Sloped baffle

If you were to try to line up the drivers how would you find the " acoustic center" of a driver. In a midrange or woofer would that be about half way out from the center or would it be further out because the majority of the area of a larger driver would be closer to the perimeter?

Hi Roy, I don't mean to beat a dead horse, but I think that in a W M T M W array, it would be very rare indeed for any of the drivers to be equi-distant to floor and ceiling, and those surfaces would typically be different enough to reflect some frequencies differently as well.
I would have guessed that in an attempt at a staggered driver time coherent horn design that the horns themselves would get in the way of each other with the surrounding horns causing early reflections. Wouldn't a deep throat coincidental multi-driver have more early reflections than a flatter design?

Sounds Real,
For an eyeball estimate, the acoustic center is approximately where the voice coil former meets a cone or dome- the glue joint. But this is true only in the upper-middle range of any driver, whether tweeter, mid or woofer, where each one's frequency response is still flat.

To measure it (within +/- 1/8th inch at best for a tweeter, much more for a woofer), one sends an impulse, a click, to a driver having no crossover.

On a `scope, one examines when that click arrived compared to when the `scope's sweep was triggered by the click electrically.

Now, what we are looking for as markers will not be the top of those two spikes that click generated. We are looking for when each spike just begins to turn upwards from 0.0 at its bottom-- when each just begins to rise up. That is a very difficult transition to judge, which leads to inaccuracy.

Regardless, that time-difference times the speed of sound is your distance from the mic to the acoustic center in a driver's upper-middle range. Compare that to the tape measure distance and you often get close to the eyeball estimate I mentioned above. Of course, the test mic will be expensive, not a $200 special, for those cheaper ones have their own phase shifts in the audible range. Figure $1000 for a proper mic, plus a $1000 wideband mic preamp. Even so, the results will still be rather inaccurate. I was able to find ways around this, fortunately.

===

Unsound,
It is not that the two woofers are equidistant from their surfaces but the fact that we have two (four in stereo) woofers rather near two surfaces with you living in between.

Do have a look at that new drawing I posted to get an idea where "the bass source really is", which is my red dot in that drawing. Imagine what standing waves would then occur in between a red dot on the ceiling and one on the floor when the measuring mic/your ear is placed somewhere in between. Double trouble has been my experience.

No doubt about the outer horn-surfaces making reflections. But those reflections would go mostly upwards, and we can apply wool felt or acoustic foam to minimize most of them. I still think the biggest problem to be getting far enough away from the speakers so stand up/sit down differences would not drive us crazy- a large living room, say 30 x 40 feet is probably enough.

I would like to hear a Klipschorn corner horn triamped with time-delays applied to its mid and tweeter, since the woofer is so far back inside (~4 milliseconds) and the tweeter is so far in front of the mid driver (~2ms). Again, one would be stuck with using second-order crossovers on the drivers with the mid driver in inverted polarity.

Best,
Roy

Roy. thanks again. ^ Wouldn't using 2nd order cross-overs compromise the whole effort?

Certainly, but a lot of other problems would be fixed.