Here is the site of Don Keele's CBT Loudspeaker Arrays.
Good to read, my future project:
http://www.xlrtechs.com/dbkeele.com/CBT.phpA Brief CBT History
CBT or Constant Beamwidth Transducer theory is based on un-classified military under-water transducer research done in the late 1970s and early 80s(Navy CBT Papers). This research describes a curved-surface transducer in the form of a spherical cap with frequency-independent Legendre shading that provides wide-band extremelyconstant beamwidth and directivity behavior with virtually no side lobes.
The theory was applied to loudspeaker arrays by Keele in 2000(Keele CBT Paper 1)where he extended the concept to arrays based on circular-arc line arrays and toroidal-shaped curved surface arrays. Keele also extended the concept to straight-line and flat-panel CBT arrays with the use of signal delays (Keele CBT Paper 2). The 3D sound-field of CBT circular-arc line arrays was analyzed by Keele in 2000 (Keele CBT Paper 3) . In 2003 Keele also described the practical implementation of CBT circular-arc line arrays (Keele CBT Paper4). In 2005, he described a design variation of the CBT loudspeaker line array, called a ground-plane CBT array, which is intended to operate very close to a planar reflecting surface
