Is DEQX a game changer?

Bruces' question: 'Btw, you referred to 'time alignment' and 'time coherence'. What is the difference between the two terms?"

My explanation is a bit lengthy (as usual!) and I cover phase coherence as well. They are inter-related....

Simple answer...
You time align speaker drivers or driver sets to each other to 'achieve' time coherence

Now the detail...
When everything starts and stops at exactly the same millisecond, such as a woofer & a tweeter or a main speaker & a sub, they are then moving in a time-coherent fashion (and are also phase-coherent)

When the BEGINNING portion of each driver or speakers' pulse arrives at the listening chair microphone or listener ears at the same instant, these are time coherent speakers. I discovered a long time ago that on my system, using the DEQX viewer and the Step Response facility, time-aligning the START of the sub(s) pulse with the start of the main speaker pulse gives by far the most natural integration and bass response. Larry has aligned Bruces' sub peak with the first impulse peak of the main speakers and both appear to start at about the same time so it should be similarly so

None of this can be relied on purely by measurement & the DEQX viewer alone however because, if you think about it, the impulse plots of any speaker or sub contains ALL the frequencies emitted by those drivers and the plot just shows one combined response against Amplitude/Milliseconds

Sound waves travel at different wavelengths/speeds from the lowest/slowest to the highest/fastest frequencies so what you are aligning to is a subset of all. Rest assured however that DEQX DOES minutely time align all frequencies WITHIN any single speaker it measures. It's just the manual bit in adding subs or anything from a diffrent measurement that needs careful interpretation to achieve the goal of 'time coherence'

That is why I have found it is best to use the plots as a guide and then fine-tune adjust by ear until 'perfect' but based on several room measurements and step responses in the viewer. It was pretty easy for me once I got to that spot because every piece of music I throw at my system sounds crisp and clear with no hint of bass bloom or a crossover

Note: with a single full range speaker containing passive crossovers, or a 2-way, 3-way measured accurately at once (ie without requiring subs), then an appropriate DEQX processor will do everything for the user and it automatically becomes time and phase coherent. All that's left to do is basic room eq or maybe time align an unequally placed speaker pair

Phase coherence means simply that the twin peaks and valleys of a test tone (such as created by DEQX during measurement), exactly line up at your ear. When those different waves also start and stop at the same time, you then have a speaker that is both phase AND time coherent

While basic 'phase coherence' is often used when setting up subwoofers, particularly 'simple' AV home setups, a phase-coherent speaker/sub may not be time-coherent. I know that because before I purchased the HDP3, my M&K sub WAS phase coherent with the main speakers & in an ideal position but the result in the room was pretty annoying to say the least. It has never moved from that spot but since setting my system up as described, it has audibly 'disappeared'

Andrew (Drewan77), thanks again for your always excellent inputs. A couple of minor clarifications to your post just above, if I may:

Sound waves travel at different wavelengths/speeds from the lowest/slowest to the highest/fastest frequencies so what you are aligning to is a subset of all.

Although the velocity of a sound wave in air does indeed vary as a function of frequency, as I understand it the amount of that variation is small enough to be negligible for practical purposes. See the graph near the lower right corner of this paper, where it can be seen that even under the worst case condition (0% humidity) a frequency of 10 Hz is less than 0.03% slower than a frequency of 20 kHz. At a listening distance of 3 meters, that would result in a propagation delay difference of less than 0.003 milliseconds between those two extremely different frequencies.

With a single full range speaker containing passive crossovers, or a 2-way, 3-way measured accurately at once (ie without requiring subs), then an appropriate DEQX processor will do everything for the user and it automatically becomes time and phase coherent.

But of course only to within a degree of accuracy and over a range of frequencies that are constrained by the duration of the correction window and by reflections that may be captured within that window.

Thanks again, though, for another excellent post. Best regards,
-- Al

Thanks for pointing that out Al, no problem at all!

I have always tried to keep my posts quite generalistic because we seem to have several potential or new users here and many of the principles behind DEQX can seem pretty bewildering at first, offputting even

Al and Andrew (Drewan) ... if I was inclined to put together a non-reflective sound box, do you have any thoughts about the materials I should use? I wonder what speaker manufacturers use to damp sound reflections in box speakers??

Andrew, notwithstanding the imperfect initial set up of my speakers because I was not able to do the time alignment adjustments outside, imaging and soundstage are greatly improved over what I had before. In many ways, I was playing stereo through two different speakers because of room EQ problems. I think you have a sense of what I was dealing with by looking at Larry's adjustments.

I'm sorry, I am not experienced with materials for acoustic panels. Maybe Nyal could comment as I have seen a couple of recent posts from Acoustic Frontiers