I enjoyed your recent piece on room acoustics in the GIK newsletter. I didn't find an easy way to comment directly.
You mentioned that SBIR (or Allison effect) problems are typically related to the distance from speaker (woofer) to the front or side wall of the listening room. I would point out that the classic, and a very common, issue is the distance from woofer to the floor. As I understand it, a response dip is expected at the frequency for which this is the 1/4 wavelength distance. I assume this is one reason that many recent floor-standing speakers have multiple woofers at differing distances from the floor.
Indeed correct. There are many examples of that now. Salk, KEF Blade, Aerial Acoustics model 8, GR Research, Legacy,etc...come to mind. That being said you'll find that it's still not completely eliminated. The effect is minimized which is always good but you still need to treat your corners +/- side wall too unfortunately (nice room pics in your gallery btw!). And...most of these speakers, you need to pull them away from the front wall for best imaging/staging anyway. It's tricky to get right but if you don't have +/- 10 dB swings that's already a plus.
As an aside, I do recall way back when that the NHT 3.3 was shaped as it was to create a "corner" for the side mounted 1259 woofer in order to minimize the SBIR/Allison effect as much as possible. That being said there is still that "dip" :https://www.stereophile.com/images/archivesart/N33fig2.jpg
I find that I have to be careful with interpreting the measurements from Sphile and the NRC. The NRC is anechoic so you won't see the effect. With Stereophile I look and see if it was an in room or quasi anechoic measurement. With the in room measurement I can trust if the loudspeaker design minimizes the SBIR effect intrinsically or does not (as long as it was setup right and there aren't large absorbers in the setup). With the quasi anechoic I may not see it at all but it still might be there.
Just a note to myself...I guess there is nothing like having the speakers in my own room and doing the measurements.
And JWL, your Audiogeekery blogs/articles are a treat I quite agree!