Sound Research
Bone Conduction
Bone Conduction
Bone Conduction is the conduction of sound to the inner ear through the bones of the skull. Bone conduction transmission can be used with individuals with normal or impaired hearing.
What’s the difference between Bone conduction headphones and normal headphones?
Bone conduction is a way of conducting sound by sending the sound into a different frequency of mechanical vibration. Sent through the human skull, bone labyrinth, inner ear lymph fluid transmission, screw, auditory nerve and auditory center to transmit sound waves. In contrast to the classical sound transmission of sound waves through the diaphragm, the bone conduction eliminates many acoustic transmission steps to achieve a clear sound reduction in a noisy environment, and the sound waves won’t affect others.
When we eat a biscuit, we can hear the sound of biscuits broken because the vibration through our teeth and skulls to our inner ear. In the 18th century, the principle of bone conduction helped the great beloved deaf composer Beethoven to hear the wonderful music. Beethoven tried a technique invented by Giovanni Phillipo, England. Where he could hear the music from the jaw bones with a stick connected to the piano. This was actually the early beginning application of the bone conduction principle.
Bone conduction technology is mainly used for military, police professional headphones. Also in hearing aids, sports headphones and other fields.
- Published in Research Work
Hearing Loss
Hearing Loss:
There is no treatment, surgical or otherwise, for hearing loss due to the most common causes (age, noise, and genetic defects). For a few specific conditions, surgical intervention can provide a remedy:
- surgical correction of superior canal dehiscence
- Myringotomy, surgical insertion of drainage ventilation tubes in the tympanic membrane. Such placement is usually temporary until the underlying pathology (infection or other inflammation) can be resolved.
- radiotherapy or surgical excision of vestibular schwannoma or acoustic neuroma, though, in most cases, it is unlikely that hearing will be preserved
- Stapedectomy and stapedotomy for otosclerosis – replacement or reshaping of the stapes bone of the middle ear can restore hearing in cases of conductive hearing loss
Surgical and implantable hearing aids are an alternative to conventional external hearing aids. If the ear is dry and not infected, an air conduction aid could be tried; if the ear is draining, a direct bone condition hearing aid is often the best solution. If the conductive part of the hearing loss is more than 30–35 dB, an air conduction device could have problems overcoming this gap. A bone-anchored hearing aid could, in this situation, be a good option. The active bone conduction hearing implant Bonebridge is also an option. This implant is invisible under the intact skin and therefore minimises the risk of skin irritations.
Cochlear implants improve outcomes in people with hearing loss in either one or both ears. They work by artificial stimulation of the cochlear nerve by providing an electric impulse substitution for the firing of hair cells. They are expensive, and require programming along with extensive training for effectiveness.
Cochlear implants as well as bone conduction implants can help with single sided deafness. Middle ear implants or bone conduction implants can help with conductive hearing loss.
People with cochlear implants are at a higher risk for bacterial meningitis. Thus, meningitis vaccination is recommended. People who have hearing loss, especially those who develop a hearing problem in childhood or old age, may need support and technical adaptations as part of the rehabilitation process. Recent research shows variations in efficacy but some studies show that if implanted at a very young age, some profoundly impaired children can acquire effective hearing and speech, particularly if supported by appropriate rehabilitation.
- Published in Research Work
Sound Localization
Localization of Sound:
There are three ways that humans localize sound (those who aren’t diagnosed with unilateral hearing loss):
- Interaural Time Delay (ITD)
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- the same sound arrives at your ears at slightly different times, so for example if a sound arrives at your left ear first you will perceive it as coming from the left. This works mostly for lower frequencies (below about 800Hz) due to the wavelengths involved compared to the size of the head. For higher frequencies, group delay – the difference in timing between direct sound and reflected sound – also plays a part
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- Interaural Level Delay (ILD)
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- very similar but instead of time differences, if a sound appears louder in one ear compared to the other, your brain perceives it to be coming from that side.
- the primary method used to pan audio in a stereo image and works mostly for sounds above about 1600Hz. (A combination of both methods works for frequencies between 800 and 1600Hz)
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- The Shape of your Ears
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- makes a big difference in terms of localization, particularly for sounds above or behind you. Your pinnae (the outer part of your ear) filters the sounds in a characteristic way so we can be more sensitive to the direction of the sound.
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As concluded in various physics experiments, there are various ways that scientists and doctors use to measure sound localization but only work 10% of the time:
- Locating sound source given the measurements of the sound field
- Sound field – described using physical quantities like sound pressure and particle velocity
- Sound pressure is measured using microphones (which has a polar pattern)
- Polar Pattern – measures sound using the angle and direction sound comes from
- Sound Pressure can be identified and measured through particle velocity
- Particle Velocity – velocity of a particle in a medium as it transmits a wave
- Particle Velocity is a vector
- Vector – a geometric object that has magnitude and direction
- Another way to identify sound localization is by Time Difference of Arrival or TDOA
- Method used to obtain source direction
- Can be used with pressure microphones and with particle velocity probes
- Published in Research Work
The cocktail party effect
The brain filters noise. This is called the cocktail party effect
Our left side of the brain is more active when we discriminate relevant sounds from background noise, according to the findings of a study by an international team of scientists. The result is the so called cocktail party effect. A night out is often a frustrating experience for hearing impaired people. They find the words of their conversation partners drowned out by the conversations of others, music or street noise. They lack the ability of people with normal hearing to separate relevant sounds from background noise – the cocktail party effect.
Left side of brain sorts out the sounds
Brain researchers have investigated what happens in the brain when discriminating between the sounds we listen for and other noise. The study was headed by Hideko Okamoto of the University of Münster, Germany. He and his team exposed a number of individuals to test sounds and background noise in one or both ears while monitoring their brain activity. The recorded brain activity indicated greater activity in the left half of the brain when discriminating sounds from noise. In other words, the cocktail party effect occurs in the left side of the brain.
As of yet, the researchers are unable to determine why hearing impaired people’s ability to discriminate sounds from noise is diminished and reduce the cocktail party effect. This is a matter for future research.
Knowledge about the brain functions including the cocktail party effect will eventually benefit hearing impaired people in terms of the development of new treatment methods and assistive devices and help them to keep the cocktail party effect.
Source: BMC Biology, https://www.hear-it.org/-the-cocktail-party-effect-how-the-brain-filters-noise
- Published in Research Work
Sound Direction And Angle
Having two ears helps us to determine the direction of sound waves.
Time lag, wave length and tone – all these factors play important parts for the brain when determining the direction of sound.
In the following description, they are treated under separate headings, but when a person registers a sound, all three factors interact, helping to determine the direction from which the sound originates.
Time lag
Time lag is of particular importance when determining so-called impulse sounds like a click or a bang.
If a sound comes in at an angle to the right of the face, the direction of the sound waves means that the sound will not reach both ears at the same time.
The time lag is due to the fact that the distance from the source of the sound to the left ear is a little longer than it is to the right ear. Therefore, the sound waves must travel a little longer before reaching the left ear which is farthest away.
The brain registers the time lag and informs us that the direction of the sound is a little to the right of the face.
Wavelength
When sounds are light treble sounds (over 1 kHz), the wavelength plays an essential role for the brain in determining the sound direction. These sounds all have a limited wavelength of less than 30 centimetres.
When a person hears sounds of limited wavelengths, the head functions as a screen. If the sound comes from a direction to the right of the face, the head will prevent the sound waves from reaching the left ear. Deep base sounds, on the other hand, have a larger wavelength, and the head will not prevent the sound waves from reaching both ears.
The tone of the sound
If the direction of the sound waves is not from the sides, but rather from above, below or immediately in front of the face, there is no time lag between the ears. In situations such as this, the outer ear is important as it helps determine the tone of the sound.
Experience has taught us that the tone can help determine the direction of the sound waves. People riding a motorbike wearing a helmet, for example, often find it difficult to hear where an ambulance is coming from, as the helmet reduces the outer ear’s ability to determine the tone of the sound.
Comments: This article has been copied from https://www.hear-it.org/The-direction-of-sound
- Published in Research Work