from The Century Dictionary and Cyclopedia
- Being outside of the tympanum or drum of the ear.
Sorry, no etymologies found.
This is certainly the case in frogs, where frequencies below 3-400 Hz apparently are received by 'extratympanic' pathways.
Since the ear is a pressure-gradient ear, the tympanic response at low frequencies is very small, that part of the low frequency sensitivity is extratympanic.