Design, positional accuracy, and application of straight-path-traversing room-acoustic-measurement system based upon low-cost servo motor and light-weight multi-field microphone

The construction, operation, and application of a straight-path traversing, acoustical microphone-based, measurement system is described. The system was designed to support test room performance measurement such as prescribed in standards ANSI/ASA S12.55-2012/ISO 3745:2012. Major system components include a taut line suspending a sliding microphone carriage drawn by a string attached to a rotating drum. Central to the overall light-weight, low-power, mechanical design is the physically small Bruel & Kjaer 4961 microphone, holder, preamp, and signal cable whose multi-field response characteristic should well support accurate room qualification measurements. The battery-powered drum drive mechanism is built using the servo motor, wheels, and gears from a Lego Mindstorms NXT kit. Precision motor rotation is remotely programmable over the NXT wireless Bluetooth interface. Commonly available sport fishing tackle composes the majority of the suspension assembly. A software interface library is also described which enables PC-based applications to automate microphone positioning in synchrony with source emission, signal acquisition, and analysis. The system has been used to document the free-field characteristic of a perimeter loudspeaker array with centrally-located listener in a fully-anechoic chamber environment. Results indicating overall microphone positioning accuracy and usefulness in investigating room acoustics are presented here.