Chapter 16 – Waves and Sound
16.1 – The Nature of Waves
A wave is a traveling disturbance that carries energy.
Transverse Wave – disturbance is ┴ to
wave direction (up and down); light, vibrating strings.
Longitudinal Wave – disturbance is // to wave direction (compression); sound.
16.2 – Periodic Waves
time required for 1 cycle (sec)
number of waves per unit time (Hertz or Hz)
length of the wave (m)
max. displacement during a cycle (m)
Period (T) -
Frequency (f) -
Wavelength (λ) -
Amplitude (A) –
The speed of a wave (v) is determined by dividing the wavelength by its period.
v fT
1fT
Remember that
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.
Sound is NOT a mass movement of air, the air molecules are in SHM
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 = 10-12 W/m2
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.
0
(10 dB) logI
I
2
0
-12 Wm
Sound Intensity
= Sound Intensity of Reference Level
(often 10 )
I
I
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
Table of sound levels L and correspondingsound pressure and sound intensity
ExamplesSound PressureLevel Lp dBSPL
Sound Pressure pN/m2 = Pa
Sound Intensity IW/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 100 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 0.00001
Conversational speech, 1m 60 0.02 0.000001
Average home 50 0.0063 0.0000001
Quiet library 40 0.002 0.00000001
Quiet bedroom at night 30 0.00063 0.000000001
Background in TV studio 20 0.0002 0.0000000001
Rustling leaf 10 0.000063 0.00000000001
Threshold of hearing 0 0.00002 0.000000000001
ASSIGN:
Chapter 16 # 8, 51, 63, 66;
Page 489
Due
Do your homework, kid
16.9 – The Doppler Effect
The observed frequency (pitch) of a sound increases as the sound comes closer; lowers as sound moves away.
16.9 – The Doppler Effect
16.10 – SKIP
16.12 – SKIP
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???
16.11 – The Sensitivity of the Human Ear
Fletcher-Munson Curve
dBA – weighted dB scale that approximates human sensitivity to different frequencies.