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 MM840 8" 4-ohm subwoofer handles up to 250 watts RMS. A copper voice coil and neodymium magnet motor drive 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:

  • 8" 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: 100-250 watts RMS
  • peak power handling: 500 watts
  • frequency response: 26-200 Hz
  • sensitivity: 89 dB
  • top-mount depth: 3-15/16"
  • sealed box volume: 0.35 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.

Hands-on research

What's in the box?

Download owner's manual

  • One 8" subwoofer
  • 1 Foam gasket
  • Eight 1-1/2" Allen head self-tapping screws
  • 8 Speed clips
  • Owner's Manual (English/ French/ Spanish/ German/ Italian/ Portuguese)
  • Online registration sheet

Product Research

Features
Enclosure Compatibility

Features

Basket: The MM Series subwoofers use high-tech carbon composite basket structures for light weight and maximum rigidity. They will not rust or flex like stamped steel designs.

Materials: The new polymer woofer cone and butyl rubber surround will not break down over time and will survive the rigors of harsh automotive environments.

Voice Coil: The high temperature, 1-1/2" diameter copper voice coil and polyamide former withstand the most rigorous use while maintaining extremely low distortion.

Terminals: The woofer has heavy duty spring terminals that will accept single banana plugs, pin connectors, and bare wire up to 8 gauge.

Marine Certified: Polk MM Series speakers are built to withstand exposure to moisture and UV rays, so they work well in boats and cars.

Klippel Measurement Technology: State-of-the-art laser based Klippel measurement technology is used to optimize the woofer's motor structure, voice coil alignment, and suspension to improve performance, even at extreme listening levels.

Enclosure Compatibility

Sealed Box Volume: Polk recommends using this woofer in a sealed enclosure; the ideal internal volume is 0.35 cubic feet.

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.

Polk Audio MM840 Reviews

Average Customer Review:

13 reviews
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Bad Little 8"

Written By Josh, Mississippi on Monday, July 02, 2012

Crutchfield Customer Review (What's this?)

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

I have one of these little bad boys in a homemade box in the back seat of my 96 Tacoma Extra cab with a Rockford Fosgate Punch P-300 amp monoblock and It KILLS!! Do not under estimate the power of this little 8", it hits hard and clean, no rattling. Great qualit and very sturdy Sub that sounds Amazing with any Genre of Music, I listen to Country, Classic Rock, Heavy Metal, Rap, Hip Hop, and everything else, and it sounds great with whatever is playing, I have, Polk DXI 6 1/2's in my doors and Polk MM 6 1/2's in the rear with this Sub plus a Alpine head unit and the little Alpine amp KTP145 somethin, it all sounds Awesome!

Pros: Good, Clean, Hard hitting Bass, even though its small, it still hits really Low notes

Cons: Nothing

big bass

Written By Rob M, Jersey Shore on Tuesday, June 05, 2012

Crutchfield Customer Review (What's this?)

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

clean loud tight bass, in a homeade sealed box. I need one more ,it sounds amazing.

Pros: need I say more polk audio rules!!!

Cons: no grill included...

Impressive

Written By adam, Palm Coast, FL on Friday, May 18, 2012

Crutchfield Customer Review (What's this?)

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

This little sub sounds amazing. I have one in a 0.6 cu ft box mounted to my decklid. Sounds great (minus the rattles which will go away when I make a new box for 2 of these). Only 2 things I would change: The basket is plastic and I could make it bend by tightening the screws. So I had to slowly turn them, one at a time, until it was snug and level. I am unsure if it would effect anything if I didnt have it evenly snugged. The other thing is the push terminals. I am using 8 ga wire (Kicker full spec 8 ga) and the wire barely fits and I am left with a few strands that dont quite make into the terminals. Also the terminals are so close to the edge of the sub that the wires are kinda wedged against the box and the side of the sub. Overall, great product for the price. Can't wait to build the new box for the 2nd sub. I think it will easily rival my old 3 JL10W6.

Pros: Sounds great from small package. Hits hard and plays low but is not overpowering.

Cons: Terminals too close to the edge, plastic basket is kinda cheap. No grille included, not a big deal, but would be nice. The plastic basket is rigid, but it flexes when the screws are tightened out of turn.

Polk Audio MM840

Written By Anonymous, laguna beach, ca on Monday, April 23, 2012

Crutchfield Customer Review (What's this?)

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

04 tundra with q logic box. Sounds great. Fit great.

Pros: All

Bangin lil 8s

Written By JediMaek, Oldsmar, Fl on Saturday, March 10, 2012

Crutchfield Customer Review (What's this?)

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

Bought these 8s for my fiancee's 4 dr civic and let me tell you these little things rock! We mainly listen to music with tight rapid hitting bass like drum n bass/techno/rock which is why we went with the 8s, but they will hit low and hard too playing stuff like dubstep or the occasional rap songs. Powered by a memphis 500 monoblock in a sealed box, these sounds real clean and loud. I'm going for the mm1040s for my 94 altima since I'm built a little bigger then her they should be just the ticket rattle my brains :)

Pros: -Top build quality -Great sq -Excellent spl for 8s -High abuse tolerance

Cons: None

Super sickk!

Written By Resiliant, Anaheim HIlls, Ca on Sunday, February 19, 2012

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

Who said an 8in sub can't bang! Got this in my 2001 Tacoma and it fills in my music nicely. This is a great buy.. Ya digg

Pros: #Price #Quality #Soundquality #8in

Cons: Too good to be true

A very impressive 8" subwoofer

Written By Russell, California on Friday, September 09, 2011

I did a great deal of research before making my subwoofer selection. I had some pretty limited choices because of the small space in my 2000 Toyota Tacoma Xtra Cab. I have owned dual 10" subs, dual 12" subs and a single 12" over the years and I was curious about how a pair of 8" subwoofers would sound. I built a custom enclosure for the subs with about 0.40 cu ft of airspace for each sub and I stuffed each side of the enclosure with a little less than 0.5 lbs of polyester fiber material.

I must say that I am very impressed with the Polk Audio MM840! The Polk Audio MM840 is a very musical sub that has a very accurate response. I am very surprised at the relative volume that I can get out of a pair of these, particularly in a listening environment such as my extended cab. You won't be shaking the asphalt lose beneath you, but this sub will definitely sound very clean and accurate and it will greatly enhance your listening experience.

I would highly recommend this subwoofer to anyone who is restricted on space and wants good, clean bass. You can never go wrong with Polk Audio in my opinion!

Terrific bargain

Written By Chris, Pacific Tech, CA on Thursday, August 11, 2011

Crutchfield Customer Review (What's this?)

I bought this and the corresponding "grill" (not really a grill) to replace a sub driver whose surround had fallen apart. My top-mounting depth available was only about 4-1/8 inches, so I needed a shallow sub. The one I had before was comfortably under 4 inches.

This sub is FAR better than the old one ever was. I have to point out though that the way they got a decent "throw" into such a shallow-mount sub was to put considerably more of the sub *above* the mounting surface. My old sub used a grille that was barely half an inch high - this one is well over an inch. This may affect your choice of mounting positions.

The Little Sub That Can And Will

Written By RockinTacoma, North Augusta , South Carolina on Thursday, June 02, 2011

Crutchfield Customer Review (What's this?)

I am simply amazed at how great this sub performs ! I have a Kenwood 8105D Mono amp pushing it with the gain turned up about halfway . The sub even sounds great at low volumes. I was impressed at how well the sub is put together as well....heavily built and very heavy for an 8 incher ! I can't imagine a better small sub for even a little more money.

attention

Written By markford, charlottesville on Wednesday, July 07, 2010

I was limited on choices because of space restrictions, thank you Polk for coming to the rescue.I'm a big bass fan but thought I had to lower my expectations because I could only use a single 8 inch sub. I'm telling you when I turn up the stero folks begin peeking in the back of my truck looking for a PAIR of twelves. I need not say any more. The Alpine pdx 5 is the perfect companion driving my four Kenwood P680c door speakers as well. Possibly the best stero related decission I've ever made.

Perfect Bass!

Written By Curtis, Topeka, KS on Monday, May 17, 2010

I have 2 of these subwoofers in a custom box which fits easily behind the back seat of a 1998 Jeep Wrangler. The thing that I love so much about these subs is that the bass is powerful and clear. Your hearing is not completely overtaken by a ridiculous amount of vibration that sounds like a collapsing building. Bass notes are very tight and can be distinctly heard while still packing enough punch to shake your body. The magnet on these subs is on the verge of ridiculous in size and weight and can easily handle the recommended 250 watts rms at a 2 ohm load. Unfortunately I have a cheap Kenwood amp powering the two subs right now, so I assume they could sound even better with a high quality Polk amp pushing them. I definitely recommend these subwoofers if you are tight on space or don't want to shake innocent by-standers 2 blocks away while still loving the bass!

Like a punch to the gut

Written By Anonymous, Lawrenceville, GA on Monday, May 10, 2010

Crutchfield Customer Review (What's this?)

I'm not a big bass fan. I like more the thud sound, like the one the feels like a punch in the gut.

I used to have two 8'' Polk Audio db840DVC, but after I got Alpine's iDA-X305s (thanks crutchfield) the sound became so heavenly clear!! I had to get me a new Mono amp for my subs. What I choosed was the Alpine MPR-M500, but somehow the 8'' Polk Audio db840DVC was not making the cut. so I got This one. It did took a week to break in, but when it did I was so blown away I had to get another one. This so not so lil' guys have the muscle at 4ohms. so imagine at 2ohms. great buy!!

POLK MM840

Written By GARRY, BATTLE CREEK, MICHIGAN on Tuesday, August 18, 2009

Crutchfield Customer Review (What's this?)

THE POLK MM840 IS A GREAT CHOICE FOR ANYONE NEEDING A SUB TO FIT
IN SMALLER VEHICLES OR TO JUST TAKE UP LESS CARGO SPACE. IT IS
EXTREMELY WELL BUILT AND HAS GOOD POWER HANDLING. FOR AN 8" SUB
IT PLAYS LOWER THAN A LOT OF OTHER 10" SUBS. IT DID NEED SOME
BREAKING IN TIME, BUT NOW IT IS STARTING TO SOUND BETTER THE MORE
IT IS USED. THE BASS IS REALLY ACCURATE AND TIGHT, WHICH IS WHAT I
WAS LOOKING FOR IN MY BASS OUTPUT. I PREFER THE TIGHT ACCURATE
BASS OVER THE BOOMY SOUND. I DO WISH A GRILL WOULD HAVE BEEN
INCLUDED BUT THIS IS THE ONLY COMPLAINT I HAVE WITH MY PURCHASE.

Get everything you’ll need to enjoy your new Polk Audio MM840

We've verified that these enclosures are a good match for this subwoofer.
It's critical to have good wire, and none is included with the sub.
Reduce ambient road noise and your vehicle's "rattles," for better sound inside your car.
These can be useful if you are building a custom box.
Sound Ordnance™ Bass Bunker

Sound Ordnance™ Bass Bunker

Pair of sealed 8" wedge-style enclosures (Model BB82W)

Item #: 777BB802

(5)

$59.99
Add to Cart
Sound Ordnance™ Bass Bunker

Sound Ordnance™ Bass Bunker

Sealed single 8" subwoofer enclosure (Model BB8-35S)

Item #: 777BB835S

(13)

$39.99
Add to Cart
T-Spec 16-gauge Speaker Wire

T-Spec 16-gauge Speaker Wire

Black/white jacket — priced per foot

Item #: 120SW16WB1

(13)

T-Spec 12-gauge Speaker Wire

T-Spec 12-gauge Speaker Wire

Black/white jacket — priced per foot

Item #: 120SW12WB1

(31)

Stinger PRO Series Speaker Wire

Stinger PRO Series Speaker Wire

Priced per foot (16 Gauge)

Item #: 541SPW516B

(53)

Dynamat 19100

Dynamat 19100

License Frame Kit

Item #: 15419100

(15)

$14.99
Add to Cart
Dynamat Xtreme Wedge Pack

Dynamat Xtreme Wedge Pack

1 sheet, 4 square feet

Item #: 15410425

(7)

$39.99
Add to Cart
Dynamat Xtreme Trunk Kit

Dynamat Xtreme Trunk Kit

5 sheets, 20 square feet

Item #: 15419405

(14)

$169.99
Add to Cart
Dynamat Dynaliner

Dynamat Dynaliner

One 54" x 32" sheet (1/8" thick)

Item #: 15411101

(6)

$69.99
Add to Cart
Metra Box Carpet

Metra Box Carpet

Carpet roll (54" x 5 yards) — available in 3 colors (Black)

Item #: 120TL3015

(24)

$39.99
Add to Cart
Polyester Fiber Stuffing

Polyester Fiber Stuffing

Make your subwoofer think it's in a bigger box (1-pound pack)

Item #: 027808

(36)

$12.99
Add to Cart
Metra Speaker Terminal

Metra Speaker Terminal

Round terminal cup with binding post connectors (for do-it-yourself box builders)

Item #: 120TCRB

(14)

Corner Protectors

Corner Protectors

Item #: 1251536

(5)

Rubber Feet

Rubber Feet

Item #: 125F1692

(4)

Metra Speaker Terminal

Metra Speaker Terminal

Round terminal cup with spring clip connectors (for do-it-yourself box builders)

Item #: 120TCRS

(6)

Metra Speaker Terminal

Metra Speaker Terminal

Square terminal cup with binding post connectors (for do-it-yourself box builders)

Item #: 120TCSB

(7)

Springback Handle

Springback Handle

Item #: 125H1051K

(2)

Metra Speaker Terminal

Metra Speaker Terminal

Square terminal cup with spring clip connectors (for do-it-yourself box builders)

Item #: 120TCSS

(7)