Week 07 Audiometry Lab

Question 1

What is intensity in relation to sound?

2 equations

Answer 1

an objective measurement of the average power (P) of sound incident perpendicular to to surface area (A) … unit of W/m²

J = P/A

can also be the square of effective pressure (P_eff) over acoustic impedance (Z)

J = P_eff²/Z

Question 2

What is loudness?

What does it depend on?

Answer 2

• a subjective psychophysical quantity representing how loud we feel** **a sound of given intensity
• depends on **frequency **and intensity

Question 3

What equation determines loudness?

What is its unit and how does it relate to “loudness level” units?

Answer 3

Stevens’ Law:

L_son = 1/16 (J/J₀)^0.3

(AKA power law)

• unit is sone
• 40 phon = 1 sone
• sone/loudness doubles every 10 phon increase
  
  • ​ex: 50 phon = 2 sone, 60 phon = 4 sone

Question 4

How is the speed of sound waves calculated?

What is the speed of sound in air?

Answer 4

speed (c) is product of wavelength and frequency

c = λ ⋅ f

C_{sound in air} is approx. 340 m/s

Question 5

What is loudness level?

What is its unit?

Answer 5

a comparitive and subjective measurement of a pure tone of any frequency that is equal to the dB of a sound at 1,000 Hz that is perceived as just as loud

L_phon = J_{dB 1000Hz}

• measured in phon

Question 6

What graph shows the dependence of loudness on frequency and intensity?

Explain it and draw it.

Answer 6

equal loudness curve (AKA Fletcher-Munson curve)

• a intensity vs. frequency graph (normal y-axis, log x-axis) with isophon (equal loudness) curves showing sounds of the same loudness level

Question 7

What kind of wave is sound?

How does it oscillate?

Answer 7

• sound is a mechanical wave which results from a periodic variation in pressure
• it requires a medium and cannot exist in vacuum
• sound waves are longitudinal waves which oscillate in the same direction of their propagation

Question 8

What is the dependence of the speed of sound on medium density?

Temperature?

Answer 8

• a denser medium results in a faster propagation
  ex: C_air = 340 m/s, C_water = 1,484 m/s
• in a gaseous medium (such as air), higher temperature results in faster propagation

(despite a decreasing density with increasing temp.??? still don’t really get this)

Question 9

What does 0 phon correspond to?

How has the significance of 0 phon changed over time?

What does 130 phon correspond to?

Answer 9

• 0 phon is the hearing threshold or minimum audible loudness
• because of increased exposure to loud noises, the hearing threshold has actually increased to approx. 4 phon
• 130 phon is the threshold of pain

Question 10

What is reference intensity?

Answer 10

the sound intensity that can just be heard at the reference frequency of 1,000 Hz

• written as J₀
• determined to be J₀= 10^-12 W/m²

or

0 dB

Question 11

What is the reference sound?

Answer 11

a harmonic sound wave of 1,000 Hz used as a reference in audiometry

Question 12

What is sound pressure?

Answer 12

a harmonic pressure variation superposed on the equilibrium pressure of its medium (p_atm)

p(t) = p₁ sin(ω₀t)

Question 13

How is hearing loss calculated?

What is its unit and why?

Answer 13

loss = measured hearing threshold - normal hearing threshold

• measured in dB because phon and sone apply only to healthy individuals