Vibrations 2 - 230508

Question 1

What is a sound?

Answer 1

A vibration that can be detected by human ears.

Question 2

Two parameters to measure a sound

Answer 2

Particle velocity (oscillations within the position).
Speed of sound (velocity of propagation).
Sound pressure

Question 3

What’s sound pressure level?

Answer 3

20 log (p/p_ref)
p_ref = 20 uPa, (weakest sound pressure that the ear can hear at 1000 Hz) = 0 dB (not that there’s no sound at all)

Question 4

Threshold of pain

Answer 4

120 dB, 140 dB
quiet forest= 15 dB (not really 0 dB, not practically possible)
plane = 120 dB

Question 5

HOW to add two sound levels?

Answer 5

Not possible to do it in dB base, since it’s a logarithmic scale.

Question 6

3dB

Answer 6

sensitivity of human ear, no change smaller than 3dB can be detected

Question 7

Addition of two sound levels

Answer 7

If there’s a strong sound and a soft one, you’ll only hear the strong one, no change in the overall perception (DO THE NUMBERS).

Question 8

Where does the spatial wave equation come from?