Friday, September 30, 9:00 am — 10:30 am (Rm 403A)
D.B. (Don) Keele, Jr., DBK Associates and Labs - Bloomington, IN, USA
P8-1 Use of Ground-Plane Constant Beamwidth Transducer (CBT) Loudspeaker Line Arrays for Sound Reinforcement—D.B. (Don) Keele, Jr., DBK Associates and Labs - Bloomington, IN, USA
Ground-plane circular-arc CBT line arrays with wide horizontal coverage offer a very viable, high performance, simple, and thrifty alternative to the usual sound reinforcement setup where loudspeakers are elevated or hung overhead. Due to the broadband constant beamwidth/directivity/coverage characteristics and narrow vertical coverage of the CBT array, the ground-plane version offers a number of strong performance and operational advantages even when they are located on stage behind the performers. Among these are: even coverage, minimal front-back variation in sound level, flat-energy response, less energy directed upwards towards ceiling, improved intelligibility, less prone to feedback, and greater performer freedom to move around on stage. In addition, these arrays minimize the use of stage monitors, require minimal installation voicing and on-site equalization adjustments, and result in a much simpler system, i.e., fewer speakers, fewer power amps, and fewer processing channels.
Convention Paper 9623 (Purchase now)
P8-2 Design of Free-Standing Constant Beamwidth Transducer (CBT) Loudspeaker Line Arrays for Sound Reinforcement—D.B. (Don) Keele, Jr., DBK Associates and Labs - Bloomington, IN, USA
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.
Convention Paper 9624 (Purchase now)
P8-3 Constant Coverage Line Arrays Using Passive Components for Beamforming—Douglas J. Button, Harman International - Northridge, CA USA
The work here within describes a cost effective method for beamforming utilizing passive components in a transmission line architecture to provide successive amounts of group delay from the middle to the ends of the array. The method also provides amplitude shading and some frequency shading that works to form a hybrid of several traditional methods. The method also provides a simple and straight forward way to change the shape (width) of the beam with changes in the passive network. The resulting network is very cost effective and rivals the performance of a multichannel DSP-based beamformer.
Convention Paper 9625 (Purchase now)