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Infinity 120.9w

Kappa Series 12" subwoofer with selectable 2- or 4-ohm impedance

9 Reviews | 6 questions - 7 answers

Item # 1081209W

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Our take on the Infinity 120.9w

Infinity Kappa subwoofers combine great-sounding bass with the wiring versatility you need to build a system that can expand to meet your changing needs. And these enhanced woofers feature superior construction that makes the thump come easy.

Infinity Kappa subwoofers combine great-sounding bass with the wiring versatility you need to build a system that can expand to meet your changing needs. And these enhanced woofers feature superior construction that makes the thump come easy.

The Kappa 120.9w 12" subwoofer features Infinity's unique Selectable Smart Impedance design, which lets you build exactly the system you want — high-power or multi-sub — without complicated wiring. Just flip the convenient impedance switch to safely choose between 2 or 4 ohms. If you're thinking about upgrading your amplifier or adding another sub down the line, this sub makes it easy to reconfigure — and it's nearly impossible to wire incorrectly.

This sub handles plenty of power and sounds great in sealed and ported enclosures, too. The coated glass-fiber cone offers remarkable rigidity that minimizes distortion, while the thick rubber surround promotes smooth excursion. Add the hefty cast aluminum basket to the mix and you've got proven delivery system for potent low end.

To drive this single subwoofer, we recommend a mono amplifier rated between 260 and 525 watts RMS at 2 ohms. For more information, please refer to our article on How to Match Subwoofers and Amplifiers.

Priced per speaker

Product Highlights:

  • 12" subwoofer with selectable 2- or 4-ohm impedance
  • coated glass-fiber cone with rubber surround
  • cast aluminum basket
  • frequency response: 23-400 Hz
  • power range: 50-350 watts RMS (1,400 watts peak power)
  • sensitivity: 91 dB
  • top-mount depth: 6-3/8"
  • sealed box volume: 1.0 cu. ft.
  • ported box volume: 2.0 cu. ft.
  • warranty: 3 years
  • Our 60-day money-back guarantee

You can not go wrong with The Infinity Kappa Series, No Distortion, Solid bass and just a clean sound. I recommend that you run this Sub from a Rockford Fosgate Punch amp and you will extremely satisfied with the results.

Christopher, Washington, DC

What's in the Box:

  • One 12" Woofer
  • Self-adhesive foam gasket
  • 3mm Allen wrench
  • Owner's manual (English/ French/ Spanish/ eleven other languages)
  • Technical data sheet
  • Warranty and on-line product registration information

Infinity 120.9w Reviews

Average Customer Review(s):

(9 Reviews)

Sound Quality and Lows

SMP from North Carolina on 6/11/2016

2008 Honda Civic EX

Fantastic subs.. they sound amazing and pound. Im running 2 of them in a vented enclosure and they are getting about 600watt rms via a Rockford punch amp which is also amazing. Being rated at 350 watts RMS is definitely under rated. I have tried to make them distort but at that level everything on the inside of the car is rattling and shaking so loudly im unable to listen for distortion. im a SQ guy but like to pound them also.. in the pictures they look gold but are actually more of a champagne color.. they are sexy!

Pros: Eat nearly twice the rated power with ease. Sound amazing with every music type Build quality is superb. The impedance selector is awesome.

Cons: NONE

Kappa Series 12" subwoofer with selectable 2- or 4-ohm impedance

Christopher from Washington, DC on 5/16/2016

2014 Volkswagen Jetta
Crutchfield Customer Review (What's this?)

You can not go wrong with The Infinity Kappa Series, No Distortion, Solid bass and just a clean sound. I recommend that you run this Sub from a Rockford Fosgate Punch amp and you will extremely satisfied with the results.

Pros: Perfect Solid Bass, No Distortion

Cons: None

Whoa! Wow!

Tracy from Twin Cities area, MN on 10/9/2013

Upgraded from an entry-level 8-inch sub. WOW! I never knew what I was missing! What a difference moving up to this 12-inch sub! I finally have the boom I always wanted (but never got with the smaller 8-inch sub). Powered by a five-channel Alpine amp that matches perfectly with this sub's 2-ohm setting, i.e., 350 watts. This sub is a dream!

Pros: Awesome boom that you can feel!

Cons: None!


JuJuBee from Gloversville NY on 12/2/2011

I bought these to replace my 2, 12 inch Blaupunkts that I blew apart after 6 years. I bought 2 and paired it with a 3.5 cap and a CL-1200 Amp. Im pushing a clean 450 watts by 2 at a constant 14 volts ( Hi output alt + Big 3 )and all I can say is WoW! When pushing these things will make my doors bow out from the pressure. It is insane. You will not be disappointed. These are true Infinity's in terms of the pure quality of the sound. I was hoping they dropped down to 20Hz but unfortunatly they dont and that is the only drawback. Everything from 25 and up is reproduced in a soundwave that is clean and powerful. Put them in a ported box. Give them at least 1.5 cu ft per speaker and get ready for the ride of your life. Also you should save your money as you will get a ticket,I have three times and it has been less than 6 months!

Pros: Quality Sensitivity Clean Accurate Sound

Cons: 2ohm-4ohm Switch can move ( I Fear ) when the bass is thumping Lowest it will hit is 25Hz


Zane from Mattoon, IL on 8/2/2011

You will not be disappointed, guaranteed. I purchased just one of these to begin with, then I loved it so much I got another one. Infinity may not be known for their subs, but these will help change that. I currently running two of these on the Infinity Kappa One amp in a Sound Ordanance dual ported box. They are getting 400 watts RMS each and they handle it just fine. These subs sound absolutely amazing. Keep in mind they are SQ subs, not SPL; however they do bring the punch! Trust me. If you are looking for a sub that is hi-fidelity and hits hard, then this sub is for you.




Sam from Charlottesville, Va on 9/29/2010

I bought this sub to replace my Alpine Type-S 12inch DVC 4ohm. The Alpine wasn't blown, I just wanted a better speaker, and this thing is definitely it. It is cleaner and deeper sounding than the type-s for sure. It will hit the low frequencies in bass drops that I couldn't even hear with my old sub. I've been pushing it with a alpine m450, which is 400 watts at 2 ohms and it is plenty for sure, but it's maxed out. So I went ahead and ordered one of the new Alpine pdx-m6 600 watt amps just to have a little more head room, which I don't think I need anymore now that the sub has broken in completely. Oh well, maybe it will be even cleaner sounding. Ah... also make sure your box is decent. I thought I had blown my new sub last night because it was putting off a "blown speaker" sound, but in reality, it had blown the seals on my box that I bought from Crutchfield three years ago, and was rattling the boards against each other. Guess what I'll be buying tonight...



You Better Believe It

homerkang from Atlanta, GA on 4/18/2010

i am now a believer in Infinity car subs. About 3 years ago, i bought my first sub (see my review here: It was one of the best subs ever made. Then recently it got worn down or something, but it started to distort no matter what adjustments i made on the rest of my system. At first, i kinda doubted it, but then i decided to give this Kappa model a try coz it looked good (lol) and ordered it from here. It came 2 days later. i put it in my ported box. Set the switchable impedance switch to 2 ohms so that it can absorb about 500 watts RMS, set my amp's ISF filter to 25Hz. And waited it out during its break in period. After a week of sounding like nothing, it now sounds as good as the Boston that i had. Although it falls short of the lower bass notes than the Boston (since this one only goes down to 23 Hz compared to the Boston's 20 Hz), i can live with that because it not only sounds clean and clear, it actually makes my Polk dB6501 components sound cleaner as well. Get this sub. For the price, it is THAT good.



Sweet sound

KenM10759 from Spencer MA on 4/11/2010

Crutchfield Customer Review (What's this?)

Just added this to complete a system that includes (4) Infinity Kappa 682.9cs speakers, a Kenwood KDC-MP345U CD receiver and an Infinity Kappa 5 amplifier. Not looking for a hard-hitting, overwhelming bass, this subwoofer in it's recommended sealed 1.0 cu. ft. box is amazing. Smooth, sweet sounds without flatulence, true quality construction and great looks. The combination of the smaller speakers and amp with this sub is a near-perfect! For the combined system's price point, I cannot imagine better sound quality.



Infinity 120.9w

Dennis from Louisa, VA on 10/17/2009

Crutchfield Customer Review (What's this?)

Looks good, sounds great, good price. It gets loud and low with accuracy in the recommended sealed box.




Hands-on research

Product Research

Enclosure Compatibility


Selectable Impedance: For increased system flexibility, the woofer impedance is switchable. There is a 2 ohm/4ohm switch above the wire terminals, this provides easy configuration of the voice coil. The power handling is the same for either setting; 350 watts RMS/1400 watts peak.

Woven Glass-Fiber Cone: The cone material is extremely stiff, minimizing cone flex; this results in very low distortion and improved clarity.

Vented Polepiece: Venting the polepiece reduces air compression under the dustcap which minimizes mechanical noise and provides more constant mechanical Q for reduced distortion.

Terminal: The set screw wire terminals will accept bare wire up to 8 gauge.

Enclosure Compatibility

Sealed Box: Infinity recommends a sealed enclosure with an internal volume of 1.0 cu/ft.

Ported Box: Infinity recommends a ported enclosure with an internal volume of 2.0 cu/ft with one 4" diameter x 13.625" long port. This equates to a tuning frequency of 30 Hz. They also recommend using a sub-sonic filter.

Sealed Bandpass Box: When using a bandpass enclosure Infinity recommends a sealed rear chamber volume of 1.0 cu/ft and a ported front chamber volume of 1.0 cu/ft with a 4" diameter x 6.625" long port. This equates to a tuning frequency of 60 Hz. They also recommend using a sub-sonic filter.

Free-air Mounting: In addition to being compatible with sealed, ported, and bandpass enclosures, the woofer can be used in free-air applications. A free-air subwoofer is designed to be mounted on a baffle board, which separates the front of the speaker from the back. For instance, you could mount this woofer to a board attached to the rear deck or placed in the trunk against the rear seat. The trunk acts as the enclosure housing the subwoofer. Because there is no specific volume of air to stiffen the suspension, the free-air power handling is approximately half that of the woofer in a box, in this case 175 watts RMS.


Thiele-Small Parameters: Because the woofer has two impedance settings, there are two sets of Thiele-Small parameters:

DC Resistance (Ω) 2.1 4.3
Inductance (mH) 1.18 1.18
Vas (liters) 54.43 54.43
Qms 4.38 2.47
Qes 0.51 0.52
Qts 0.46 0.43
Fs (Hz) 27.2 27.2
Radiating Area (m²) 0.05188 0.05188
Xmax (mm) 17.5 17.5
Motor Force Factor (TM) 12.47 18.37

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.

Q & A

Customer Q&A

Crutchfield asked  
Why did you buy this?

I bought an infinity kappa sub woofer in 1998 it still works bought a JL in 2005 five does not work anymore if you're looking for quality and longevity infinity is the only way to go [ ROBERT  May 07, 2016 ]
Infinity sounds great! [ Jeremiah  Mar 07, 2016 ]

6 questions already asked

The Infinity 120.9w is a single voice coil model with an adjustable impedance switch that sets the woofer to either 2 or 4-ohm. There wouldn't be any way to present a 6-ohm load to your amplifier with this model. I hope that helps. My Bio: [ Larry  Jun 04, 2016 ]  Staff
there's a selector switch that allows you to pick between two or four ohms no way wiring sequence [ ROBERT  May 31, 2016 ]
It will stick out 0.75" past the mounting surface. [ Paul  Dec 09, 2015 ]  Staff
That amp can power this subwoofer and you shouldn't have to run the amp at full output either. [ Paul  Dec 06, 2015 ]  Staff
Thanks, Jeff. Yes, that worked. I tightened up all the connections, and it works great now! No more cutting in and out. Sub is A W E S O M E !!!!!! [ Tracy  Jan 01, 2014 ]
This sounds like a loose connection somewhere inside the box. I would recommend checking that wiring first. [ Jeff  Dec 27, 2013 ]  Staff