ZRS-1 20X20X20 cm  Subwoofers for Home Studios, Gamers and   Base Guitar players  

ZRS-1 Desktop Subwoofers- Front &  Back View

Design Considerations

The vast majority of small near field monitors do not reproduce the low notes between 30 and 60 Hz because low frequency Inter modulation with mid range frequencies degrade clarity and imaging , therefore the low frequency range is sharply filtered out.

Most near field monitor speakers use ported enclosure to enhance bass response but the result is overhanged sustained bass transient response.

Adding a subwoofer with well designed crossover filter can eliminate these issues thus much louder SPL with low distortion can be attained.

However, most commercial subwoofers have large floor standing enclosures,  they  heavily excite room reflections and therefore poorly blend with near field monitors.

Thermoguide's small size ( 20X20X20 cm ) near field subwoofers are intended to be placed on desktop with low cost monitor speakers placed on top of them, thus perfect acoustic wave front alignment can be achieved at listener's ear height.

With desktop Near Field Subwoofers, room reflection effects are significantly mitigated. 

Our Desktop subwoofers blend well with any near field monitors by using 4th order Linkwitz Riley cross over filters at 100 or 200 Hz where the monitors are relatively flat with smooth phase shift.

By using MFB, tightly controlled bass transients can be reproduced without the over hanged  sustained response that are so common with ported enclosures.

Our Subwoofers can compliment any commercial Near Field studio monitors with the much needed bottom octave of 30-60 Hz, with superb clarity and stereo image.

ZRS-1 Subwoofers underneath  KH M402 monitors 
( Photo by courtesy of Yuval Silberstein, www.yuvalsound.com


 

ZRS-1 Plate Amplifier

MBF control circuit, high power class D amplifier and a powerful switching power supply  are combined on our plate amplifier, ready to be used with any driver with enclosure size from 20x20x20 cm to infinite baffel. Flat frequency response can be achieved by selecting only a few control parameters.

Voice coil temperature is monitored real time preventing voice coil overheating damage.

Features:

- Subwoofer Volume control.

- Selectable 100/200 Hz 4th order linkwitz–Riley crossover.

- Selectable full range 30-400 Hz response for external crossover.

- Bypass mode switch, in bypass mode the input signal is routed to the monitors while the subwoofer is muted.

- Mono (L+R bass signals summed) or full Stereo operation.

- Real time voice coil  thermal protection.

- Red light indicates near clipping/overdrive.  

- Power saving activated after 5 minutes without input signal.

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Driver and enclosure selection

For our desktop subwoofer we use an off the shelf  6.5" driver with our custom designed sensor bonded on the voice coil former.

This driver was engaged  with the ZRS-1 plate amplifier in a 20X20X20 cm enclosure that is small enough to fit under many near field monitor speaker.

ZRS-1 Subwoofers underneath  Neumann KH120 monitors
 ( Photo by  Yuval Silberstein, www.yuvalsound.com)
 

ZRS-1 Desktop  Subwoofer –Test Results

Speaker acoustics theory teach us that voice coil acceleration is directly proportional to the acoustic output of a woofer with sealed enclosure when in piston mode  bellow the breakup frequency.
In the following chart Green plot shows  the Voice coil acceleration without MFB, Red plot shows the response with MFB activated .
It is also known that very close microphone measurement on the acoustic axis of  the driver is closely proportional to free field measurements.
In the second chart , Red plot shows microphone output with 100 Hz crossover filter , Blue plot  with 200 Hz crossover, Green plot with full subwoofer bandwidth .