Simply plug F-MODS crossovers in-line with the patch cords feeding your amplifier. They filter out unwanted frequencies, with a 12 dB per octave slope. Low-pass models let frequencies below the cut-off point through and filter out the highs. High-pass models let frequencies above the cut-off point through and filter out the lows.

F-MODS Reviews

Average Customer Review:

8 reviews
Review this product
Great Gear Giveaway

Submit a review and then enter to win a $350 rewards card


Review this product:

Thanks for taking the time to share your experiences about this product. Please be sure to focus your comments on the product itself. Read our Review Guidelines for more information.

Your email won't be visible. Please use the email address that is associated with your order.
(e.g., JohnD) Your review will be signed using the display name and location
(e.g., Charlottesville, VA)

Click on a star to rate the overall product on a scale of 1-5
1500 characters left
  Attach a YouTube Review
Crutchfield Video Review Guidelines
  • Only submit videos that you made or are authorized to use.
  • Do not submit videos that contain music, video or visuals that are copyrighted and belong to someone else.
  • Please see our Review Guidelines for more information.
500 characters left
500 characters left


Written By bradsh, Grand Rapids, MI on Friday, December 24, 2010

Crutchfield Customer Review (What's this?)

Worked for a grand total of 3 minutes before one channel began sputtering and then dropped. Wiggling the connection worked a little, but I couldn't get it to
stay working. So essentially, this item was DOA. I took it apart and the wiring inside was very weak with a poor solder. Resoldered it but the wire just broke

For the 3 minutes that they worked, they were functioning correctly.

Great alternative to an active crossover

Written By Steve, Monroe Township, NJ on Monday, August 30, 2010

Crutchfield Customer Review (What's this?)

These F-MODs worked great! They filtered out the unwanted frequencies by simply
plugging in-line with your amp. I used them to filter out the low frequencies from by full
range speakers because my head unit has separate subwoofer outputs. Just make
sure that you have enough clearance at the amplifier inputs to accommodate the 2 inch
long F-MOD. I used right angle RCA adapters to give me enough clearance. Just
remember, the F-MOD male end goes into the female input to the amp.


Written By Kou, Denver, Colorado on Friday, April 09, 2010

Crutchfield Customer Review (What's this?)

Work as advertised. Tricky thing is to make sure you are either getting high pass or low pass - this makes a big difference!

F-Mod Installation Direction

Written By Joseph, Albuquerque, NM on Monday, July 27, 2009

Crutchfield Customer Review (What's this?)

I have used dozens of F-Mod audio crossovers for decades. They work flawlessly, but only if they are installed in the correct direction. They do not come with installation instructions. I have seen many F-Mods installed by other people that were in backwards; in fact about half of those were in incorrectly. Harrison Laboratory should include a small diagram showing the proper direction of installation. The F-Mod male plug goes into the female connection on the amplifier, not into the female connection on the preamplifier.

Works Like a Charm

Written By Greg M, Massachusettes on Wednesday, June 24, 2009

Crutchfield Customer Review (What's this?)

Absurdly simple to use, and they work great. Fantastic product.

Great simple product

Written By Clinton, Sacramento, CA on Wednesday, March 25, 2009

Crutchfield Customer Review (What's this?)

Great product if your using a 2 channel amp for a sub and the crossover doesnt go low enough.

Unconventional use

Written By John, Chicago on Tuesday, May 08, 2007

Crutchfield Customer Review (What's this?)

I used one of these to convert an old spare subwoofer into a mid-bass enhancement speaker for my home theater. Works great. Maybe not equal to a $500 mid-bass module especially designed for this use, but close enough and only a fraction of the cost.


Written By Stewart, Ketchikan, Alaska on Sunday, June 11, 2006

Crutchfield Customer Review (What's this?)

Needed for a 70v system, hoped for more isolation. Completely met expectations. Recomend product, well made.

Hands-on research

What's in the box?

Download owner's manual

  • 1 Pair of F-Mod crossovers (200 Hz Low Pass)

Product Research


Overview: The F-Mod (filter module) is an active crossover simulator, made by Harrison Laboratory, that connects in-line with your RCA patch cords. They require no power, and can be combined with other types of crossovers to change the slope and crossover frequency point. F-Mods have virtually no noise or distortion, and do not cause turn-on thumps. F-Mods can handle a maximum signal of 10 volts RMS, and have a slope of 12dB per octave.

Construction: The F-Mod is made of brass with 24 kt gold plating.

Color Codes: The manufacturer's label is silkscreened on the barrel of the device in two colors. A red label indicates a high pass filter, while black indicates a low pass filter. A colored ring near the male RCA end of the barrel indicates the frequency of the filter (-3dB). There is a frequency increase at 10K ohms (8% Low-pass, 25% High-pass) and a frequency decrease (8% Low-pass, 15% High Pass) at a 47K ohm load. A high-pass F-Mod and a low-pass F-Mod can be combined for bandpass operation.

Frequency Codes: The available F-Mods frequencies are:

Frequency Band Color Frequency (Low Pass) Frequency (High Pass)
@10K @47K @10K @47K
50 Hz Brown 54 Hz 46 Hz 62 Hz 43 Hz
70 Hz Purple 76 Hz 65 Hz 87 Hz 60 Hz
100 Hz No Band 108 Hz 92 Hz 125 Hz 85 Hz
200 Hz Blue 216 Hz 184 Hz 250 Hz 170 Hz
500 Hz White 540 Hz 460 Hz 625 Hz 425 Hz

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.