1. Chapter 16 – Waves and Sound

2. 16.1 – The Nature of Waves
A wave is a traveling disturbance that carries energy.
Longitudinal Wave – disturbance is // to wave direction (compression); sound.
Transverse Wave – disturbance is ┴ to wave direction (up and down); light, vibrating strings.

4. 16.2 – Periodic Waves
Period (T) -
time required for 1 cycle (sec)
Frequency (f) -
number of waves per unit time (Hertz or Hz)
Wavelength (λ) -
length of the wave (m)
Amplitude (A) –
max. displacement during a cycle (m)

5. The speed of a wave (v) is determined by dividing the wavelength by its period.
Remember that

6. 16.3 – SKIP
16.4 – SKIP
16.5 – The Nature of Sound
Sound – L-wave created by a vibrating object; needs a medium (solid, liquid, gas) for the disturbance to travel.

7. Sound is NOT a mass movement of air, the air molecules are in SHM

8. Threshold of hearing = 10-12 W/m2
16.6 – SKIP
16.7 – Sound Intensity
Sound waves carry energy that can do work.
POWER = Energy/Time [Joule/sec] = [Watt]
Sound Intensity (I) – Power/Area [Watt/m2]
Threshold of hearing = W/m2

9. 16.8 – Decibels (dB) The ear responds to sound in a logarithmic way.
Intensity Level (β) – compares sound intensity to a reference level; logarithmic ratio.

10. Ex. 70 dB is twice as loud as 60 dB.
A 1-dB change in intensity level is smallest change noticeable by humans.
When intensity level increases by 10 dB, the new sound seems ~ 2X louder.
Ex. 70 dB is twice as loud as 60 dB.
REVIEW of TERMS…
Power – [Watt], Intensity – [Watt/m2]
Intensity Level – [dB], Loudness - subjective

11. Sound Pressure Level Lp dBSPL Sound Pressure p N/m2 = Pa
Table of sound levels L and corresponding sound pressure and sound intensity
Examples
Sound Pressure Level Lp dBSPL
Sound Pressure p N/m2 = Pa
Sound Intensity I W/m2
Jet aircraft, 50 m away
140
200
100
Threshold of pain
130
63.2 10
Threshold of discomfort
120 20 1
Chainsaw, 1m distance
110
6.3
0.1
Disco, 1 m from speaker 2
0.01
Diesel truck, 10 m away
  90
0.63
0.001
Curbside of busy road, 5 m
  80
0.2
0.0001
Vacuum cleaner, distance 1 m
  70
0.063
Conversational speech, 1m
  60
0.02
Average home
  50
0.0063
Quiet library
  40
0.002
Quiet bedroom at night
  30
Background in TV studio
  20
0.0002
Rustling leaf
  10
Threshold of hearing
    0

12. ASSIGN: Chapter 16 # 8, 51, 63, 66; Page 489 Due
Do your homework, kid

13. 16.9 – The Doppler Effect
The observed frequency (pitch) of a sound increases as the sound comes closer; lowers as sound moves away.

14. 16.9 – The Doppler Effect

15. 16.10 – SKIP
16.12 – SKIP

16. 16.11 – The Sensitivity of the Human Ear
The ear can respond to sounds within the 20 to 20 kHz range.
The ear is most sensitive to sounds b/w 1-5 kHz
Most alarms (and screams) are near the 1-5 kHz range.
Did human speech evolve to match the frequency band the ear is most sensitive to OR did the ear evolve to be sensitive to the frequency band humans mostly speak at – OR is it all just a coincidence???

17. Fletcher-Munson Curve

18. dBA – weighted dB scale that approximates human sensitivity to different frequencies.