FMOD Crossover Pair 20 Hz High Pass Review

Wednesday, December 29, 2010 by Vera Smith | Posted in General, harrison lab fmod 900073 - 20 hz high-pa...

Average Reviews:

(More customer reviews)Harrison Lab FMOD-900073 (20 Hz high-pass filter)

Gold-Plated
20 Hz High-Pass Filter
-3 dB point @ 20 Hz
@25 Hz : 25% frequency increase at 10K ohms
@17 HZ : 15% frequency decrease at 47K ohms

This high-pass filter is supposed to cut frequencies below 20 Hz, as we know the human ear can hear from 20 Hz to 20,000 Hz, so frequencies below the 20 Hz point can't be heard, and usually most speakers will not be able to produce that low frequency --most speakers don't produce audible sound below 25 Hz--. With that said, the frequencies below 20 Hz are still reproduced and amplified by your amplifier, so first you may damage your speaker feeding it power that won't be heard and make only cause your voice coils to get extra hot. Second your waster amplifier power by producing sound that won't be heard.

The FMOD solves this, you insert it before your amplifier so that the AMP will never get sound below 20 Hz.
This high-pass filter has other names like (crossover, rumble-filter and sub-sonic filter). Nowadays you find most amplifiers with sub-sonic filters built-in, so if you have one of those you don't need this FMOD high-pass filter.

Anyhow, my personal take on this filter is negative. As soon as it was inserted it caused audible noise -to the sensitive ear with high quality equipment-- and caused the bass to sound bad, soft and distorted. I removed it the next day after confirming this many times.

With low grade equipment you may want to give it a try as you may not feel the difference, but if you're an audiophile and can sense any change in sound then don't go for this and get yourself a decent amplifier with built-in Sub-Sonic filter.

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Product Description:
What is an FMOD?The FMOD is an active crossover simulator.It is better than a much more expensive electronic crossover that requires power to operate.FMODs are packaged in pairs and can be combined with other FMODs to obtain bandpass ranges or with other types of crossovers to change the slope and crossover frequency point.FMODs feature a 12 dB per octave crossover slope and are compatible with all RCA type input amps...simply place the FMOD in-line with the patch cable running between the source (head unit) and the amplifier.24 kt gold over brass construction, 10 volts maximum RMS input.One-year manfacturer warranty.Made in the U.S.A.