Sound Perception & Measurement

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Questions and Answers

Explain the relationship between phons and decibels (dB) at 1000 Hz.

At 1000 Hz, the phon value is defined to be equal to the decibel (dB) value. A sound measured at 60 dB at 1000 Hz is also 60 phons.

If a 40 dB SIL sound at 1000 Hz is perceived to be as loud as a sound at 100 Hz, what is the loudness of the 100 Hz sound in phons?

The loudness of the 100 Hz sound is 40 phons, because loudness in phons is based on the equivalent perceived loudness of a sound at 1000 Hz.

Describe how the auditory canal amplifies sound before it reaches the tympanic membrane.

The auditory canal acts like a funnel, directing acoustic energy into a smaller area. Because the area of the tympanic membrane is smaller than the opening of the ear canal, the sound is amplified to increase the pressure.

Explain how the inverse square law affects sound intensity as distance from the source increases. Provide a specific example.

The inverse square law states that sound intensity decreases proportionally to the square of the distance from the source. For example, if you triple the distance from a sound source, the intensity decreases by a factor of 9. Signup and view all the answers

What is the role of the pinna in sound reception?

The pinna helps to direct sounds into the auditory canal. Signup and view all the answers

Besides the auditory canal, what other structure in the outer ear contributes to sound amplification?

The pinna (outer ear) also helps direct sounds into the auditory canal. Signup and view all the answers

What is the range of sound frequencies that humans can typically detect, and what unit is used to measure frequency?

Humans can detect frequencies ranging from 20 Hz to 20,000 Hz. The unit used to measure frequency is Hertz (Hz). Signup and view all the answers

The area of the tympanic membrane is approximately half the area of the opening of the ear canal. By what factor is sound amplified due to this difference in area?

The sound is amplified by approximately a factor of 2. Signup and view all the answers

Describe the relationship between the physical properties of sound (intensity and frequency) and our perception of sound (loudness and pitch).

Sound intensity corresponds to perceived loudness where higher intensity equates to higher perceived loudness. Sound frequency corresponds to perceived pitch where a higher frequency equates to a higher perceived pitch. Signup and view all the answers

List the three bones (ossicles) found in the middle ear.

The three bones are the malleus, incus, and stapes. Signup and view all the answers

Why is the logarithmic decibel scale used to measure sound intensity level instead of a linear scale using W/m^2?

The logarithmic decibel scale is used because the human ear has a wide dynamic range, responding to sound intensities over many orders of magnitude. Using the logarithmic scale allows for a more manageable and perceptually relevant representation of sound intensity levels. Signup and view all the answers

How do the processes in the ear amplify sound?

The ear amplifies sound through several processes. The pinna initially gathers the sound and funnels it to the ear canal which exhibits resonant properties. Further amplification occurs via the ossicles acting as levers and the tympanic membrane transferring vibrations to the smaller oval window. Signup and view all the answers

What is the function of the ossicles in the middle ear?

The ossicles connect the tympanic membrane to the oval window and transmit sound vibrations. They also amplify sound. Signup and view all the answers

What do the terms threshold of hearing and threshold of pain refer to in the context of sound intensity and what approximate decibel levels do they represent?

The threshold of hearing is the minimum sound intensity that can be detected by the human ear, approximately 0 dB. The threshold of pain is the sound intensity at which pain begins to be felt, generally around 120-140 dB. Signup and view all the answers

If the intensity of a sound wave increases by a factor of 100, how many decibels does the sound intensity level increase?

For every factor of 10 increase in sound intensity, the sound intensity level increases by 10 dB. Thus, if the sound intensity increased by a factor of 100 ($10^2$), the sound intensity level would therefore increase by 20 dB. Signup and view all the answers

Describe how the cochlea detects different frequencies of sound.

The cochlea is tonotopically organized, meaning different locations along its length respond maximally to different frequencies. The basilar membrane vibrates in response to sound, with higher frequencies causing maximal vibration near the base and lower frequencies near the apex. Signup and view all the answers

Explain why the Sound Intensity Level (SIL) is measured on a logarithmic scale instead of a linear scale.

The SIL is measured on a logarithmic scale to better represent the wide range of sound intensities that humans can perceive. It also better reflects how humans perceive loudness, as our perception of loudness is approximately logarithmic. Signup and view all the answers

If the sound intensity doubles, by approximately how many decibels does the Sound Intensity Level (SIL) increase?

3 dB Signup and view all the answers

What is the significance of the 'threshold of audibility' in the context of Sound Intensity Levels (SIL)?

The threshold of audibility represents the quietest sound a human ear can detect. It serves as the reference point (0 dB SIL) against which all other sound intensities are compared when determining their SIL values. Signup and view all the answers

Describe what is meant by the 'threshold of pain' in acoustics, and provide an approximate sound intensity value associated with it.

The threshold of pain is the intensity level at which sound becomes uncomfortably loud and can cause pain or damage to the ear. It is around 1-10 $\frac{W}{m^2}$. Signup and view all the answers

A sound has an intensity of $10^{-8} \frac{W}{m^2}$. Is this sound closer to the threshold of audibility or the threshold of pain? Justify your answer.

This sound is closer to the threshold of audibility. The threshold of audibility is $10^{-12} \frac{W}{m^2}$, while the threshold of pain is around 1-10 $\frac{W}{m^2}$. $10^{-8} \frac{W}{m^2}$ is closer to $10^{-12} \frac{W}{m^2}$ on a logarithmic scale. Signup and view all the answers

Explain why two sounds with the same intensity but different frequencies can be perceived as having different loudness.

The ear's sensitivity varies with frequency. We are more sensitive to frequencies in the 1 kHz to 4 kHz range, so sounds in this range will seem louder than sounds of equal intensity at lower or higher frequencies. Signup and view all the answers

How does doubling the distance from a sound source generally affect the sound intensity and perceived loudness? Assume you are outside with no reflections.

Doubling the distance from a sound source will result in a fourfold decrease in sound intensity (inverse square law). This corresponds to a decrease of approximately 6 dB in SIL, resulting in a noticeable decrease in perceived loudness. Signup and view all the answers

Describe a scenario where understanding Sound Intensity Levels (SIL) would be crucial for protecting human health.

Understanding SIL is crucial in occupational safety, particularly in industries with high noise levels (e.g., construction, manufacturing). Monitoring and controlling noise exposure based on SIL measurements can prevent noise-induced hearing loss among workers. Signup and view all the answers

Explain how the ossicles contribute to sound amplification in the middle ear, detailing the mechanical advantage gained through their lever action.

The ossicles act as a lever, providing a mechanical advantage of approximately 2, effectively amplifying the force of the vibrations. Signup and view all the answers

Describe the role of the tympanic membrane and oval window in sound amplification, specifying how their difference in area contributes to this process.

The tympanic membrane has an area about 20 times larger than the oval window. This difference concentrates the force, resulting in a mechanical amplification by a factor of 20. Signup and view all the answers

What is the total mechanical amplification of sound pressure achieved by the middle ear at 3000 Hz, and how does this amplification affect the intensity of sound at the oval window?

The total mechanical amplification is about 80 times. Because intensity is proportional to pressure squared, the intensity at the oval window is amplified by a factor of approximately 6400. Signup and view all the answers

Explain how the ossicles transform sound vibrations as they pass from the tympanic membrane to the oval window.

The ossicles transform low force, high amplitude vibrations at the tympanic membrane into low amplitude, high force vibrations at the oval window. Signup and view all the answers

Describe the general structure of the cochlea and name the three key membranes found within it.

The cochlea is a snail-shaped, fluid-filled structure in the inner ear. The three key membranes are the basilar membrane, the tectorial membrane, and Reissner's membrane. Signup and view all the answers

Explain the 'place theory' of frequency detection in the cochlea, and specify which frequencies are detected at the base versus the apex of the basilar membrane.

Place theory states that different frequencies stimulate different locations along the basilar membrane. High frequencies are detected at the base, while low frequencies are detected at the apex. Signup and view all the answers

How does the varying stiffness of the basilar membrane contribute to the detection of different sound frequencies?

The basilar membrane exhibits different degrees of stiffness along its length, with the base being stiffer and more responsive to high frequencies, while the apex is more flexible and responsive to low frequencies. Signup and view all the answers

Outline the overall process of how sound waves entering the ear are eventually processed into frequency information within the cochlea.

Sound waves are amplified by the middle ear and then transmitted to the cochlea, where the basilar membrane vibrates according to frequency. Different locations on the membrane, corresponding to different frequencies, are stimulated, thus enabling frequency detection. Signup and view all the answers

Flashcards

Sound Intensity

Sound power per unit area, measured in W/m².

Decibel Scale

A logarithmic scale to measure sound intensity levels, using decibels (dB).