This subwoofer was reviewed as part of a groupo in our Oct-Nov 2015 issue. The original pages and the comparison grid for all subwoofers tested can be seen on the PDFs under the red button on the right.

In our introduction to this group test, we noted how ‘conventional’ designs are generally called so for a reason — namely that they work. For subwoofers, that’s a large driver and bass reflex port on the front, connections on the back, plenty of power, and preferably the largest enclosure possible — the larger the enclosure and driver, the easier time it has of producing the sweet deep tones, and consequently the lower the distortion.

South Australian loudspeaker maker Krix has done just that with the Seismix 3 (officially in its version 6.0), one of the lowest-cost units in this round-up. The enclosure is a solidly-built and good-sized box weighing over 15kg. The built-in amplifier packs 300W of power.

The 275mm driver — an unusual 11 inches — is located towards the bottom right of the baffle. That makes room at the top left for a very large bass reflex port. So no worries with placement here, especially as the Class-D amplifier generates relatively little heat. There are no heatsinks at the rear needing airflow.

The review unit was finished in black ash-look vinyl, as pictured, which is what you get for $1095. If it will be tucked away, largely invisible, in a room corner then that makes for great value. But if you need it to be prettier you can choose  from a real Black Ash, Cola or Ironwood veneer for $1245, Atlantic Jarrah or Blackwood for $1365, or a custom finish for $1545.

A fairly basic set of connections were provided on the rear: left and right inputs (you use the right one for the LFE output of a home theatre receiver) and left and right outputs. These last are labelled ‘Loop Through’, and they are just as the name implies: they pass on the input signal without any filtering.

A switch allows you to choose between auto on/off (via signal detection) and always on. There’s a level control of course, plus a low-pass filter control, with markings from 50 to 200Hz. The top setting is also labelled ‘Bypass’, but this doesn’t actually take the crossover out of circuit, it simply marks the best spot to set the control when connected to an LFE output. The phase adjustment switch provides, unusually, a continuously variable adjustment from 0 to 180 degrees, rather than just switching between the two. Since a phase adjustment in degrees is necessarily frequency dependent, this marking is a convention — it actually acts as a group delay, and by its continuous nature provides increased flexibility in matching the subwoofer  with the main speakers.

Performance
First things first — after plugging the subwoofer in, switching it on, running the rest of the system, I stuck my head into the corner right above it while nothing was playing. And was greeted by perfect silence. There was no hum at all, which is what you’d expect from a Krix subwoofer, designed by people who live in a 50Hz nation. Other subwoofers in this group weren’t so quiet.

Then it was on to music. Playing my favourite recording of Bach’s ‘Passacaglia and Fugue in C minor’ (a recording by Telarc of a massive pipe organ in which the bottom C pedal has a fundamental of 16Hz), I was impressed by the ability of the Seismix 3 to excite the room when that pedal was hit at the end of each phrase. Which reinforces the fact that in the real world, acoustic instruments also have trouble really plumbing the depths.

What the subwoofer was reproducing — what all of them do, really — was the second harmonic of this pedal’s pipes, and above, and it’s that 32Hz that does most of the room shaking. But not all. As the Passacaglia section came to its climax, the missing 16Hz did reduce the sense of spacious awe that my usual subwoofer generates.

But, then, no subwoofer in this price category can go that low.

The bass guitar on Jeff Beck’s ‘Beck-Ola’ was full, clear and tuneful. Likewise on Oregon’s ‘Leather Cats’, although on this one there was some variability in level, tied to the notes being played. The kick drum was delivered with good clean slam, and no sense of harmonic distortion being added by the unit. This is a tuneful sub.

The unit did do a nice job with movie explosions. It went very loud, very cleanly, particularly above around 30Hz. But there were no infrasonics of note, and no real sense of pulsating air. Nor would you expect them at this price.

Conclusion
The Krix Seismix 3 v.6.0 subwoofer offers a larger driver than is usual in this price category, while maintaining this model’s heritage of providing a rock solid design providing good midrange performance — and at a very reasonable price. SD

MEASUREMENTS: In our listening room, in subwoofer corner, measured close, the Krix Seismix 3 v.6 delivered an honest 29Hz to 153Hz. As is typical with bass reflex designs, once the limit of bass extension is reached, the dropoff is precipitous. In this case the output was down by 30dB at 20Hz (that is, making no practical contribution to the sound).

At 30Hz and 90dB SPL at one metre, the second harmonic distortion was a reasonable 3%, while the potentially more objectionable third harmonic was just over 0.5%. Higher-order components were much lower.

Krix Seismix 3 v.6.0 
Price: $ 1095

Drivers: 1 x 275mm, forwards firing

Enclosure: Bass reflex

Inputs: 1 x stereo line level

Outputs: 1 x stereo line level

Low-pass crossover: 50-200Hz

Quoted power: 300 watts

Measured room response (pink noise -6dB): 29-153Hz

Level at 20Hz: -30dB

Dimensions: 450 x 360 x 410mm

Weight: 15.65kg

Warranty: 5 years (1 year for amplifier)