1. SOUND a range of compression wave frequencies to which the
human ear is sensitive

2. 1. reeds 3. membranes 2. strings 4. air columns
Sounds are produced by vibrating matter.
1. reeds
3. membranes
2. strings
4. air columns
Sound is a mechanical wave (longitudinal).
It will not travel through a vacuum.

3. PITCH = The impression about the frequency of Sound
high pitched – high frequency (ex: piccolo)
low pitched – low frequency (ex: fog horn)
The frequency range for normal human hearing is between 20 Hz and 20,000 Hz (for younger people, older people lose the higher frequencies)
Infrasonic or subsonic = Sounds below 20 Hz
Ultrasonic = frequencies above 20,000 Hz

4. Range of Some Common Sounds

5. Intensity Range for Some Common Sounds

6. Compression waves travel through air or along springs.
These waves travel with
areas of compression and rarefaction.
The medium does not travel from one place to another, but the pulse that travels.

7. Sound wave requires medium
Any matter will transmit sound, whether it is a solid, liquid or a gas.
However; sound cannot travel through a vacuum.
No Sound
DING
VACUUM

8. The velocity of sound in air depends
on the air temperature. The speed of
sound in dry air is m/s at 0 ºC.
This speed
increases
with temperature: about 0.6 m/s
for every 1 ºC increase in temperature.

9. Speed of Sound
The speed of sound in dry air at 00 C is about m/sec. (1200 km / hr) [or ~ .000,001 x the speed of light of 300,000 km / sec]
So air at room temperature (~20oC) is ~340 m/sec.
QUESTION : How far away was the strike if there is a 3 second delay between the lightning flash and the sound of the thunder?
340 m/sec x 3 sec = m, over 1 km (~2/3 mile) away

10. Sound generally travels fastest in solids and slowest in gases,
but there are some exceptions.
Medium Velocity (m/s) Medium Velocity (m/s)
Air Carbon dioxide 260
Helium Hydrogen 1270
Oxygen Water 1460
Sea water Mercury 1450
Glass Granite 5950
Lead Pine wood 3320
Copper Aluminium 5100

11. Speed of Sound
The speed of sound in a material does NOT depend on its density (mass per unit volume [g/cm3 ]).
The speed of sound in a material DOES depend on the elasticity of a material.
Elasticity = the ability of a material to change shape in response to an applied force, then resume its original shape when the force is removed.
Steel is elastic, putty is inelastic.
Sound travels 15 times faster in steel than in air and about 4 times faster in water than in air.

12. LOUDNESS
The intensity of a sound is proportional to the square of the amplitude of the sound wave. (i = ka2)
Loudness is measured in decibels (dB)
The decibel scale is logarithmic, increasing by factors of 10
AMPLITUDE
MICROPHONE
VIBRATING
LOUDSPEAKER
OSCILLOSCOPE

13. LOUDNESS TABLE of Loudness Levels SOURCE OF SOUND LEVEL (dB)
Jet Engine (from 30 m)
Threshold of pain
Loud rock music
Old subway train
Average factory
Busy street traffic
Normal speech
(Shshshshhh!) A library
Close Whisper
Normal breathing
Hearing threshold

14. Forced Vibration
Sounding boards are used to augment (increase) the volume (amplitude) of a vibrating object (like a string).
STRINGS
SOUNDING
BOARD

15. Natural Frequency
Everything vibrates, from planets and stars to atoms and almost everything in between.
A NATURAL FREQUENCY is one at which minimum energy is required to produce forced vibrations
and also requires the least amount of energy to continue this vibration

16. Resonance
Resonance – when the frequency of a forced vibration on an object matches the object’s natural frequency, a dramatic increase in amplitude of the vibrations occurs.
For example, a swing, or the hollow box parts of musical instruments are designed to work best with resonance.
In order to resonate, an object must be elastic enough to return to its original position and have enough force applied to keep it moving (vibrating)

17. closed-pipe resonator
A resonant air column is
simply a standing longitudinal
wave system, much like
standing waves on a string.
closed-pipe resonator
tube in which one end is open
and the other end is closed
open-pipe resonator
tube in which both ends
are open

18. l = {(1,3,5,7,…)/4} * l A closed pipe resonates when the length
of the air column is approximately
an odd number of quarter
wavelengths long.
l = {(1,3,5,7,…)/4} * l
With a slight correction for tube diameter,
we find that the resonant wavelength of a
closed pipe is given by the formula:
= 4 (l + 0.4d),
where  is the wavelength of sound,
l is the length of the closed pipe,
and d is the diameter of the pipe.

19. l = {(2,4,6,8,…)/4} * l An open pipe resonates when the length
of the air column is approximately
an even number of quarter
wavelengths long.
l = {(2,4,6,8,…)/4} * l
With a slight correction for tube diameter,
we find that the resonant wavelength of an
open pipe is given by the formula:
= 2 (l + 0.8d),
where  is the wavelength of sound,
l is the length of the closed pipe,
and d is the diameter of the pipe.

20. Interference
Sound waves interfere with each other in the same way as all waves.
Constructive interference - augmentation
Destructive interference - cancellation

21. Beats
BEATS - A periodic variation in the loudness of sound (faint then loud, faint then loud and so on … )
What is the frequency when a 262 Hz and a 266 Hz tuning fork are sounded together ?
The 262 Hz and 266 Hz forks will produce beats per sec. and the tone heard will be half way between at 264 Hz as the ear averages the frequencies.