Zera Jan, Mlynski Rafal
Central Institute for Labour Protection - National Research Institute, Czerniakowska 16, 00-701 Warsaw, Poland.
J Acoust Soc Am. 2007 Oct;122(4):2082-96. doi: 10.1121/1.2756973.
Attenuation of high-level acoustic impulses (noise reduction) by various types of earmuffs was measured using a laboratory source of type A impulses and an artificial test fixture compatible with the ISO 4869-3 standard. The measurements were made for impulses of peak sound-pressure levels (SPLs) from 150 to 170 dB. The rise time and A duration of the impulses depended on their SPL and were within a range of 12-400 mus (rise time) and 0.4-1.1 ms (A duration). The results showed that earmuff peak level attenuation increases by about 10 dB when the impulse's rise time and the A duration are reduced. The results also demonstrated that the signals under the earmuff cup have a longer rise and A duration than the original impulses recorded outside the earmuff. Results of the measurements were used to check the validity of various hearing damage risk criteria that specify the maximum permissible exposure to impulse noise. The present data lead to the conclusion that procedures in which hearing damage risk is assessed only from signal attenuation, without taking into consideration changes in the signal waveform under the earmuff, tend to underestimate the risk of hearing damage.
使用A型脉冲的实验室声源和符合ISO 4869-3标准的人工测试夹具，测量了各种类型耳罩对高强度声脉冲的衰减（降噪）情况。对峰值声压级（SPL）在150至170 dB之间的脉冲进行了测量。脉冲的上升时间和A持续时间取决于其声压级，范围在12 - 400微秒（上升时间）和0.4 - 1.1毫秒（A持续时间）之间。结果表明，当脉冲的上升时间和A持续时间减小时，耳罩的峰值级衰减增加约10 dB。结果还表明，耳罩杯下的信号上升时间和A持续时间比在耳罩外记录的原始脉冲更长。测量结果用于检验各种规定脉冲噪声最大允许暴露量的听力损伤风险标准的有效性。目前的数据得出结论，仅根据信号衰减评估听力损伤风险而不考虑耳罩下信号波形变化的程序，往往会低估听力损伤风险。
