Assessment of FM systems with an ear canal probe tube microphone system

A technique is described to measure the real-ear performance of an FM system using an ear canal probe tube microphone device. The method involves placement of the FM microphone next to the monitoring (compression) microphone of the probe tube assembly to produce a constant sound pressure level input to the FM system. With the probe tube in the ear canal, a hearing aid alone is measured with a 60 dB SPL input and the FM system attached to the hearing aid (personal FM system) is assessed with an 80 dB SPL input to account for the higher input levels that occur due to the 6 inch distance between the speaker's mouth and the FM microphone. This technique permits a rapid comparison of the real-ear response of the hearing aid and the FM system.