In 2009, in its prototype phase, the cartilage conduction hear-ing aid used a bimorph-type piezoelectric vibrator. Its output was low at 1,000 Hz or less. It required a power supply of 3 V or more and consumed over 60 mW. (A typical hearing aid consumes about 1 mW.) It was therefore concluded that us-ing this type of transducer was unlikely to lead to the develop-ment of a marketable product.Vibrations of a transducer in the cartilage induce vibrations in the cartilage of the external auditory canal, generating air-conducted sound in the external auditory canal.How a cartilage conduction hearing aid conduction sound (in the presence of an external auditory canal) Edited by Professor Hiroshi HosoiCan Sound Be Conducted Via Cartilage?— The Road to the Development of the Cartilage Conduction Hearing Aid—PROJECT STORYA Documentary of Product Development at RionIn 2017, Rion introduced the world’s rst* carti-lage conduction hearing aid, a product that drew on the newly discovered third auditory pathway.Let’s see how this hearing aid was developed and how it’s entering widespread use.*According to September 2017 company surveyHiroshi Hosoi, M.D.President and Chairman of the Board of Nara Medical University, Director of the MBT (Medicine-Based Town) Institute. He discovered the phenomenon of cartilage conduction hearing and published 16 pa-pers on the subject. He played a central role in joint research with Rion on cartilage conduction and guided the successful de-velopment of the cartilage conduction hear-ing aid.e Unexpected Discovery of a Completely New Auditory PathwayIt all began with the idea that sound could be conducted by inducing vibrations in the cartilage surrounding the ear. Professor Hiroshi Hosoi of Nara Medical University discovered cartilage conduction and initi-ated the productization of the new type of hearing aid. He says: “Sound is conducted from the external auditory canal to the ear-drum, and then to the ossicles. Eventually, it’s converted into a nerve impulse in the inner ear that the brain perceives as sound. e primary medium that conducts sound is air; sound perceived from the vibration of air is referred to as air conduction hearing. Sound can also be conducted by directly inducing vibrations in the temporal bone, which houses the inner ear. is type of sound perception is called bone conduction hearing. For quite some time, air conduction and bone conduction were believed to be the only pathways for sound transmission. en, in 2004, I unexpect-edly discovered a third auditory pathway, cartilage conduction.”While the bone and cartilage inside our ears resemble each other, they’re completely dierent types of tissue. ey’re two distinct components of the ear. It was known for a long time that sound could be perceived via vibrations in the bone, but no one considered the possibility that sound could be perceived via vibrations in the cartilage. en, one day in 2004, Professor Hosoi made his great discovery.Mention hearing aid, and most people picture an in-the-ear (ITE) or behind-the-ear (BTE) device. Since these hearing aids transmit sound to the eardrum, they’re not useful for people whose external audi-tory canal is occluded—a condition that prevents the transmission of sound to the eardrum. Examples include patients suf-fering from external auditory canal atresia. Bone conduction hearing aids of the head-band or implant type are commonly prescribed for such patients, but these devices involve a certain level of physical discomfort. In response, we developed a cartilage conduction hearing aid, which uses a small element called a trans ducer tted to the ear in place of a receiver. e device represents a dramatic step for-ward. It’s easily and comfortably worn by patients with occluded external auditory canals or by those with ear discharge due to middle ear infection or the like. is was the world’s rst hearing aid to rely on the phenomenon of cartilage conduction.“I was placing a transducer against various parts around the ear and listening to the sound it made. I noticed something odd. e sounds I heard when I held the trans-ducer against bone and against cartilage diered. e observation wasn’t based on any theories or predictions, since I had none at the time. e sounds just seemed dierent. is strange discovery prompted me to carefully press the transducer against various parts around the ear. I conrmed that the sounds I perceived were quite dierent. Had I been an expert in bone conduction, I might have been trapped by the preconceived notion that the only auditory pathways are air and bone. I might not have noted this dierence. is discovery drove my subsequent research to understand the reason for this dierence.”Professor Hosoi named this sound Interview and article by Editorial CommitteePhoto by Yuki AkabaTransducer2

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