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 |
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. |
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. |
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 |
