Is DEQX a game changer?

Thanks for posting that article, jeffrubin. I stumbled upon another article I thought was germane to this thread given all the talk of measuring speakers and interpreting frequency response graphs in the DEQX calibration software. I got an extra kick out of this since I own the Revel F208s that are featured in this test.

http://www.soundandvision.com/content/speaker-measurements-101#RUfrx2HukdlGAS8i.97

I just stumbled upon this story in TAS form 2008:

http://www.theabsolutesound.com/articles/magico-ultimate-loudspeaker-1/

Alon Wolf of Magico used a DEQX crossover in his own Ultimate speakers.  That certainly is a big validation of the transparency of these units!

Ah good, the volume settings could solve the problem.  May seriously consider just sticking with 2 channel for TV if the voices can be tuned correctly.  

Definitely going to measure outside.  Big grass lawn next to my house and easily moved Raidho D1 monitors.  My old ML CLXes would not have been contenders for outside measurements!

Output volume levels from the DEQX can be set higher or lower on any or all of the four configs so you can adjust accordingly. 

If 2 channel is your priority then in my experience nothing comes close to DEQX, especially if you are able to conduct initial measurements outdoors. 

Andrew

Thanks Andrew.  That's extremely helpful on the bypass question.  My other concern though is having to max the volume on the prepro source and the risk of switching sources forgetting to turn the volume back down.  One solution I thought of is putting my current preamp between the HDP5 amp outputs and the amps.  I would run all of my two channel from the HDP5 to a passthru input on the preamp and the prepro directly to another passthru input.  The preamp would essentially just act as a line level switch between 2 channel and surround.  The problem is that I HATE to put an additional piece in the chain and I was hoping to sell off the preamp to mitigate the price of the HDP5.

Another option is simply to add another pair of main speakers and a dedicated amp (I have a set up in another room that I never use) and literally run two separate systems in the same room only sharing sources.  This is kind of cool, but a bit cluttered and I'm not sure if the additional speakers in the room will cause unwanted resonances when I'm listening to just 2 channel.

My third option is to just go all 2 channel.  I read somewhere (maybe here) that the fully corrected system sounds so good and the center is so optimized that surround is not critical.  I watch regular TV and am not critical of theater sound at all while being fanatical about my 2 channel music.  I know that I could also work a profile to optimize the voices as well, that is key.  So this may be a good option and would let me sell off even more gear...maybe get a nice 'table! 

Thanks also for the validation regarding sound quality.  this is what I am hearing pretty much everywhere, but best when it comes from a long term user.  I will definitely post my journey when I decide to move forward.

Thanks!

Jeff

Hi Jeff
Although I do not use my HDP-5 & HDP-3 processors in a home theatre setup, you have the facility to use one of the four (remote control selectable) config setups as a bypass.

If the Main Filter is set to "Bypass correction or crossover for this loudspeaker, but still use filters" & then against Limit Filters, untick both low & high pass filters (a new config defaults to this anyway), the speakers will still operate but in bypass fashion.

Any further queries, I recommend you contact Alan Langford at DEQX to confirm: alangford@deqx.com

Please also note that Roon for DEQX is shown as 'coming soon' on the Roon site.

As a largely analogue listener, digital processing is undetectable in my setup. Clarity/transparency is outstanding & I suppose that the things DEQX corrects have far greater benefits than any DSP impact, even if it's there.

Let us know how you get on.....

Andrew

Hi all,

I recently became interested in DEQX and discovered this epic thread.  I read through most of it and it has been very helpful.  I am seriously considering an HDP-5.  The weak links in my system are my Oppo BDP105 which I use as my DAC and a dbx 223 crossover that I use with my JL f113 sub.  I've been considering upgrading both the DAC and crossover and in a discussion about DIY speakers, a knowledgeable friend mentioned DEQX.  

I am a pretty knowledgeable audiophile, but I had not heard of DEQX.  It is a revelation!  I immediately realized that not only is the HDP-5 an upgrade on my Oppo as a DAC and a vastly superior crossover, but it can also replace my preamp (offsetting about half the cost of the HDP-5) and adds amazing time and room correction -both of which should be highly beneficial to the challenging sub integration process.  What an incredible machine.  

Then there is the icing on the cake.  I just discovered that the HDP-5 supports the incredible Roon server on board, without a PC and USB!  This is a terrific feature.

My one concern remains putting my signal though digital processing, although most everything I've read indicates this is a non issue.   My only other concern is the lack of home theater prepro passthru.   I run a hybrid system and frequently switch between 2 channel and surround.  Any suggestions on how I can best create a passthru set up with the HDP-5?   Thanks!

I'd be very curious to hear about other folks who are using the digital output too, and curious to hear what DACs seem just comparable to DEQX (similar sound or a sideways move), and those that are a big upgrade over the DEQX internal DAC. 

As some of you may have seen, John Darko is doing a multipart review of the DEQX Premate+.

Part 1 (with popular KEF LS50):
http://www.digitalaudioreview.net/2016/06/next-level-kef-ls50-with-the-deqx-premate/

Part 2 (with ELAC B6): 
http://www.digitalaudioreview.net/2016/07/get-a-room-deqx-correcting-the-elac-debut-b6/

One more part (on room correction with LS50) to come. 

I'd asked Darko to comment on the DEQX DAC quality compared to others he's tried or has in house, but he said that it wasn't likely that he'd do that as part of these reviews. He chose to focus on the speaker and room correction functionality. 

Kingrex here again.  Some more insight if I may ask.  I am interested in experiences with people using their unit as SPDIF in and SPDIF out to the DAC.  For a very reasonable price I can get my Mate upgraded to process the signal in the digital domain only and it should have the same sonic quality as the higher level models.    I am interested in what others have experienced with tonal shifts when installed this way.  I currently have a First Sound Preamp and Transition Audio Monoblocks.  My gear is all tube and has a lot of harmonic warmth and richness.  My system is not designed to be high in analytical clarity.  Its all about a big warm engaging blanket of good clean sound.  In others experience, if you are using tube equipment, did you feel you lost any of the warmth and harmonics, or was it so transparent nothing changed when in bypass as compared with physically pulling the unit out of the signal path.  You know, compare the tone with the DEQX in the system, in bypass, then take it completely out.    Once again this would be with digital in and out only.  Thanks for any input.

Wow very informative tread!

Good info, Kingrex.  Thanks!

BTW, although it undoubtedly has no relevance in the case of your Mate, I'll mention that according to a communication I had with Alan Langford of DEQX last year, incorporation of Larry's mods into a unit that is under factory warranty will invalidate that warranty.

Best of luck as you proceed.  Regards,
-- Al
 

Andrew (Drewan77), congratulations on the new HDP-5!  And thanks once again for the many valuable inputs you have provided to this thread.

Best regards,
-- Al
 

Since I last posted on here I have added an HDP-5 processor/preamp and as Almarg mentions, this has a low noise switch mode power supply. My HDP-3 uses a linear supply and both sound equally transparent with no top end glare that I can detect. Most of my listening is analogue input from two turntables and my various power amps & subs are also connected via unbalanced RCA cabling.

The HDP-5 has slightly greater clarity and openness to the soundstage than the HDP-3 & I will be using them together in a 4-way stereo setup (0-60hz, 60-200hz, 200-3100hz, 3100khz+), the HDP-3 managing just the subs.

FWIW my HDP-5, which has superseded the HDP-4 as DEQX’s top-of-the-line model, uses a switching power supply. I don’t know if it is the same supply that is used in your Mate, but it is an XP Power model ECL30UD02-S. Here is the datasheet for that series of supplies.

I use the HDP-5 as my preamp. I have never sensed that it is causing any glare whatsoever in any part of the spectrum. I am connecting my phono stage (a Herron VTPH-2) to it via unbalanced RCA cables. I am connecting my main digital source (a Bryston BCD-1 CD player used just as a transport) via an AES/EBU digital cable. Those are my two critical sources. I am connecting the HDP-5 to my power amp via unbalanced RCA cables.

I don’t recall what connectivity the Mate provides, but if you are using balanced analog connections to its inputs or outputs perhaps a contributing factor to the issue you described might be an internal balanced/unbalanced converter stage or transformer needed to interface to its presumably unbalanced internal signal path. Or if you are connecting to a digital input, perhaps waveform degradation due to signal reflections resulting from small impedance mismatches is occurring, resulting in jitter that might be improved by changing the length and/or type of the digital cable.

That’s about all I can think of in response to your question.

Good luck. Regards,
-- Al

Thanks for the comments, gentlemen. Sounds like a plan, Roscoe!

Yes, I would think that a DEQX will generally make speaker positioning at least a bit less critical than it would otherwise be, as a result of the corrections and equalizations it can introduce with seemingly no sonic downside.

Unrelated to the DEQX, I’ve made one change to what I said in my 12-2-2015 post. Instead of purchasing a Dynavector 17D3 phono cartridge, based largely on the many accolades that have been posted here recently I’ve purchased an Audio Technica AT-ART9. I just started listening to it today, with promising results. But the reported experiences seem to indicate that it improves considerably during the first 50 or so hours of breakin, so I’ll wait until I’m significantly into that period before attempting to fine tune the various tonearm adjustments.

Roscoe, best of luck as you proceed. And thanks very much for the kind words you posted recently in another thread.

Enjoy! Best regards,
-- Al

Almarg, good to read your 12-02-2015 post where you wrote that making your speakers time-coherent has been very beneficial to you. :-) Great to read this. :-) Great to see that now there are 2 independent members who've put in much effort to go the time-coherent route only to reap its immense gains & that I was not out-of-line on insisting on this path....
Naysayers of time-coherent speakers take particular note!  

Al, 

Somehow I missed this excellent post when originally posted (damn end-of-year push at work I suppose). That's great to hear that you've finally gotten the room correction work done. 

Now that winter is forcing me indoors for longer periods, I'm about to get back on the horse and dial in the DEQX. May go back to the beginning and redo my speaker measurements based on the recommendations you made. Also got some Giant Gliders from Herbies to give me a little decoupling from the floor which should also make moving the speakers around a bit easier. That'll also enable me to dial in my speakers positioning in the room first, before beginning the room correction (as an aside, I wonder if the DEQX makes speaker positioning less crucial than it otherwise is? Within limits of course). 

I’ve posted a couple of screenshots of the room corrections/equalizations that I’ve settled on, at least for the time being, at this link.  One depicts the full spectrum, and one has an expanded view covering just up to 500 Hz. The room corrections I’ve settled on just extend up to 400 Hz, which just by coincidence happens to be the lower limit I had chosen for the speaker calibrations, for which I previously provided screenshots.

As you can see in the listings on the left side of the screenshots, I had made a total of 11 different measurements of each speaker, all in the vicinity of the listening position but at various distances and heights (all of them centered between the speakers). (“D” in the measurement position listings indicates distance from the plane of the speakers in feet, and “H” represents the measurement height in inches). Eventually I chose the measurements that were performed at a 12 foot distance and a 36 inch height to work with in deriving the corrections. The screenshots show those particular measurements, together with the equalization curves I’m now using.

The 12 foot distance corresponds just about exactly to my usual listening distance. The 36 inch height is about 2 inches above the mid-point between the two tweeters that are approximately centrally located on the vertical axis of the baffle area of my speakers. That height is also within a couple of inches or so of the height of my ears and my wife’s ears, when we are seated in the (quite low) Wassily chairs you can see in my system description photos.

You’ll note in the full spectrum screenshot that the upper treble rolls off significantly at the listening position. That occurs even though, as you can see in the speaker measurements I posted some time ago, the speakers themselves have a significant rise in frequency response in the top octave (the magnitude of that rise, remarkably, being similar to the magnitude of the dip at the listening position), and it occurs even though a mild dip in the 5 to 10 kHz area which the speakers exhibited in the close up measurements was pretty much compensated for in the speaker calibration process. But I’ve nevertheless chosen not to introduce any room correction equalizations in the treble region, after taking into account recommendations I had received from both Nyal Mellor of Acoustic Frontiers and Alan Langford of DEQX suggesting that it is generally best to leave the upper treble region alone, as well as my ongoing satisfaction with the tonal balance of my speakers in that region, as well as the impression I’ve formed over the years that a system which measures flat at the listening position throughout the treble region will sound too bright to most listeners.

Another point I found to be particularly striking, when I compared the measurements I had taken at the various distances, is that as might be expected the numerous peaks and valleys in frequency response occurring in the bass region as a result of room reflections will be located at frequencies that differ significantly depending on the specific measurement position. Meaning that basing a correction on a measurement performed at a distance that is a foot or two greater or less than the listening distance can result in an equalization boost being applied to a peak instead of a valley, or an equalization cut being applied to a valley instead of a peak. Particularly if one is aggressive in trying to correct for relatively narrow peaks or valleys.

Summing up my experience with the DEQX to this point, I would say that it has provided significant benefit to me as a result of its speaker calibration function, its room correction function, and as a preamp, and as a DAC. As I alluded to in an earlier post, speaker calibration seems to be especially beneficial in my system on recordings that are sonically mediocre, or worse. @Bombaywalla had said some time ago, either in this thread or in the “Sloped Baffle” thread, that that can be expected to be a consequence of improvements in time coherence, and my experience with the DEQX appears to confirm that.  

So I am glad I chose to make the substantial investments of money and time that have been involved. The time factor presumably would have been considerably less if I had chosen to utilize the DEQXpert service, but while I have no way of knowing whether the results of doing that would have ended up being better than, worse than, or similar to what I have accomplished, I feel that the learning experience resulting from doing it all myself has been sufficiently valuable that I don’t regret not having utilized that service.  

Next on my list, now that I have added the excellent and LOMC-capable Herron phono stage to my system (as I mentioned in an earlier post), is that in the next couple of weeks I’m planning to purchase an LOMC cartridge, to use in place of or as an alternate to my Soundsmith re-tipped vintage Grace F9E moving magnet. I’m planning on getting a Dynavector 17D3, in part because of the excellent reviews it has received over the years, but particularly because member @Rodman99999 had mentioned to me in a thread a while back that it is “magic” in the vintage Magnepan Unitrac tonearm he and I both use.

Thanks for reading. Best regards,

-- Al

^Oh, and something like the DEQX could possibly get me on the way towards analogless;-).

Al, as usual, you've nailed it. My thoughts, exactly!

Hi Unsound,

I presume that your Thiel speakers are designed to be time coherent, and if so presumably the DEQX speaker calibration function would not be beneficial to you. I would expect, however, that the equalization functions a DEQX can provide would allow you to eliminate the speaker's line-level analog equalizer from your system, and avoid the sonic tradeoffs that are inherent in that equalizer. (As you've probably seen in the past, Larry Archibald commented on those tradeoffs in this 1989 review).

And even though I haven't yet addressed room corrections in my system, I don't doubt that with sufficient tweaking (which can be done in real time, while listening), that function can provide significant benefit in most circumstances.

Also, as you no doubt realize a DEQX, depending on model, may be able to serve as a preamplifier, as well as providing remarkably transparent A/D and D/A converter functions.

Whether all of those potential benefits would to you be worth the not inconsiderable cost is, of course, your call. (And figure on $745 for the optional reference microphone kit on top of the cost of whichever DEQX model you might choose. Having some experience with both inexpensive and high quality professional mics for other applications I would not rely on the inexpensive mic that is included in the base price of the unit).

FWIW, in my own case I'm glad I made this investment, notwithstanding that as I've described earlier in the thread it has in my case turned out to be a bit of a science project at times. Albeit one that to me has been interesting and educational.

Best regards,
-- Al

^Thanks for the prompt response. Obviously I'm curious as to your impressions of this component.

Not yet, Unsound. I should be addressing room corrections next week. Meanwhile my listening has been focused on the upgrades I alluded to above, most notably the new phono stage, and I've also had to devote a lot of time to activities unrelated to audio.

BTW, you can check out updated photos and descriptions of the recent system changes in my system description thread.

Best regards,
-- Al

Hi Al, Any updates to report?

^Thanks for the prompt response. It appears as though your going to be a rather busy audiophile. Best of luck with all the new toys.

Hi Unsound,

No, I still haven't addressed the room correction part of the effort, and I probably won't during the next few weeks. The microphonic tube issue I mentioned a few weeks ago was readily resolved with the purchase of a couple of NOS tubes. But subsequently an unrelated hardware issue arose in my system, which among other things has prompted me to put into motion a phono stage upgrade I've had in mind for some time.

So I've just placed an order with Herron Audio for his highly regarded VTPH-2 phono stage. It will replace what I have been using for that purpose for many years, the phono section of a vintage Mark Levinson ML-1 preamplifier (accessed via the ML-1's tape outputs). I should receive the VTPH-2 in about two weeks or so. I've also ordered an Adona isolation platform for it to sit on, and I may have to also make some changes in the system's power distribution setup.

I'll then want to spend some time familiarizing myself with the sonics the VTPH-2 will provide, and perhaps also give it some additional burn-in (although the burn-in and test Keith Herron provides prior to shipment amounts to 48 hours, according to the manual).

After the dust settles on all of that, I'll resume the process of dialing in the DEQX.

Best regards,
-- Al

Al, any updates?

Thanks for that info Al. Very impressive considering how resolving the Star are known to be. Not to mention the removal of any room effects.

Not much progress with my HD-4 of late. Played with the window for speaker correction and moved it to 600Hz from much lower. An improvement, but I haven't had the chance to do the necessary room correction. Family matters came up before I could get to it. I'll report back when I have more done.

Andrew (Drewan77) ... when dealing with an artifact in the signal path, it's hard to get below zero when it comes to impact on the signal integrity. Not quibbling, but it is quite remarkable to me how little impact there is when sending a signal through the DEQX in pass-through mode.

What can I say ... but kudos to DEQX.

User observations about 'transparency' always seem to generate controversy on internet audio forums. People who have not listened to a DEQX corrected system often assert that absolute transparency is not possible with the amount of digital correction taking place.

However, those of us open minded enough to own and use DEQX seem to notice transparency and clarity as some of the most apparent features. Too often, audio equipment is pre-judged by specifications and not by listening.

Al, your experience and comments about the sound difference between the DEQX DAC as compared to your Bryston CDP are consistent with my experience. I thought my DEQX PreMATE was a "squeak" better than my ARC CD-8 CDP, but just a bit.

I too am surprised that the DEQX is as transparent as it appears to be. I agree with your comment that "the DEQX continues to ... be perfectly transparent. Which is amazing, of course, considering the A/D and D/A conversions it puts into the signal path."

Please keep the reports coming.

Regards,

Bruce

Thanks, Roscoe.

When listening to LPs via the Stax headphones, which are of course very revealing, the DEQX continues to seem to me to be perfectly transparent. Which is amazing, of course, considering the A/D and D/A conversions it puts into the signal path.

With CDs, for which I'm now using the DEQX as the DAC and my Bryston BCD-1 just as a transport, on some recordings it has provided a slight benefit compared to using the BCD-1's analog outputs routed to the Stax headphone amp via tape outputs of my previous preamp (a Classe CP-60), while on others there seems to be little if any difference. I suspect, though, that eventually I'll want to experiment with some different digital cables, and also different cable lengths, between the BCD-1 and the DEQX. I'm presently using an inexpensive Mogami AES/EBU cable, in a 6 foot length.

How has your HDP-4 been working out lately?

Best regards,
-- Al

Quite the odyssey Al. Enjoy those new tubes!

And how are you liking the DEQX as a DAC to your headphones, relative to other digital sources you have used with them?

An update for those who have been following my progress with the HDP-5: There will be a further delay until I perform the room corrections, due to an unrelated issue that has arisen in my system.

I've recently been noticing significant loss of definition on high frequency percussion, especially on high frequency piano notes. That has not been evident with my Stax headphones, however, just via the speakers. Since the headphone amp is driven by an output of the DEQX, in bypass mode of course, that pointed to my power amp as being responsible. And sure enough, when I lightly tapped on its tubes with an eraser, with the amp powered up, I found that one of its four vintage Sylvania 6SN7GTB's had become highly microphonic.

I have a number of other 6SN7GTB's on hand, but I don't want to use them for anything involving critical listening, such as the room corrections, as I had tried them in the amp a couple of years ago and didn't care for their sonics. So I'm ordering some additional tubes ("tubes" plural, as I'll want to replace the corresponding tube in the other channel with one that matches).

I'm pretty certain, btw, that this issue would not have affected the speaker measurements or speaker corrections I have performed. The problematical tube is only in the path of one channel, and the speaker measurements and correction profiles turned out to be very similar for the two speakers. Also, the tube still measures fine on my Hickok tester, and when I performed the speaker measurements the speaker was considerably further away from the amp than when in its normal position, and was pointed in the opposite direction of the amp.

Best regards,
-- Al

Al and I already traded PMs about his progress. For the benefit of others, I mentioned in PMs to Al that room correction will take him across the goal line.

I also surmise that Al may find that he like a different room correction adjustment for each type of music that he likes. For example, he may like bass augmentation when he plays pop and rock. In contrast, he may like a flatter FR adjustment when he plays classical.

That's the beauty of the DEQX. It enables the listener to fine tune his or her system to his or her specific tastes and preferences.

Thanks, Andrew (Drewan), for your always valuable inputs.

For the time being, at least, I’ve completed my assessment of the two correction filters I described in my previous post. The clear winner was filter 2 (the one that was created from measurements taken at a 42 inch distance), vs. filter 1 (created identically except from measurements taken at a 30 inch distance), and vs. bypass mode (which was outperformed by both filters), and vs. the several filters I had tried some time ago which were created from measurements that were compromised by close placement of the acoustical panels I used.

Most of the evaluation was performed with classical music, which is what I and my wife primarily listen to. Some rock, pop, and folk was also included. The degree of the differences between filter 2, filter 1, and bypass mode varied widely depending on the recording, ranging from barely perceptible to quite dramatic.

Perhaps most notable among the differences that I and my wife perceived were on some recordings having overly bright string sound, including some string quartets as well as symphonic recordings. Those became much more enjoyable with the filters engaged. Not because the sound was dulled down, but because there seemed to be increased detail and improved definition in the upper midrange and lower treble, as opposed to a more homogenized presentation of those notes, which in turn resulted in the brightness being less objectionable. I recall that some time ago, either in this thread or in the “sloped baffle” thread, Bombaywalla had commented that time coherence will provide benefits along those lines. Both this experience and many previous experiences I’ve had comparing sonics between my speakers and my Stax electrostatic headphones have me convinced that he was right.

Room corrections, which I haven’t yet addressed at all, are next in the queue!

Best regards,

--Al

Good progress Al. As you mention, over the coming days when you start to evaluate by listening, I recommend you play familiar music, preferably with a fair amount going on in the bass frequencies. It's at this point that you may choose to vary the correction limits slightly and load four marginally different configs to compare how they sound side-by-side.

As you become more familiar with the software, you may repeat this several times until you arrive at exactly what you want. Nothing beats playing the most 'challenging' music in your collection and making minor corrections until you have eradicated every possible irritation. In my case, I am quite inquisitive and experimented by slightly changing the correction limit frequencies, amplitudes, crossover points, slopes etc until I learned the impact of each variable. All the time keeping close to the original recommendations of Alan Langford and the DEQXperts I consulted. The only aspect that I have never modified is the original measurement window boundary.

This took around six months or so because I am also dealing with digital crossovers and time alignment to two separate subs which in themselves needed alignment together so the setup has more complexity and variables. More than two years later I have not found any music that needs me to change anything so the effort was well worth it.

I’ve spent some time studying the measurements I previously described having taken, and observing on the computer screen the results of applying various window durations to them. As a result I’ve chosen two specific correction filters to evaluate sonically in the coming days. I’ve uploaded jpg files depicting those filters, which can be viewed here. There are ten files, five for each filter, depicting the corrections in terms of frequency response, group delay, impulse response, step response, and phase response. In interpreting them, be sure to take into account the scales marked on the vertical axes. (To see the markings clearly, click on the image thumbnails to expand them). The measurements, window durations, and correction limits that were used in creating these filters are described below.

The ways in which I narrowed down the many possible correction filters to these two are as follows:

As you may recall, I had performed measurements of each speaker at distances of 30, 36, and 42 inches, with the grilles removed, and also at 36 inches with the grilles in place. The grilles appeared to make essentially no difference.

I found that both 36 inch measurements of the right speaker had a huge group delay spike at about 420 Hz, which was not helped significantly by smoothing, and which did not appear in the 30 or 42 inch measurements of that speaker, and which did not appear in any of the measurements of the other speaker. I have no idea why that occurred, as the two speakers and the mic were positioned identically when they were measured, within perhaps 1/8” or less. The only variable that seemed to be present, which in turn seems very unlikely to have anything to do with that spike, is that the design of the speakers is such that their rear surfaces, rather than being parallel to the front baffle, or being otherwise identical between the two speakers, are mirror-imaged at an angle such that the side of each speaker that is closest to the other speaker (in their normal positions) is 1.5 inches shorter than the other side. In any event, due to that spike I eliminated the 36 inch measurements from consideration.

I experimented on the computer with windowing of the 30 and 42 inch measurements at three different points, each of them just prior to what appeared to be significant reflections or increases in reflections, at about 13, 17, and 21 milliseconds. The 21 ms window resulted in significant frequency response wiggles in the 500 Hz to 1000 Hz area, so I eliminated that choice.

The 13 and 17 ms window durations provided results that looked fairly similar, but 13 ms (which terminated just prior to what I’m pretty certain was a ceiling reflection, based on its timing) looked slightly more promising. So that’s what I went with, for both measurement distances, that also being exactly what Andrew (Drewan77) had suggested the other day after looking at the measurements I had posted.

The (approximately) 13 ms window duration (actually 13.1 ms for the 30 inch measurement and 13.2 ms for the 42 inch measurement) corresponds to 7.4 ms after the initial sound arrival for the 30 inch measurement, and 6.7 ms after the initial sound arrival for the 42 inch measurement.

Regarding the correction limits I set, I used the default amplitude limits, which in turn were not called into play at all within the frequency response limits that I set. For both correction filters, Filter 1 corresponding to the 30 inch measurements and Filter 2 corresponding to the 42 inch measurements, I set frequency response limits such that corrections were only performed between about 400 Hz and 10.5 kHz. Those choices being made taking into account suggestions from both Nyal Mellor of Acoustic Frontiers and Alan Langford of DEQX to be conservative in dealing with the top octave, and to avoid correcting further into the bass region than seems reasonable in relation to the window duration. With the latter determination being made in the manner I described in my post dated 6-22-15. And, also, taking into account a presumption I made that both the high frequency and low frequency limits should be chosen such that abrupt discontinuities in frequency response are not introduced at the limit points.

Finally, in deriving the correction filters all parameters which I haven’t mentioned were used at their default values, including 100% smoothing.

Best regards,
--Al

I've performed the experiment I indicated I would be doing to investigate the glitch at 0.7 ms which was evident in the measurements I posted the other day, as well as in the measurements I described taking from other distances.

What I did today was to measure one speaker in its normal position, from a distance of 30 inches, with and without a boom on the mic stand. The resulting impulse response plots made clear that the glitch had indeed been caused by a reflection from the mic stand. However, in comparing today's results with and without the boom, there was little or no difference in the step response at or near that point in time. Also, despite the much greater room reflection content of today's measurements compared with the ones I made the other day with the speakers in the center of the room and with acoustic panels placed as shown in the photos I posted, aside from the deep bass region the frequency response plot derived from today's measurement with the boom matched remarkably well with the frequency plot taken from the same distance the other day (without the boom, with the speaker in the center of the room, and with the acoustic panels in place).

So, thankfully, I can proceed without having to re-do the measurements, which in my case involved a laborious 5 hour effort. :-)

Best regards,
-- Al

The group delay plot should be relatively smooth post windowing, and should not have any "spikes", if you have those it is a sign of reflections corrupting the measurement.

Yes Al your interpretations are correct. It's also worth pointing out that my graphs are the 'sum' of tweeter and midrange readings taken concurrently for each speaker so I could produce comparative graphs to your own (I am using six channels of amplification in this setup and these graphs relate to four of them).

When I look at the individual midrange or tweeter plots, the Group Delay variances are quite a lot lower than the summed result you see. I am also able to view each measurement graph per driver and that helped me during the prototyping phase of developing the speakers to arrive at both the measurement and the sound I was after.

In each measurement I took, it was gratifying to see how close the plots of each speaker became. I had specified matched pairs of drivers when I purchased them and the workshop cutting the various speaker panels programmed the CNC to very fine tolerances based on my drawings. The finished speakers measured to be virtually identical even before DEQX calibration (not to imply that they sounded good until after correction).

Andrew (Drewan) thanks for the clarification. That would certainly explain why your group delay plot appears as it does. Also, I note that the excursions in the plot appear to be greatest in the vicinity of what is probably the crossover point between the two drivers. Which makes sense, as in that vicinity the measurement mic would be receiving comparably strong outputs from two different drivers which are at two different physical locations.

Also, since DEQX was providing for you a lot of the optimizations that would be provided by the manufacturer in the case of speakers such as mine and Bruce's, the criticality of your speaker measurements being as accurate as possible (i.e., taken outdoors) figures to have been increased correspondingly.

Best regards,
-- Al

P.S. to my last paragraph above: Bruce, I think that in my step response plot (the expanded version, covering the first 10 ms) there may be a natural tendency to judge the time alignments of the drivers based on the zero crossings of the waveform, which would be misleading and cause the woofer outputs to be interpreted as being excessively delayed from those of the other drivers. However that would not be a meaningful comparison, because the slopes (risetimes and falltimes) of the woofer outputs will inherently be far slower than those of the other drivers, due to the limited bandwidths of both the woofers and their associated low pass crossover network.

So a more meaningful way to assess that plot would be to compare the points at which the tweeter outputs, the mid-range outputs, and the woofer outputs BEGIN to appear. Which in turn, for the woofers, would be where the slope of the initial output from the mid-range appears to begin to slow.

In this case the location of that point is made a bit ambiguous by the glitch at 0.7 ms, but it is clearly somewhere around the time of the first negative peak in the output of the mid-range, somewhat less than 1 ms after the start of the initial sound arrival (that being from the tweeter, of course). And as I indicated earlier, that delay between arrival times from the woofers and the other drivers will be considerably greater at the closeup mic position that was used for the speaker measurements than it would be at the listening position, due to the much smaller angle between the drivers as perceived from the listening position.

Best regards,
-- Al

A word of explanation when viewing the plots I have posted and comparing with those of either Bruce or Al who use manufacturer optimised speakers:

These are Open Baffle speakers for only midrange & treble frequencies. The outdoor measurements are of the raw speakers themselves, containing only one (ribbon tweeter) capacitor per speaker, no passive crossover components and with no phase, time or group delay correction whatsoever. I have let DEQX handle all of that - which it does superbly

Thanks for the responses, gentlemen. And thanks, Andrew (Drewan) for providing your measurements for comparison.

Kotjac, I suspect that you're right. Tomorrow I'll probably make a quick experimental measurement with the speakers in their normal position, with the mic on a boom, to see if that glitch occurring at 0.7 ms after the direct sound arrival goes away, or at least improves.

Andrew, your interpretations are correct.

Bruce, I'm not entirely sure either of how to explain the wild looking group delay plots. However there are several things that leave me feeling encouraged about them:

1)All three of our group delay plots (mine, the one Andrew posted, and yours that were taken by Larry/DEQXpert last year) look similarly wild. (And mine appear to be the best of them, actually, when viewed on the same vertical scale :-))

2)Despite the wild appearance, as we know Andrew achieved outstanding results **with no smoothing.**

3)Applying 100% smoothing to my GD plot (and Nyal had recommended to me that I use 100% smoothing) results in essentially a perfect straight line above about 2.7 kHz, with the wiggles getting progressively larger below that frequency, and exceeding just a few ms only below around 500 Hz. And I suspect I won't be correcting much below 500 Hz anyway (I'll be addressing that region in the room correction process), and I also suspect that a major contributor to the group delay anomalies below several hundred Hz is the path length difference between the measurement mic and my woofers, relative to the path lengths from mic to tweeters and mids. Which by virtue of simple geometry will be much less of an issue at normal listening distances than at the 3 foot mic distance.

Bruce, regarding your question about the step response, the handoff between mid-ranges and woofers looks to me to be reasonable, and not particularly dissimilar to many step response plots JA has provided in Stereophile reviews. Aside, that is, from the aforementioned glitch at about 0.7 ms which as mentioned may be due to a mic stand reflection. And, again, the delay between the initial arrival of the woofer outputs and the outputs from the other drivers is presumably contributed to by the differences in path lengths from the close up mic position.

Best regards,
-- Al

Bruce - I believe that Al's measurements are of full range speakers and the amp & cabling running to the speaker in the photos (+ the descriptions in the plots themselves) seem to confirm this. I don't see separate step response graphs for tweeter/mid and woofer but two graphs of the same measurement where Al has changed the scale (0-10ms on the 1st, 0-40ms on the 2nd).

Group delay is the time that it takes for the modulation signal to pass through the system/air and arrive at the microphone, measured against frequency. In simple terms, it's an indicator of how much the signal will be distorted - the DEQX introductory video on their website demonstrates this 'smearing' effect.

Al, more questions than answers. Looking at the step response graphs. The tweeter and mid look pretty closely aligned .. off maybe a couple of mSecs. The woofer step looks unusual. Can you or Andrew explain what I see there??

Also, the group delay graph makes little sense to me. Again ... can you or Andrew interpret the graph.

I suspect that the DEQX will clean up your FR graph. Most of the bumps and saddles are probably room related.

As an aside ... just finished another session with Larry. He tamed the time alignment specs as measured at my listening position. He also spent a lot of time smoothing out the saddles and bumps. Overall presentation is more natural sound presentation.

P.S. Larry told me that he does factory authorized mods to the DEQX, many which source from the HDP-5. I may take him up on the upgrade this fall. Many of the changes relate to improved power supply, better op amps ... all of which make for faster transient response and dynamic headroom.

I have linked here to the same measurements for my speakers (midrange-treble only) for comparison.

These were taken outdoors and you can see a similar reflection from the mic (or maybe the grass surface), starting at 26ms.

Almarg, from your measurements I would initially window just before the reflection at 14ms and calibrate from there