Investigation of hearing ability of divers in hyperbaric helium-air mixture environment in submergence

1. 在1ATA ~ 31ATA的环境压力下，测量了6种耳机的频率特性。雅马哈HP-1最适合目前的用途，因为它的频率特性即使在高环境压力下也很稳定。2. 在1ATA ~ 31ata范围内，用rionaa -71测听仪测量了最小可听声压级（MAP）和等响度轮廓（ELC）。为了防止背景噪音，HP-1的耳机单元内置了耳罩。测量了正常空气和5米深度的map值。由于保护耳无法降低低频噪声，因此仅在高于1.5KHz的频率下测量深度大于20米的map。ALCs受环境压力影响较大。深度大于120 m的ALC曲线呈字母“w”形，表明ALC在2KHz和6KHz处有局部最小值，在3KHz处有峰值。3. 测定骨传导听力阈值（BCT）。BCT随环境压力的变化小于MAP。通过对耳道的电子电路建模，发现高压条件下耳道声传输特性的改变是导致MAP峰值频率变化的部分原因。5. 测量了三种吸声材料在高压n2 -空气和he -空气条件下的吸声系数。吸收系数曲线向高频区偏移。换句话说，在高压下吸声系数降低。结果表明，吸收系数保持不变的频率与气体密度与速度的立方次方乘积的指数成正比。玻璃棉指数为0.7，毛毡指数为0.5，吸水海绵指数为0.7。6. 我们在个人计算机上实现了一个氦语音数据库。目前，用音素标签记录的数据有3000条。

1. Frequency characteristics of six kinds of headphones were measured at ambient pressures of 1ATA to 31ATA. A YAMAHA HP-1 was best suited for the present purpose because its frequency characteristics were stable even at the high ambient pressures. 2. The minimum-audible sound pressure level (MAP) and the equal-loudness contours (ELC) were measured at 1ATA to 31 ATA with an audiometer RION AA-71. To prevent the background noise, the headphone unit of HP-1 was build in an ear-protector. MAPs in normal air and at 5 meter depth were properly measured. Since the lower frequency noise could not be reduced by the ear-protector, MAPs at deeper than 20 meter were measured only at higher frequency than 1.5KHz. ALCs were widely changed by the ambient preesures. The curve of ALC at deeper than 120 meter were looked like a letter "w", showing that ALCs have local minima at 2KHz and 6KHz, and a peak at 3KHz. 3. The bone-conduction hearing thresholds (BCT) were also measured. The variation of BCT by the ambient pressure was less than that of MAP. Using an electronic circuit modeling of the ear canal, a shift of peak frequency of MAP in hyperbaric pressures was partly reasoned by change in acoustic trans-mission character of the ear canal. 5. The sound absorption coefficients of three absorber materials were measured at hyperbaric N_2-air and He-air. The curves of absorption coefficients were shifted to higher frequency region. In other words the sound absorption coefficient were reduced in hyperbaric pressure. It was found that the frequencies at which the absorption coefficient remains unchanged were proportional with the exponent of the product of gas density and cubic power of velocity. The exponents are 0.7 for glass wool, 0.5 for felt, and 0.7 for absorption sponge. 6. We have implemented a helium speech database on a personal computer.At present, there are 3,000 data recorded with phoneme label.