Science: Substitute Ear

After syphilis had destroyed the hearing of the late great Composer Ludwig van Beethoven, that melancholy genius discovered that by clenching a stick in his teeth, holding it against the keyboard of his piano, he could discern faint sounds. Had Beethoven been in Manhattan last week, he could have seen what a century’s progress has done to his primitive device.

Announced for early marketing by both Dictograph Products Co., Inc., and Sonotone Corp. were similar portable devices for hearing by bone-conduction of sound Dictograph’s instrument was new, Sonotone’s an improvement on one it began marketing last November. That was developed by Sonotone’s Dr. Hugo Lieber, after Sonotone gave up the U. S. distributing rights to “Fortiphone”, hearing aid produced by Berlin’s Siemens & Halske.

In normal hearing, airborne sound waves enter the outer ear, set up vibrations in the ossicles (“hammer, anvil & stirrup”) of the middle ear. These transmit their vibrations to the liquid medium of the inner ear wherein lie the auditory nerves which carry them to the brain.

Sound waves are more easily conveyed through some solids, among them human bone, than through air. The devices announced last week simply short-circuit the outer and middle ear, transmit sound vibrations directly to the auditory nerves via head bones. Sound waves are picked up by a transmitter, passed through a pocket amplifier to a tiny oscillator, which a head band holds snugly against the mastoid bone behind the ear. (Sonotone’s improvement consisted in eliminating an oscillator “button” which protruded uncomfortably against the head.)

Deafness is often commonly caused by some obstruction in the outer ear passage or by hardening of the middle ear ossicles. Present, familiar air-conduction hearing devices are simply modified telephone receivers which step up sound vibrations to penetrate through the obstructed passage to the inner ear. Advantages claimed for the bone-conduction instrument are a mellower, more natural tone, an increase in hearing range. No more than the air-conduction instrument will it restore hearing to people whose auditory nerves are impaired.