6-3/4" midbass speaker with 8-ohm voice coil

Item #: 236RTX658

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8 Reviews | 2 questions - 3 answers

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They'll hear you coming
Are you looking to play your music loud? If so, you'll want to check out MTX's Road Thunder Extreme speakers, which use PA system technology to bring concert sound levels to your car. MTX built the RTX658 6-3/4" midbass speaker to fill in the frequencies in between where your tweeters and subwoofers play. And, believe us — this incredibly efficient speaker will give you plenty of volume when you feed it some serious power.

RTX658 6-3/4

Built for high power
The RTX658 handles up to 100 watts RMS thanks to its hefty magnet, treated paper cone, and cloth surround. You can also easily run two of these 8-ohm speakers with a single amplifier channel, great news if you're installing two in each door. You can install this speaker in an enclosure if you want, but it works great in a free-air applications.

Note: This package contains one speaker. You'll need an external amplifier to drive this speaker properly — an in-dash stereo won't have enough power.

Product Highlights:

  • 6-3/4" midbass speaker with 8-ohm voice coil
  • treated paper cone
  • treated foam surround
  • power range: 25-100 watts RMS (300 watts peak power)
  • frequency response: 136-6500 Hz
  • sensitivity: 94 dB
  • mounting depth: 2-5/8"
  • warranty: 1 year
  • Our 60-day money-back guarantee

Hands-on research

What's in the box?

Download owner's manual

  • One 6-3/4" Midrange
  • Specification sheet

Product Research



  • Fs (resonant frequency): 148.7 Hz
  • Qms (mechanical Q at Fs): 8.298
  • Cms (suspension compliance): 0.133 mm/N
  • Mms (diaphragm/coil mass, including acoustic load): 8.588 g
  • Rms (suspension's mechanical resistance): 0.967 kg/s
  • Vas (equivalent compliance volume): 3.327 liters
  • Xmax (maximum linear peak): 0.295mm
  • D (cone diameter): 5.11"
  • Sd (cone area): 132.73 cm² (0.013273 m²)
  • Vd (peak displacement volume): 0.004 liters
  • Qes (Electrical Q at Fs): 1.272
  • Re (voice coil DC resistance): 5.97 Ω
  • Le (Voice coil inductance): 0.326 mH
  • Bl (force factor): 6.14 Tm
  • Qts (total Q at Fs): 1.103
  • η0 (reference efficiency): 0.827%
  • Peak Power: 300 watts
  • SPL: 94.0 dB
  • Frequency Response: 136 Hz to 6.5 kHz
  • Recommended Crossover: 500 Hz high pass


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 open the box, verify contents, 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.

MTX RTX658 Reviews

Average Customer Review:

8 reviews
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Written By M, Woodland, WA on Wednesday, July 09, 2014

Pretty good speakers

Pros: Good sound

Cons: Little buzzing at times


Written By Anonymous, Phoenix arizona on Saturday, January 18, 2014

Crutchfield Customer Review (What's this?)

Great sound. They need lots of power. I little week on the lower spectrum absolute crystal clear high end have six total in my dodge ram and am very happy. Paper cones sound the best.

6" MTX speaker

Written By Alex, Sacramento on Saturday, November 02, 2013

Crutchfield Customer Review (What's this?)

It's the bomb

Pros: Top quality, top service. I like

Cons: None

These Are Very Loud And Great For The Price..

Written By Racerboi01, Kissimmee,Fl on Friday, September 13, 2013

Crutchfield Customer Review (What's this?)

There Speakers At this price Are GREAT, They Are Very Loud, I Have 4 Of Them In My Car And It's Very Clear.

Pros: Wish They Were A Not Made Of Paper.

Cons: They Still Sound Great


Written By AL, YORK PA on Thursday, July 18, 2013

Crutchfield Customer Review (What's this?)



Cons: NONE

"Mid-Bass" is very misleading.

Written By Bob, Chesapeake, VA on Thursday, June 20, 2013

Crutchfield Customer Review (What's this?)

I agree with other reviews that the highs are very clear and the speakers are very loud, but they are by no means "mid-bass" speakers. They are mid-range loudspeakers that lack any low end. They are advertised as having a frequency response of 135Hz-6.5kHz but there is not much response at all below 2kHz. Never again will I buy a product that doesn't publish the frequency response plot along with it. Lesson learned.

Pros: Very loud, clear highs.

Cons: Absolutely no low-end (below about 2kHz). Sound like extraordinarily loud tweeters.


Written By Jason, Lacona ny on Friday, April 26, 2013

Crutchfield Customer Review (What's this?)

Very loud. Good quality product. Excellent value

awesome deal

Written By ray, cleveland OH on Sunday, May 20, 2012

Crutchfield Customer Review (What's this?)

if your looking for loud clear hi's these are the best deal so insanly loud

Get everything you’ll need to enjoy your new MTX RTX658

Reduce ambient road noise and your vehicle's "rattles," for better sound inside your car.
You'll need speaker wire to connect your speakers to your amp.
Keep your speakers clean and dry. They compress to fit behind your speakers.
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Questions & Answers Ask the community. Share your knowledge.

2 questions already asked

You will want to contact an Advisor by phone or online chat to discuss compatibility with your factory system. They will be able to pull up your vehicle and see if this will integrate. If it does not, then they will also be able to discuss other options with you. [ Jeff  Dec 26, 2013 ]  Staff
IM not sure... [ RICHARD  Dec 11, 2013 ]
I don't know the weight, but they sound great in my application. [ GARY W  Dec 11, 2013 ]

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