Design of Free-Standing Constant Beamwidth Transducer (CBT) Loudspeaker Line Arrays for Sound Reinforcement

This paper presents design guidelines for choosing the parameters of a free-standing CBT line array including its physical height, circular arc angle, location, and downward pitch angle to appropriately cover a single 2D straight-line audience sound-reinforcement listening region with direct sound. These parameters and conditions include: (1) array circular-arc angle and its associated beamwidth, (2) array height and low-frequency beamwidth control limit, (3) array mounting location that includes its height and setback from the front of the seating plane, and (4) the array's on-axis aiming location and associated downward pitch angle. These parameters are particularly easy to determine in advance for a CBT line array because of the extreme uniformity of its sound field with both frequency and distance, and its inherent constant-directivity characteristics. This paper describes a design scenario that allows the designer to easily choose these system parameters to optimize the direct-field coverage in the prescribed straight-line seating region while minimizing the use of sound-system design and prediction software. The design technique forces the SPL at the front and rear of the listening region to be equal by aiming the array at the rear of the listening region and then choosing its beamwidth (and its associated off-axis rolloff) to provide this front-rear SPL equality. The SPL and frequency response at intermediate points of the covered region are then set by the inherent well-behaved off-axis rolloff of the CBT array.