Portable Instrumentation for Monitoring Sound Pressure Levels within the Ear

The sound pressure levels experienced by an individual exposed to noise can be obtained irrespective of the nature of the source or the presence of acoustic barriers by monitoring the sound field within the ear. The apparatus developed for this purpose consists of a miniature microphone located on the base of the concha connected to a lightweight instrument package strapped to the subject. The latter contains a modified cassette tape recorder, power supplies, and an oscillator used to record a calibration signal onto each tape and check the performance of the system. A pressure transformation is applied during analysis of the data to compensate for the frequency response of the components or to generate an equivalent sound field that would exist at the center of the head in the absence of the subject. Potential applications of the device include measuring the sound level experienced by operators of machines in use, evaluating the insertion loss of various forms of headgear, and assessing occupational exposures to noise.