They don't exist apart from speakers with dipole bass where you won't get enough output to cover the last octave for things like home theater and organ music (symphonic works at subjectively realistic levels or 90dBC rock/techno are fine with Linkwitz Orions in reasonable sized rooms like 2500 cubic feet or 13x19x8 but open on most of one wall to the entire 600 square foot floor).
With monopole woofers placement for mid+high frequencies is never going to be good for low (below the Schroeder frequency where the resonances no longer overlap thus imposing significant peaks and nulls on the bass response) frequencies because good low frequency placements are not symmetric.
With dipoles there's little (-20dB from the on-axis sound in practical examples) output towards the ceiling and along the dipole nulls 90 degrees off-axis horizontally. The speakers put audibly and measurably less energy into the room's height and width modes. You also get multiple bass sources stimulating the room length-wise with different phase although integrated dipole bass isn't going to be in an ideal location for this.
Linkwitz Orions, some of the Emerald Physics speakers, and the Audio Artistry line which are still made to order have dipole bass.
The better solution is probably designed to integrate with separate bass systems that are placed separately. Audio Kinesis, Lyngdorf, and Gedlee do that. NHT's Xd system did (there may be 10 pairs left).
Earl Geddes is applying custom transfer functions to each of the multiple sub-woofers which should work better than sending them the same signal. Duke could comment on what he's doing.
With monopole woofers placement for mid+high frequencies is never going to be good for low (below the Schroeder frequency where the resonances no longer overlap thus imposing significant peaks and nulls on the bass response) frequencies because good low frequency placements are not symmetric.
With dipoles there's little (-20dB from the on-axis sound in practical examples) output towards the ceiling and along the dipole nulls 90 degrees off-axis horizontally. The speakers put audibly and measurably less energy into the room's height and width modes. You also get multiple bass sources stimulating the room length-wise with different phase although integrated dipole bass isn't going to be in an ideal location for this.
Linkwitz Orions, some of the Emerald Physics speakers, and the Audio Artistry line which are still made to order have dipole bass.
The better solution is probably designed to integrate with separate bass systems that are placed separately. Audio Kinesis, Lyngdorf, and Gedlee do that. NHT's Xd system did (there may be 10 pairs left).
Earl Geddes is applying custom transfer functions to each of the multiple sub-woofers which should work better than sending them the same signal. Duke could comment on what he's doing.