Next level KEF LS50 with the DEQX PreMATE+


Waiting for a mate. Recent years have seen the KEF LS50 hold their ground at (close to) the top of goto lists for loudspeaker auditions in the sub-US$2K space. Rolled up inside an enclosure that makes a break from the aesthetic conservatism of the past sits KEF’s Uni-Q driver configuration: a 2.5cm aluminium dome tweeter coaxially aligned with a 13cm magnesium/alloy bass-mid driver.

Not having heard every other standmount in and around the LS50’s price point, I might not comfortably assert ‘best’. What I can say with confidence is that the baby KEFs are popular. Four years on from the LS50’s (initially limited) release, this loudspeaker continues to resonate with the buying public — maybe because, when we boil it down to bare essentials, they sound good and they look good.

The LS50’s talents with punch, poise, clarity and (especially) imaging have seen them as a DAR staple for the best part of three years. Last year I traded in an original “50th Anniversary Edition” black pair with the gold Uni-Q driver array to the limited edition Racing Red finish with the black/silver woofer/tweeter; a matter of appearances and nothing else.


This week though, the LS50 sound quite a bit better than they did last week. From Grace Jones to The Flaming Lips to Ancient Methods, the Red Racers present with a fuller midrange, a more refined top end and mode cleanly defined player outlines.

What upstream change could possibly net such a pronounced result?

The amplifier remains the same (a Devialet Expert 200). Ditto the D/A converter (again the Devialet). The loudspeaker haven’t changed – still AudioQuest’s Rocket 88 – and the connection between Roon Endpoint box (an Antipodes DX Gen 2) and the Devialet remains a Blue Jean Cable S/PDIF coaxial.

That leaves only one possibility: a change to the Roon Endpoint hardware. However, this switcheroo isn’t simply a matter of lowering noise or jitter but the digital domain execution of something more radical: loudspeaker correction.

As good as the LS50 is, it isn’t perfect. No loudspeaker is no matter what the marketing materials tell us.

“Speakers do their best to convert the voltage representing amplitude to a precise air pressure arriving at our ears at any given instant in time. Compared to the upstream electronics that drives them, loudspeakers must integrate several uncompensated mechanical transducers (bass, midrange and tweeter drivers) as transparently as possible and it’s very difficult to get that exactly right.”

“Every speaker driver introduces errors to varying degrees whereby the sound they produce differs from the signal driving them at certain frequencies or frequency groups. Some frequencies will play slightly louder or softer than specified (frequency response errors) and be variously delayed compared to others (group delay errors).”

Those are the website words of Australia’s DEQX (pronounced “Decks”) whose PreMATE+ digital processor (US$5995) can pre-emptively correct for a loudspeaker’s frequency and timing errors. In other words, the LS50’s 2-way driver output can be improved.

“If we correct for group delay (timing errors) then any frequency response anomalies are also corrected – the two are mathematically intertwined”, says DEQX General Manager Alan Langford.

The Sydneysider elaborates: “It [the DEQX PreMATE+] corrects speaker frequency-response and timing errors by adjusting thousands of frequency groups, depending on your speakers’ measurements, so that they arrive at the correct time. Traditional analogue and digital EQ corrupts the timing coherence around the frequencies that they’re trying to equalise for volume.”


“DEQX Processors slow down on-time and early-arriving frequencies so that slower frequencies can catch up. DEQX uses real computing horsepower to make that happen with a 240-megaflop, 32-bit floating-point Digital Signal Processing Engine that essentially achieves zero distortion.”

If that causes your brain to perform hitherto unwitnessed mental gymnastics then you’re not alone. As with many things in hifi, one doesn’t necessarily need to fully understand the engineering theory to enjoy the end result.

Think of it this way: just as eyes are metaphorical windows on the soul, our loudspeakers are windows on upstream electronics. The way Langford tells it, loudspeakers introduce more distortion than any other component in the system; frequency and timing (group delay) errors erode ultimate output resolution. Correct for those errors and some resolution can be reclaimed.

Frequency errors means some frequencies are reproduced more loudly than others. The loudspeaker engineer’s pursuit of a ruler flat frequency response – all frequencies reproduced at the same volume – is but a pipe dream. (Discussions on the validity of ‘flat’ as as the optimal target remain well beyond the scope of this coverage)

Group Delay on the other hand refers to groups of frequencies arriving at the ear before others. These are sometimes referred to as timing errors. We don’t want that either

DEQX’s proposition is to apply a long, linear phase FIR filter to correct for group delay anomalies. As we shall see, this is turn evens out a loudspeaker’s measured frequency response.


Compensating for group delay errors can, according to Langford, only be executed in the digital domain. DEQX’s PreMATE+ applies a digital filter to the signal before it reaches the D/A conversion stage; either the PreMATE+’s own internal DAC (which in turn spills its analogue output via balanced XLR or single-ended RCA socketry) or a third party decoder connected to the unit’s solitary digital output (S/PDIF BNC).

“We don’t publish which model DAC chip is used in the PreMATE+”, says Langford. Moving on…

On the PreMATE+’s digital inputs, we count five: TOSLINK, S/PDIF BNC, S/PDIF RCA, AES/EBU and USB. As alluded to above, the PreMATE+’s official stamp of Roon Readiness is imminent. MPD compatibility is also offered.

In (over-)simplified terms, we might describe the PreMATE+ as a pre-amplifier with digital domain volume attenuation. We might then incorrectly infer that vinyl spinners and tape spoolers aren’t invited to the party. But they are. A 24-bit Cirrus Logic ADC running at 96kHz greets analogue signals arriving at the DEQX box’s unbalanced RCA and balanced XLR sockets.

Analogue purists might bristle at the thought of turning over their phono stage’s or reel-to-reel’s output to ones and zeroes but ultimately such prejudice is their quite literal loss (of resolution). The audible gains from DEQX-correcting the KEF LS50 more than offsets any real or imagined ‘analogue magic’ surrender.

Back at DEQX’s online FAQ: “Normally, this high resolution impulse response convolution adds around a quarter second (250 milliseconds) to process, so synchronising a ‘corrected’ soundtrack to video for example is a problem to say the least. DEQX maintains high resolution adding only around 5% of the time usually taken, or about a quarter film frame’s delay of the audio that’s not noticeable.”

In dodging unnecessary latency, a pair of high power SHARC DSPs run the 500,000+ lines of DEQX-Cal™ code. These are not to be confused with the ARM A8 processor is charged with a) marshalling USB and Ethernet data and b) running the 480px x 270px touchscreen that offers an additional layer of hands-on device control over and above the more basic remote wand. Virtual VU meters too!


How is the loudspeaker correction linear FIR filter calculated?

For those not comfortable going it alone with the 172-page user manual, the company’s DEQXpert service brings online support via Teamviewer and Skype. You move the microphone, DEQX takes care of the rest. Stateside DEQX-ers enjoy time-zone appropriate support.

I had the home turf advantage of living 25kms from DEQX’s Sydney HQ. Alan Langford delivered the PreMATE+ review unit in person and guided me through the basics. Plug and play it is not but you get out what you put in – literally and figuratively.

Be advised that what follows extended my knowledge of loudspeaker design and functionality to new limits. To say that I learnt a lot is an understatement.

The basic process is this: measure the loudspeaker, have DEQX’s Calibration software calculate its correction filter, load it into the PreMATE+ over USB and then re-measure the loudspeaker in order to verify the filter’s corrective capabilities. Measure – Calibrate – Verify. 1 – 2 – 3.

The heavy lifting is carried out by DEQX’s own Windows-only software application which, connected via USB to the Pre-Mate+, interprets the reading of frequency sweeps made by a microphone connected to the DEQX box’s XLR socket. Langford supplied the Dayton Audio EMM-6 (US$79.99) and mic stand as loaner items.

For an anechoic-like measurement the microphone’s nose is placed 60cm or so in front of the left LS50, itself standing in as much free space as possible.

The Calibration runs several frequency sweeps before reporting back with the KEF standmount’s impulse response:


From this impulse response measurement the DEQX Calibration software derives frequency response:


Note that the DEQX-measured curve is entirely consistent with KEF’s own sheeted specification for the LS50: 79Hz – 28kHz (±3dB). In other words, between 79Hz and 28kHz the red line wanders not above +3dB or below -3dB. According to Langford, the peak at 40kHz is most likely the tweeter’s resonant frequency.

Group delay is also calculated:


Here we see timing errors really begin to swing with frequencies below 200Hz. Langford suggests that this probably isn’t the loudspeaker’s doing but more likely an indication that the room has begun to interfere with the near field measurement.

Looking back at the impulse response (above) confirms as much. Note the squiggle just beyond around 10ms? That’s the room coming into play. Throwing it back to high school science, we recall that time corresponds to frequency: 1000ms equates to 1Hz. Similarly 10ms converts to 100Hz.

Keeping it safe, Langford chooses to have the PreMATE+ gate the loudspeaker correction at 200Hz. Only frequencies above 200Hz will enjoy the Calibration software’s auto-calculated fix up.


[Side note: the bigger the room, the lower the frequency at which it comes into play and therefore the wider the bandwidth that can be corrected for group delay errors.]

Once calibrated the filter is loaded into one of four preset locations on the PreMATE+. Remote control access to these four positions means A/B-ing from the listening position is a snap.

You already know my thoughts on how much the corrected LS50 sounds – but how does it measure? Time to verify by engaging the correction filter and re-measuring.

Group delay above 200Hz comes out like this:


Moving from the original measurement in red to the corrected measurement in blue, we note a more evenly distributed group delay.

What implications for the LS50’s frequency response? Original in red, corrected in blue:


DEQX corrected, we get a smoother, more even response from the LS50.

These measured improvements seem to correlate with the subjective listening assessment that the KEFs now sounded better.

Verifying the correction filter’s SQ lift by subtracting it confirmed as much. Without DEQX FIR filter intervention the LS50 present as a few kilos lighter from the female voice region down to the midbass but also less settled/organised up top. Accusing the uncorrected LS50 of less high frequency extension would stand up in an audio court (should it exist) but it’s not quite as simple as that – it’s also less coherent.

The DEQX PreMATE+’s loudspeaker correction proves itself on screen and in-ear that it can take an already great loudspeaker like the KEF LS50 and make it sound (and measure) even better.

The audible improvements are more pronounced than switching up cables, server/streamer, DAC or amplifier. Such is the power of low-latency group delay correction through DSP. Australians say “Maaate”, I say “Bloody marvellous!”.

And yet, this DEQX box’s software-hardware one-two does quite a bit more than just loudspeaker correction.

In Part 2 we look at how the PreMATE+ can correct for the room. Before that, a quick analysis of Devialet’s SAM.

Further information: DEQX



Written by John H. Darko

John lives in the NOW + HERE = NOWHERE. He derives an income from the ad revenues of DAR. John is also an occasional staff writer for Stereophile, 6moons and TONEAudio.

Twitter: DarkoAudio
Instagram: DarkoAudio
Facebook: DAR


Leave a Reply
  1. Hey John,

    Thanks for this well-written introduction to what appears to be a very credible new technology for improving the listening experience. I don’t see any smoke and mirrors here – the problem definition and stated solution make sense to a suspicious mind. 🙂

    I’m really impressed with the engineering at DEQX, but also with what is apparently 24/7 live support for installing and tuning the PreMATE+. This is no doubt a tool that could cause as much harm as good, in careless hands.

    I’m curious, however, as to why they gated the correction at 200Hz. My first instinct would be to calibrate the entire spectrum. What did you mean by “Keeping it safe…?” Was this done to make the calibration “portable” – so that the speakers can be placed in various rooms without the need for re-calibration? And, contrary to the photo shown in the article, why wouldn’t I place the microphone at my listening position – or was the close proximity shown in that photo selected, again, for the purpose of coming up with a “generic” calibration for portability?


    • The correction was gated at 200Hz because that’s where the room began to interfere with the measurement. Check out the smaller squiggle at around 11ms on the impulse response chart.

  2. Really pleased to read your experiences in DSP-based correctors. Agree with you that such electronic treatments seem to provide more sizeable treats than new cables, DACs and other bits and bobs. For some time I have been running a much more humble box of tricks than the DEQX – a trusty DSPeaker Antimode 2.0 – which I don’t think corrects individual speakers, just room anomalies, yet I swear by it. Everything sounds much more controlled, less bloated and err more in time. As you can tell, I don’t understand the technicalities but I like what it does. Can’t wait to hear your views on the DEQX’s room calibration capabilities in part 2. As I should imagine is the case with most readers, physical room treatment is just not practical or pretty in the average family lounge room so these devices are a great alternative.

  3. That will be a marvellous system indeed. I do have the low budget alternative compromising Dirac Live room correction software (2 channel version), KEF X300A with subwoofer output modification and a 12″ sealed subwoofer from SVS. Room and speaker correction technology does an amazing job!

  4. The really fun bit with DEQX is using it with speakers without crossovers. The DEQX than totally transforms the speakers.

  5. Very interesting!
    Now I undrestand the meaning of all those wiggles.
    I have just found a new function on my pioneer receiver that should be handling group delays or phase control.
    I am curious. How many group of frequencies does the deqx handles?
    How the group delays are compensated?

  6. I tried the Deqx technology on my system with mixed results, although a speaker issue may have been a large part of the problem. But I did get a noticeable ‘hum’ through the speakers that isn’t there with other DACs, and that was also with the correction turned off. But the technology is really clever, albeit not easy to implement without help. I did suffer some inconsistencies and found that using the correction facilities within J River was easier to get right. But I do believe that what Deqx is doing here is great – just needs VERY careful implementation. And of course if you move your speakers or change your furniture or room round you need to start again. So, might not be for everybody and the sound without correction was not of the highest order to my ears.

  7. The Devialet has speaker correction as wel, any chance of a comparison? The DEQX has always intrigued but everyone talks of hard to use and that doesn’t sound appealing to pay someone every time I change my system.

    • Possibly. But the above is all you get for now. This kind of coverage takes longer than a standard review. The Devialet Expert 200 hard to use? Nope, not at all. It’s FAR more intuitive than the Phantom.

  8. I am pleased that you are giving your attention to the domain of digital ‘correction’. This is an area that has enormous potential benefit to all audiophiles but I personally don’t have a firm handle on and hope to learn more through your writing. One tidbit I picked up was a rule of thumb along the lines of ‘above 200Hz it’s speaker correction, below 200Hz its room correction’. What exactly is the difference and why that matters is something I hope you will cover in Part Deux along with what the heck is the importance phase/timing correction when using these solutions.
    Finally, while acknowledging the reality that you typically get what you pay for, what are the key differences in scope or capability between a Dirac MiniDSP and the DEQX. I mean, are they trying to do they same thing? Are they even attempting to solve the same problem? Any light you can shed on this would be appreciated.


    • Hey David. As per the article, the 200Hz threshold was decided upon because the impulse response graph shows the room beginning to affect the nearfield speaker measurement at that point. Look for the second blip on the line, to the right of the green ‘gate’ line – that’s first reflection! If we’re doing speaker correction we don’t want to be correcting for the first or any other room reflections. That threshold is specific to the LS50 in MY listening room. In a bigger room the reflections will arrive later and therefore the threshold frequency can be reduced. It makes sense to me but alas I don’t know to explain it any more clearly than that.

  9. Life gets far more interesting when you have a DEQX and speakers like the Larsen 8’s where the notion of anechoic measurement becomes complex, if not too difficult. Figuring out how to measure the direct sound component is rather brain imploding.

    The difficulty lies with the Larsens being designed to work with the listening room walls and floors, so the 200Hz plus signal is a mixture of direct and reflected; the Larsens have to be located hard against the back wall.. And the Larsen 8 has a HF driver pointing vertically upwards to the ceiling, 10dB down, which adds another level of complexity to the direct/reflected sound field process; where do you place the mike?

    Take the Larsen’s into the middle of the room and the bass is diminished, (300Hz and below), So you might measure it for 300Hz and above, but the triangular baffle/tweeter assembly is angled upwards and inwards (speakers are mirror pair), so where to put the mike to get the best response? And then the speaker seems to have a purposefully engineered dip around the 3000Hz zone as well, so DEQXing is no beer and skittles situation.

    I’ve given up needless to say and opted for a response smoothing curve rather than making it tonally flat. Group delays etc simply can’t be measured sensibly either.

  10. Reading everything you’ve written thus far about having gated the calibration at 200Hz, I’m still confused. On the one hand, you are saying that once calibrated for a given room, we will have to recalibrate for a different room, and yet, you’re also saying that the cutoff frequency was selected at the point where the room began to influence the measurements – which would imply that the calibration is “portable.” The only way I can reconcile those two statements is as follows: The DEQX has no ability to compensate for room reflections. Calibration can only begin at the frequency where the room begins to influence measurements taken with the microphone in close proximity to the speaker. That’s why the microphone is not placed at the listening position. Even so, the calibration must be repeated if the room is changed, because the cutoff frequency used for the original calibration might no longer be appropriate. Is all of this correct? If so, I’m still left scratching my head with this question: Why can’t the DEQX calibrate for room reflections? In other words, why can’t we put the microphone at the listening position and set the cutoff frequency at 10Hz? My head is never going to be mere inches from each speaker, unless I’m intentionally setting up near-field monitors.

    • Room correction comes AFTER loudspeaker correction and I haven’t written about that…yet. This piece centres on loudspeaker correction and loudspeaker correction ONLY, hence only measuring the LS50 in the near field. The reason we didn’t correct the LS50 beneath 200Hz in this case is because if we do, we are also correcting for the room’s first reflection. Remember: we are doing speaker correction only in this post.

      The room calls for a different process altogether where, as you say, the mic is moved to the listening position. And as per the final para, room correction is coming next.

      • Somehow, I had missed that last sentence in your article. My mistake. I will patiently await part 2. 🙂

  11. John,

    Thanks for the excellent write up. Clearly, DSP products like this have a significant future (well, present). I notice that this product works it’s magic without a hostile takeover all the entire digital playback and production chain a’la MQA. It appears to work with any DAC and any digital file format (correct me if I am wrong). So apparently this kind of improvement does not require an anti-consumer stance by the company via end-to-end requirements, NDA and IP, etc.

    • Dear Cranky,

      The article is about DSP not MQA which I am guessing doesn’t float your boat.

      I am also pretty sure that in an earlier post which DID address the emergence of MQA it was made abundantly clear that MQA is an offering to which the consumer can ‘opt in’ or choose not to.

      There are no MQA Logo’d Black Helicopters on the Whitehouse lawn.

      • Gents – appreciate robust debate but let’s leave the name calling at the door please. I’d also appreciate this thread staying on track with the DEQX’s loudspeaker correction (despite the time domain connection with MQA). Plenty of places to discuss MQA elsewhere on DAR.

  12. Any comparison of DEQX’s correction to the Devialet SAM speaker correction? I’ve heard SAM on the Atohm speakers and can appreciate what the correction did for such a small speaker. I also know that the fantastic LS50’s are also in SAM’s database. It would be nice to hear a first hand account of the comparison in the same room, with the same speakers, and the same set of ears!

    • Never mind… I found your other article with the comparison. Nice to see the graphs too… Especially when the results were captured with the same DEQX software. Interesting in how the group delay is exaggerated by SAM in the lower octaves. My guess is that would smear the audible results, revealing why you would prefer the less congested sound of having SAM turned off. Thanks for the excellent coverage!

  13. Look forward to your thoughts on the DEQX room correction. Great articles on some fascinating DSP approaches.

  14. I’m also very curious about how the DEQX stacks up as just a DAC. What other DACs us it comparable to in bypass mode? What are the strengths and weaknesses as a DAC?

    • I’m not sure that kind of coverage is on the horizon at this stage, Roscoe. I can only do so much with the allotted time and speaker/room correction obviously take priority. My follow up piece on what Devialet’s SAM does to the LS50 already bit a big chunk out of this month’s schedule.