Is DEQX a game changer?

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

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

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

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