External ear resonance in children with otitis media with effusion. A middle ear effusion has been shown, in KEMAR, to increase the height of the resonant peak of the external auditory canal by 6 dB SPL. It has also been shown that the hearing impairment due to otitis media with effusion is related to the volume of middle ear fluid. Therefore, it was hypothesized that measurement of the height of the resonant peak of the external auditory canal could be used as a method of assessing the magnitude of any hearing impairment due to otitis media with effusion. 182 ears from 182 children aged 3-12 (mean 6.3) years were studied. Pure-tone audiometry and impedance tympanometry were performed, and the acoustics of the external auditory canal were measured using the Rastronics CC1-10 frequency response analyser. The mean height of the resonant peak (17.9 dB SPL) of children with a type A tympanogram was significantly different from the mean value (23.6 dB SPL) of those with a type B tympanogram. There was a significant correlation between the height of the resonant peak and the speech frequency average of the pure-tone thresholds. The sensitivity and specificity of using the height of the resonant peak to detect hearing impairments in different age groups were calculated and compared with the sensitivity and specificity of tympanometry. The test did not provide the same degree of sensitivity as tympanometry but was more specific. The additional advantages of the test are that it is quick, taking less than 1 min per ear, and is well tolerated by children in whom there was a 99% compliance. 