Sonotubometry. An acoustical method for objective measurement of auditory tubal opening

The sound conduction method for measurement of the Eustachian tube opening has been studied and modifications made in the test procedure to increase its easy performance and reliability. By holding the sound source near to the nostril, mounting the microphone into a circumaural ear defender and by feeding the output of the microphone through a filter with a very narrow bandwidth (3.16 Hz) many of the pitfalls of the sound conduction technique described earlier could be removed. Recording of the transfer function between the nasal tip and external auditory meatus and recording of the spectrum of swallowing sound revealed that the useful frequency rang for the measurements was upwards from 5--6 kHz. By using the three frequencies 6, 7 and 8 kHz the method showed tubal opening in 90 or 95% of normal ears depending on whether the minimum amplitude accetped was greater than or equal to 5 or 1--4 dB, respectively.