PMC

(A) Transmission line model of the cochlea as first proposed by . The stimulus travels through the resonant stages in series. The circles represent current detectors (nerve cells). (B) Equivalent circuit of the vibrating reed frequency meter, with the signal rail connected directly to all the resonant stages and a small capacitor reactively coupling each stage to its neighbours. The stimulus drives all stages in parallel, giving direct and stronger off-frequency forcing than the transmission line. The vibrating reed system is effectively a coupled filterbank model of the cochlea. Image credits: A, from , The auditory masking of one pure tone by another and its probably relation to the dynamics of the inner ear, Physical Review 23:266–285; B, from , A resonance approach to cochlear mechanics, PLOS One 7:e47918.

(A) Arrangement by which the reeds are excited by an oscillating magnetic field. (B) Graded tuning of the reeds, in this case 11 reeds ranging from 55 to 65 Hz. (C) End-on view of the reeds, showing maximum vibration of the middle reed, indicating a mains frequency of 60 Hz. Image credit: from Fig. 1-47 of , Introduction to circuit protection, control, and measurement, NAVEDTRA 14175, US Navy.

Graph showing drift rate on vibrating reed electrometer for CO₂ from toluene solution of benzoic acid-7–C¹⁴ versus weight of sample of toluene solution of benzoic acid-7–C¹⁴.

Because the vibrating reed system is linear, the global response of all 201 reeds when driven in parallel at 1.75 kHz (A) can be considered to be a superposition of the responses of each of the reeds driven individually. One of these responses, for reed 116 of natural frequency 1.75 kHz (dashed line) is shown in (B), and it shows that the response of this reed is largely due to its external forcing, with very little activity passing to neighbouring reeds. When the response is plotted logarithmically (C), it is clear that energy passing towards lower frequency reeds (leftwards, in the direction of the traveling wave) is less attenuated than energy moving to higher frequency reeds (to the right, as a reverse traveling wave).