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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?

    Dynaudio Sub 250 II – position 2.

    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.

    Three Dynaudio Sub 250 II in-room positions measured.

    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:

    DEQX-corrected Dynaudio Sub 250 II, 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.

    In-room response of Spatial M4 and Dynaudio Sub 250 II, time- and level-aligned.

    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


    John H. Darko

    Written by John H. Darko

    John is the editor of Darko.Audio, from whose ad revenues he derives an income. He is an occasional contributor to 6moons but has previously written pieces for TONEAudio, AudioStream and Stereophile.

    Darko.Audio is a member of EISA.

    Follow John on YouTube or Twitter


    1. That $6k DEQX PreMATE+ looks very cool! It was a bit outside of my budget, though, so when I dipped a toe into room correction, I went with AudioVero’s Acourate instead. It’s a software-only solution, so you do have to add an audio interface and calibrated mic. The FIR filters it creates are compatible with JRiver’s convolution engine, so if you’re a computer audiophile, integration is pretty simple. Mitch Barnett has published a book on Amazon called “Accurate Sound Reproduction Using DSP” that’s essential to getting things setup correctly. Acourate almost certainly requires more effort than DEQX, but the price-point will be attractive to folks who like to tinker or have a bit more time than money. 🙂

      • That’s exactly what I thought when I was reading these articles on the DEQX PreMATE+:it is so cool but so expensive, I have to look into the AudioVero products!
        But two things do not convince me:
        – How can I connect a preamp where the filters reside to my avr? My avr has so many sources and most of them are digital (hdmi and optical)
        – it is not clear what is the HW I have to buy and steps needed to go through all the process
        Probably I am missing something, but most audio products are far from simple to set up and it is always very difficult to see the light of an all-in-one solution at the horizon…

        • I’m not aware of any AVRs (assuming audio/video receiver) that are compatible with the FIR filters that Acourate generates. From what I understand, it is possible to create 5.1 filters with Acourate and to play video with a multi-channel soundtrack using JRiver. In this case, JRiver adds enough delay to the video to synchronize the audio. I have not attempted this.

          Outside of JRiver, FIR filters typically won’t work well with A/V sources because of the one or two second time delay in the audio. I think you’d have the same problem with DEQX, although the latency may be small enough that you can live with it.

          I know of at least one person who is using Acourate Convolver running on a dedicated PC with attached audio interface. This add-on software uses ASIO drivers and performs the analog to digital conversion, applies appropriate FIR room correction filters, and routes the corrected analog signal to the outputs of the audio interface. In effect, Acourate Convolver + Audio interface (eg. Focusrite Scarlett 2i2 gen 2) + PC gives you similar functionality as the OpenDRC-AN from MiniDSP. You still need Acourate and a calibrated mic to design/create the FIR filters in either case. You would insert a rig like this in the analog processor loop of your preamp or between your preamp and stereo amp if the audio interface is sufficiently quiet.

          Integrating any digital room correction solution that’s more sophisticated than what’s built into your AVR or pre/pro is always a challenge and typically either involves an extra ADC/DAC step somewhere in the signal path or limiting your source to a single device (eg., PC running JRiver) that can apply the filters internally. I’m sure this will get easier with time as more preamps, pre/pros, and AVRs are able to handle FIR filters. For example,

          • “Outside of JRiver, FIR filters typically won’t work well with A/V sources because of the one or two second time delay in the audio. I think you’d have the same problem with DEQX, although the latency may be small enough that you can live with it.”

            Careful here. Without having heard a DEQX, you might not know that its super-low latency troubles not video/sound lip-sync.

            • Fair enough…based on my lay person’s understanding of how FIR filters work and the fact that DEQX uses FIR filters, I have (perhaps incorrectly) assumed that DEQX adds some latency during playback.

              Note that this latency (if present) would not be easy to hear or observe unless you have a way to hear the source directly and then immediately switch to the corrected output. The latency might be similar to switching between live and the tape loop on a 3-head deck, for example.

              Not having a DEQX product on-hand, I had another look at the FAQ on their website where they describe their patented solution as a hybrid FIR/IIR solution. Perhaps they use IIR for correction below 300Hz and FIR for frequencies above that? Not sure. Here’s a quote:

              What is impulse response and what does DEQX do with it?

              A speaker’s impulse response refers to the reaction of its drivers to an input as a function of time. One of DEQX’s main features is providing low-latency impulse response correction. This new generation of low-latency FIR/IIR digital signal processing was actually pioneered by DEQX for speaker calibration in the 1990’s.

              The speaker’s measured impulse response defines its timing/phase and amplitude accuracy at any given frequency. DEQX uses Convolution FTT to redefine the speaker’s impulse response to correct the relatively dramatic errors it introduces compared to the more subtle errors of other component your system.

              The audio signal is processed prior to the power amplifiers that drive the speakers so it is connected like a traditional equalizer but that’s where all similarities end. DEQX compensates for the errors measured in your speakers! This is very different from traditional equalization that’s unable to correct critical phase errors at different frequencies.

        • Dirac doesn’t do digital crossovers and therefore wont’t integrate a subwoofer as per the above method. Dirac is also limited to running on a Mac/PC, Arcam/Emotiva amps or miniDSP box whose latency might also preclude watching TV. Running it on a Mac/PC means no vinyl either.

          The DEQX is an single box that does speaker correction, room correction and sub integration via digital crossover and it does all this with a low enough latency that it doesn’t compromise lipsync when watching movies and doesn’t red card a phono stage or other analogue input. It’s not for everyone but it’s for those who want it all without having to stitch numerous boxes together.

        • Dirac is okay, but it uses IIR filters which limits the types of correction possible. DEQX and Acourate use FIR filters which are much more powerful but add latency. For a better understanding of the differences, check out:

          I’m not an expert, but I do know what I hear. I have the full version of Dirac on my Emotiva XMC-1. It works fine for my home theater, but I was disappointed with the results for serious 2-channel listening. JRiver convolution using FIR filters created by Acourate, on the other hand, produces better results. Like DEQX, the amplitude response is corrected while also improving group delay, step response, timing, etc.

          • Is the filter’s latency not a function of the processing power that applies it? In the case of this DEQX unit, the latency is audidbly imperceptible.

            • Since FIR filters perform corrections in both the frequency and time domains, some latency is unavoidable regardless of processing power. It makes sense when you think about it…how can you perform time domain corrections that affect group delay and step response without adding latency? Corrections at low frequencies introduce more latency in a pure FIR filter implementation. DEQX introduces less latency because it apparently uses a hybrid IIR/FIR design that applies low latency IIR filters to low frequencies. I have no idea how this actually works, but hats off to DEQX for figuring it out! 🙂

    2. Great article’ John. Have you considered adding another subwoofer? I doubt it will get rid of your dip there between 50-100 hz, but it might bring it up a bit. My room has very similar dip there.

    3. Another DEQX alternative on a budget would be the mini DSP products. I use the Mini DSP Open DRC DI for speaker and room correction (with active speakers and two subwoofers). The results are terrific! Full FIR filtered correction starts at approx. 400usd plus cost for the room correction software. Depending on the model one still needs to add a DAC and pre amp (which are often in place already).

      In any case I would not want to go ahead without a DSP anymore, especially to reign in the subs.

      • It’s my understanding that the filters in the miniDSP products aren’t as long or processed as speedily as those in the DEQX and therefore might not resolve as much detail or process without latency. Anyone out there *heard* both DEQX and miniDSP *in their own system* care to comment?

    4. Indeed sealed subs are way to go. Two subs are usually better than one. Next to the main speakers.
      If hooked up as left and right sub (stereo) it widens the soundstage considerably. Enjoy the deep grooves.

    5. Welcome to the suburbs, John -:)

      Once you’ve heard proper infrasonics, you wouldn’t want to be without them. Proper integration is essential of course so kudos for laying out one way to do it!

    6. Answering Johns’ question: “Anyone out there *heard* both DEQX and miniDSP *in their own system* care to comment?”

      Yes, I tried several miniDSP devices before purchasing a DEQX HDP-3 in 2012 & the difference in transparency, imaging, realism and lack-of-grain was very significant – in favour of the DEQX (their algorithms are said to address phase and timing at all frequencies, beyond the levels achieved by other DSP systems).

      Since then I have purchased an additional HDP-5 and use a multi amp + twin sub Open Baffle arrangement (3-way, 2 channel stereo). In the future I plan to daisy chain the HDP-3 to the HDP-5 and create a 4-way speaker & twin sub arrangement. For now I have 2 setups in 2 different rooms.

      Correctly time aligned, my system sounds pretty spectacular and the room has zero audible impact. These processors are worth every penny & most significantly, since 2012 I listen to music with no niggling doubts about whether it could sound better. For over 40 years previously, that wasn’t the case 🙂

      • I don’t have either of these, but I have experienced similar results when comparing Dirac (IIR filters) to Acourate (FIR filters). As you have suggested, the more sophisticated FIR filters and algorithms are what make the difference. I also understand that the analog circuits, power supplies, and general build quality of the DEQX hardware are all excellent…so that can’t hurt. 🙂

        Agreed that DEQX gear is probably worth the money…especially if you have a complicated setup and/or don’t enjoy doing a lot of DIY tinkering to get the best results.

    7. I am not an expert on filter types but I am an advanced DEQX user (2 channel only, I don’t use it with a home theatre setup).

      If someone wished to check latency on an AVR system (most likely ‘audibly imperceptible’ as JD suggests), this can easily be compared on-the-fly by setting one of the four remote control presets to ‘bypass’ and switching between this and any of the other three presets from the listening position.

      • I stand corrected…since it seems that DEQX uses a patented combination of IIR and FIR filters, they are able to achieve lower latency than a full FIR system. FIR filters add significant latency at low frequencies but very little for mid/high frequencies. My guess is that DEQX came up with a clever way to merge the two corrections–using low latency IIR filters for low frequencies while retaining the time domain benefits of FIR for the mid/high frequencies. Kind-of a best-of-both-worlds thing. This is what you’d expect from a $6k unit, and it’s actually brilliant. 🙂 Based on this review and discussion, I’m definitely going to make an effort to hear DEQX in action!

        However, in a dedicated 2-channel (digital) system, a couple of seconds of latency is rarely a problem. You hit [PLAY] on JRemote (a tablet/phone app to control JRiver Media Center), and instead of starting immediately, the music starts a few seconds later. When you hit [SKIP] or [STOP], those operations may take up to a couple of seconds as well, but if you listen to an album or playlist straight through from start to finish, you won’t experience any lag or latency. Gapless playback works as expected; there’s no delay or pause between adjacent tracks on the same album or even different tracks in a playlist. Latency is not a big deal unless you’re trying to synchronize playback with something else…like video or monitoring live singing with processing enabled, etc.

        Based on what you and others have said about DEQX, it sounds like the most convenient, flexible, high-performance way to get started with FIR based digital room correction–either doing subwoofer integration or just working with full-range loudspeakers. It has a generous set of digital and analog inputs, can provide selectable correction for all of them, and even integrates with home theater environments. I really can’t wait to check it out myself.

        The point of my original post is that Acourate is a lower cost yet less featureful entry point into room correction that’s also worth checking out. It’s ideal for simple 2-channel playback systems that have a PC running JRiver (or perhaps HQPlayer) and a USB DAC as their primary source. Like DEQX, you need a “calibration kit”, which typically consists of a calibrated condenser mic (eg, the EMM-6 from Cross-Spectrum Labs), stand, and cables. Since Acourate is software only, you’ll also need an audio interface with a mic preamp that provides phantom power (Focusrite Scarlett Solo or 2i2 Gen2 is fine), and a PC or laptop. Assuming that you have the laptop already, the kit should cost less than $300 unless you go with the Earthworks M23! The Acourate software is 286€ for US customers (~$320), so about $620 in total.

        Acourate and DEQX both use FIR filters to perform room correction, but that’s just about all that they have in common. DEQX is a sophisticated preamp/processor with an internal ADC/DAC that does room correction while Acourate just builds FIR filter files that are compatible with JRiver’s convolution engine, HQPlayer, and Acourate Convolver plus some of miniDSP’s OpenDRC products. Which one you choose really depends on your requirements and budget. Either way, once you have a properly integrated FIR based digital room correction system, you’ll never want to go back. This is definitely an exciting time to be involved with this hobby!

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