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MTX Amplified ThunderForms

Custom-fit powered subwoofer for 1999-07 GMC/Chevrolet Extended Cab (Charcoal)

Item #: 236CXP2ACN

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4 Reviews | 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. But with custom ThunderForm enclosures, you can fill the nooks and crannies of your car, truck, or SUV with low tones that stand out.

MTX engineers evaluate the "sonic signatures" of top-selling vehicles so they can design ThunderForms as custom acoustic matches. With "rotational molding," MTX ensures that each ThunderForm fits and blends inconspicuously into your vehicle. They're made of high-density polyethylene resin to curb resonances and deliver bass that's tight, hard-hitting, and way down low.

This molded MTX ThunderForm comes loaded with two premium-quality 10" Terminator subwoofers modified especially for amplified Thunderforms, with a specially-designed amp that puts out 200 watts of power. It mounts under the rear seat on the driver side of 1999-up GM/Chevy Extended Cab models, and 1999-2002 GMC pickups (3-door and Extended Cab 4-door models). It's seamless and airtight, with the correct internal volume to yield optimum bass response from the subwoofers.

The ThunderForm bolts to the floor of the vehicle, with the woofers firing downwards. There is no loss of leg room and the factory jack kit is not disturbed. Hardware is included.

Product Highlights:

  • custom-fit powered subwoofer
  • enclosure fits under rear seats
  • two Terminator 10" subwoofers
  • built-in 200-watt RMS amplifier
  • high-density polyethylene enclosure
  • variable low-pass filter (50-150 Hz at 12 dB per octave)
  • preamp- and speaker-level inputs
  • 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:

4 Reviews

Big sound in a space saving way!

Written by: Gino Mtz. from Immokalee,Fl on February 14, 2015

Crutchfield Customer Review (What's this?)

Totally exceeded my expectations.Very satisfied & will say this I have friends that have had custom built boxes underneath the seat & I think this one sounds way better!



MTX Amplified ThunderForms

Written by: Anonymous from Benton la 71006 on November 5, 2013

2007 Chevrolet Silverado 1500 Classic
Crutchfield Customer Review (What's this?)

Fit like a glove. Awesome performance!



This thing rocks!

Written by: Jeff G from San Tan Valley, AZ on March 11, 2013

Crutchfield Customer Review (What's this?)

5 stars because I love the sound of my stereo now. The thunderform arrived about a week after I ordered it, no problem. I did have to get some 2.5" screws. The 2" screws that came with it do not reach the floor when the thunderform is in place. And it is very easy and obvious when it is seated correctly. It fits snug in there. No biggie.

The RCA cables that come with it are only RCA on one end and wires on the other. Forget that. I got an RCA cable that was 16.5 ft long (male/male), it was perfect. The battery terminal connector in the instructions is for top post. My truck (the one the MTX was built for) is a side post terminal. Even that connector was supposed to be there but was not. No issues Crutchfield mailed one right away. But since it was install time and I was out of patience for hearing this thing, I went to a local shop and the installer guy there showed me exactly what I needed so I was back in business. I had to buy an inline 20amp fuse for the power line, (another missing peice) so went to a parts store and got one for a couple dollars. For this MTX install it all went in with no problem once I had all the right parts/peices. I ran the power line through the same grommet as the e-brake line. Sound is amazing! Truck: 2001 Chevy 2500 HD Ext Cab Head Unit: MEX-BT4100P Speakers: Polk DXi460p & DXi650s Front Amp: Alpine KTP-445U **Do get the door trim and panel remover tool! Worth every penny.

Pros: Color match is spot on Fits and looks like its supposed to be there Sound is amazing! (I turned it all the way up with no distortion but did back it down a little)

Cons: Had to run around a bit to get some minor peices for the install. Would gladly help MTX rewrite the installer guide.


Written by: gearhead_x from minnesota on November 1, 2012

Crutchfield Customer Review (What's this?)

Rock solid construction, fits nice without moving any stock components. Installation was a breeze. Sound quality is superb if you know how to properly tune and balance a system. Fills out the lows really well in my trucks little cab with the subs turned up only a quarter of the way, nice hard punchy low-end. It seemed best with the phase flipped to reverse, the low-end became huge sounding! Like with anything audio just use your ears! Speakers push air and that air pressure moves your eardrums and all that. If you can't get this sub setup to sound good, you won't get any sub to sound good IMHO. Sometimes people let wattage numbers, speaker models, and brand names hit their eardrums before the sound pressure actually does.

Pros: Made for the truck, comes all you need (mostly). excellent sound quality! Glad i bought one before they are most cool things are.

Cons: Should have also included a line level RCA cable along with the high level speaker out to RCA cable. Oh well....

Hands-on research

What's in the box?

Download owner's manual

  • Amplified ThunderForm enclosure loaded with two 10" Terminator subwoofers
  • Two 20 amp fuses (1 in-line/1 installed in the ThunderForm)
  • Wiring harness (20' power lead/3' ground lead and 3' remote turn-on lead)
  • Speaker-level to RCA harness
  • Electronic Bass Control (wired remote) with attached cable
  • Mounting hardware
  • Installation instructions

Product Research



Vehicle-Specific Custom Enclosure: This MTX ThunderForm enclosure is specifically designed to fit select full size GM extra cab pickups. Please refer to the Crutchfield Car Selector to confirm fit for your vehicle.

Enclosure: The ThunderForm enclosure is made of molded high-density polyethylene resin, which dampens resonance and is rigid enough to resist flexing. The color of the enclosure matches factory GM colors. It is an acoustic suspension (sealed) chamber.

Mounting Location: This enclosure is designed and molded to mount under the rear seat. The jack does not need to be relocated. Note: The provided dimensions are taken at the widest points of the enclosure. Keep in mind that these enclosures are custom made to fit in this particular vehicle, so the enclosure will fit properly in only one specific location.

10" Terminator Subwoofers: This enclosure comes loaded with two 10" MTX Terminator subwoofers. The woofers have an unusual impedance, specifically designed for the built-in amp, and cannot be replaced with standard MTX models.

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 subwoofers in the enclosure.

Electronic Bass Control (EBC): The EBC is a wired remote and allows you to adjust the bass level from anywhere in the vehicle. Installing the EBC is optional.

Low-pass Crossover: The low-pass crossover point is adjustable from 50 to 150 Hz for a seamless transition between the output of this unit and that of the other speakers in the vehicle.


  • Gain Control: rotary control; set the gain of the amplifier is match the input
  • Crossover Control: rotary control; adjust the crossover from 50 to 150 Hz

Auto Turn-On Feature: When 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 preamp level inputs are used, connecting the remote turn-on lead is required.

Tools Required: The manual provides this list of required tools:

  • Powered Screwdriver
  • #2 Phillips Head Bit
  • Wire Cutters
  • T50 Torx
  • 5/16" Wrench
  • Terminal Crimper
  • 6" Bit Holder Extension
  • 7mm Nut Driver


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

I forwarded your question to an Advisor and they responded with the following: The range is 29-150 Hz. If you would like to discuss further you can contact an Advisor directly by phone (1-800-324-9695) or online chat. [ Krissy  May 12, 2015 ]  Staff

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