Noise shielding of acoustic devices for insect detection

Abstract

The need to monitor hidden insects and automate the acquisition of data for grain management has led to development of electronic sound detection devices. Typically, insect feeding and movement sounds are low in intensity, and they attenuate rapidly in grain. The main sound pressure level (SPL) generated by rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae), larvae in wheat kernels is only 23 dB (referenced to 20 μPa) as measured by a microphone immersed in a grain sample 3 cm from a larva-infested kernel. Unless the noise background is reduced below these levels by 10 dB or more, an insect cannot be detected reliably. To establish guidelines and procedures for shielding acoustic detectors in a grain elevator or other noisy environment, a multilayered enclosure was constructed that attenuates sound by 70-85 dB between 1 and 10 kHz. This level of noise reduction is sufficient to enable detection of internally feeding larvae in grain samples at inspection facilities at commercial grain elevators, which have 50-80 dB SPL noise backgrounds between 0.1 and 10 kHz.