1930: The Model B6
Samuel F. Lybarger started with Radioear Corporation shortly after graduating from college in 1930. At this time, the company primarily manufactured large vacuum tube hearing aids for schools, theaters, and lecture halls. It began to research in the area of wearable hearing aids.
As Head of Engineering, Lybarger designed portable vacuum tube devices which used carbon microphones instead of the original coil microphones. His expertise led him to design the company’s first fully wearable hearing aid. The first iteration of a device like this was the Model B6.
Carbon Microphones
A small chamber filled with loose carbon granules is inside a carbon microphone. These sit between two metal plates. The front plate is a thin diaphragm that moves when sound hits it. A steady electrical current passes through the carbon.
When sound makes the diaphragm vibrate, it exerts varying pressure onto the carbon granules. These varying pressure levels translate into varying levels of resistance, which in turn vary the electrical current passing through the microphone. That varying resistance modulates the current, creating the audio signal.
Carbon microphones were a bit finnicky. They couldn’t be laid flat because the current wouldn’t flow at that angle, and the sound produced would be weak. When held at an angle or vertically, the carbon shot or dust touched both the rear conductor and front conductors at the same time, and sound would be produced.
Carbon Microphone, c.1920
By Daderot - Own work, CC0, https://commons.wikimedia.org/w/index.php?curid=35103283
Creating More Volume
Carbon hearing aids produced more volume by increasing the current flow. To do this, designers often wired multiple microphones in parallel to reduce overall resistance. The more microphones in parallel, the less the resistance. If you halve the resistance, you double the current, and thus the volume of the carbon hearing aid.
As a result, carbon hearing aids commonly had 2 or 4 microphones.
The Model B-6
The Model B-6 had two carbon microphones, flashlight batteries, and a miniature receiver and earmold.
The primary setback of this era was battery life. Driven by both the complexity of supplying enough current to make a hard-wired connection portable, but also ensuring a reasonable battery life. Because of the limited access to energy, the B-6 could not take advantage of more modern vacuum tube hearing aids.
Because of this, carbon hearing aids were not as effective as a grounded system. They lagged in sound clarity and tonal range.
The B-6 worked well for the individuals with light hearing impairment but did not have the sound range to accommodate for those with intense hearing impairments.
The First One-Piece Radioear
“First One-Piece Radioear”. Radioear Corporation Records, 1900-1990, AIS.2023.21, Archives of Industrial Society, Archives & Special Collections, University of Pittsburgh Library System, Box 46, Folder 57.
Sam Lybarger modeling the Radioear B-6 hearing aid
“Model B6 Radioear with Flat Receiver, S.F. Lybarger”. Radioear Corporation Records, 1900-1990, AIS.2023.21, Archives of Industrial Society, Archives & Special Collections, University of Pittsburgh Library System, Box 46, Folder 57.
The B-6 ran on “flashlight batteries” or what would be known today as D batteries.
Note that the majority of the hearing aid is taken up by its battery pack, illustrating just how power hungry the B6 was for its era.
A dream championed and a project led by none other than Lybarger himself, the B-6 was a large step towards compact, wearable hearing aids.
The B-6 with its battery pack open; notice how much space is taken up by its batteries
“Experimental Model of B6 Radioear”. Radioear Corporation Records, 1900-1990, AIS.2023.21, Archives of Industrial Society, Archives & Special Collections, University of Pittsburgh Library System, Box 46, Folder 57.
Sources
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Skafte, Marjorie. “A “Living Legend”: Samuel F. Lybarger”. The Hearing Review. August 1994, https://hearingreview.com/wp-content/uploads/2022/04/SamLybarger_0794HR.pdf
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Bauman, Neil, and Hugh Hetherington. “Carbon Hearing Aids—General Information” The Hearing Aid Museum, https://hearingaidmuseum.com/gallery/General_Info/GenInfoCarbon/info/generalinfo-carbon.htm 2006-2019
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Bauman, Neil. “The Hearing Aids of Yesteryear.” Canadian Audiologist, Canadian Audiologist | The Official Publication of the Canadian Academy of Audiology, 22 Aug. 2020, canadianaudiologist.ca/the-hearing-aids-of-yesteryear/.
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“The History of Carbon Microphones and Artifacts from the Shure Archives.” Shure, 29 Apr. 2020, https://www.shure.com/en-US/insights/the-history-of-carbon-microphones-and-artifacts-from-the-shure-archives