Is DEQX a game changer?

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

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).

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.