Chapter 10: Sound and the Ears

Question 1

Physical characteristics of sound

Answer 1

• The physical stimulus for hearing is a change in the pressure of the surrounding medium (usually air, but could be any fluid)
• Pressure change achieved with any vibrating surface
• Molecules of air alternately compressed and released

Question 2

Three physical dimensions of a sound wave

Answer 2

• Frequency/pitch
• Amplitude/loudness
• Complexity of waveform/timbre

Question 3

Frequency/pitch

Answer 3

How many cycles in a unit of time (measured in Hertz(Hz))
inverse of wavelength
Human hearing ranges from 20 to 20,000 HZ

Question 4

Amplitude & Loudness

Answer 4

-We are sensitive to a very wide range of sound amplitudes between threshold for detection and threshold for pain
-If we wish to talk about sound pressure efficiently, we need a simple unit of measurement
-For this reason the decibel unit was developed
-This unit is unusual in that it is not an absolute value, but a ratio of two sound levels
(why use ratios? - recall that ratios may better describe our ability to discriminate sensory stimuli

Question 5

dBSPL

Answer 5

decibels of sound pressure level: SPLreference is taken as 20 micropascals, a value that is very close to the normal absolute threshold of hearing
converts a range of 0.0002 (threshold) to 2000 (jet take-off) to a range of 0 to 140 dB

Question 6

Calculating Decibels

Answer 6

• 20 dB = 10x increase in sound pressure
• 100 dB = 100, 000 x more intense
• how many decibels for a doubling in sound pressure? 6

Question 7

Noise induced hearing loss above?

Answer 7

85 decibals

Question 8

Equal loudness contour

Answer 8

Curve showing the amplitude of tones at different frequencies that sound about equally loud


Question 9

Phon

Answer 9

A unit of loudness

Question 10

Timbre, Waveform or Complexity

Answer 10

Quality of the sound
consequence of the complexity of the wave
Fourier analysis
Fourier spectrum

Question 11

Fourier analysis

Answer 11

A mathematical procedure for decomposing a complex waveform into a collection of sine waves with various frequencies and amplitudes.

Question 12

Fourier spectrum

Answer 12

A depiction of the amplitudes at all frequencies that make up a complex waveform.

Question 13

Fundamental frequency

Answer 13

The frequency of the lowest-frequency component of a complex waveform; determines the perceived pitch of the sound.

Question 14

We’re best at what frequency of sound?

Answer 14

3000-5000Hz critical to human conversation.