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Polk Audio's Mobile Monitor Series subwoofers bring out superior performance from lighter materials, so you'll get the impact you want without the extra weight of a conventional system. Advanced engineering and optimized components reproduce your sound with uncompromising accuracy, for low end that is rich and clear.

The MM1240 12" 4-ohm subwoofer handles up to 425 watts RMS. A copper voice coil and neodymium magnet motor drives the polymer cone with exceptional efficiency. The carbon composite basket features a "wagon wheel" design that resists flexing during heavy excursion, so your sub hits solidly without distorting.

This sub is certified for marine use, and Polk includes corrosion-resistant stainless steel mounting hardware.

Priced per speaker

Product Highlights:

  • 12" 4-ohm subwoofer
  • polymer cone with butyl rubber surround
  • carbon composite basket
  • certified for marine use
  • optional matching grille complements the basket design
  • power range: 100-425 watts RMS
  • peak power handling: 800 watts
  • frequency response: 22-200 Hz
  • sensitivity: 92 dB
  • top-mount depth: 4-11/16"
  • sealed box volume: 0.88 cubic feet
  • ported box volume: 1.58 cubic feet
  • warranty: 1 year
  • Our 60-day money-back guarantee

What's a component sub and why would I want one?

A component sub is simply a speaker that's designed to reproduce bass once it's installed in a compatible enclosure. Think about the impact of a movie soundtrack in a big theater or even in your own home HDTV setup. A component sub can add the same kind of power to the music in your car. And a car sub is not all about the boom that you hear on a street corner (although that's cool too) - you can pair a component sub with your choice of enclosure to get bass just the way you like it, from tight and punchy to fat and loose. And once you experience music in your car with a well-tuned subwoofer, you'll never go back.

Polk Audio MM1240 Reviews

Average Customer Review:

11 Reviews

great product

Written by: Doug from michigan on December 26, 2014

  • "Coolness Factor"
  • Build Quality
  • Ease of Use
  • Sound Quality
  • Value

I've had this speaker for over a year now and it is by far the best speaker I have ever owned. I stuffed it behind the seat of my 97 crew cab powerstroke in a sealed box matched up with a polk amp and it packs a big punch without giving up any space in the cab. A+++



Polk Audio MM1240

Written by: no from il on September 6, 2013

Crutchfield Customer Review (What's this?)

  • "Coolness Factor"
  • Build Quality
  • Ease of Use
  • Sound Quality
  • Value

got this is a open box item saved money on it sounds great it can fit in a variety of boxes to save trunk space

Pros: great price great sound seems like polk audio my hat off to you

Cons: wish polk made more high end car audio like they use to


Written by: fp from kent island md on November 14, 2011

Crutchfield Customer Review (What's this?)

  • "Coolness Factor"
  • Build Quality
  • Ease of Use
  • Sound Quality
  • Value

i have a ford explorer with the third row and two kids who love sitting in the third row. before i had a 12w6v2 that took up the space for the third row. long story short i got rid of i needed something small to go behind the third row. i have purchased polk compnent speakers before with great satisfaction, so i decided to go with there shallow sub. WOW i am very satisfied. i am powering my system with a pdx5 with 300 watts going to the sub. with sensitivity of the sub hight the 300 watts pouds very well. i am a polk fan for life:)

Pros: shallow, power handling, volume

Cons: nothing

sounds good

Written by: manju from goa, India on August 14, 2011

hi, I have installed this sub in my Toyota Innova, it is powered by a JVC 2ch amp for a while with just 130 RMS and believe me even with such a small amp it sounds great. Hope it will further improve with Jbl GTO 1004 (320 RMS). Please don't go on its size and weight hear it to believe it. Cheers



Great SQ with a Hint of Punch

Written by: LuxurySport from Olathe, KS on January 4, 2011

Crutchfield Customer Review (What's this?)

I went from 2-12" Alpine Type-Rs to two of these MM1240s. I notice a lot "punch" in my system, while still delivering outstanding sound quality. I've not messed too much with Polk Audio or shallow-mount subs, but I decided to give them a shot and I'm a little more impressed than I thought I'd be. I haven't found time yet to make a specific box for these subs so I've been using a Sound Ordnance box. I'm pushing 375wmrs to each sub and I have to say they sound clear and don't distort at lower Hz. If you want to get a good deal on these subs it's best to buy these in the scratch and dent section and get the Square-Trade 2-year warranty. Good luck and enjoy!



Excellent Sub

Written by: Jake R from Oswego, NY on March 23, 2010

Space limtations on a 08 Chevy crew cab for enclosure size were frustrating, after talking with a Crutchfield advisor I decided to give the Polks a try. At first powered by an Alpine PDX600.1 i was impressed but wanted more, subs sounded good but not enough bump for my taste. Swapped out the amp for a PDX1000.1 and this is amazing. This convinced me to swap my PDX 100.4 to an PDX 150.4 for my four 6 3/4 Alpine type R components and this truck is down right amazing. Buy the Polk subs and power them big, you won't be disappointed.



Amazing Soud Quality and Sound Pressure Levels!

Written by: Greenpeanut from Salt Lake City, UT on January 7, 2010

I bought this sub to replace an Alpine Type R because although I liked it, I didn't feel I was getting the volume I wanted. After reading up on how sensitivity relates to power and sound output, I decided to try Polk Audio for the first time and was very impressed! This sub is rated truly at 92 db at 1 volt. Some other manufacturers pad this number by rating it at higher (Usually 2.83 volts) which usually increases the measurement by 4 to 5 db higher than the true number with 1 volt.

I have it set up with a sealed enclosure powered with a Rockford Fosgate P500.2 bridged with 500 watts. This sub hits a lot harder and cleaner than my Alpine Type R even when the volume levels are cranked. By the way the Type R has a sensitivity of 85 db. Although I know this number doesn't mean everything, just between these subs I can say I am very impressed with this sub! Awesome sound quality coupled with great SPL can't be beat, usually its only one or the other, but this has both! I will now recommend Polk Audio to anyone.

Also this sub is pretty shallow and fits in tight spaces like the trunk of my Acura Integra. Great sub!!!



great sub

Written by: Eric from az. on May 16, 2009

this a great sub. i have 2 of them running off an alpine mrp1000. that's 500 watts going to each of them. they do need about 20 to 30 hours to break in according to polk. its been about 3 weeks know and they are sound great. i have them in sealed enclosures w\ right about .88 to .90 airspace and and 1/2 pound of polly fill in each one which is ideal according to polk. which i would have say is spot on. i listen to all kinds of music and it all sounds good. i am also running mm6501 and mm651 in my car. i really like this polk mm line. i tried the db's and they just didn't sound right to me. crutchfield service is tops. car audio is kind of trial and error you have to put it in and try it and then be able to switch to something else if not satisfied. but know that i am with alpine electronics and polk mm speakers everything sounds awesome.




Written by: Adetokunbo from Clinton ,MS on April 1, 2009

I wanted a sub with a smaller box to replace my 12 inch JL AUDIO W3's in a
ported box all my other speakers in my car are POLK so I decided to give
them a try in a sealed box in a 2008 Nissan maxima. I tried Boston,Alpine,
and Kicker the bass didn't make it past the back seat. When polk says
sound quality they mean it two sealed polk 12's in a trunk sound way
better than my JL's and they are in a sealed box . JL is good but when it
comes to sealed sound quality polk cant be beat and when I turn it up I
BEAT THE BLOCK DOWN!! It hits hard when I want it too.



Hits hard and fits where others wont!

Written by: Anthony from Long Beach, CA on January 26, 2009

I've had this sub for a while now and I love it. Not only does it sound great, but it's extremely shallow for a 12" sub. I own a single cab Dodge Dakota. For those of us single cab truck owners, it's hard to fit decent subs and amps into the cab. Well, I was able to fit this sub behind the seats with the correct box dimensions and still have room to move the seats all the way back. This is an awesome sub that sounds great, hits low, and fits where most subs wont. Definitely recommended (especially if you have a single cab truck).



Very nice sub

Written by: Sam from Houston, TX on August 10, 2008

I've had many sub's over the last 15 years or so. I have to admit that this
sub is hands down the best sub I've ever owned. Don't let the price scare
you. Its well worth the money. Anyways, the darned thing hits like no
other. I am hearing freq's that I've never heard before in some songs. I'm
pushing it with an Alpine MRP-F350 mono block amp. Great response and
no distortion whatsoever. I ran it through the paces when I had it finally
installed. I'm very impressed thus far.



Hands-on research

What's in the box?

Download owner's manual

  • 12" Single 4-ohm voice coil subwoofer
  • Foam gasket
  • 8 Mounting screws
  • 8 Speed-clips
  • Owner's Manual
  • Product Registration Information sheet

Product Research

Enclosure Compatibility


Klippel Optimized: Using a state-of-the-art Klippel Distortion Analyzer, Polk engineers were able to optimize the woofer's motor structure, voice coil alignment and suspension for the best possible performance, even at extreme listening levels.

Polymer Woofer Cone with Butyl Rubber Surrounds: The Polymer Woofer Cones and Butyl Rubber Surrounds will not break down over time and will survive the rigors of harsh automotive environments.

High Temperature Copper Voice Coil (50mm) and Polyamide Former: High Temperature 50mm Copper Voice Coil and Polyamide Former withstand the most rigorous use while maintaining extremely low distortion for bass punch and output.

Carbon Composite Basket: The woofer's carbon composite basket is lightweight and will not flex during music audio peaks.

Nickel Plated Heavy Duty Input Terminals: Nickel plated heavy duty input spring-post terminals accommodate speaker wire up to 8 AWG or twisted pairs of 12 AWG.

Preconditioning Period: Mobile Monitor subwoofers will achieve even greater performance once they are thoroughly broken in. To break in your new MM subwoofer, play 20 to 30 hours of music at moderate levels.

Marine Certified Woofer: Polk MM Series speakers are built to withstand exposure to moisture and UV rays, so they work well in boats and cars. They also include stainless mounting hardware for corrosion and rust resistance.

Enclosure Compatibility

Recommended Sealed Box Volume: Polk recommends mounting this woofer in a sealed enclosure made out of 3/4" MDF with an internal volume of 0.88 cu/ft.

Recommended Ported Box Volume: Polk recommends a ported enclosure made out of 3/4" MDF with an ideal internal volume of 1.58 cu/ft using a slot port measuring 13.5" wide x 1.5" tall x 18.5" deep.

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.