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5 Acoustics in Biology and Medicine
character of white light. White noise has a masking effect, not only blocking the
sensation of other sounds, but diverting attention from other senses, including
mild pain. White noise can be produced by converting to sound the amplified
thermal fluctuations of electrons in electronic devices.
• Speech Power: The human vocal sound energy output per unit time
• Audiometry: A device for evaluating hearing through ears and possibly through
the mastoid part of the temporal bone
• Otoscope A device for viewing the eardrum through the ear canal. A light source
is used to illuminate the eardrum through the same optical path used by the
viewer.
• Acceptable noise levels: A sound level range between 0 and 100 dB. The noise
level in a quiet room is about 40 dB.
• Anechoic room: A room with sound absorbing walls, ceilings and suspended
floors; used to test hearing and low level sounds. Humans can hear their own
heartbeat in such a room. The effects are often psychologically disturbing.
Anechoic rooms are usually constructed with cones coated with absorbing
surfaces covering the walls, floor, and ceiling, all facing toward the chamber.
People enter on a metal screen platform to keep their weight off the floor cones.
Sound entering a cone will reflect a number of times as it heads toward the cone
vertex, each time losing energy.
• Stereo hearing: Having two good ears gives us the ability to judge angular direction to a source of sound, i.e., a stereo-sense, also called binaural sound detection.
Below about 3000 Hz, this deduction uses the phase difference between the
waves arriving at the two ears, while much above 3000 Hz, information about
the times of arrival of a pulse of sound to each ear comes into play.
• Infrasonics: Sounds below the frequency heard by humans, i.e. below about
20 Hz
• Ultrasonics: Sound above the frequency heard by humans, i.e. above about
20 kHz
• Sound level change sensitivity: The ability of humans to detect a small change in
sound level. Humans can detect a change in sound level if the change is above
one decibel.
• Sound frequency change sensitivity: The ability of humans to detect small
changes in frequency. At 1000 cps, most humans with healthy ears can detect
a change of f = 0.3 cps.
• Sound direction sensitivity: The ability to sense from where a sound came. This
is also known as stereo sense, or binaural sense. Sensitivity is: 2 ◦ if sound come
from near the front of the head, 10–15 ◦ if the sound comes from the side. The
detection is via delay time, relative phase, and intensity variation from ear-to-ear.
• Time resolution: The smallest time detectable between two sharp pulses of sound,
or the smallest detectable gap in a sound (about 1 ms for humans)
• Sound Diffraction: Bending of sound wave around boundaries (greater for
wavelengths comparable or larger than boundary dimensions)
5 Acoustics in Biology and Medicine
character of white light. White noise has a masking effect, not only blocking the
sensation of other sounds, but diverting attention from other senses, including
mild pain. White noise can be produced by converting to sound the amplified
thermal fluctuations of electrons in electronic devices.
• Speech Power: The human vocal sound energy output per unit time
• Audiometry: A device for evaluating hearing through ears and possibly through
the mastoid part of the temporal bone
• Otoscope A device for viewing the eardrum through the ear canal. A light source
is used to illuminate the eardrum through the same optical path used by the
viewer.
• Acceptable noise levels: A sound level range between 0 and 100 dB. The noise
level in a quiet room is about 40 dB.
• Anechoic room: A room with sound absorbing walls, ceilings and suspended
floors; used to test hearing and low level sounds. Humans can hear their own
heartbeat in such a room. The effects are often psychologically disturbing.
Anechoic rooms are usually constructed with cones coated with absorbing
surfaces covering the walls, floor, and ceiling, all facing toward the chamber.
People enter on a metal screen platform to keep their weight off the floor cones.
Sound entering a cone will reflect a number of times as it heads toward the cone
vertex, each time losing energy.
• Stereo hearing: Having two good ears gives us the ability to judge angular direction to a source of sound, i.e., a stereo-sense, also called binaural sound detection.
Below about 3000 Hz, this deduction uses the phase difference between the
waves arriving at the two ears, while much above 3000 Hz, information about
the times of arrival of a pulse of sound to each ear comes into play.
• Infrasonics: Sounds below the frequency heard by humans, i.e. below about
20 Hz
• Ultrasonics: Sound above the frequency heard by humans, i.e. above about
20 kHz
• Sound level change sensitivity: The ability of humans to detect a small change in
sound level. Humans can detect a change in sound level if the change is above
one decibel.
• Sound frequency change sensitivity: The ability of humans to detect small
changes in frequency. At 1000 cps, most humans with healthy ears can detect
a change of f = 0.3 cps.
• Sound direction sensitivity: The ability to sense from where a sound came. This
is also known as stereo sense, or binaural sense. Sensitivity is: 2 ◦ if sound come
from near the front of the head, 10–15 ◦ if the sound comes from the side. The
detection is via delay time, relative phase, and intensity variation from ear-to-ear.
• Time resolution: The smallest time detectable between two sharp pulses of sound,
or the smallest detectable gap in a sound (about 1 ms for humans)
• Sound Diffraction: Bending of sound wave around boundaries (greater for
wavelengths comparable or larger than boundary dimensions)