Re. the horn design I hope it's helpful to cut/paste these paragraphs from the B-215 page at my website:
A great deal of consideration went into choosing the horn size. The horn needs to go low enough and high enough, have large enough round-overs to minimize mouth reflection and diffraction, but be small enough to limit the distance to the mid-bass drivers to avoid venetian blind effect. As part of our optimization the mouth's inside and outside round-overs are unique, each chosen for its role.
There is a worthwhile advantage to using a single driver to cover the frequency range from 700 Hz on up. According to David Griesinger, it is particularly important that the phase of the overtones above 1 kHz (and ideally above 700 Hz) be preserved. The format we use enables this and goes one step further: the depth of our Oblate Spheroid horn corresponds with the phase-rotation-induced delay imposed on the mid-woofers, so the acoustic centers of compression driver and mid-woofers are effectively aligned. This avoids the time-domain smear often present in conventional speakers which have high-pass and low-pass drivers technically “in phase” in the crossover region, but with the woofer delayed by one wavelength relative to the tweeter. We avoid choosing between the elegant simplicity of woofer and tweeter on the same baffle, and the superior time-alignment of stepping the tweeter back by a sufficient distance to effectively align their acoustic centers. The depth of our horn is our tweeter set-back. So, the fundamentals and overtones arrive at the same time, or much more nearly so than is normally the case without DSP.
So why don't we rely on DSP? DSP is a different path with its own set of tradeoffs, and we think its use comes with an audible price. And we would like for our customers to have the option of enjoying an all-analog signal path if they so choose.
Duke designed the horn employing Dr. Earl Geddes' latest mathematical formulas. One claim to fame for this horn is extremely high tolerance matching the horn's entry angle to the compression driver's exit angle.
Re. the mid-bass bin: I presume Duke mentioned above that our friend and business associate Hans Looman of Infigo Audio gave us the posted renderings (Hans was the chief designer/engineer @ Resonessence Labs.)
We plan to include a grille about 17" wide; its cloth being flush with one piece of solid wood flanking each side of the 15s. I am currently thinking the vertical corners of the solid wood and grille frame shall have a radius: the former for cosmetic beauty for rare cases when the grille is removed, the latter to help stretch and fasten cloth on the frame. Two adjoining radii should accent the vertical and "slim" the appearance of the baffle.
The 15s cross circa 700 Hz, a 1.6 foot wavelength, hence radius or not there is zero risk of diffraction from the 3/4" grille frame and flanking solid wood. Ditto, grille cloth is invisible to a 1.6 foot wavelength. The grille frame has a silk pull tab at the base center.
Also included standard shall be an aluminum dress ring covering the mounting flange and fastening screws for each 15. Ring surface and outer machined circumference is black powder coat; the inner machined surface is natural.
Our first demo Bohemian 215 appears @ 2021 RMAF. The mid-bass bin shall be an even darker version of our so-called "chocolate walnut," with the aforementioned solid walnut flanking the 15s.
The horn front/sides/back shall be a dark green, kind of a smoky gray/blue/US Army green. The 8" cylinder around the compression driver and the 9" x 6" (H x W) sides of the cradle that support it shall be beech or anigre. Fastened atop each beech or anigre side panel is a 1" thick piece of blue/gray/white granite with random small flecks ranging from light gray to dark gray blue. Each granite piece has a radius on the forward-facing 9" dimension (from the lower front corner to the upper rear corner, mirror imaged pairs.)
