: When the speaker level inputs are used, the system will automatically turn on and off with the radio.

Note: The auto turn-on feature does not operate when the preamp level inputs are used, unless the remote turn-on lead is connected.


5 Year Warranty Terms: Starting January 1st, 20013, 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

I agree, worst instructions ever. Anyway, if you don't have rca out on your stereo you will splice the rca cables that came with the woofer to the left and right speaker wires. So one of the rca cables, mine came with a purple one and a green one, will be spliced into the R positive and R negative speaker wire, and the other rca cable will be spliced into the L positive and L negative speaker wire. I used the Tap-It connectors and they are fantastic. You can tap into existing wires without actually cutting the wire. Watch a you-tube video on them and then buy. It makes life very easy. Then the L rca and R rca plug into the back of the sub and you are all set. You are going to need to run the power wire from the sub to the battery and remote line (the thin blue one) to behind the stereo. So while you are behind the stereo you can splice the rca cables into the speaker wires. 2 things to remember, you don't have to splice into the speaker wires behind the stereo, you could actually remove the speakers and tap into the speaker wire there, and make sure your power wire and your rca wires are spread out when you are running them from one end of the car to the other, otherwise the power line could cause interference with the signal from the rca line. I just finished installing mine and it's working great. Hopefully this was helpful. Good luck. [ JEFFREY  Aug 06, 2015 ]
If you purchased the product from Crutchfield, feel free to contact our Tech Support team. Our toll-free Tech Support number is printed on your invoice, and is also available under the "My Orders" tab in the "My Account" section of our website. If you did not purchase the unit from Crutchfield, then you may want to contact the manufacturer. You can also post your question in our forums: Or try our online support center: [ Jeff  Aug 03, 2015 ]  Staff

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