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The Subwoofer For Audiophiles With The Need To Play Upper Bass

For audiophiles looking for uncompromising accuracy in bass, upper bass, and higher crossover frequencies up to 250Hz, our FM8 subwoofer is the ultimate choice. It features two low mass 8" drivers with our Direct Servo technology to ensure accuracy and definition.

The Low-music and Low-HT positions on the extension filter allows the FM8 to be used as a regular subwoofer. The "high" position implements a 4th order LR filter to allow FM8 to only play down to 50Hz and crossover to low bass subwoofer unit at 50Hz.

For upper end extension, this sub is will effortlessly play up to 250Hz. FM8 can cover more than a decade of frequency range from below 20Hz to 250Hz.


100% MONEY




Direct Servo Technology

All our subwoofers use our patented Direct Servo technology, providing high end performance at an affordable price. It allows us to use lighter and more efficient drivers and still achieve deep bass without using excessive amounts of power. The servo reduces memory effects, counteracts thermal compression and various forms of driver non linearities.

HX585 Amplifier and DS800 Driver

FM8 uses two Hypex Ucd class D modules in the power amplifier with each module independently driving an 8" driver. Hypex Ucd modules are considered as one of the best sound quality class D modules available. The standard amplifer is HX585 (300WRMS x 2 for a total of 600WRMS), It has two RCA inputs and one highpass filter output. Three different finishes are available: piano black, black matte vinyl, and black oak vinyl.

FM8 is particularly suitable for pairing with front speakers with small woofer or planar/ribbon speakers with limited extension. Customers are tempted to use them as speaker stands. This usage method severely limits the placement choice and hence also hinders the efficiency. For front speakers with 8" or larger woofers, we recommend other 12" or larger models such as F12.

Integration guide




Features & Options

Product features include:

  • Patented Direct Servo technology
  • 8" light weight cone mass high excursion driver
  • Solid and very inert enclosure available in a range of finishing options
  • Bass extension controls allowing adjustment of bass extension and excursion control
  • Selectable 12/24 db/octave crossover filter slope
  • Parametric EQ
  • 120V-240V switchable power


Direct Servo technology

All our subwoofers feature our Direct Servo technology, which is our secret to achieving tight and accurate bass. The benefits are far more than simply achieving low distortion.

Direct Servo closed loop technology

Learn more in our technology articles >

Dual 8" cast frame paper cone high excursion drivers


Driver features include:

  • Low moving mass paper cone and foam surround to ensure an exceptional transient response
  • Large magnet for high flux density in the gap to ensure low distortion
  • Flux de-modulation shorting rings to lower inductance and improve linearity
  • Extended upper bandwidth response allowing up to 200hz crossover point (-6db at 250hz and therefore can be used for Linkwitz Riley for crossover point up to 250hz).

Quality enclosure

Our enclosures are very solid and well braced to minimize any cabinet resonance or coloration. The enclosure is heavily braced and the sub has a net weight of 53 lbs.

We also provide a range of finishes. Our range of attractive and excellent value vinyl finishes including:

  • black matte veneer
  • black oak veneer
  • piano black

Black piano gloss finish is also available in our signature edition.

Bass extension controls

FM8 features a unique bass extension control, shown below.

The bass extension control enables the user to customize the frequency response of the low end for the best trade-off between output and extension. If set to low music, bass below 18 Hz will be filtered. The damping factor of this mode is 0.5 for the best time domain response. However, the disadvantage is slower attenuation of subsonic signals. For HT application, we recommend low-HT mode which incorporates a 3rd order highpass filter to filter out subsonic signals below 20hz. 50hz/24 setting implements a 50hz 24db L-R filter, recommended when using FM-8 as a midbass module to work with larger low bass subwoofer crossovered at 50hz 24db slope.

Crossover options

To suit different setups, we provide a 12 db and 24 db/octave crossover (as shown in the above photo) with adjustable range from 50hz to 200hz.

RCA input and RCA HPF input

PEQ parametric version

FM8 accepts two RCA inputs and one channel RCA HPF @150hz output. The HPF is derived from L input only. Plugging same signal to both L and R inputs increase the gain by 6db.

PEQ parametric version

PEQ parametric version

PEQ in FM8 is similar to those in our models except the frequency has doubled. Room modes between 50hz and 150hz is very common because of ceiling height. Using FM8 to cover that frequency band with PEQ can affectively alleviate the problem.

120V-240 Switchable Voltage Selection

Correct voltage must be selected before use. Voltage switch is shown below.

voltage selection



The bass extension switch allows the user to customize the deep bass extension and the rumble filter to control cone excursion. For HT application, one can set the extension to Low-HT or High for higher SPL output. For music one may prefer a lower cut off such as Low-Music setting. Changing the settings can also result in a better integration with the acoustic gain of the room.


Driver dual 8" high excursion with custom sensing coil
Driver materials paper cone with lightweight foam surround
  Cast aluminum basket
  Aluminum flux de-modulation shorting rings
Amplifier 600WRMS class D (dual Hypex Ucd modules) patented servo controlled
Dimensions 11-1/2"(W) x 20" (H )x 15-1/2" (D) with grille and amplifier knobs
Shipping Weight 68 lbs
Frequency Response 18 - 250 Hz (-3 dB @ 20Hz) 50-250hz (at "HIGH" bass extension setting)
Crossover slope Selectable 12 or 24 dB / octave
Crossover range (Low pass) 50 - 200 Hz
Rumble Filter (High pass ) 20 Hz 18 dB / octave
Phase response 120 degrees phase shift at 20 Hz
Phase adjustment 0 - 180 degrees continuously variable
Bass damping factor Low music (Q=0.5), Low-HT(Q=0.9), and high (Q=0.8)
Standy power 7W (standby, red light), 13W(ON,green light)
Finishes Available in black matte vinyl or black oak vinyl
  (Piano Gloss available in signature edition only)
Warranty 5 years warranty on driver and 3 years on electronics
  45 day satisfaction guarantee



In the chart below, with bass extension controls set to Low Music, the response is 3 db down at 20Hz. The response is flat and extended.

sealed response

FM8 features bass extension switch similar to F8, allowing users to select among 3 different modes: Low Music (Q=0.5), Low HT (with a 18db/oct rumble filter at 20hz), and High (24db L-R filter at 50hz). In the following, we plot the FR of HIGH position (also known as the midbass module position).

sealed response


FM8 provides a 12/24 db/oct switchable low pass filter to so that it can easily integrate with any front speakers.

Another aspect of getting a correct integration is phase alignment between the front speakers and the sub. We have written a guide on how to achieve a phase aligned subwoofer. F8 has a phase/delay adjustment knob. More >



Many of our customers marvel that we are able to produce such exceptional subwoofers at such a low price. Our Direct Servo technology makes it possible, allowing us to get the most out of an 8" driver without the need for kilowatts of power. Don't be fooled into thinking that other more expensive subwoofers with much more powerful amplifiers will offer more output. The output of a subwoofer is determined by how much air the driver can displace, not the power rating of the amplifier. We could supply a more powerful amplifier, but there would be no increase in output, only extra cost.

These are some of the finest subwoofers ever manufactured and the difference in sound quality between these subwoofers and the typical big-box ported subwoofer is surprising. You will hear the difference the very first time you listen and as so many have said, you will never go back to a non-servo subwoofer.

Rythmik FM8 Dual 8" Subwoofer

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