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Ultrasonic Noise Measurements in the Work Environment
Published in Dariusz Pleban, Occupational Noise and Workplace Acoustics, 2020
In general, ultrasonic noise measurements at workstations do not require the use of any windshields, all-weather protection kits, or correction nose cones to be installed on microphones. However, should such need occur, then the frequency characteristic of the microphone in configuration with such accessory should be known in view of its significant effect on the measurement result—up to 5 dB for 40 kHz [Radosz and Pleban 2018]. Although microphone preamplifiers are characterized with low output impedance and high output current value, the use of long extension cables which constitute a leading load for the preamplifier, may affect the output voltage value and the frequency characteristic of the microphone-preamplifier system and decrease the upper limit of the usable frequency range. The effect depends on capacitance of the cables as well as on the upper limit of the measured signal dynamics range and is practically negligible for low-level signals and typical two-meter long cables. To estimate the potential effect of cables on measurement results, it is necessary to make use of the manufacturers’ data. Some providers of acoustic measuring equipment (e.g., sound level meters) provide corrections for the effect of extension cables on the measuring system frequency characteristic. A good solution is also determination of the frequency characteristic of the whole system including extension cables of various lengths planned to be used in the course of measuring sessions, as part of the system calibration procedure.
Evaluation of a prototype local ventilation system to mitigate retail store worker exposure to airborne particles
Published in Journal of Occupational and Environmental Hygiene, 2023
Taekhee Lee, Teresa L. Barone, David S. Yantek, Lee Portnoff, Yi Zheng
Due to the nature of the LVS, it is anticipated that noise would be a major concern. The LVS was placed inside a hemi-anechoic chamber and suspended using a gantry crane so that the distance between the LVS air outlet and the ground was 2 m. A-weighted equivalent continuous sound levels, LEQ,A, were measured under the LVS and to the sides of the LVS a 12.7-mm-diameter microphone (model 15 7052E, ACO Pacific, Belmont, CA, USA) with a microphone preamplifier (model SV15, Svantek, Warsaw, Poland) connected to a dual-channel noise dosimeter meeting Class 1 according to IEC 61672 (model SV102+, Svantck, Warsaw, Poland). A windscreen was used to cover the microphone to prevent wind-induced noise and the microphone was oriented so that it was parallel to the ground. The measurements were taken 25.4 cm and 50.8 cm beneath the LVS. The measurement to the sides of the LVS was taken at a distance of 1.83 m from each side of the LVS at a height of 1.52 m. Three LEQ,A measurements were taken at each location and the average value for each measurement was calculated by equation (6):