Hellstrom P A, Axelsson A
Lindholmen Development, Hearing Research Lab, Gothenburg, Sweden.
J Acoust Soc Am. 1993 Feb;93(2):907-19. doi: 10.1121/1.405452.
The use of a miniature microphone probe tube for sound-pressure level measurements in the outer earcanal was studied in four experiments. The main reason was to evaluate this method for clinical applications and for measurements of hearing protector attenuation. All measurements were registered in 1/3-oct bands. The dynamic range, frequency response of the microphone system, the insertion loss of the probe tube walls, and the influence of the probe tube in the ear canal on the sound-pressure level were examined. The first experiment attempted to determine an optimal placement of the probe tube in the earcanal. Sound-pressure levels resulting from a known free-field sound stimulus were measured at 12 different positions in the earcanal of human subjects. The results indicated that the position which is least sensitive for small movements of the probe tube on the measure was within 1 to 3 mm of the tympanic membrane. In a second experiment the changes in sound transfer function to the tympanic membrane caused by the microphone itself, when positioned just outside the ear canal entrance, were studied for 72 angles of sound incidences in ten subjects. A few minor but significant changes were observed with the microphone in this position. In a third experiment, sound transfer functions were measured from free sound field to the tympanic membrane in 19 subjects. The measurements were performed in 1/3-oct frequency bands (0.2 to 20 kHz) with sound incidences from 24 azimuthal positions and for each of these, three different elevations. The inter- and intrasubject-variability are analyzed and discussed. Finally, the reliability of probe tube microphone measurements was evaluated by repeated measurements of the sound transfer function, five times in ten subjects with the sound incidence from one position. The results indicated very small variations between repeated measurements.
在四项实验中研究了使用微型麦克风探头管在外耳道中进行声压级测量。主要目的是评估这种方法在临床应用和听力保护器衰减测量中的适用性。所有测量均在1/3倍频程频段内进行。研究了麦克风系统的动态范围、频率响应、探头管壁的插入损耗以及探头管在外耳道中对声压级的影响。第一个实验试图确定探头管在外耳道中的最佳位置。在人类受试者的外耳道中12个不同位置测量了已知自由场声刺激产生的声压级。结果表明，在测量时探头管小幅度移动最不敏感的位置在鼓膜1至3毫米范围内。在第二个实验中，研究了在耳道入口外放置麦克风时，对于10名受试者72个声入射角，麦克风本身对鼓膜声传递函数的影响。在这个位置观察到了一些微小但显著的变化。在第三个实验中，测量了19名受试者从自由声场到鼓膜的声传递函数。测量在1/3倍频程频段（0.2至20千赫）进行，声入射角来自24个方位位置，并且对于每个方位位置，有三个不同的仰角。分析和讨论了受试者间和受试者内的变异性。最后，通过对10名受试者从一个位置入射声音时声传递函数进行五次重复测量，评估了探头管麦克风测量的可靠性。结果表明重复测量之间的变化非常小。
