The BarnOwl directional noise monitor comprises three Brüel & Kjær outdoor microphones, positioned a precise distance apart in an array. Digital signal processes analyse the three signals in real-time to determine the level and directional component. Every 1⁄2 second, BarnOwl measures the level and the bearing of the dominant noise to a resolution of 5 degrees. As well as measuring the total noise, as with a standard noise monitor, BarnOwl employs further processing to determine all sources. These exclude noise from wind, anything at more than 15 degrees from the horizontal plane and anything very close to the monitor. It also excludes noise without any definite direction such as insect noise.
The data is further processed to provide the required noise metrics such as sound level, Leq and statistical levels.
The three BarnOwl microphones are mounted on a plate that correctly positions the microphones. The plate is in turn mounted onto a small mast or tripod, typically 2 metres off the ground. Microphone cables run from each microphone down the mast to the processing unit, which is mounted nearby in an environmentally sealed enclosure. In addition to the processing unit, the enclosure contains a power supply, communications device and other equipment intended to ensure continuous operation and provide remote access.
For correct operation the unit is required to be more than 4 metres away from large reflecting surfaces. Setup is provided as part of the Noise Sentinel service, which includes commissioning, setup and everything to ensure correct operation.
Power is most commonly provided from wired mains with a battery backup that ensures continuous operation in the case of short-term power failure. Other power configurations are possible, including solar power where climate conditions permit.
Communications are provided either by 3G digital wireless communications or by a wired LAN connection to the Internet. The use of proprietary data communications networks is possible where these exist.
In addition to permanently sited units, BarnOwl may be provided within a trailer configuration to facilitate mobile monitoring for periods of up to several months at a time.