Patent ID: 7886869

Claim:
Apparatus comprising: an acoustic waveguide characterized by modes; a plurality of acoustic drivers each characterized by a diameter, the acoustic drivers mounted in the waveguide so that at least two of the acoustic drivers are mounted at least a diameter apart, and so that the acoustic drivers radiate into the waveguide so that radiation from each acoustic driver excites one mode at a position in the waveguide at which a modal function corresponding with the one mode is non-zero and so that the total excitation of the one mode is substantially zero wherein the acoustic waveguide is an open-closed acoustic waveguide; and wherein the acoustic drivers are positioned according to the formula MF n ⁢ ⁢ λ 4 = sin ⁡ ( n ⁢ ⁢ π 4 ⁢ l ⁢ x 1 ) + sin ⁡ ( n ⁢ ⁢ π 4 ⁢ l ⁢ x 2 ) + sin ⁡ ( n ⁢ ⁢ π 4 ⁢ l ⁢ x 3 ) ⁢ ⁢ … + sin ⁡ ( n ⁢ ⁢ π 4 ⁢ l ⁢ x a ) = 0 , where n is an odd number 3, 5, 7. . . , a is the number of acoustic drivers, l is the effective length of the waveguide, and x l . . . x a indicate the proportional distance from the open end the waveguide.