Ch. 3: Sound and Its Measurement

Question 1

Sound Waves

Answer 1

• The succession of molecules being shoved together and then pulled apart set up a motion called waves.
• Waves through the air are made up of compressions and rarefactions (see Fig 3.1)

Question 2

Compression

Answer 2

Molecules are compressed

Question 3

Rarefaction

Answer 3

Molecules are spread apart

Question 4

Frequency

Answer 4

• The number of complete sine waves that occur in one second makes up the frequency of that wave
• If it takes one second to go through the whole cycle, then the frequency is said to be one cycle per second
  
  • If you think of a pendulum, when it goes from still to the far right and swings through the original position to the far left and back to the point of origin can be considered “one cycle”
• The unit of measurement for frequency is hertz (Hz) which is cycles per second
  
  • The time required for each cycle is called the period

Question 5

Intensity

Answer 5

• Intensity is how far an object vibrates
• The intensity of a sound wave is the amount of force per unit of area
  
  • When vibrating bodies move to and fro, a certain amount of force is exerted on adjacent molecules
  • The greater the force, the greater the displacement of the molecules
• Intensity is measured in decibels (dB)
  
  • The decibel is a ratio, uses a logarithm, is a relative unit of measure, and may be expressed in various reference levels (which must be specified)

Question 6

What are the psychological correlates to the physical properties of sound?

Answer 6

Loudness

Pitch

Question 7

What are complex sounds and how do they differ from pure tones (not too specific)?

Answer 7

Complex Sounds - Most sounds contain a number of different frequencies, amplitudes, and phase relationships

Pure tones only vibrate with one frequency and does not have overtones

Question 8

How are frequency and intensity expressed (their units of measurement)?

Answer 8

Frequency - hertz (Hz)

Intensity - decibels (dB)

Question 9

What do the descriptors behind dB represent and why are they needed (SL, SPL, HL)?

Answer 9

dBSL - Sensation Level

dBSPL - Sound Pressure Level

dBHL - Hearing level

Audiologists are more accustomed to making measurements according to what they are using the data for rather than intensity terms