Bring the bass back with DEQX and Dynaudio

The midrange is where the music lives. It’s a cliché as old as your grandfather. The implication is that bass, especially low bass, matters not as much. Experience tells us otherwise. Deprived of its lower frequencies, for some listeners a system can sound dry and perhaps a little edgy. For the electronic music fan, especially the darker dubstep served up by Burial and Zomby, a pair of standmount loudspeakers is unlikely convey the complete picture.

Sooner or later, we might ask ourselves, “What’s missing?”.

Even the floor-standing Spatial Audio Hologram M4 Turbo S respond with “Quite a bit, actually”. That’s no criticism of the Utah-made open baffles – their in-room response is rated down to 45Hz +-3db by the manufacturer – but it had me thinking: what could a subwoofer bring to the Spatial M4 party?

By way of their Australian distributor (Busisoft), Dynaudio offered up the Sub 250 II as an apartment-appropriate contender: inside its sealed MDF cube, a 200 watt amplifier drives a ‘long throw’ 24cm woofer. On the back panel, an LFE input hands off config n’ control to an upstream A/V receiver. For the stereo purist bereft of such home-theatre-like connectivity, manual configuration comes by way of three rotaries: low-pass filter (50 – 150Hz); phase (0 -180); and gain.

On your knees. That’s where the usual subwoofer story usually goes next. With the newly added bass box placed at – or close to – the listening position, we are asked to crawl the floor in order to ferret out its acoustically optimal location. Audio nirvana isn’t easily found, especially if domestic arrangements specify only a handful of positional possibilities. See here:

After that, the battle with everyday life starts – what if the subwoofer’s best sound comes from a mid-thoroughfare location? Whatever follows will be a compromise, either to sound quality or to one’s living arrangements.

Moving on. Once positioned, we set the subwoofer’s crossover point and gain. Then comes the phase adjustments that ensure its low frequency output arrives at our ears at the same time as the remainder of the frequency spectrum spilling from the loudspeakers. A shot in the dark? Perhaps.

For the average Joe, subwoofer installation isn’t plug n’ play. Hooking up the Sub 250 II to the Peachtree nova150’s variable output means the bass bin’s settings must be applied by ear and with trial and error. It’s a task that’d drive OCD-ers and optimisers to distraction. I might think I have the Dynaudio dialled in just so but how do I really know for sure?

It doesn’t have to be this way.

Previously we have seen DEQX’s PreMATE+ digital processor correct a loudspeaker’s response and then ’correct’ the room in which it sits.

In this third slice of PreMATE+ coverage, these two features combine to a third: subwoofer installation. The PreMATE+, its associated DEXQCal software and a microphone removes the guesswork from the process and moves it closer to an exact science.

DEQX’s general manager Alan Langford visited DAR HQ to walk us through the PreMATE+’s subwoofer calibration and integration smarts.

System setup went like this: Spatial M4 Turbo S loudspeakers lassoed with AudioQuest Rocket 88 cable to a Peachtree nova150 running in power amplifier mode (activated by a long press on the input selector). On pre-amplifier duties and connected via AudioQuest Yukon to the nova150’s line level input came the DEQX PreMATE+ itself, which in turn directly fed the Dynaudio Sub 250 II’s LFE port from one of two subwoofer outputs; the second output is for second sub.

A Krispy Kable interconnect which builder Cameron Pope describes as “straight-forward shielded OFC cable with gold-plated copper locking RCAs” joined the dots between DEQX and Sub 250 II. With the Spatial M4’s measured and corrected, the Krispy cable’s length took us to the next stage in the process: subwoofer placement.

Five whole meters of wire meant three distinct position possibilities could not only be aurally auditioned but their in-room response measured by a microphone located at the listening position: Position 1) immediately adjacent to the right-hand speaker; Position 2) on the speaker plane but splitting its distance 3:2 in favour of the left-hand Spatial; Position 3) a tight corner behind the right-hand speaker where the subwoofer would be hemmed in by sideboard and front wall.

Note position 3’s (magenta) 60 – 100Hz dip that, according to Langford, is unlikely to be cured by electronic compensation alone. Our man from DEQX then described position 2 (red) as “OK” with a narrow Q-d and likely inaudible null at 70Hz. Position 1 (blue) was both better and worse than position 2. Its 70Hz null displayed a marginally wider Q but a also flatter response up to ~130Hz.

Aesthetically, I preferred the wall-proximate position 3; its sound not so much. The measurements confirmed positions 2 and 3 as the better-sounding choices. I couldn’t split the two choices with my own ears so deferred to Langford’s greater expertise. Which one would he choose? 1 or 2?

The answer was neither. Langford’s first party trick would allow us to hold fast to position 3 by utilising the DEQX’s loudspeaker correctional facilities. FIR filter application by the PreMATE+ meant the Dynaudio sub could remain adjacent to the front wall where it would be measured, corrected and then that correction verified. Cake and eat it. Here’s the Sub 250 II’s corrected frequency response:

Then came a second party trick: software-based crossover construction. To the Spatials, a high pass filter at 50Hz with 24db/octave slope was applied. This relieved Clayton Shaw’s open-baffles of any low bass burden; heavy lifting that would then be done by the Dynaudio box. Applied to the Sub 250 II, a low pass filter at 60Hz with a 36db/octave slope. A 10Hz-wide window would blend loudspeaker and subwoofer.

Next up, something Langford refers to as “Time and Level”. SPLs from the Spatials and Dynaudio would need to be matched. Each’s impulse response must also be time-aligned — a process that (ordinarily) sees the loudspeaker output delayed so that its output arrives at the ear alongside that of the subwoofe. Putting the theory into practice, the PreMATE+/DEQXCal once again handled microphone measurements and corresponding calculations.

Verifying the end result proved to be a gratifying experience on two levels. The in-room verification measurement showed a nicely executed crossover point with the Spatials and Dyanudio combined talents carrying us all the way down to 24Hz with nary a bump or dip in sight. At 20Hz we were only 10db down.

On audible results of the new combo, I noted better bass grip and more satisfying low-frequency texture which in turn resulted in an uptick in overall tonal glossiness. Playing via the PreMATE+’s Roon Ready network input, Sly & Robbie’s Dub Sessions 1978 – 85 picked up some punch and dropped a little dryness but on Spring Heel Jack’s Suspensions EP the big guns really arrived. What was previously missing was laid bare: a whole other layer of depth and heft that laid out sturdier foundation for the percussion that skittered above its surface.

One click from the PreMATE+ remote returned us to ground zero – the Spatials running solo, full-range and uncorrected – and that freshly unearthed river of bass paved over.

The byproduct of the Dynaudio Sub 250 II’s augmentation of L.S.G.’s My Time Is Yours EP and (the first few cuts) from Michael Mayer’s Immer 3 saw my notes alliterate with three S’s: more substance, aggrandised subtlety through the midband and greater surefootedness below.

Results that proved far superior to my own experiments with manual subwoofer integration prior to the DEQX unit’s re-introduction to the system. Results that (would) cast much of this reviewer’s electronic music collection in a new light. Results that ultimately pull the curtain back on what’s missing.

The DEQX PreMATE+ has proven to be quite the revelation, both audible and educationally. Advance Australia Fair – indeed.

Further information: DEQX | Dynaudio