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Polk Audio FXi A4

Dipole/bipole surround speakers (Black)

Item # 107FXIA4B

Add the Polk FXi A4 surround speakers to your home theater system and enjoy dramatic rear-channel sound effects...

Add the Polk FXi A4 surround speakers to your home theater system and enjoy dramatic rear-channel sound effects...

Item # 107FXIA4B

Temporarily out of stock

Expected: 8/31/2020

$399.99 -$150.00 Special purchase

$249.99 pair

About the Polk Audio FXi A4

Add the Polk FXi A4 surround speakers to your home theater system and enjoy dramatic rear-channel sound effects with your favorite movies. These cleverly designed speakers feature two tweeters aimed 45° from each other, for an ideal mix of direct and indirect sound.

Add the Polk FXi A4 surround speakers to your home theater system and enjoy dramatic rear-channel sound effects with your favorite movies. These cleverly designed speakers feature two tweeters aimed 45° from each other, for an ideal mix of direct and indirect sound.

Dipole/bipole operation for flexible placement
A dipole/bipole switch lets you position the FXi A4s on the rear or side walls of your home theater room — you'll get great results either way. If you place them behind your listening postion, set them to bipole mode for distinct, directional sound. Or set them to dipole mode for side placement, and they'll create a more diffuse soundfield for convincing wraparound effects.

A high-tech approach to accurate sound
Polk carefully designed the drivers using laser testing to help identify and eliminate resonance points. The acoustically inert MDF cabinets fight internal vibrations that can compromise performance. It all adds up to enveloping surround sound that fully immerses you in the movie action.

Got wire?
Most speakers don't include any. Learn about choosing and installing speaker wire at the Crutchfield Learning Center.
Shop our selection of speaker wire.


Product highlights:

  • bass-reflex (ported) design
  • frequency response 60-26,000 Hz (-3dB)
  • recommended amplifier power: 20-125 watts
  • two 1" silk/polymer dome tweeters
  • 5-1/4" Dynamic Balance® polymer composite woofer
  • 8-ohm impedance
  • sensitivity 88 dB
  • dipole/bipole switch
  • keyhole slot for easy wall-mounting
  • 5-way binding post terminals
  • voice-matched to Polk's RTi tower and bookshelf speakers and CSi center channel speakers
  • 11-5/16"W x 12-1/16"H x 7-13/16"D
  • warranty: 5 years
  • Our 60-day money-back guarantee
Priced per pair
  • MFR # AM4425-B

What's in the box:

  • 1 Black left surround speaker
  • 1 Black right surround speaker
  • 2 Self-tapping screws
  • 8 Self-adhesive rubber feet
  • Owner's Manual (English/French/Spanish)
  • Template
  • Online registration sheet
  • Polk Audio product brochure

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Crutchfield response

<< >>

More details on the Polk Audio FXi A4

Stacey B.

Features & specs

Enclosure Bass Reflex
Bipole or Dipole Bipole/Dip
Tweeter Soft-Dome
Midrange size (inches) N/A
Woofer size (inches) 5-1/4
Connector Type 5-way post
Power Range 20-125
Sensitivity 88 dB
Impedance (Ohms) 8
Frequency Response 60-26k Hz
Height (inches) 12 1/16
Width (inches) 11 5/16
Depth (inches) 7 13/16
Weight (pounds) ---
Mounting Bracket Included Keyhole
Parts Warranty 5 Years
Labor Warranty 5 Years
The Polk Audio FXi A4 replaces these items:

Product Research

Driver Technology
Enclosure Design
Mounting Options

Driver Technology

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.

Polymer Composite Woofers: Each speaker features a 5.25" polymer composite woofer for smooth wide-range response with low distortion. For high performance durability, each woofer uses a butyl rubber surround.

Silk/Polymer Tweeters: Each speaker has dual 1" silk/polymer dome tweeters that provide clear, detailed highs and spacious surround effects. Each tweeter uses a heat sink on the Neodymium magnet for superior heat dissipation, power handling and reliability.

Frequency Response: The overall frequency response is 50Hz-27kHz and the -3dB frequency response is 60-26kHz.

Enclosure Design

Enclosure: Each enclosure has a triangular shape with the speaker faces angled at 45 degrees. One face has a tweeter and a woofer, while the other face has a tweeter and port tube opening. A switch for selecting Dipole or Bipole operation is located on the rear of the speaker above the speaker's 5-way binding post speaker terminals. One of the speakers is specifically designed for the "left" channel and the other for the "right" channel.

Acoustically Inert Cabinets: Each speaker cabinet features all-MDF construction with internal bracings that virtually eliminate sound-muddying resonance. The speakers are finished in either a black or white laminate finish.

Anti-Diffraction Grilles: The floating anti-diffraction grilles minimize grille diffraction for spacious, 3-dimensional imaging.

Port: On the side with only a tweeter, there is a single port tube opening for increased and extended bass response.


5-Way Binding Posts: The gold-plated 5-way binding posts will accept bare wire, pin connectors, spade connectors, banana plugs, and dual banana plugs.

Mounting Options

Dipole/Bipole Switch: There is a switch that allows each speaker to be used as a Dipole (out of phase) or Bipole (in phase) speaker. If you're mounting the speakers on the side walls in line with your listening position, the dipole mode will create a diffuse, ambient soundfield. If you're placing them behind your position, the bipole mode fires the drivers in phase to flood your room with surround sound. When used with a Dolby Digital system, the surround speaker setting should be set to small.

Wall Mounting: The bracket on the back of each speaker has two keyhole slots, allowing the speaker to be mounted on the wall using the supplied 2-1/2" wood screws.

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Customer Q&A

Crutchfield asked: Why did you buy this?
I have Rti A9 tower speakers for my main room & surround with Tsi 400 for another room. both awesome speakers & sound. so to up grade my rear channel speakers these seam/sound like a natural choice to go with the Rti A9 to create a GREAT surround system. so since the other Polk Audio speakers are so great why screw with a winning set up. I think That Polk makes GREAT speakers and I don't think you'll find better sounding ones for the money. I haven't Thank you, Mike McIntosh [ Michael  Jun 20, 2020 ]
Excellent ratings Good looking speakers! [ Barry  May 04, 2020 ]
I purchased these speaker because I felt they would be perfect for my Atoms ceilings speakers [ JUSTIN  Apr 26, 2020 ]
I've used Polk Audio products for years and have always been satisfied. [ J  Apr 07, 2020 ]
Match existing front speakers, positive reviews. [ Bradford  Apr 07, 2020 ]
Brand, bipolar, surround [ Romel  Feb 17, 2020 ]
I had recently purchased a pair of RTIa9's and the CSia4 and needed some decent surround speakers. I liked the FXia4's because the dimensions would fit in the space I had available (same reason I got the CSia4 and not the CSia6). I usually keep the front grills off and it's nice that all of these share the same 5 1/4" midrange / woofers. Looks and sounds terrific! [ DOUG B  Nov 09, 2019 ]
Price and recommendations. [ Angel  Oct 30, 2019 ]
Polk Audio is very good brand. I have their bookshelf speakers and this will provide top notch surround sound. [ Lauri  May 13, 2019 ]
These speakers are voice matched to the bookshelf and center speakers that I purchased from Crutchfield. The salesman named Zac was most helpful in describing to me how these speakers work. [ Maria  Mar 26, 2019 ]
Sound matching to my existing Polk speakers as well as prior positive experience with Polk Audio products. [ Daniel  Jan 28, 2019 ]
I needed a good surround sound speaker plus it had good reviews. [ Maurice A.  Jan 11, 2019 ]
Polk makes excellent products and Crutchfield provides great support before and after purchases. [ Todd  Dec 12, 2018 ]
Highly recomended! [ Dave  Nov 27, 2018 ]
Bi-modal flexibility and power when you need it. [ Ian  Nov 26, 2018 ]
Recommended by your help group [ Rafael  Nov 23, 2018 ]
Quality, function & price. [ JERRY  Nov 22, 2018 ]
To complete my Polk surround sound [ HENRY  Jul 30, 2018 ]
I wanted Surround Speakers that offer a solid dispersion and would compliment my MartinLogan XLM's for LCR, but without the Motion FX price tag. [ RICHIE  Jan 31, 2018 ]
I am unable at this time to go to a 7.1 setup so I am taking a chance on these. Reviews were good on Youtube and Crutchfield so when they went on sale I figured it was time. [ Michael  Jan 24, 2018 ]
To enjoy full background sound [ Terry  Jan 13, 2018 ]
Upgrading the surround speakers in my Polk Audio system [ stickywicked447  Jan 10, 2018 ]
recommended by polk audio to match the RTia3 [ David  Dec 04, 2017 ]
Polk makes good audio equipment. $150 savings on these speakers is a great deal !! [ John  Dec 01, 2017 ]
Looking for a good surround speaker and Polk's reputation is excellent to say the least Reading through the reviews I didn't see any negative feedback at all [ Chad  Nov 26, 2017 ]
On sale, good manufacturer, upgrade for rear channel sound [ Jeremy  Oct 17, 2017 ]
Polk Audio Rocks [ ERIC  Oct 12, 2017 ]
Quality Polk products [ Jeffrey  Sep 17, 2017 ]
On-Line Reviews and Feedback from customers;. Sale Price. [ Mike  Sep 17, 2017 ]
Cost and quality. [ L  Jul 29, 2017 ]
From reviews and should work good for my surrounds and back speaker [ Keith  May 09, 2016 ]
To match and compliment my existing Polk Audio gear. (3) 265rt's (L-C-R), (2) 255crt's in ceiling (Atmos) and (2) PSW505 subwoofers, for a complete 5.2.2 Home Theatre setup! [ Greg  Apr 10, 2016 ]
Upgraded receiver to 7.2 from a of speakers are 10 year old Polk and wanted to maintain the same quality that I have been satisfied with for a decade [ JOE  Mar 22, 2016 ]
Good reviews, and matches/compliments the RTI A9's and CSI A6 I purchased as well [ James  Feb 27, 2016 ]
Have seen great reviews and can not wait to setup. [ ZION C  Jan 24, 2016 ]

7 questions already asked

I wish to connect these to a sonos connect to use in my garage as standalone pair. I realize they are intended for surround but what is your opinion of them as standalone bookshelf speakers?
[ David  Dec 27, 2019 ]
4 answers
I can tell you they are awesome for surround. I have 4 of them rounding out the side and rear. I would move towards something with more power for any other purpose. Besides with all the great choices crutchfield has, why settle on a surround speaker for that application.
[ Frank  Feb 01, 2020 ]
One word.. AwesomeEnter an answer to this question.
[ DONALD  Jan 07, 2020 ]
I personally use this as a surround speaker for my home theater system. If you use as standalone stereo speakers ,you may not get the best sound.
[ Ravi  Jan 07, 2020 ]
The very design and physical orientation of the drivers in these speakers intends their use as surround speakers only. My opinion would be a decent pair of 6"/ 8" woofer bookshelf types would sound much better and be better suited for your intended use. After all, it is just a garage, right ?? Even the Polk Atrium ( patio-type ) speakers would sound decent. ( I also have these ). ( I am not sure of the Sonos connectivity for either, however- ) Good luck. Your garage will sound very good -
[ Otto  Dec 27, 2019 ]
I am building a new 7.1 channel system and am thinking of using these FXI A4's for all 4 of the surrounds (pair on side and pair in back). Is this advisable or are they really only best for a 5.1 setup? I am planning on the CSI A4 center and the RTI A3 bookshelf speakers for the fronts.
[ Steven  Jun 05, 2018 ]
2 answers
Work great for side and back.
[ steve  Jun 05, 2018 ]
Yeah I don't think I'd do that. These are big- look at the measurements- these are bigger than the fronts you want to buy. I have them as 90 degree side surrounds in a 7.1 setup and they're great. They're also designed to be back a little further and make a 5.1 system sound more like a 7.1. If I were you would get those A3's but use them as your Surround Backs and then get either the A5 or A7's for your fronts (I have the A7s and love them).
[ Kellan  Jun 05, 2018 ]
do you have to mount these on the wall or is a stand OK?
[ S  Dec 27, 2016 ]
9 answers
They come with mounting plates but I'm sure stands would work as well.
[ James  Feb 19, 2017 ]
I have mine mounted on the wall, but I would imagine that they will work just as well if placed on a shelf or stand. They are fantastic speakers and you will not be disappointed!
[ FRANK A  Dec 29, 2016 ]
I have mine mounted. I think they'll work fine either way.
[ Robert  Dec 29, 2016 ]
I have mine mounted to the wall. If the floor stands you have except a wall mount bracket that would work as well.
[ Randy  Dec 28, 2016 ]
Either way. I have mine on the wall. Have these in my vacation home. I have Rti a3 at home also on the wall. Polk make the best all around speaker.
[ PATRICK  Dec 28, 2016 ]
Either way will work. I wall mounted mine.
[ jason  Dec 28, 2016 ]
The speakers are very solid and fairly heavy. I mounted mine on a wall with the integrated bracket, but I'm sure they would do fine on a properly sized speaker stand.
[ Rick  Dec 28, 2016 ]
These can be placed on a stand, table or shelf, as well as wall mounted.
[ GEORGE  Dec 28, 2016 ]
Stands should be ok, depending on location. Like any surround speakers.. location, location, location!!! Stands of course will be fine and work, so Good Luck!!
[ Greg  Dec 28, 2016 ]
I have a pair of polk 7LSI speakers. 2 questions. 1 will my speakers make a good match to polk FXI A4? 2 what one would you suggest as my back speakers? Currently using polk up front and dieing infinity in back with a klipsh center.
[ Rodlet  Jan 30, 2016 ]
2 answers
1. The Polk FXi A4 will make a satisfactory match for the LSi front speakers. 2. However you would achieve more seamless sound effects when you also add LSi surround speakers. I would recommend the Polk LSi M702 F/X as your surround speakers.
[ NORBERT  Jan 31, 2016 ]
i have all polk speakers and think they all match up well to each other, You cant go wrong. i use the FXI A4 on the sides and back. Love all 4 of them! I have the Polk Monitor 70 as my mains and the Polk CS2 as my center. go for it.
[ Martin  Jan 30, 2016 ]
I have the Infinity Primus PC253, PC351 and the PS312. Will the Polk Audio FXi A4 go with it?
[ Louis  Oct 03, 2015 ]
2 answers
yes they will and they sound very good
[ RICHARD  Oct 07, 2015 ]
I forwarded your question to an Advisor and they responded with the following: I would try to stay within manufacturer as much as possible. The reason for this has to do with voice matching your speakers. Ideally you want the same type of components in your speakers so that a motorcycle traveling front to back on your speakers will sound the same all the way across. The tweeter on the Polk FXi A4 will be a bit softer of a material and may give you too much of a warm sound versus the bit brighter sound of the Primus you already own. I would look at the Infinity Reference R152 which has a tweeter is made with much closer material than the Polk which will allow it to mesh better. If you would like to discuss further you can contact an Advisor directly by phone (1-800-324-9695) or online chat.
[ Krissy  Oct 06, 2015 ]  Staff
Will the Polk Audio FXi A4 or A6 make a good match with my system that uses Polk Monitor 75Ts?
[ Bruiser  May 15, 2015 ]
1 answer
Yes, both are a good match with the 75T. The FXi A4 is similar in price rage to your 75T. I have the FXi A4's and they produce excellent surround sound. i feel like i am sitting in a movie theatre.
[ JOHN B  May 17, 2015 ]

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