Skip Navigation

Polk Audio MM840

Mobile Monitor Series 8" subwoofer

21 Reviews

Item # 107MM840

This item is no longer available.

Shop all Component Subwoofers

New model available

Polk Audio MM 842 SVC

$159.99

Overview

Our take on the Polk Audio MM840

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.

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

Small in size large in volume and thump

Mike, Salt Lake City, UT

What's in the Box:

  • 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
Reviews

Polk Audio MM840 Reviews

Average Customer Review(s):

(21 Reviews)

Amazing sound for such a small sub

Mike from Salt Lake City, UT on 1/5/2017

2013 Fiat 500
Crutchfield Customer Review (What's this?)

Small in size large in volume and thump

Pros: Fit in my stock set up, (beats audio in my Fiat 500 Abarth). Amazing sound and deep pounding bass.

Cons: None

Polk Audio MM840

Anonymous from Clemmons, NC on 12/5/2016

Crutchfield Customer Review (What's this?)

I put 2 of these in my triton it has a very good solid base .

Pros:

Cons:

Polk Audio MM840

Anonymous from Denver, CO on 10/16/2016

Crutchfield Customer Review (What's this?)

Works great, installed in the oem enclosure of my 2014 wrangler, modified and re-used the oem grill. Plays lower and louder than several other aftermarket speakers I have tried. It is connected to a 300w amp.

Pros:

Cons:

Polk Audio MM840

Mike H from Northern Ca. on 8/31/2016

Crutchfield Customer Review (What's this?)

Sound is clean, bass is tight, and hard hitting. Chose this speaker for bass without being overbearing,since I listen to mainly classic rock,some metal and punk. Met all expectations. U can't go wrong with this purchase. Would make great mids if your system has 12's and/or 15's

Pros: All

Cons: None

Polk MM840 Subwoofer

MrBajaDoug from Wichita, KS on 8/1/2016

Crutchfield Customer Review (What's this?)

Purchased this sub (MM840) for a stealth rear-deck install in an older Mercedes. Built a .4 cf box attached to the under side of rear deck. Broke the sub in on an old Hifonics amp (circa 1992) with 150w rms for about a month. Sounded good. Not great. Yet. Re-wired system to include and old MTX mono amp of 300w rms....WOW !! sub really came alive with the extra power !! Tight,clean, & controlled bass !! A very musically-detailed sub that hits the low notes !! The included hardware is good quality. The foam sealing-ring is a nice touch (unless you use the Polk sub grill...grill doesn't sit flush with box because of the thickness of the foam ring)

Pros: Clean & tight bass Well built Great price from Crutchfiled

Cons: none

Alternative Use

G.Reed from Saginaw, MI on 7/22/2016

Crutchfield Customer Review (What's this?)

I am using this woofer as a replacement for a Klipsch SW 350. After a few adjustments I got it to fit. This sub does not have a spec for a ported box, but if it did I imagine it would be close to the dimensions of the Klipsch enclosure, it sounds better than the original!

Pros: Good power handling, decent range.

Cons: Check the size of the mounting hole, I had to do some adjustments and use caulk to seal around the edges. Not so much a con, a Klipsch subwoofer just mounts differently.

excellence

c c from pitt pa on 6/7/2016

1994 GMC Sierra
Crutchfield Customer Review (What's this?)

excellent sound quality what you expect from Polkhaven't hooked up to Rockford Fosgate 500receiving 300 watts into 4 ohm this sub takes it with ease .35 sealed box

Pros: small powerful excellent sound quality

Cons: absolutely none

Accurate and loud

Installation guy from Stevens Point, WI on 4/8/2016

2011 Scion tC

Awesome build quality, it's very stout and takes the rated power happily. I ran a pair in sealed boxes and they're accurate and get loud in my hatchback. I can't say enough good things about these. The basket is fairly shallow, too, so it's applicable to a lot of tight spaces or truck applications. In my opinion they're a really nice looking sub, too.

Pros: Good build quality, sturdy, shallow

Cons: N/A

Bad Little 8"

Josh from Mississippi on 7/2/2012

Crutchfield Customer Review (What's this?)

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

Rob M from Jersey Shore on 6/5/2012

Crutchfield Customer Review (What's this?)

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

adam from Palm Coast, FL on 5/18/2012

Crutchfield Customer Review (What's this?)

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

Anonymous from laguna beach, ca on 4/23/2012

Crutchfield Customer Review (What's this?)

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

Pros: All

Cons:

Bangin lil 8s

JediMaek from Oldsmar, Fl on 3/10/2012

Crutchfield Customer Review (What's this?)

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!

Resiliant from Anaheim HIlls, Ca on 2/19/2012

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

Russell from California on 9/9/2011

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!

Pros:

Cons:

Terrific bargain

Chris from Pacific Tech, CA on 8/11/2011

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.

Pros:

Cons:

The Little Sub That Can And Will

RockinTacoma from North Augusta , South Carolina on 6/2/2011

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.

Pros:

Cons:

attention

markford from charlottesville on 7/7/2010

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.

Pros:

Cons:

Perfect Bass!

Curtis from Topeka, KS on 5/17/2010

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!

Pros:

Cons:

Like a punch to the gut

Anonymous from Lawrenceville, GA on 5/10/2010

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!!

Pros:

Cons:

POLK MM840

GARRY from BATTLE CREEK, MICHIGAN on 8/18/2009

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.

Pros:

Cons:

Details

Hands-on research

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 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.

Accessories
Q & A

Customer Q&A

Crutchfield asked  
Why did you buy this?

This sub sounds good in my trunk. Gives exactly the bass I was looking for to accompany my rear deck Kenwood 6x9's. Looking forward to receiving and installing my Polk component speakers for the door/kick panels to complete the sound stage.[ Pierre  Jan 02, 2017 ]
I chose the Polk Audio Subs because of previous ownership and customer reviews. Literature that Crutchfield provided also helped.[ Gregory  Dec 31, 2016 ]
It will replace and fit in the Beats System sub box. Keeping the stock look in my Fiat Abarth[ Michael  Dec 12, 2016 ]
Weatherproof and great sounding sub for my jeep[ jason  Oct 04, 2016 ]
Have used Polk Audio products in the past and they provide a great speaker at a good value. This subwoofer will be a perfect fit under the seat in our 2003 Sea Ray Sundeck.[ Beth  Jul 19, 2016 ]
The Polk Audio name and great Crutchfield price[ Andre  Jun 18, 2016 ]
I've had a pair of Polk MM1540's for three years and love them, so when I needed something smaller for the wife's car I chose the 8" version of the same line. The overwhelmingly positive reviews didn't hurt, either.[ CHRIS  Apr 13, 2016 ]
Articles