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Rythmik FV15 subwoofer

15" Ported Servo Subwoofer

The FVX15 is our answer to the need for a "bang for buck" home theater solution that retains the dynamic and accurate bass that we have become known for. We recommend this subwoofer for systems in which home theater has a high priority. FVX15 also features multi-tune capability. Customers can select either one-port or two-port operation.

arrow Patented Direct Servo technology
arrow High output, front ported design
arrow 400 watt, Hypex module HX405 amplifier
arrow Adjustable damping

arrow Save $$ when purchasing dual subs*
arrow Save $$ when purchased with speakers*

*discounts will appear in shopping cart, one discount only, exclusive of sale items

arrow Free continental US ground shipping
arrow 45-day satisfaction guarantee
The FVX15 is a lower power version of the our highly regarded FV15HP. It is our answer to the need for a "bang for buck" home theater solution that retains the dynamic and accurate bass performance that we have become known for. Correctly integrated, our vented subwoofers can achieve the tight bass normally associated with a sealed enclosure, yet with greater low frequency output. We recommend this subwoofer for systems in which home theater has a high priority. FVX15 also features multi-tune capability. Customers can select either one-port or two-port operation.

It features Direct Servo™ to ensure accurate frequency and transient response, precise detail and extremely low distortion levels at even high output levels. As a discerning listener you appreciate that bass is the foundation of a satisfying music or home theater experience. You also appreciate that there is more to a home theater subwoofer than simply shaking the room, and that music can be far more satisfying with a subwoofer that can play deep.

What makes this subwoofer unique? It's not that it can plumb the depths with authority. There are already many subwoofers on the market which can do that. The difference is that this subwoofer will reproduce bass with a level of realism that matches what our loudspeakers are famous for...

We are most proud to represent these astonishing new subwoofers.

Direct Servo technology, US Patent #6,104,817: What is it?

Direct Servo Diagram

Conventional subwoofers have extremely high distortion. Well regarded conventional subwoofers typically have measured distortion levels exceeding 15% at 20 Hz at 100 dB. This includes many subwoofers costing more than US $3000. We think this is far too high. A well designed servo subwoofer will achieve distortion levels under 3% under the same conditions.

A servo is essential in a subwoofer that aims to be true to the original source material. The benefits are clear:

  • No voice coil thermal-induced compression or distortions.
  • Spider and surround distortion reduced by 6 - 9 dB
  • Flat frequency response that is less dependent on T/S parameters.
  • Audiophile bass sound at an affordable price: articulate, tight, transparent, and well-defined bass

These benefits are all unique to a servo controlled subwoofer, and can't be achieved in a practical and affordable way without a servo.

How it works

Direct Servo uses a very thin sensing coil which is wound adjacent to the voice coil. This coil induces a signal which is fed back into the summing points of the amplifier. This signal is used to correct sources of distortion, and this is achieved without placing any active devices such as transistors or operational amplifiers in the signal path. This simplicity eliminates any secondary or mechanical effects which plagues other technologies.

What are memory effects?

A subwoofer driver contains parts which have a memory effect. This means the driver will not respond perfectly to the signal. The spider and surround both contribute to memory effect in a driver. The voice coil which carries the signal that drives the cone also exhibits a memory effect. This is because the temperature of the voice coil changes with operation, and this changes the resistance. The result is a loss of dynamics. As the driver excursion and power input level increases, both effects get worse in conventional subwoofers. Detail and resolution is lost.

Direct Servo corrects both mechanical and thermal memory effects. The result is much lower distortion, and bass that is true to the original, preserving the subtle details, capturing dynamics and revealing a level of detail well beyond the reach of most conventional subwoofers.

How is Direct Servo different?

The primary philosophy is to make audio products as simple as they can be. Less is more. These subwoofers put as little into the signal path as possible. This approach applies to the amplifiers, Direct Servo technology and drivers. Most servo subwoofers use an accelerometer, which is another mechanical system with its own limitations. Also extensive protection circuits are required, and these further degrade the signal. As a result, accelerometer based servos are not as accurate as Direct Servo. The superiority of Direct Servo is derived from its simplicity.

Frequency Response:

FVX15 has two port openings. With one port open, the max extension is 12hz and the bass extension toggle switch should be set to either 1P-music or 1P-HT. The latter is recommended for HT playback. The bass extension toggle switch needs to match the number of ports used. The following is the frequency response when bass extension is set to 1P-HT with one port open.

Fig 1.0 - FVX15 Frequency response chart with LFE input 1P-HT and one port open

FVX15 Response Graph

To achieve lower group delay in one port operation (such as for music playback), users can set the bass extension switch to 1P-Music. It has a more gradual roll-off compared to that of 1P-HT. The following is the frequency response comparison between these two modes.

Fig 1.1 - FVX15 Frequency response comparison of 1P-music and 1P-HT with LFE input

FVX15 Response Graph

For highest SPL HT playback output, users should select 2P mode with both ports opened. While the extension is only limited to 18hz, the power of the amplifier is better utilized for the audible frequency band instead of the less audible sub-sonic band. The following is the requency response of 2P mode.

Fig 1.3 - FVX15 2p mode response with LFE input and two ports open

FVX15 Response Graph

Unique bass extension controls:

All of our subwoofers feature unique bass extension controls which are not normally found on consumer subwoofers. This enables the user to customize the output and extension to achieve the best compromise in any room. Most subwoofers neglect to provide bass extension control, and the result is that dynamic headroom is compromised.

FVX15 ControlsThe bass extension control enables the user to customize the frequency response of the low end. It combines multi-tune specific frequency contouring and damping control in one switch. The damping control determines the slope of roll-off and the amount of time domain ringing. High damping provides the least amount of time domain ringing and the most gradual roll-off curve. Low damping provides the steepest roll-off at the low end at the expense of added time domain ringing. There are two positions for 1 port operation which extends to 12hz. 1P-music uses high damping while 1P-HT uses low damping. High SPL playback should use 2 port setting. The damping in this position is low.

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.

120V-240 Switchable Voltage Selection:

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

FVX15 Controls


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...

Specifications FVX15:

FVX15 uses our new Hypex module based HX405 amplifier. We also develop a new DS1502 driver featuring two stacked 25mm magnets to improve excursion limit. Its physical dimension is exactly same as FV15HP. As a result, one can expect the full benefit of FV15HP design but with 2.5db less output. The quickguide of the amplifier can be found here.

Frequency Response LFE Input 12 - 200 Hz (-2 dB @ 17 Hz, -6db@12hz)
Frequency Response Line-in Input 12 - 90 Hz (-2 dB @ 17 Hz, -6db@14hz)
Multi-tune option 18Hz (2 ports open) and 12Hz (1 port open)
Woofer 15" high excursion with custom sensing coil
Woofer Material Black anodized aluminium with rubber surround, Cast aluminium basket, Copper flux de-modulation shorting rings
Amplifier 400w RMS Hypex Ucd servo controlled
Dimensions W x H x D 18" x 24" x 24" (25.5" deep with grille and knobs)
Shipping Weight 120 lbs each
Crossover Slope Selectable 12 or 24 dB / octave
Crossover Range (Low Pass) Continuously variable 25 - 100 Hz
Rumble Filter (High Pass) 18Hz 18dB/octave for two port tuning
Phase Adjustment 0 - 180 degrees continuously variable
Bass Damping Factor Settings High (Q=0.5), med (Q=0.7), and low (Q=1.1)
Finish Black Matte and Black Oak
Warranty 5 years on woofer / 3 years on electronics
45-day satisfaction guarantee