KLS10 Subwoofer Kit 

Designed to compliment KLS10 Gold stand mounters by providing a deep and open bass.
The subwoofer is inexpensive, easy to build,
comprising a simple crossover network to a high quality 8 inch Aerogel dual voice coil unit.
A must for all KLS10 Gold customers. Sens. 89dB, volume 25 litres,
external dimensions 28cm(w) x 43cm(h) x 34cm(d).

 This simple, effective subwoofer endows our small
but perfectly-formed KLS10 loudspeaker with the sort of bass you'd expect
from a large floor stander.

THE CONCEPT

KLS10 was conceived as a small, high-quality monitor.
Trouble is, whilst small loudspeakers can do many things very well,
they do not produce deep bass. To cover this drawback,
from the outset we planned to design a matching subwoofer for KLS10 - and here it is.
Subwoofers take many forms, from a single drive unit in a box up
to powered 'active' types with equalisation and other paraphernalia.
Our subwoofer comprises a single cabinet of modest 25litre volume with one driver,
an Audax HM210Z2 High Definition Aerogel unit with twin voice coils.
The resulting kit is effective, inexpensive and a doddle to build.

THE DESIGN

The subwoofer attenuates bass output from the KLS10s to avoid bass boom,
as well as extending bass down to 20Hz - a very low frequency,
especially from a relatively inconspicuous cabinet, one that can even double as a small table.
A single-box subwoofer relies on the fact that most bass is recorded equally on both stereo channels,
and that in any case the ear cannot locate a low-frequency source below about 100Hz. Therefore,
we have pressed into service a special twin-coil bass unit from Audax.
The coils sum output from the stereo channels, a simple but effective method
that results in high efficiency. Filters feed bass signals to this driver,
removing higher frequencies. However, the rate of roll-off has been made slow,
in order to provide some midrange information, which the HDA cone of the driver
can reproduce faithfully. Note that both channels of the amplifier feed the subwoofer,
and a signal is then fed out to the satellites.
Upper frequencies are removed from the subwoofer signal by low-pass filtering,
and lower frequencies are removed from the satellite signal by high-pass filtering.
These filters can be adjusted, and the port of the subwoofer can be tuned too,
so there's plenty for inveterate experimenters to play with here.
Distributing bass power between drive units improves power handling.
The system will go loud without strain. Officially it will take 60watts,
the max power rating of the drive units, but this is a very conservative
continuous power rating used by Audax.
Note we use two bi-wire terminal dishes, one per channel.
This gives a set of input and output terminals per dish.
The amplifier feeds the subwoofer, and the subwoofer feeds the satellites.

SOUND QUALITY

After running in, the subwoofer was linked up to the KLS10s,
both driven by our own amplification
as well as a Creek OBH-12 passive pre-amplifier and
Musical Fidelity's 300watt X-A200 monoblocs.
Obviously, the best way to find out how low a subwoofer
goes is to throw at it a recording with some real bottom-end grunt;
cue Joe Beard's Blues Union on a JVC XRCD disc. Compared to the '10s sans sub,
this bass-enhanced trio had much more smack and weight, which put a lot of the low-down,
dirty grunge back into the Blues and an extra gravelly growl into JB's vocals.
Bass isn't only about quantity, it's about quality too - the last thing you want is
an octave of low-frequency sludge rumbling away regardless of what the music's doing.
With Mahler's Symphony No7 (performed by the Cleveland Orchestra,
Pierre Boulez conducting) inside Pink Triangle's Litaural CD player,
the KLS10s and subwoofer steered clear of this pitfall. Complementing the grainless,
spit-free treble of the gold-dome piezo tweeter was a lithe, extended,
open bass which didn't squander detail and tonal character when handling double-bass and cellos.
If you prefer leather boots to slippers, you'll find a change of genre won't phase this sub
and satellites; they Rocked along happily to Ocean Colour Scene's Moseley Shoals
without sounding harsh or bloated, Aerogel, carbon fibre and gold dome marrying harmoniously.
And if you're a fan of Dance, sit back, turn the volume up and enjoy beats which will put a happy,
basshead smile on your face.