7_TSH Sound Amplification and Detection

Sound

A longitudinal pressure wave that requires a medium (typically air, but can also travel through fluids and solids) for propagation.

Sound Propagation

The process by which sound energy travels through a medium, facilitated by the vibration of particles in the medium back and forth in the direction of the wave's travel.

Frequency

The number of wave cycles passing a fixed point per second.

Frequency unit

Hertz (Hz)

Human Hearing range

The range of frequencies that can be detected by the average human ear, typically from 20 Hz to 20,000 Hz.

Perceived properties of sound

Intensity (amplitude of the wave) & frequency (pitch)

Sound intensity (I)

defined as sound per unit area (W/m2)

Inverse Square Law of Sound Intensity

Intensity of sound decreases with distance from the source; doubling the distance reduces intensity by a factor of 4.

Sound Intensity Level (SIL)

Utilized due to the wide dynamic range of human hearing (12 orders of magnitude in intensity); expressed in decibels (d

Doubling Intensity

Results in a 3 dB increase on a logarithmic scale.

Threshold of Audibility

The lowest detectable sound intensity, considered to be 0 dB at 1 kHz.

Threshold of Pain

The loudest sounds we can tolerate, occurring at intensities of approximately 1-10 W/m².

Typical Sound Intensity Levels (SIL)

Examples of common sounds and their corresponding decibel levels; helps illustrate the range of human hearing

Auditory Response

The way the ear processes sounds, responding differently to various frequencies.

Loudness vs Intensity

Human ears vary in sensitivity to different frequencies; sounds of equal intensity can be perceived differently on a loudness scale. Units for perceived sound: phon.

Phon

A unit that measures individual perception of loudness, referencing a standard frequency of 1000 Hz. For example, a sound perceived as having the same loudness as 60 dB at 1000 Hz is measured at 60 phons.

Pinna

The outer ear structure that directs sound into the auditory canal and enhances sound transmission to the tympanic membrane.

Tympanic Membrane

A thin membrane that vibrates in response to sound waves, converting them into mechanical energy; its area is approximately half the area of the ear opening.

Sound Amplification by the Pinna

The acoustic energy is funneled into a smaller area, increasing sound pressure level, allowing sound waves to effectively vibrate the ossicles in the middle ear.

Sound Amplification Factor

Sound is amplified by a factor of 2 by the pinna and tympanic membrane.

Ossicles

A chain of three tiny bones in the middle ear: malleus, incus, and stapes, that amplify sound vibrations from the tympanic membrane to the oval window of the inner ear.

Mechanical Advantage of Ossicles

The ossicles provide a mechanical advantage of approximately 2, which increases the force of sound vibrations transmitted from the tympanic membrane to the oval window.

Total Mechanical Amplification

The total mechanical amplification of sound pressure in the 3000 Hz range is about 80 times, resulting in an intensity amplification at the oval window by a factor of about 6400 due to the proportionality of

Cochlea

A snail-shaped structure in the inner ear filled with fluid that converts sound vibrations into neural signals.

Basilar Membrane

A key structure within the cochlea that vibrates in response to sound waves, enabling detection of different frequencies.

Tectorial Membrane

A gelatinous structure atop hair cells in the cochlea that deflects hair cells as sound waves pass through, initiating neural response.

Reissner’s Membrane

A membrane in the cochlea that separates the scala vestibuli from the scala media, crucial for maintaining fluid ionic composition.

Place Theory

A theory that explains how different frequencies of sound are perceived based on the location of maximum vibration along the basilar membrane, where higher frequencies stimulate the base and lower frequencies stimulate the apex.