For those who aren't quite clear how the cancelation works, let me share a related idea known as the double bass array.
I'm really surprised to see that the "Double Bass Array" (DBA) is not very popular outside Germany. I searched for key words, but found only one thread in the AudioCircle forum. Maybe someone is interested in this concept, since it is by far the smartest way to get a linear frequency response...
When this idea was developed, it worked well at completely eliminating bass modes in a room at any location. It had two problems, first, it made the room effectively anechoic at low frequencies and it only worked below 80hz or so (whatever the subwoofer crossover point was). It was also impractical.
Dirac us using the same underlying principles, but because we still maintain reproduction of the direct sound from the speaker sources (and we don't cancel that), we don't lose spatial bass. We also can make it work much higher since we rely on surround speakers and subwoofers for this.
Thank you for that explanation, now I understand where you are coming from.
However if this is going to require a multiplicity of speakers channels, that is not practical in the home. The spaces need to sound good and be livable. The other thing with the number of channels recently proposed by "Experts" on a recent Audioholics YouTube video that concern me is this. You can bet there will be a problem somewhere often, given that complexity and huge increase in electronics especially amps. So I maintain this is NOT practical.
Now to switch gears I do not seem to have the magnitude of bass problems the rest of you seem to wrestle with. I think that comes for two reasons, the first is that my main systems have been TL based for over 60 years, and I have a vast experience with them now. All my speakers except the two surrounds and the four ceiling speakers which are sealed, are aperiodically damped transmission lines. I have had many experienced engineers use and visit my systems over the years, and the comment is that the bass quality is what separates my systems from the rest.
When I was still in practice in Grand Forks, Bob Carver came to deliver and set up his ribbon system that one of my colleagues had purchased. He had heard about my system, the speakers were then the speakers that are now my rear backs. He had a prototype of his Sunfire Woofer with him.
Anyhow, he was enthralled and stayed for hours and sampled lots of musical selections. Needless to say his Sunfire sub, which I hooked up was no match for the TLs.
I am not sure of what the physics is behind all this, but I am convinced there is something different about the way a pipe couples to a room.
I have spent quite a bit of time with organ builders over the years. They have demonstrated to me how the character of pipes is totally different from loudspeakers.
The pipe uniformly fills large spaces, and wherever you are in the room the sound is uniform, especially the bass. Where as use speakers and the sound falls away fast as you move further away from the speakers. Organ builders refer to this phenomenon of pipes as encirclement. I know for certain this a real phenomenon. I don't believe it has been investigated the way it should have been.
This also applies to TL speakers I believe. TL speakers do seem to fill rooms evenly in the lower decades and seem to not excite room modes to the extent other forms of bass loading do. I really have no idea why, but others have also noted this.
I should say, that all my speaker are run full range except the four ceiling speakers which are crossed over. The right and left speakers are fully integrated full range speakers down to 20 Hz with a prodigious bass output. The center rolls off at 47 Hz second order, the surrounds have an F3 of 52 Hz and roll off second order,
The rear backs roll off around 27 Hz and still have plenty of output to 20 Hz.
I have never found the system produce even remotely close to boomy reproduction. The room is on the whole evenly filled with bass, with a slight elevation in the rear of the room. My measured room responses confirm a very even sound distribution in the bass decades and throughout the audio band for that matter. This is without any EQ other than levelling the active speakers and correctly setting BSC, which due to design is easily adjustable. In addition properly mixing the Sub/LFE channels with the BSC signal to the long lines of the left and right speakers. There is no other electronic manipulation.
I really doubt things would be improved adding channels and complex algorithms.
I would here pay tribute to the work and research of George Augspurger and his development of an accurate design model for TL loudspeakers. That has made my life a lot easier! I feel honored and privileged, that he has entrusted me with the body of that work and make it freely accessible to all.
Mathew, you are welcome to visit here any time, and hear first hand. With people advocating such complex solutions, I think all avenues need to be explored. I think George's work on TLs has been disgracefully ignored. I am certain you would find a visit well worth your while.