[Bone conduction hearing aids]Types of bone conduction hearing aids The hazards of bone conduction hearing aids
Introduction to bone conduction hearing aids
Most of the sounds we hear are sound waves that travel through the air to the eardrum, where the sound waves vibrate the eardrum and transmit the sound to the ear. Another way is that the sound waves travel directly to the inner ear through the vibration of the skull without going through the eardrum. This is also one way people hear their own voice. This sound transmission method is bone conduction.
A hearing aid made of this bone conduction principle is called a bone conduction hearing aid.
How bone conduction hearing aids work
Under normal conditions, we listen to sound in at least two ways: bone conduction and air conduction.
Bone conduction means that the sound signal vibrates the skull and is not directly transmitted to the inner ear through the outer ear and middle ear; while air conduction means that the sound is transmitted through the outer ear and the middle ear to the inner ear.
The latter has an absolute advantage in the two modes of transmission. Therefore, most people ignore the importance of bone conduction transmission, and then ignore the role of bone conduction hearing aids.
Usually, what we call box-type, behind-the-ear and in-the-ear hearing aids are all air conduction hearing aids. Air conduction hearing aids transmit amplified sound signals through the earplugs into the outer ear canal. However, due to the severe and even extremely severe patients requiring higher gain, ordinary air conduction hearing aids are difficult to meet, that is, if the gain is small, you cannot hear it, and when the gain is large, it is very easy to produce feedback whistling. The performance is adjusted to avoid howling, but the actual effect is not satisfactory.
At the same time, because the air conduction hearing aids simulate the conduction mode of air conduction, the earplugs need to be inserted into the external auditory canal. Most patients will feel blocked after wearing them, which makes some deaf patients unwilling to wear them.
Bone conduction hearing aids are different. Strictly speaking, bone conduction hearing aids ultimately generate not sound signals but vibration signals. Bone conduction hearing aids don’t have so-called “headphones” or earplugs, but instead are an oscillator that generates a vibrating signal. Pressing the oscillator against the bulging mastoid bone behind the ear, the vibration of the oscillator causes the skull to vibrate and transmit the signal across the outer and middle ears—the advantage of bone conduction hearing aids—and directly to the inner ear.
Types of bone conduction hearing aids
There are three types of bone conduction hearing aids: hairband type, head clip type and glasses type. It is suitable for patients with external auditory canal atresia, stenosis, etc., or for patients with congenital malformation of the middle ear, chronic suppurative otitis media with repeated purulence, relatively large degree of conductive hearing loss, and general air conduction hearing aids are ineffective.
Hazards of bone conduction hearing aids
Bone conduction hearing aids are not comfortable to wear, long-term use will make the skin hard and painful, and the output has certain limitations It has an influence on the directionality of the sound, and it can provide little amplification for the sound above 3000-4000 Hz.
