Middle ear transmission losses caused by tympanic membrane perforations in cats

Losses (determined by measuring microphonic responses) were essentially identical, regardless of whether produced by admittance of sound into the middle ear via perforations in the tympanic membrane (TM) or in the bulla. With SPLs monitored directly at the TM, losses increased at 12 dB/oct with inverse frequency for f less than 1 kHz, a pattern determined by the changes in the (calculated) net sound pressure acting from front and back on the TM. Clinically, hearing losses due to TM perforations are frequency-independent. The difference between the two situations has mainly to do with the use of precalibrated SPLs in Clinical Audiometry.