P.S. to my post just above: When I said ... What strikes me as perhaps the most significant concern, that I see initially, is the spike in the impulse response occurring just 0.7 ms after the direct sound arrival. I'm not sure what that is, although based on its arrival time I suppose it figures to be a baffle reflection.... I'm thinking that perhaps it also could have been a reflection from the mic stand. Can any of the experienced DEQX users offer an opinion as to how serious an issue that spike, and the subsequent brief ringing, might be? Best regards, -- Al |
I finally found the time today to re-do my speaker measurements, as I had previously indicated I was planning to do. A link to photos of the measurement setup and screenshots of some of the measurements is provided further down in this post. Once again I moved the speaker being measured to the center of the room. However, instead of positioning the large acoustic panels I had purchased (Clearsonic S5-2D's) close to either the microphone or the speaker, as I had previously done (which created early reflection problems from the panels themselves), I positioned one of them in front of the fireplace on the left, and one in front of the large antique radio/phono console on the right. I also positioned a third panel, which I purchased subsequent to performing those initial measurements, on the floor, under the mic stand and extending to the front of the speaker. It pretty much eliminated a significant floor reflection that was evident in the earlier measurements, despite pillows having been placed on the floor at that time. The panels on the sides were located 50 inches from the nearest side of the speaker. The front baffle of the speaker was 10.5 feet from the wall and window behind it. The nearest objects in front of the speaker were for the most part around 7 or 8 feet away, and not directly in front of the speaker or directly behind the mic, although some objects off to the side were as close as 5 or 6 feet. I measured each speaker from distances of 30, 36, and 42 inches. The 30 and 42 inch measurements were performed with the speaker grilles removed. The 36 inch measurements were performed both with and without grilles. As it turned out, though, the 36 inch measurements looked essentially identical with and without grilles. I've uploaded to flickr.com three photos of the measurement setup, as well as a set of screenshots of the 36 inch measurements sans grilles. Each of the screenshots includes measurements of both speakers, superimposed, and with no smoothing. You can see all of this here. Looking at the impulse response screenshots, the small wiggles occurring at around 14 ms (about 8 ms following the direct sound arrival) I'm pretty certain are a reflection from the ceiling. What strikes me as perhaps the most significant concern, that I see initially, is the spike in the impulse response occurring just 0.7 ms after the direct sound arrival. I'm not sure what that is, although based on its arrival time I suppose it figures to be a baffle reflection. In the coming days, or more likely weeks, I'll be creating and sonically assessing a number of correction profiles. When I settle on one that seems best, I'll then address room corrections, which I haven't addressed at all so far. Apologies for the slow progress to those who may be interested in the conclusions I'll ultimately reach. Best regards, -- Al |
It's not possible to answer that question Ptss, I'm afraid because there are too many variables involved, not least the impact the room has on the sound and your ability to optimise that. However speaking personally, I am confident from the experience I have that DEQX can significantly improve any speakers/room you would be confronted with because I have already done this several times using a DEQX processor. The JBL 250Tis are a 3-way design and if you are brave enough to do it, bypassing the internal circuitry and using 6 channels of amplification (ie HDP-4 OR HDP-5) and digital crossovers are what I would do. Even a Premate or Express will help you get the best from these without modification but whatever you consider, the end result will only be as good as the time and effort you are prepared to invest. |
Yeah Al, I see what you mean. Not too concerned about sensitivity. My amp is pretty muscular. Also, the low end uses a self powered woofer which should take heat off the amp. Some of the other measurements raise yellow flags for me as well. That said, the DEQX might be able to smooth out some the Quatros' FR aberrations. I wonder how the Quatro CT specs out?? I surmise that "real audiophiles" might say, "ignore the specs; use your ear." Not sure I buy 100% to that position. In any case, let us know how you make out. Regards, BIF |
Hi Bruce, The Quatro CT does seem intriguing to me, with respect to your circumstances. Presumably there would be no need with it to go to the trouble of doing speaker calibrations with the DEQX, and of course doing room corrections is a much simpler process that does not involve moving the speakers. Also, I would think you could do away with the sub you are using. So there would be some nice simplifications, albeit for significant $. On the other hand, though, JA's measurements of the earlier version of the Quatro raise some caution flags in my mind, starting with the sensitivity measurement that is significantly lower than specified. Best regards, -- Al |
Al, Logically, I should probably try going "sans" Ref 5 SE (linestage) too and solo it with the PreMATE as my preamp (like you). But I can't bear to part with my beloved ARC gear. I think ... but am admittedly not sure ... that inserting the Ref 5 SE into the signal path does little harm. So it stays. At some point, my speaker curiosity may get the better of me, but for now I am standing down on that upgrade. I have no way of meaningfully and reliably making a decision unless a dealer is willing to permit a home audition. And even then, I'd have to reconfigure my PreMATE. Too much of a PITA. So, I'm holding where I am for now. Maybe ... I'll take a run up to John Rutan's shop in Verona, NJ and do some serious listening to a pair of Vandy Quatro CTs. Anything larger will not fit in my basement. I'm thinking about Vandies because they are purportedly time coherent. Also, Johnny R is an ARC dealer and can hook an ARC amp to the Quattros to effect a better sound comparison. And, I've read very good reports on the Vandy CT (carbon fiber) tweeter. Anyway ... just my late Saturday night ramblings. Looking forward to reading an updated report when you get a chance to turn back to your HDP-5. Regards. BIF |
Bruce, no, as it turned out I didn't get a chance to re-do the speaker measurements this week. And I've got a number of other things scheduled for the next several days. So it might be another week or so before I'm able to do the measurements. Meanwhile, though, the HDP-5 continues to please just as a preamp and DAC upgrade, used in either bypass mode or with the one fairly conservative speaker correction profile I indicated early on was superior to the others. Best regards, -- Al |
Interim update: The plan I previously mentioned to re-measure my speakers has been delayed a bit, in part because last week a sudden and particularly violent thunderstorm resulted in damage to the power supply of my HDP-5. But to make a short story shorter, DEQX responded in an incredibly prompt and supportive manner, and I was back in business within a few days. I now expect that I'll have time to perform the measurements sometime next week. Kudos to DEQX! Best regards, -- Al |
Good question, Roscoe, as I should have clarified that statement further. If I position the window cursor close to the direct sound arrival, say within 3 ms or so to cite an extreme example, and then look at the frequency response on the next screen, there will be a downtrend in the frequency response below something like 500 Hz, roughly speaking. Presumably that occurs because the short duration of the window doesn't make it possible to sufficiently capture low frequency information. (Consider that 3 ms is less than one cycle of all frequencies that are below 1/0.003 = 333 Hz). If the window cursor is then moved way out, to say 20 ms or so, the frequency response shown on the next screen will show a substantial rise in bass response at many low frequencies, with perhaps a narrow dip or two at certain frequencies. Intuitively it seemed to me to make sense to set the lower frequency limit of the calibration around the inflection point below which that decrease or increase in bass response starts to occur for the chosen window duration. This is all consistent with a comment Nyal had made to me that a common mistake is to correct to too low a frequency relative to the duration of the truncation window, the result being an excessive bass boost. And consistent with various statements in the calibration manual, the subsequent room corrections should be a more suitable means of addressing the bass region, or at least most of it. Best regards, -- Al |
Many thanks for that great explanation and for passing along the recs you have gotten from experts on this matter. One thing I'd like some clarification on: You say: "In doing that I tried to set the lower frequency limit of the calibration above the frequency at which significant differences started to become apparent in the frequency response plot as I varied the duration of the truncation window." What did these "significant differences" look like. What should we be keeping an eye out for? |
Bruce, yes, thanks for sharing these things with me. I'll look forward to the measurements and/or pics, in part because I'm curious as to what kind of room configuration they would consider to be too small for your speakers. Roscoe, so far I've tried 7 different speaker calibrations, based on my initial set of measurements (which I will be re-doing from scratch as described above). The lower frequency limits I've used in those calibrations have ranged from 300 to 600 Hz, depending on where the truncation window was terminated. Nyal had advised that I start out very conservatively with respect to that parameter, even as high as 900 Hz if the end of the truncation window would have to be as close as 5 ms after the direct sound arrival (with other rule of thumb combinations being suggested such as 600 Hz/10 ms, and 350-400 Hz/15 ms, if the truncation window could be extended to those points without encompassing major reflections). Those are obviously more conservative limits than the ones suggested in the manual, but he also suggested doing additional trials calibrating to progressively lower frequency limits, and trying to identify the point beyond which the sound starts to worsen. In setting the limits I kept those rule of thumb guidelines in mind, while also, as I created each calibration, going back and forth between the screen on which the truncation window is set, and the following screen which depicts the resulting frequency response. In doing that I tried to set the lower frequency limit of the calibration above the frequency at which significant differences started to become apparent in the frequency response plot as I varied the duration of the truncation window. Also, at the other end of the spectrum Nyal had advised that I should avoid monkeying very much with the speaker's natural rolloff at high frequencies. And in a separate conversation I recently had with Alan Langford of DEQX, (regarding an unrelated matter involving a very minor quirk I had noticed and reported in the operation of the touchscreen that is provided on the HDP-5, about which they were extremely responsive and will be resolving shortly with a couple of changes the user can easily incorporate, mainly a firmware update), he suggested limiting the high frequency limit of speaker calibration to 10 kHz. Given also that my particular speakers have a rise of a few db between 10 and 20 kHz, according to the DEQX measurements, followed by a rolloff above 20 kHz, I certainly plan to follow their advice on the subsequent calibrations. Although the ones I've done so far have had various limits ranging from 10 to 23 kHz. As you'll realize from my previous recent posts, I can't really say much at this point from my listening experiences as to which of those limits (both at the low end and at the high end) work best with my speakers, because the anomalies caused by non-optimal placement of the acoustic panels when I did the initial measurements affected the middle frequencies and mid-treble too greatly for those other limits to matter very much. BTW, during the course of the conversation with Mr. Langford he indicated that as a general rule of thumb outdoor calibration often tends to be less necessary for box-type speakers than for other kinds. As for my status at this point, I've just received the third acoustic panel I ordered the other day, but most of this week I'll probably be too tied up with various family and other obligations to perform the next set of measurements. Hopefully I'll get them done within about a week. Best regards, -- Al |
Addendum to my last post ... it occurred to me that there was another factor that may have impressed my stepson other than the DEQX. Namely, since his last visit, I sprung for the SE upgrade to my ARC Ref 150 amp. As many may know, it involved switching out the KT-120 tubes for KT-150 tubes, plus ARC made some proprietary circuit changes. Now I'm not sure. But what the heck ... my rig sounds better than before and that's what counts. |
Thanks for the update Al. I've been offline since Tuesday/Wednesday and haven't been tracking your progress. I looking forward to reading your future reports. As you know, I already shared with you via a PM Larry Owen's general philosophical comments about speaker and room correction. I sent a copy to Nyal as well. Al ... I intend to send you a PM with some room measurements and maybe some pics too if I can figure out to work my cell phone camera. I'm not sure I buy into the point made by Larry and PJ that my speakers and sub are too big for my room. I think my room is so crappy that it could mess up speakers of any size or quality. BUT, the DEQX tamed my rotten room situation so that is more tolerable. In fact my stepson came in from out of town this weekend to spend father's day with me and played one of his favorite LPs. He was pretty WOW'ed (sp?). He hadn't heard my rig since the first set up attempt. Cheers, BIF |
Thanks very much, Pete, for the nice words and the interesting comments. An update: I've created and assessed three more speaker calibration profiles, this time based on the measurements I took with no acoustic panels in place. (As I had previously described, the visibly cleanest and most reflection-free measurements had been the ones taken with panels surrounding the measurement microphone, but I found that very early arriving reflections from the panels themselves caused significant differences in the calibration profiles for the two speakers, which worsened in proportion to the duration of the truncation window. The same held true for the measurements taken with panels surrounding the speakers, to a slightly lesser degree but coupled with increased pickup of room reflections. Recall, btw, that I did not have the panels in precisely the same positions when I measured the two speakers, which fortuitously led to me discover the significance of the early arriving panel reflections). Also, I should mention that when I performed the measurements even though I had pillows and a folded back (double thickness) Persian rug on the floor between the speaker and the mic, the waveforms captured by DEQX for all of the measurements clearly show a significant floor reflection (as can be determined based on its arrival time, beginning a little under 3 ms after the direct sound arrival). There is also evidence of a ceiling reflection arriving a little under 8 ms after the direct sound arrival, although it appears likely to consist mainly of low frequencies that I'm not addressing in the speaker calibrations. Although all three of the new profiles sounded reasonably good, ultimately I was not satisfied with any of them. Most notably on classical solo piano, where the presentation had a slightly mechanical quality, and a slight loss of definition in the mid-treble, that were not present in bypass mode. Given all of that, what I've decided to do is to order a third double-section acoustic panel and then re-do the speaker measurements. This time I will place one panel up against the fireplace you can see along the left wall in my system description photos; one panel up against the antique radio/phono console on the right; and one panel on the floor between the mic and the speaker being measured (positioned once again in the center of the room). In my circumstances it is reflections from the sides and the floor, and possibly the ceiling, that appear to be the main concerns. I believe that moving the speaker being measured to the center of the room gets them far enough away from the front and rear walls to allow those reflections to be windowed out without significant compromise to the calibrations. Apologies for the slow progress to those who may be awaiting the conclusions of this adventure. I haven't even begun to address room correction yet. But from my perspective the slow progress has not been bothersome, as what I have in bypass mode and with one or two of the correction profiles is already better than what I had previously (which in turn I was pretty satisfied with). And it's been an interesting learning experience. Best regards, -- Al |
It's important to realize that you do not have to use the speaker correction functionality (the part of the DSP that is best with measurements taken outside). The DEQX has other functions - digital pre-amp, digital crossover and room correction that make it great even without the speaker correction. The better the speakers the less improvement from speaker correction (as the drivers will be closer to flat and better pair matched). With speakers like YG or ATC the improvements from speaker correction are small (but still noticeable). The sound quality of the DEQX is good enough without speaker correction that I think it stands up as an exceptional product even without turning on the speaker correction. |
Bombaywalla - Without re-reading my earliest posts, I believe I may have mentioned my reaction from the very first time I played the DEQX corrected system. I swore out loud - it was that good compared to what I was familiar with. That was from the initial (indoor) measurement Over extended listening I noticed the slight nasal quality and after re-running the measurements outside I was able to eradicate this. I expect a first time listener may not notice that, or more likely, others may not be as critical as I am |
Drewan77, OK. thanks for the clarification. So, we are talking degrees of perfection here & not something that blatantly wrong when doing an indoor correction. And, judging by your last post, it seems that if one of us listened in your room with your indoor correction, we, not knowing your system, might not even be able to tell the slight nasal quality to the mid-bass. You are aware of this since you have done an A/B comparison many times. "Slight" is a fuzzy term but I'll take your word that it's hardly perceptible & maybe only if you point it out to the listener. |
I'm sorry to say that I don't quite agree with that last sentiment Bombaywalla. Unless someone has heard this themselves, they may not understand how good the resulting sound can be from a good indoor measurement and the majority of people will be extremely satisfied with that Its a bit like saying that someone buys a top-range sports car but only drives it to 60% of its speed-handling capability. Another owns the same car but takes it to track days at a local circuit. Who is to say which owner gets the most pleasure? DEQXs' main selling point is the ability to tame the room/speaker interface and it does that better than anything else I have experienced - we are talking about degrees of perfection here and each user will have different expectations I mentioned a slight nasal quality to mid bass and by 'slight' I really do mean that. Many people probably wouldn't even notice or worry about it. I have listened to two other European DEQX setups, both sounded amazing and the owners were very pleased. Neither sounded quite as smooth or natural as mine does....to MY ears and MY tastes, which is the point I am trying to make |
For sure there are still going to be a lot of very satisfied users provided measurements are taken to the optimum in the environment availablethe fact that anechoic or outdoor measurements is the only way to get the best out of the DEQX has to be considered a (big) down-side to this piece of software. The people at DEQX are obviously smart (since they've come up with this clever DEQX box). At the same time don't they realize that audio gear is almost always very heavy esp. speakers? They've got to realize that 99% of people will simply not have the opportunity to take their gear outside or to an anechoic chamber for many reasons. This, then, would create a sub-optimum DEQX setup & would eventually count against DEQX in the long run. It's also going to be a (big) deterrent for many others reading this thread & realizing that there's no way to get the best from or the most natural sound from DEQX unless they carry their gear outdoors/anechoic chamber... In my books this is a major ding against DEQX. |
I can only report my own experience and with music playing, it sounds totally believable from the outdoor measurements. Using the same settings from calibration to configuration with the best indoor readings I could achieve, music and especially mid-bass had a slight hollow-nasal quality to it and was not as natural I am using Open baffle speakers which I appreciate are very different to those being used by Al, Bruce etc but this quality was also present in the full range Shaninians when comparisons were originally made I feel at a loss to convey with words just how close to perfect a well set up DEQX enabled system can get. For sure there are still going to be a lot of very satisfied users provided measurements are taken to the optimum in the environment available |
Psag and Mapman, thanks very much. Obviously I don't have to finalize any decisions just now, and we'll see how things develop in the coming weeks. But while I certainly value the experience-based inputs from Drewan and Psag, and while it's certainly clear that realizing the full potential of DEQX requires an essentially anechoic measurement, what doesn't seem clear (and probably can't be, given how many application-specific variables are involved), is the degree of compromise that will result in any given situation from doing the measurement indoors. Obviously Drewan and Psag are strong advocates of outdoor measurement. On the other hand, though, in this post by Forrestc, who also seems very experienced, indoor measurement is described as "by no means a deal breaker." And in Kal's (Kr4's) review in Stereophile the speakers he calibrated on his own, and I presume also the other pair he used, which were calibrated remotely by DEQX, were done indoors. The pair he did himself, with good results, were done with the impulse response truncated at only 5.5 ms after the direct sound arrival, and with the correction performed down to 200 and 150 Hz in the two profiles he created, with the latter even being slightly preferred! Perhaps one relevant variable influencing the degree of compromise resulting from indoor measurement, btw, is how much correction is needed by the particular speakers that are involved. In that regard I've noted that the impulse and step responses I've measured on my speakers, during the first few tenths of a millisecond or so and with no panels near them or the mic, seem to me to look pretty good. Relative, that is, to the step response plots I've seen JA present in Stereophile in conjunction with reviews of other floor-standing speakers which do not use first order crossovers. So we shall see. Thanks again for your inputs. Best regards, -- Al |
Al, outdoor measurement is mandatory, IMO. With the help of two people, we moved TAD Reference1 (almost 400 lb apiece) and four monoblock amps from my listening room to my driveway. We used a dolly, easily purchased on the internet. If you are willing to invest the time and cash on DEQX, you really owe this to yourself. |
Andrew (Drewan), thanks very much for providing the info in your system description thread. As I indicated there, it provides a good quantitative perspective for DEQX newbies such as myself on what is possible in the speaker calibration process. Mapman, thanks also. Regarding DEQX's recommendations for how to approach speaker calibration, on the one hand the manual states: The microphone should be mounted about 2 ft to 3 ft (or 60 cm to 1 metre) from the speaker and lined up with the tweeter axis. Best results will be obtained if you use a microphone stand with a boom to support the microphone. If larger speakers are used it may be necessary to mount the microphone further from the speaker, in order to reduce the angle between the drivers and the microphone (and anyBut on the other hand they state: The longer the delay for the first room reflection to arrive relative to the time it takes for direct sound to reach the measurement microphone, the more bass information can be gleaned. A minimum target would be 3 milliseconds, which will limit measurement usefulness to frequencies above about 400Hz. Doubling this to 6 milliseconds for example, achieves an additional octave of bass resolution: down to about 200Hz, which is the lower correction limit used for this case. In this example, if you attempt to correct below 200Hz phase distortion will be introduced to the filter, which will make the resulting sound dull and flat - worse than the uncorrected speaker.The 3 and 6 ms 400Hz/200 Hz guidelines seem very aggressive (optimistic) compared to inputs that were provided to me by Nyal, and that have been cited by others earlier in this thread, and that were used by the DEQXpert people when they set up Bruce's (Bifwynne's) system. (They terminated the "truncation window" about 17 ms after the direct sound arrival in his case, as contrasted with the 3 and 6 ms figures cited in the manual. Also, the corresponding figure in Drewan's case was about 18 ms). So it seems that given the great number of variables that are obviously involved DEQX is understandably not able to provide a specific quantitative feel for the degree of compromise that will be introduced at various points along the continuum between ideal measurements taken under essentially anechoic conditions, and points that are significantly less than ideal. 06-07-15: Drewan77Pretty much. Just moving my speakers off and then back onto the bases and footers I have them on, which elevate them less than 5 inches, involved non-trivial effort and careful logistical planning, as they weigh 108 pounds each. To get them to a location outdoors that is both level and not close to reflective surfaces they would have to traverse several steps and approximately 50 feet, and then I would have to provide some non-reflective means of tilting them back, to minimize ground reflections. Also, less significant additional complications would be that I would have to run about 50 feet of speaker cable (my amplifier also weighs more than 100 pounds), and a 40 foot or so XLR extension for the mic. Well before deciding to purchase the DEQX I had realized from the comments earlier in the thread and from reading the DEQX literature that as a practical matter I would be unlikely to realize its full potential. But as long as it ends up providing me with a substantial improvement over what I had I won't be disappointed. As Mapman aptly said just above, "it might be a dilemma for which one practically just has to accept some kind of compromise." Best regards, -- Al |
Al, Interesting findings so far. Sounds like the good news is the unit is providing you the information needed to get it set up optimally as it should, and that you are well versed to interpret and use it. I wonder what the general recommended apporach from teh vendor is? Is anechoic measurements the norm for geting things calibrated initially? Sounds like it. In which case, there may be no equally effective substitute for some kind of plan for accomplishing measurements outdoors as suggested. Or in some other kind of anechoic environment. How about a recording studio? Maybe there is something like taht nearby at a school or other professional facility that might be accessible. Of course, no way to avoid the pain of having to move heavy and delicate audio gear that way. So it might be a dilemma for which one practically just has to accept some kind of compromise. I'm sure its going to work out well one way or another in due time. |
I have posted a couple of screenshots under 'System' at the foot of my posts for anyone with a DEQX processor to compare the plots The measurement shows how 'clean' the frequency plot may look relative to an indoor reading that others may have taken and the impulse response illustrates that there is only a tiny reflection from the microphone itself (The measurement is a raw image from the mid-high range speaker before any correction & at 0% smoothing. Indoor calibrations tend to use up to 100% smoothing and a closer windowing, both of which reduce accuracy and have an impact on the sound in my experience) |
Thanks Al and Andrew. I guess I'll hold up on buying the panels for a bit. I'll wait for future reports. Andrew, it may be that I will bite the bullet and schlepp my whole rig outside one day. Gotta tella ya though ... I am concerned about damaging gear by doing this. As I've already mentioned, my rig is tucked away in my basement/sound-room. At a minimum, I'd have to haul up the steps: two 100 pound speakers; an 80 pound amp; and the DEQX. And what about my 110 pound sub?? I assume I can leave the other gear downstairs. |
A very interesting summary Al and I sympathise with the challenges you face At the risk of repeating myself (apologies), are you absolutely sure that there is no chance of taking an outdoor speaker measurement? I originally made several attempts to achieve a good indoor measurement but none came close to those taken outdoors. Once I saw the cleanness of the resulting plots, any further speakers or subs were always measured this way - including manhandling a huge Miller & Kreisel sub into the garden and then up onto the measuring platform which was a great deal of effort It does make a significant difference and I believe that is why music created from the resulting calibrations sounds so remarkable. I am rather a 'perfectionist' so I couldnt have rested knowing that I wasn't getting the maximum performance from DEQX Yes, this can involve a lot of time and commitment (in my case around three hours from start to finish, moving the gear etc) but provided you use a high number of averaged measurements (I recommend 1.4s/96K x at least 18 sweeps) and the day is completely dry without much wind, the measurements only need to be taken once and are extremely accurate, virtually anechoic if done well. Any random birdsong or other faint wind noises appear to be completely disregarded by the averaging feature of the software Somewhere I may have photographs of the setup but they are not on this computer so I will have to look for them. If anyone is interested I would try to find them plus some of the resulting measurement plots and post them as images on 'my page' |
Caution: Very long post :-) Well, it seems that my forward progress has taken a step backward, although the step backward has resulted in discoveries that will hopefully be beneficial in the end, to me and to others who may read this. After evaluating four different speaker correction profiles on numerous recordings, all based on measurements taken with the acoustic panels I purchased placed around the measurement microphone, Ive concluded that even though those measurements, when viewed on impulse response plots over a reasonable time scale (e.g., 30 ms), looked considerably better than the measurements taken with no panels and with the panels placed around the speaker being measured, the panels were doing more harm than good. And I say that even though there were no points on the impulse response plots at which reflection amplitudes appeared to look greater with the panels placed around the mic than in the other plots, and at the great majority of points reflection amplitudes looked significantly smaller with the panels placed around the mic compared to the other two cases. As will become clear later in this post, what I probably should have done was to place the panels up against the nearest reflective surfaces (the fireplace on the left and the large antique radio/phono on the right, as seen in my system description photos), rather than surrounding the mic with them on three sides, at a fairly close distance. Ill first say that one of those four profiles (one of the first two I tried, with the impulse response truncation window terminated 7.2 ms after the initial sound arrival, and corrections only performed between 600 Hz and 10 kHz), on most but not all recordings sounded distinctly better than bypass mode and than the other three profiles I tried (all of which had the window terminated about 18 ms after the initial sound arrival, with corrections over a somewhat broader range of frequencies). However I noted especially on the last two profiles I tried that the image was shifted considerably to the right, even though bypass mode (as always) was perfectly centered. And that right channel boost (the difference being in the area of 2 to 6 db depending on frequency, and occurring primarily between about 200 Hz and 1 kHz) could be clearly seen when the correction profiles were viewed in the DEQX software, with the profiles for the two speakers placed on the same graph and the scale of the vertical axis suitably adjusted. I also found while doing further experiments with the software that the volume difference between the two channels increased dramatically in proportion to the duration of the truncation window, which really puzzled me at first, and also increased in proportion to the distance of the measurement microphone from the speaker (meaning also that it increased as the distance between the mic and the panels behind it became smaller). And the volume difference was worse for correction profiles created from the measurements made with the panels surrounding the mic than for correction profiles created from the measurements made with the panels surrounding the speaker. And, as mentioned above, I found that the issue occurred primarily (although not exclusively) in the area of 200 Hz to 1 kHz, especially around the middle of that area, with the volume difference varying considerably at different frequencies. After a lot of study of frequency response plots, impulse response plots, and step response plots, I concluded with a fair amount of certainty that the cause of the different corrections for the two speakers was that I didnt have the panels placed in precisely the same locations when I measured the two speakers. The reason for the slightly different placements being that since I was making measurements with the panels surrounding the speaker as well as with the panels surrounding the mic, and it happened that I did the measurements with the panels surrounding the speaker last, I moved the panels aside when the first speaker being measured was moved away from the center of the room, and the second speaker was moved into that position. Upon very close examination, the consequences of that can be seen in terms of slight differences between the timing of the wiggles of the impulse response measurements for the two speakers in the area of about 3 ms after the initial sound arrival, and can also be especially seen in the form of a roughly 1 db difference occurring at that same instant between the step response plots of the two speakers, in the cases of the measurements taken at 3 and 3.5 foot distances which I used for the correction profiles. So, I wondered, if the issue was being caused by reflections from the panels occurring just 3 ms or so after the direct sound arrival, why would the consequences of those reflections in the correction profiles get worse as the truncation window was extended much further out in time, for instance from 7 ms to 18 ms and beyond? Im not totally certain, but I believe the answer to that is inherent in the mathematics of the Fast Fourier Transform, some variation of which I assume is what the software uses to convert between the time domain (impulse and step responses) and the frequency domain (frequency responses). Now if I were to redo the measurements while making a point of placing the panels at precisely the same locations for both speakers, I could evidently eliminate the inter-channel differences in the corrections. However, the fact that slight differences in panel placement caused dramatic differences in calibration profiles between the speakers would seem to say that even if I were to achieve identical profiles for both speakers, that identical profile would reflect (pun intended) significant adverse effects of the panels. So for that reason, in addition to the effort that would be involved in re-measuring the speakers, Im not planning to do that. Instead Im now planning to simply try some correction profiles that Ill create based on the measurements Ive already taken with no panels in place. If those dont work out well, then Ill consider re-measuring the speakers, with the panels much further from the mic and probably placed against the reflective surfaces I mentioned earlier. Also, if I were to try to correct the inter-channel differences using the equalization capabilities of the DEQX, given the extensive variations of those differences as a function of frequency I suspect that the effort would be extremely time-consuming, and would probably result in a less than ideal set of complementary colorations. So although my efforts have had a bit of a setback here, its probably a good thing that I didnt make a point of placing the panels in exactly the same positions for the measurements of the two speakers. If I had done so I probably wouldnt have discovered any of this, and I would very conceivably have ended up deriving less benefit from the DEQX than I hopefully will, eventually. So, undaunted, I shall persevere and carry on. Due to various unrelated upcoming activities, my next significant update will probably be in about a week. Meanwhile, just using the DEQX in either bypass mode or with the one correction profile I mentioned as being superior to the others, provides (despite a bit of channel imbalance in the case of the latter) a modest but notable improvement on what I previously had. Best regards, -- Al |
Roscoe, no, I didn't take any pix while making the measurements. Upon re-reading the description I provided of the setup, I would just add that I of course moved the chairs that are visible in my system description photos out of the room, and I mounted the measurement mic on a small professional mic stand which allowed it to be placed at the 30 inch height I mentioned. Best regards, -- Al |
Drewan77- From your posts above it looks like might have some advice for me as I consider taking this route to upgrading the SQ of my system which can read about here. I am considering actively crossing over the output from the pre-amp so as not to run the field coils on the OB full range. Since my gear is in the LR, I do not have any realistic options for room treatment. I would like to insert the DEQX in the processor loop of my Doshi pre-amp because first, I love its sound, second, I use two sources, and third, I may want to use its DAC someday when my Transporter goes legs up, networked to my server. I am not a very technically oriented guy, so please keep that in mind. Also, if you think we should take this off-line, just send me a pm and I'll get back to you. One concern I do have is that the newer DEQX products seem to be very much oriented to an all-in-one PRE/DAC/EQ use and I'm not sure if that makes sense in my situation. Luckily, I have the ability to (relatively) easily move my speakers out onto a large screen porch to get speaker response measurements. |
