Polk Audio continues its tradition of making brilliant-sounding speakers in stylishly designed packages — their Mobile Monitor (MM) Series speakers look great and sound even better. Each speaker utilizes an extra-strong, extra-small neodymium magnet that saves space and weight, allowing these speakers to fit into more places in more vehicles while still delivering a full sound with lots of kick. Their lightweight carbon composite frames provide strong, flex-free support for the speakers' motor assemblies.

The Polk MM651 6-3/4" speakers feature honeycomb-textured woven glass fiber composite woofer cones that respond very quickly for a clean, crisp, and powerful sound. Large voice coils — over an inch in diameter — give the speaker high power handling capability and extended reliability.

1" silk dome tweeters add a sweet high end that blends perfectly with the low notes so your music stays in harmonic balance, from the electric bass all the way on up to the cymbals. Swivel mounts on the tweeters allow you to aim the high notes to produce a superior sound stage in your car.

Important Note: These Polk speakers use a low-impedance design to pull more power safely from your car stereo or amplifier. This design is compatible with all factory and aftermarket stereos.

Note: Polk describes this model as a 6-1/2" speaker. Most manufacturers designate this same frame size as a 6-3/4" speaker. For simplicity's sake we list it as a 6-3/4" speaker.

Priced per pair

Product Highlights:

  • 6-3/4" 2-way speakers (pair)
  • woven honeycomb glass fiber composite woofer cone with butyl rubber surround
  • 1" silk composite dome tweeter with swivel mount
  • certified for marine use
  • 2.7-ohm impedance for extra power (compatible with all factory or aftermarket car stereos)
  • power range: 15-100 watts RMS (200 watts peak power)
  • frequency response: 40-25,000 Hz
  • sensitivity: 94 dB @ 1 watt
  • top-mount depth: 2-5/8"
  • warranty: 1 year
  • Our 60-day money-back guarantee

Why replace your factory speakers?

The speakers that originally came in your car were made from inexpensive materials, designed to create acceptable sound at the lowest possible cost to the manufacturer. If you love music, you deserve better. Name-brand aftermarket speakers deliver fuller, richer sound with considerably more detail and nuance, and they're capable of playing louder and cleaner than factory speakers. Connect new speakers to your factory radio and you'll get the best possible sound from your dealer-equipped system. Pair them up with a new car stereo for a level of enjoyment that can rival a high-fidelity home audio experience.

Hands-on research

What's in the box?

Download owner's manual

  • Two 2-way 6.75" speakers
  • 2 Grilles
  • 2 Passive crossovers
  • 2 Mounting ring adapters (includes GM/Chrysler 6-3/4G)
  • 8 Hex-head screws
  • 4 Phillips-head screws
  • 8 Speed clips
  • Owner's Manual
  • Product Registration information sheet

Features and Specs

Design 2-way
Tweeter Design 1" Soft dome
Tweeter Composition Silk/polymer composite
Woofer Composition Glass Fiber Composite
Woofer Surround Butyl Rubber
Parts Warranty 1 Year
Labor Warranty 1 Year
Sensitivity 94 dB at 1 watt
Frequency Response 40 - 25k Hz
RMS Power Range (Watts) 15-100
Peak Power Handling (Watts) 200
Impedance (Ohms) 3
Top-mount Depth (Inches) 2 5/8
Bottom-mount Depth (Inches) N/A
Cutout Diameter or Length (inches) 5

Product Research


Dynamic Balance: Dynamic Balance is a proprietary Polk Audio technology using laser imaging to determine what combination of speaker materials create the least amount of resonance. Eliminating resonance in speakers results in a wide, smooth response and low distortion.

Woofer Cones: Woven glass composite cones feature tremendous stiffness-to-mass ratio. Lower mass means faster transients and finer detail.

Butyl Rubber Surrounds: For a smoother response and improved durability, the woofers use butyl rubber surrounds. The airtight rubber surrounds stand up to moisture, sunlight and extreme temperatures while allowing long excursion linear motion and years of reliable use.

Silk/Polymer Composite Swivel Tweeters: The 1" liquid-cooled, silk/polymer composite tweeters provide clear, detailed highs. The 15-degree swivel tweeter housings deliver direct, detailed imaging; instantly adjustable through the grille.

Neodymium Magnets: The speaker's neodymium magnets offer exceptional strength to performance ratio and is extremely lightweight.

Large Diameter Voice Coils: Large diameter, 30mm voice coils increase the speaker's reliability and power handling capacity.

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

Crossover: The speaker comes supplied with two separate 2-way crossovers; one for each speaker. Each crossover input 36" lead is terminated with tinned wire, and the two 20" output leads (one for the woofer and one for the tweeter) are terminated with female quick-slides. The positive woofer lead has a 0.250" female quick-slide and the negative woofer lead has a 0.187" female quick-slide. The positive tweeter lead has a 0.187" female quick-slide and the negative tweeter lead has a 0.110" female quick-slide. These quick-slides connect directly to the woofer and tweeter terminals on each speaker. The separate 2-way crossover network sends the appropriate frequencies to each driver for cleaner sound and better imaging. Dimensions: width = 3.515", height = 1.015", depth = 2.645"

Mounting: The speaker itself has 4 mounting holes for a standard 6-3/4" application. The supplied mounting ring has multiple mounting holes for non-standard 6-3/4" applications, allowing the speaker to fit more vehicles.

Grilles: Strong ABS plastic grilles are included. These computer optimized grilles feature a spoke-wheel design.

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.

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.

Polk Audio MM651 Reviews

Average Customer Review:

20 reviews
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MM651 - 2010 FLTRX Road Glide

Written By MattE, Rhode Island on Friday, December 14, 2012

Not much to say other than BUY THESE SPEAKERS. The efficiency of the drivers is outstanding, people who are not familiar with audio equipment always overlook this rating. 94dB@1Watt is extraordinary, especially when used in a motorcycle environment as in my case, they are also 3 Ohm impedance, which will draw more power from your source/amplifier (if it doesn't melt it first). The MM651 also has arguably the highest RMS/Peak power handling (when comparing realistic claims). Butyl Rubber surround, 1" tweeter and flexible installation options round out the great features of Polk's moderately priced superstar. Just do a Crutchfield comparison between the Polk MM651, the Focal K2 Power 165KRC, the JL Audio C5-650X, the Focal Performace PC 165, the Alpine SPR-60, and the Focal Integration IC 165. This comparison included speakers labelled as 6-3/4" with a (listed) price range of $199.99 all the way to $679.99. I know some people have more dollars than sense and will always buy the most expensive item available; regardless of what it is, however, I personally find it hard to stomach an extra four hundred thirty-dollars. As always Crutchfield is the go-to-source for all of the best equipment for your home and auto.

Pros: Performance > Price, 94db Sensitivity, Butyl Rubber Surround, 1" Dome Tweeter, 3-Ohm Impedance, Frequency Response, Power Handling... May I stop now?

Cons: I can only fit two on my Harley.

Polk Audio MM651

Written By JordanZ, SLC, UT on Friday, August 03, 2012

Crutchfield Customer Review (What's this?)

These speakers do install into both the front and rear doors on a 2012 Subaru Impreza with the same caveat that Crutchfield mentions for the front doors, you have to drill new mounting screw holes. The rear doors have plenty of clearance and I just used some foam weather stripping around the speaker hole to seal up any gaps in both set of doors, it's a couple dollars at most hardware store. Other than that they couldn't sound better for being pushed with the stock receiver, can't wait till someone makes a dash mount for this car and I can throw in my receiver, amps, and subs from my old car. I know these things will sound even better with a decent amp pushing them. I grabbed these to replace the 5x7" Polk MOMO's I had in my old car that don't fit here.

Polk Audio MM651

Written By Anonymous, jersey city, nj on Sunday, June 10, 2012

Crutchfield Customer Review (What's this?)

these speakers trully deliver a punch for such small package

Pros: excellent bass

Polk Audio MM651

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

Crutchfield Customer Review (What's this?)

these speakers are amazing...they sound soo good in my silverado, perfect fit. I live the external x-over..clean sound...

Pros: ez install , handle lots of power

Cons: none

Polk Audio MM651

Written By Anonymous, Tucson AZ on Sunday, May 20, 2012

Crutchfield Customer Review (What's this?)

These are amazing speakers. Such an improvement over the stockers. Nothing I can complain about. Crutchfield even had the lowest prices as well has having them in stock.

Pros: Ease of install Great sounding

Cons: Had to pay for them

Excellent Speakers

Written By BrentB, Denton, TX on Thursday, May 10, 2012

Crutchfield Customer Review (What's this?)

Great sound quality and build. Using them in my tower speakers on my boat.

Pros: 2 ohms, crossovers included

Cons: none

Polk Audio MM651

Written By Anonymous, Philadelpha on Monday, April 02, 2012

Crutchfield Customer Review (What's this?)

Love these speakers. I was a little worried about the crossovers that were included, but I got some connectors from Radio Shack, and it worked great. And the directions from Crutchfield were excellent!

Pros: Great sound. Easy for DIY with the directions.

Cons: None


Written By Kelly, Texas on Friday, March 16, 2012

Crutchfield Customer Review (What's this?)

Replaced Polk DB speakers in front door 2007 chevy pickup. Major improvement! Have the DB 4x6 plate speakers in rear. Hooked both up to 900w amp and WOW, cant believe how clear and loud. Cant lose with this speaker!


Cons: None


Written By Mcaletzr, ochester,ny on Monday, March 12, 2012

Crutchfield Customer Review (What's this?)

I'm amazed that after ordering he mm651 Polk speakers and then receiving them, the amazement kick in when extra parts was included It made my day. Job was simple because of Crutchfield.

Pros: Parts are included

Cons: None


Written By Chris, AZ on Saturday, March 10, 2012

Crutchfield Customer Review (What's this?)

Huge improvement in sound quality over factory speakers!! I was hesitant about buying these at first because Crutchfield says they do not fit in my rear doors, but a simple template ring took care of that. No complaints at all.

Pros: Solid bass response for a 6.5in coaxial, impressive warmth.


Written By ScottP, Moore, OK on Saturday, March 03, 2012

Freakin love these speakers. I catch myself turning the radio down to find out what the unfamilar sound is, just to realize it's part of the song I'm listening to but never heard the "clarity" that you should hear. Nice base for a 6 3/4" speakers. Dropped right in on my 02 Sierra front door panels. Plan on getting some 6X9s to put under the back seat in some small enclosures... will definately go with the MM691s. In a word... Awsome.

Pros: Well made, compact magnet, Sound wicked sick Includes crossovers

Cons: NONE


Written By anonymous, Columbia, MO on Wednesday, February 08, 2012

Crutchfield Customer Review (What's this?)

Using these as front speakers in an Impreza, with db651's in the rear doors. God, I wish these fit all 4 doors easily. I am using the stock head unit with no aftermarket amp or sub. These sound great. Very full sound, even at the bottom end. I listen to rock (the who, zeppelin, kyuss, local h, blue oyster cult) and these handle that type of music well. If you're into rap, get a sub. If you're cheap and still wanna rock, these are great.

Pros: full sound only need sub in very demanding applications

Cons: external crossover meant installation took 3 extra minutes of my precious time weren't free.

Polk mm651

Written By Jaycue, Deer Park, NY. on Saturday, February 04, 2012

Crutchfield Customer Review (What's this?)

These speakers sounds excellent. They put out really nice highs and midbass, the soundstage is really good. Had to modify the rear deck of my 2010 civic coupe. Sound really good at low levels.

Pros: Sound stage and quality.

Nice speakers

Written By Tim, South WIndsor, Ct on Friday, September 16, 2011

Crutchfield Customer Review (What's this?)

These are great all around full range speakers. I bought these to compliment the mm components I had already installed. Crutchfield says they don't fit in a 2011 jeep wrangler but they do! In fact they fit excellent. The overall sound is good off just the deck. I have the front components amped and they sound great, so these are used to provide rear-fill. And as always, Crutchfield is superior in all ways that I have ever dealt with them. They truly are a rare company with the perfect mix of qaulity gear.

Great sound....fitment issues.

Written By Old Subaru WRX, Earth on Thursday, June 23, 2011

Cons: These speakers have a very wide basket (but are not overly deep, which is a plus). They didn't fit in the rear openings without taking an ANGLE GRINDER to my car! That said, the old WRX has terrible speaker fitment issues anyway, with any brand. Crutchfield warned me about this, but I did it anyway, so it's my fault. Also, there's a bit more work with mounting the crossovers and running dual wires, but not much.

Pros: The sound. Once in, they sound amazing. Like other reviewers, there seemed to be a few-day "break-in" period with these speakers. After about a week, you can really hear all the details better, and they hit very hard for a door speaker running off a JVX XR610 (excellent, BTW) head unit. At 2.7 ohms, they will go uncomfortably loud with no distortion, and after 6 months, everything works great.

Highly recommended. They sound amazing. Fitment issues were really the problem with my car and I.

Perfect complement

Written By KENCP6, Bakersfield, CA on Wednesday, August 11, 2010

Crutchfield Customer Review (What's this?)

After installing infinity reference in my rear doors and the polk mm componets in the front i quickly realized i needed an upgrade in the rear as the infinitys were not getting the job done up against the polks, "doc" at crutchfield recomended these and what a difference they are the "match" to the polk components and made all the difference, i could tell there was something missing with the infinitys but not now, putting these in the rear doors with some dynamat all around totally kicked my system up a big notch, i would recomend these to anyone looking to upgrade weather or not you have power behind it.

amazing bass

Written By curtis, alaska on Wednesday, October 28, 2009

Crutchfield Customer Review (What's this?)

I have 2 sets of these in each of my vehicles. I cannot believe the amount of bass these put out. When they are broken in they sound amazing. Dont settle for a cheaper speaker , these rock!

Polk Audio MM651

Written By gerald, titusville Fl. on Sunday, January 18, 2009

I purchased 6.5's and the 6x9's to match. I replaced premium series ($500.00) 6.5's that had blown with 50 w rms and a x-over. I couldnt afford the top of the line polks, and hoped that these would tide me over till I could. AT FIRST... they sounded so horrible I couldnt believe it. I read about people saying they got better over time. They where right. After I sold the amp with built in x-over and installed diff. amp w/o x-over, I realized how much bass they really put out. The quarts couldnt compete at all as far as bass and mid bass. That extra bass pumping through them now broke them in, in a hurry. Now they sound fantastic. I wont lie and say as spacious and natural as the quarts, but the sound stage is high (right over the dash), their frequency extension is good with no harshness (the bane of Boston Pro's), and also very focused with no hole in the middle. MUCH better than I was expecting. They didnt sound good at high volume levels at first but after the break in period, now they get darn loud and sound great. The only draw back is how much my door rattles now, and the cone is kissing my factory grill making it buzz. For the price you cant beat them. Double ,triple or quadruple it and now your out of their class. Two thumbs up for me at this price.


Written By ERNIE, NASHVILLE on Monday, December 15, 2008

Crutchfield Customer Review (What's this?)

polk mm651,installed in avalanche,all 4 doors, mounted the crossovers in the doors, mounted speakers in stock locations,trimmed the plastic round opening of the door panel so the speaker had additional clearance on excursion.use crutchfield speaker mounting rings on front doors and the polk mounting rings on the back doors,all 4 speakers are top mounted,this way you will have the clearance needed for the windows.speakers sound excellent, punchy on the lows,clear and smooth on the mids and highs.powerd by jvc headunit(20Wx4).no sub.I tryed db651s first,lack of lowend clarity.the mm651 have much better lowend.,with an over all audiophile sound,the cost differance was worth it.crutchfields service is excellant,thank you(Jordan,Jason).the next step would be to add an amplifier.

Polk Audio Rules

Written By Richard, Elizabethtown, KY on Sunday, September 21, 2008

I now have ten Polk Audio speakers crammed into the cab of a GMC cube van(used to be a moving rental van). A pair of component, two pair of eight inch subs(MM2084), and the pair of full range MM651s, all of which are driven by twenty- five hundred watts of amplifiers. I used the MM651s to "fill in a void" located in the center of the cab and BOY HOWDY did they fill it in. Now I fell like I'm "in the speaker" instead of being surrounded by them. Better yet, I can't here myself sing anymore!!!

Get everything you’ll need to enjoy your new Polk Audio MM651

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.
These speaker connectors are handy if you're running new speaker wire or if your speakers have oversized terminals.
The right tools will help keep your installation simple and clean.
Dynamat 10415 Xtreme Speaker Kit

Dynamat 10415 Xtreme Speaker Kit

Two 10-in. x 10-in. Sheets

Item #: 15410415


Add to Cart
Dynamat 10435 Xtreme Door Kit

Dynamat 10435 Xtreme Door Kit

With four 12" x 36" sheets — covers two doors

Item #: 15410435


Add to Cart
Dynamat SuperLite Tri-Pak

Dynamat SuperLite Tri-Pak

Triple package — 3 sheets, 12 square feet (Model #10612)

Item #: 15410612


Add to Cart
T-Spec 16-gauge Speaker Wire

T-Spec 16-gauge Speaker Wire

Black/white jacket — priced per foot

Item #: 120SW16WB1


T-Spec 12-gauge Speaker Wire

T-Spec 12-gauge Speaker Wire

Black/white jacket — priced per foot

Item #: 120SW12WB1


Stinger PRO Series Speaker Wire

Stinger PRO Series Speaker Wire

Priced per foot (16 Gauge)

Item #: 541SPW516B


Boom Mat 6-3/4

Boom Mat 6-3/4" Speaker Baffles

Protect your speakers
Regular and slim-line sizes (Slim-line: 3" depth)

Item #: 696B050341


Add to Cart
XTC 6-3/4

XTC 6-3/4" Speaker Baffles

Protect your speakers (Slim-line: 3-3/8" depth)

Item #: 237XT62


Add to Cart
Metra Female Quick Slides

Metra Female Quick Slides

An assortment of female quick slide connectors for connecting to speaker terminals

Item #: 120FQS10PK


Metra Crimp Tool and Connectors

Metra Crimp Tool and Connectors

Package contains crimp tool and over 150 pieces

Item #: 120CRIMPKT


Add to Cart
S&G Wire Cutter/Stripper Tool

S&G Wire Cutter/Stripper Tool

Cuts and strips 12- to 22-gauge wire

Item #: 18119100


Add to Cart
S&G Tool Aid 87615

S&G Tool Aid 87615

Window and Door Clip Removal Tool

Item #: 18187615


S&G Tool Aid 87650

S&G Tool Aid 87650

Door Trim and Panel Removal Tool

Item #: 18187650


Bojo Trim Panel Tools

Bojo Trim Panel Tools

Set of 6 pry tools — helps remove interior and exterior trim and door panels

Item #: 126CR6NGL


Add to Cart
Skewdriver Pro SPK4042

Skewdriver Pro SPK4042

Ratcheting straight and offset screwdriver set with 40 bits (Skewdriver Pro with ratchet handle, pictured)

Item #: 180SPK4042


Add to Cart
Spec Tools SQR-200a Squeeze Wrench

Spec Tools SQR-200a Squeeze Wrench

Narrow space ratchet kit with 18 sockets

Item #: 180SQR200A


Add to Cart
Install Bay 3320

Install Bay 3320

Auto-ranging digital multimeter

Item #: 1203320

Add to Cart
Install Bay IB35400

Install Bay IB35400

Premium door panel and trim tool

Item #: 12035400

Add to Cart
Bojo Trim Panel Tools

Bojo Trim Panel Tools

Set of 6 pry tools — helps remove interior and exterior trim and door panels

Item #: 126CR6LNGL


Add to Cart