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Polk Audio MM5251

400W Max 5.25" 2-Way MM Series Component Loudspeaker System

In Stock. Only 2 Left!
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Butyl Rubber Surround, Silk/Polymer Tweeter and Woven Glass Composite Woofer:
Perfect for Moto/Marine, Boat or Car Installs

List price $399.95

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Polk Audio MM5251

400W Max 5.25" 2-Way MM Series Component Loudspeaker System


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NVX 25 ft. of True Spec 12 Gauge Speaker Wire

100% OFC wire with EnvyFlex metallic jacket insulates and protects against damage from extreme conditions.


Car Stereo and Speaker Installation Tool Kit

Includes Test Light, Crimp/Splice Tool, Multi-bit Screwdriver and more.


NVX SDDK12 Door Kit

Eliminates speaker panel distortion and reduces door vibration, rattles and squeaks!



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10% off on Sound Dampening!

For a limited time, save 10% off the NVX SDVK4 Versa Kit with a qualifying pair of speakers! Sound dampening will eliminate rattles, insulate against heat, and also improve the sound and output of your speakers! This offer cannot be combined with any other coupons or offers.




Polk Audio MM5251



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NVX SDVK4 - 90mil 2.3mm THICK


Special Price $17.99 ($19.99 if purchased separately)

NVX SDVK4 - 90mil 2.3mm THICK

• Eliminates Road Noise
• 2.3mm (90.55mil) thick for better performance
• Quiets Vibrations
• Stops Rattles
• Increases SPL
• Reduces Heat
• Simple To Install
• Easy To Form Aluminum
• Four Step Peel and Stick Installation
• One 18" x 32" Piece

(Offer 1 of 1)

Combined Total Price


You Save $2.00

Will fit most 6x9" and 5x7"/6x8" locations,
with appropriate speaker adapter. Click "Related Items" Tab.

Polk Audio Store

MM Series - Superior Performance

The Mobile Monitor Series by Polk Audio is the result of 3 years of research and development. The series uses high quality materials and the newest loudspeaker technology to bring the listener an unforgettable experience. The best part about the MM Series is the affordable price. The new MM series have been designed to offer unparalleled sound quality with exceptional fit to meet virtually any application. Borrowing technology from our flagship SR Series, the MM Series offers exceptional value for the price. Through the use of high-tech carbon composite baskets, powerful neodymium motor structures using oversized voice coils, and state-of-the-art woven glass composite cones, Polk Audio offers high-end audio performance normally found only in the most expensive loudspeaker systems. In addition, these space age materials offer weight savings that can mean higher performance for your Car, ATV/UTV or Boat.

General Features:

  • 5-1/4" MM Series - Marine Certified - Component Speakers System
  • Power Handling:
    • Peak: 400 watts per set / 200 watts each side
    • RMS: 180 watts per set / 90 watts each side
  • Woven glass composite cone woofer
  • Butyl rubber surround for a smoother response
  • High-tech carbon composite basket
  • 1" Silk/Polymer composite swivel tweeter
  • Soft dome tweeter
  • 2-Way crossover with a 2-Position tweeter level
  • Klippel optimized components for distortion-free sound
  • 30mm large diameter voice coil
  • Neodymium magnet structure for more power
  • Nominal impedance: 2.7 ohms
  • Frequency Response: 50 - 25,000 Hz
  • Sensitivity: 92dB
  • Top-mount depth (woofer): 2-3/8"
  • Cut-out diameter (woofer): 4-5/8"
  • Authorized Internet Dealer
  • 1-year Manufacturer's Warranty

Priced Per Complete Component System: 2 midwoofers, 2 tweeters and 2 crossover networks.

Check out the Polk Audio MM5251 Owner's Manual

Note: Polk Audio specifies the nominal impedance of these speakers to be 2.7 ohms. The product box states the impedance to be 4 ohms and the speaker magnet shows 2 ohms, this has been confirmed by Polk Audio to be an incorrect specification. The product manual is correct in stating the nominal impedance of the MM series of speakers to be 2.7 ohms.

Speaker Specifications

This is the manufacturer product line of speakers.
MM / Mobile Monitor (Polk)
Priced Per
Car Speakers are typically sold in pairs so you will receive 2 speakers for each speaker purchase on speakers marked "Priced Per Pair". If a speaker is marked "Priced Per Each" then the speaker is sold individually and each purchase you make will result in 1 speaker. High-powered tweeters, midrange and full-range pro audio for car speakers are typically sold per each speaker.
Speaker Size
Refers to the size of the speaker measured in inches. Every vehicle has standard application sizes. Please use our vehicle fitment guide for your vehicle's specific speaker sizes if you do not know them.
The number of individual drivers in a car speaker. Speakers with 2 drivers are known as a 2-way, and 3 drivers are known as a 3-way. Component systems are often referred to as "separates" because the tweeter is not attached to the midwoofer (main speaker driver) and mounts separately in a location such as a door post. Component systems typically come with an external crossover so you can easily adjust the high and low frequencies sent to both the midwoofer and the tweeter. Center channel speakers are great for those looking to have surround sound in their vehicle.
2-way Component System
Tweeter Design
Designs such as cone, dome, semi-dome, balanced dome, and whizzer are most popular. Cone tweeters are simple, efficient and typically are the most reasonably priced. Dome tweeters are used in most home speakers, and provide a smoother and more accurate sound. Semi-dome design is one with a dome placed inside a cone. A Balanced dome driver is a semi-dome with equal reproduction area given the cone and dome portions of the driver. A whizzer tweeter is a separate tweeter cone driven by the voice coil of the woofer.
Tweeter Size
Refers to the size of the tweeter. Typically, smaller tweeters produces less output with higher frequency response.
Tweeter Composition
Materials such as polypropylene, silk, cloth, and paper are the most common, where as many more recent tweeters are now manufactured with composites such as Aluminum, Titanium, Mylar, and other materials.

PEI is an acronym for "Polyetherimide" which is an amorphous, amber transparent, high-performance thermoplastic.

Silk-Polymer Composite
Woofer Composition
Lightweight woofer cone materials are essential for efficient operation. Poly cones produce exceptional sound and are sturdy against various changes in temperature. Paper cones are very efficient, and when treated for moisture resistance, will perform at a high level. Poly refers to polypropylene, which is thermoplastic or fibers that are polymers of propylene. IMPP refers to injection molded polypropylene, a commonly used process and material in speakers.
Woven Glass Fiber
Woofer Surround
A speakers surround is part of the suspension system. The surround protects the cone and prevents it from being displaced as it flexes out from the basket. It is usually made of a durable material like treated foam or rubber in order to withstand the strenuous job of producing bass frequencies.
Butyl Rubber
Peak Power Handling
Peak power handling refers to the amount of power a speaker can handle during a brief musical burst. The RMS power range figure is a much more reliable rating for determining the speaker's power requirements. The Peak power handling specification is typically rated per speaker unless otherwise noted.
200 watts
RMS Power Handling
The RMS power is the amount of power the speaker requires to operate safely and properly. RMS Power Handling refers to the amount of power a speaker can handle on a continuous basis. We recommend powering your speakers or subwoofer with 80%-120% of its recommended RMS rating. The RMS power handling specification is typically rated per speaker unless otherwise noted.
90 watts
An efficiency or sensitivity rating tells you how effectively a speaker converts power into sound. The higher the number, the more efficient the speaker and the louder it will play with the same input power. An efficient speaker helps you maximize your available power. Most sensitivity ratings measure the speaker's output with 1 watt of input, 1 meter from the speaker. Some speakers' sensitivity is measured with 2.83 volts of input, instead of 1 watt.
Efficiency (1w/1m) is not an accurate indicator of a subwoofer's output capability and should not be used as a comparison to other speakers or subwoofers to determine which one is "louder".
92 dB
Frequency Response
The range of frequencies the speaker will reproduce (lowest frequency to the highest). Bigger is better, meaning the wider the range, the better. The optimal range is 20 - 20,000 Hz (which is the range of human hearing).
50 - 25000 Hz
Impedance (Per Voice Coil)
The load value (in ohms) that the speakers present to the amplifier per voice coil - the amount of resistance to the current flow. This is a key specification as subs wired in parallel or low impedances can create problems with your amplifier and potentially void all warranties. We encourage you to ask our support department prior to purchase if you do not understand which impedance level will suit your application best.
Shallow Mount Installation
This means that the subwoofer/speaker is designed to be installed in areas that do not have a lot of space. Shallow mount subwoofers are typically found under a seat or behind the seat in some trucks.

Shallow mount speakers will typically have a mounting depth of 2" or less, while shallow mount subwoofers will typically have a mounting depth of 3" or less.

Top-Mount Depth
The depth when installed on top of the mounting surface. Measured from the bottom of the speaker's magnet to the bottom of the mounting holes on the rim of the speaker.
Cutout Dimensions
Refers to the dimensions of the hole, measured in inches, required to contain the speaker.
Hi-Res Audio Compatible
This feature refers to if the product is capable of Hi-Res Audio (HRA) playback.
Speaker Grilles
A grating or screen of metal or plastic bars or wires, mounted in front of a speaker as protection. If yes, the speakers will include matching speaker grilles. If no, there are no grilles included.
Number of Speakers
This is the number of speaker that is included in the package. Each purchase will result in receiving the number of speakers indicated here. Please note that some items will have multiple woofers in the same enclosure. For sets of component speakers, this number will refer to the number of sets of speakers (For example, 2 would indicate the purchase includes 2 woofers and 2 tweeters).

Please refer to the product image and description for further details about the speaker.


Warranty and Return Policy

Parts Warranty Duration
1 year
Labor Warranty Duration
1 year
Warranty Provider

Summary of Customer Ratings & Reviews

Rating Distribution

5 Star
4 Star
3 Star
2 Star
1 Star

Average Attribution Rating


Louisville, OH

Great Value

October 11, 2010

There are a few better sounding speakers out there, but not many. And nothing even close to this price range. Very clean and crisp sound. You have to get creative with the tweeter mounting, but it's easy for someone with installation experience.

34 of 39 found this helpful

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Santan Valley

Clean sound

August 14, 2012

I chose this set over the db series based on the freguency range and Polks reputation for there home monitors. I was taken back by the size of the driver magnet, or the lack thereof. It provides easy fitment in tight spaces. The sound is amazing, capturing sounds that weren't heard on other systems that I've used. One draw back, if your looking for mid bass response, it lacks kick. Of course, that's not really what the mm series were intended for. My listening experience has been enjoyable on the long drive to work, and overall I believe that this is an excellent choice.

31 of 36 found this helpful

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Redondo Beach, CA

Great speakers if you don't have the room for the 6501s!

October 29, 2009

The MM5251s are awesome speakers, but the slightly larger MM6501s have a much lower frequency response and therefore sound much better.

If you don't have the space, or if you have a sub, then it does not matter!

I know because I have both sets in two different cars.

I highly recommend all Polk MM series speakers for their build quality, design, and warm clear sound.

26 of 31 found this helpful

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Liberty, NC

Amazing sound

September 17, 2013

I have owned Boston Acoustics, MB Quartz, and Infinity component speakers. The Boston and the Infinity sounded great, but they could not handle power well. This time I decided to try the Polk Audio MM series components, WOW! These speakers sound so good and they have no problem with power. I`m running a Rockford Fosgate Power series 600-4 on my mids and highs with these speakers. They sound so good that I have bought 3 sets to replace all of the speakers in my two vehicles (97 Buick Lesabre and 06 Infiniti G35). I have be into aftermarket stereos for over 20 years and for the price you can`t beat these components.

26 of 32 found this helpful

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Ryan K.


Good Speaker

October 24, 2012

I had these polks installed for about 7 months in my audi for the front doors. They are wonderful sounding speakers. Crisp highs that sound great, good mids to fill in the gap, but no lows. Do not think that these make bass. That is wrong. They are for really capturing the upper to mid notes and reproducing them as clean as only these speakers can. No rap or rock song will pound on these. It will just sound clean. I give them a five star on pure sound quality. Polk is a great brand and these prove that.

26 of 32 found this helpful

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Phoenix, AZ

Polk Audio MM5251

September 27, 2009

I have read other speaker reviews when the writer would speak to "hearing notes and instruments I had not heard before..." Now I know what they're talking about. I haven't even installed my sound processor or amp and my OEM stereo sounds great.

25 of 30 found this helpful

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Kirksville, MO

Great Speaker

January 20, 2010

These speakers sound amazing. They produce great highs and amazing lows and mids. The best speakers I have ever owned! I recommend these speakers to anyone and everyone.

23 of 29 found this helpful

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Virginia Beach, VA

Great marine speakers, but only good car speakers

December 22, 2011

The frequency response, distortion levels, and punch on these speakers are second to none; however, those attributes come at the cost of fidelity. I purchased a set of JBL GTO938 6X9 Speakers, and based on the reviews and relative cost, I expected the MM5251 to blow them away. I was wrong: the 938's reminded me that I purchased marine speakers. If you want maximum sound for your money, get these speakers. HOWEVER, if you're looking for a high quality sound, I recommend you look elsewhere.

23 of 30 found this helpful

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Roswell, GA

Polk Audio MM5251 Review

August 10, 2010

I would highly recommend this product.

What I like: The speakers produce accurate and clear music - they sound excellent. The highs are extremely crisp and the mids are strong, but not overwhelming. The sound quality continues into the ear-bleeding intensity levels - I have not yet heard noticeable distortion.

What I don't like: The mounting on the tweeters is not conducive to flush mounting. Neither me nor the stereo installer could find a way to flush mound the tweets, so my truck has them protruding from the dash and it looks terrible. If I had known that they would not flush mount, I would have selected an alternate brand, even through the sound is so good.

21 of 26 found this helpful

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Matt K.

Richmond, VA

Just go ahead and buy these

June 14, 2010

I want to say don't go cheap on your speakers, but these really aren't even that expensive. especially for how great they sound. I have these up front and a pair of 90w coaxial polk speakers in the rear powered by a 90w x 4 channel polk amp, with a pioneer deck. and i couldn't be happier with the way it sounds. crystal clear. songs literally sound better with these. I wish i could help to give a more well rounded rating by giving some cons, but i cant think of any. buy these!

22 of 28 found this helpful

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Accessory Tools and Products

Accessories added

NVX 25 ft. of True Spec 12 Gauge Speaker Wire

100% OFC wire with EnvyFlex metallic jacket insulates and protects against damage from extreme conditions.

Your Price $39.99

Streetwires 25 ft. of True Spec 12 Gauge Speaker Wire

You need speaker wire to connect your speakers!

Your Price $36.99

Belva 23 ft. of True Spec 12 Gauge Speaker Wire

100% Copper Clad Aluminum, high strand count with ultra-flexible PVC blended jacket for easy installation

Your Price $14.99

Car Stereo and Speaker Installation Tool Kit

Includes Test Light, Crimp/Splice Tool, Multi-bit Screwdriver and more.

Your Price $18.99

NVX XTGSP2 Tone Generator and Speaker Polarity Tester

Perfect for safely troubleshooting and testing audio systems

Your Price $19.99

Belva Five Piece Installer's Panel Removal Tool Kit

Easily removes dash/trims, door clips, panels and pins, rubber grommets and vehicle emblems.

Your Price $11.99

Universal Wire Puller & Grabber

Running wires has never been easier! This wire puller allows you to run wires through those hard to reach places!

Your Price $7.99

Encore Universal Four Door Power Door Lock Kit

Add Power Door Locking and Unlocking while you have the Door Panels removed

Your Price $29.99

NVX SDDK12 Door Kit

Eliminates speaker panel distortion and reduces door vibration, rattles and squeaks!

Your Price $47.99

Dynamat Xtreme Door Kit 10435

Enough sound dampening to cover most doors!

Your Price $69.97

Stinger Roadkill Door Kit

Use this to eliminate rattle from your doors!

Your Price $39.95

NVX Sound Dampening Rubber Roller

Install your Sound Dampening with ease using this heavy duty rubber roller!

Your Price $7.99

Speaker Baffles for your Speakers

Enhance the sound of your speakers with these easy to install speaker baffles.

Your Price $9.99

5" to 5-1/4" Round Foam Speaker Baffles

Creates a tight, acoustic seal behind the speaker to enhance the sound quality.

Your Price $8.99

12-10 AWG Butt Connectors

These yellow butt connectors are ideal when connecting thicker speaker wire your new aftermarket speakers.

Your Price $5.99

12-10 AWG Quick Disconnect Connectors

These yellow quick disconnect connectors make it easy to connect and disconnect speaker wire your to your new aftermarket speakers!

Your Price $11.99

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Browse 3 questions and 5 answers
Hide answersShow all answers | Sort by
Why did you choose this?
Sonic Electronix Store
A friend says that Polk speakers are super high quality... I am going to try them out.
Dan R on Jan 11, 2015
2004 BMW 325CI convertible w/ business class hifi audio system. I will be replacing the factory deck to BOSS AUDIO BV9967B w/ Polk 6 1/2 for doors 5 1/4 polk 3/4 component for rear side panel w/ a powered Infinity Subwoofer in trunk. Do I need a "output Converter" for the factory AMP and speaker wire hookups?
Erik R on Mar 1, 2016
Polk Audio MM5251
Polk Audio MM5251
Polk Audio db651s
Polk Audio db651s
Boss BV9967B
Boss BV9967B
Polk Audio 2-db651s
Polk Audio 2-db651s
Best Answer: No you will not need an output converter just a wiring harness. You can use the output from your new radio that is label (Front Rear Sub out) by hooking the power sub using rca audio cable to your sub out on the radio to the power woofer. No speaker wire is needed just a radio harness. But for better sound add a outboard amp to power those speakers you will a happy man. You will need speaker wire and a amp kit to hook everything up. Look at the NVX product line will have everthing you need.
Reply (1) · Report · Brandon H on Mar 1, 2016
· Add Answer · I Have This Question Too (0)
What is the cutout diameter of the tweeter for flush mount?
Longdrive on Sep 19, 2015
· Add Answer · I Have This Question Too (0)

Product Summary


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Internal SKU


Internal Product ID


Sonic Electronix Wiring Guide

Wiring Diagram Legend

Warning: The image depicted shows the resistance change when wiring multiple subwoofer terminals. Please refer to your subwoofer's owner's manual for the proper wiring of its terminals. Sonic Electronix, Inc. is not responsible for damage caused to your audio system or vehicle due to improper installation. Please call tech support at 1-877-289-7664 if you require additional assistance.

Product Name: Polk Audio MM5251