Hearing 1: sound & function of external Ear

Question 1

What is sound, and how is it produced?

Answer 1

Definition: Sound is a stimulus for hearing.
Production: It is produced by a vibrating object causing alternating compression and rarefaction in the medium.

Question 2

Describe the theoretical representation of sound in wave form.

Answer 2

Sound is theoretically represented in a wave form with alternating peaks and bottoms.

Question 3

In what order does sound travel at different velocities?

Answer 3

Sound travels at higher velocity in solids > water > liquid and has zero velocity in a vacuum.

Question 4

Explain the movement of air particles in a sound wave.

Answer 4

A sound wave does not cause any net flow of air in the direction of motion. The air particles move to and fro around their main position.

Question 5

List the characteristics of a sound wave.

Answer 5

a. Wavelength: Distance between two successive peaks or bottoms.
b. Frequency (Pitch): Measured in Hertz (Hz), correlating with the pitch of the sound.
c. Amplitude (Intensity): Subjective correlate of loudness, measured in decibels (dB).

Question 6

What is the unit of intensity for sound, and how is it measured?

Answer 6

Unit: Decibel (dB) = 0.1 bel.
Measurement: P_sound = the pressure of the sound stimulus, and Pspl = sound pressure level at the threshold for human hearing.

Question 7

Define the threshold of hearing and provide examples of sound levels.

Answer 7

Threshold of Hearing: Standard sound reference level.
Examples:
Talking or whisper: 25 dB
Normal conversation: 40 dB
Traffic noise: 60 dB
Pneumatic drill: 80 dB
Jet plane: 100 dB
Painful, damaging to auditory receptors: > 140 dB

Question 8

List the functions of the external ear.

Answer 8

Collection of sound stimuli.
Increase sound pressure at the tympanic membrane.
Sound localization, mainly through higher cortical interactions.
Protective function:
A. Secretion of wax with bactericidal effect.
B. Maintenance of moist, near-body temperature air in the external canal.
Function of the tympanic membrane: transmission of vibrations from outside to the middle ear.

Question 9

Describe the characteristics of the tympanic membrane.

Answer 9

A. Elastic
B. Tense
C. Aperiodic (no natural frequency)
D. Damping: Stops vibrations when the sound stops, rate of vibrations = rate of sound frequency (acts as a resonator).