musical acoustics chapter 1 what is sound? the science of sound
Post on 20-Dec-2015
237 views
TRANSCRIPT
![Page 1: MUSICAL ACOUSTICS Chapter 1 What is Sound? The Science of Sound](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d415503460f94a1bd09/html5/thumbnails/1.jpg)
MUSICAL ACOUSTICS
Chapter 1
What is Sound?
The Science of Sound
![Page 2: MUSICAL ACOUSTICS Chapter 1 What is Sound? The Science of Sound](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d415503460f94a1bd09/html5/thumbnails/2.jpg)
EXAMPLES OF WAVES
Longitudinal waves (air molecules) in a sound wave created by a loudspeaker.
Transverse waves on a rope shaken up and down at one end.
![Page 3: MUSICAL ACOUSTICS Chapter 1 What is Sound? The Science of Sound](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d415503460f94a1bd09/html5/thumbnails/3.jpg)
VIBRATING BODIES drum head
air column of a trumpet air in the vocal tract piano soundboard CHANGING AIRFLOW vocal folds opening and closing lips of a brass player siren TIME-DEPENDENT HEAT SOURCE electric spark lightning SUPERSONIC FLOW ”crack” of a rifle bullet sonic “boom”
SOME SOURCES OF SOUND
![Page 4: MUSICAL ACOUSTICS Chapter 1 What is Sound? The Science of Sound](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d415503460f94a1bd09/html5/thumbnails/4.jpg)
EXAMPLES OF SOUND SOURCES
(d)
Vibrating drumheadcauses pressure Changes In the air nearby
Holes in a rotatingsiren alternately pass and stop an air stream
Explosion rapidlyHeats the air nearby
Supersonic airplane creates shock waves
![Page 5: MUSICAL ACOUSTICS Chapter 1 What is Sound? The Science of Sound](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d415503460f94a1bd09/html5/thumbnails/5.jpg)
Curves of uniform and
changing motion
Shrinking Δy and Δt to obtain instantaneous
speed
Speed as a function of time
GRAPHICAL REPRESENTATION
OF MOTION
![Page 6: MUSICAL ACOUSTICS Chapter 1 What is Sound? The Science of Sound](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d415503460f94a1bd09/html5/thumbnails/6.jpg)
Stroboscopic observation of motion:
Constant speed
Increasing speed
Constant speed Increasing speed
![Page 7: MUSICAL ACOUSTICS Chapter 1 What is Sound? The Science of Sound](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d415503460f94a1bd09/html5/thumbnails/7.jpg)
DISTANCE BETWEEN TWO POINTS IN A COORDINATE SYSTEM
![Page 8: MUSICAL ACOUSTICS Chapter 1 What is Sound? The Science of Sound](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d415503460f94a1bd09/html5/thumbnails/8.jpg)
MOTION
![Page 9: MUSICAL ACOUSTICS Chapter 1 What is Sound? The Science of Sound](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d415503460f94a1bd09/html5/thumbnails/9.jpg)
FORCE – can be described as a “push” or a “pull”
Applying a force may result in a distortion, an acceleration, or both
Acceleration is proportional to force: a F
Newton’s second law of motion: a=F/m (or F=ma)
The force of gravity (W) produces an acceleration (9) W=mg (compare F= ma) g=9.8 m/s2 (≈10m/s=2)
Don’t confuse Force and PressurePressure = Force/Area
![Page 10: MUSICAL ACOUSTICS Chapter 1 What is Sound? The Science of Sound](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d415503460f94a1bd09/html5/thumbnails/10.jpg)
VIBRATORY MOTIONin which y, v, and a all change with
time
![Page 11: MUSICAL ACOUSTICS Chapter 1 What is Sound? The Science of Sound](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d415503460f94a1bd09/html5/thumbnails/11.jpg)
PRESSURE and BUOYANCY
PRESSURE in a containerof fluid: (a) acts on all surfaces; (b) is proportional to depth.
BUOYANT FORCE (dashed arrow) on the immersedobject is due to the excess upward force.
![Page 12: MUSICAL ACOUSTICS Chapter 1 What is Sound? The Science of Sound](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d415503460f94a1bd09/html5/thumbnails/12.jpg)
BUOYANCY OF ICE
![Page 13: MUSICAL ACOUSTICS Chapter 1 What is Sound? The Science of Sound](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d415503460f94a1bd09/html5/thumbnails/13.jpg)
![Page 14: MUSICAL ACOUSTICS Chapter 1 What is Sound? The Science of Sound](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d415503460f94a1bd09/html5/thumbnails/14.jpg)
GRAPHICAL REPRESENTATION OF A SOUND WAVE
![Page 15: MUSICAL ACOUSTICS Chapter 1 What is Sound? The Science of Sound](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d415503460f94a1bd09/html5/thumbnails/15.jpg)
WORK AND ENERGY
WORK is average FORCE times DISTANCE moved parallel to the force
W=Fd
If an object with weight mg falls a DISTANCE h, the WORK done by gravity is W=mgh
A baseball moving at speed v has KINETIC ENERGY KE=1/2mv²
An object lifted to a height h above the floor has POTENTIAL ENERGY PE=mgh
![Page 16: MUSICAL ACOUSTICS Chapter 1 What is Sound? The Science of Sound](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d415503460f94a1bd09/html5/thumbnails/16.jpg)
POWER
POWER IS ENERGY (or WORK) DIVIDED BY TIME P=W/t
ENERGY IS EXPRESSED IN JOULES (J)
POWER IS EXPRESSED IN WATTS (W)
1 watt = 1 joule/second
![Page 17: MUSICAL ACOUSTICS Chapter 1 What is Sound? The Science of Sound](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d415503460f94a1bd09/html5/thumbnails/17.jpg)
UNITS
The preferred system (used all over the world) is the SI (Système International) or mks (meter-kilogram-second) system.
Besides the three basic units (meter, kilogram, second) the system includes such units as newtons, joules, watts, pascals, hertz, etc. which are derived in a logical manner from the basic units.
newtons (force)
energy (joules)
power (watts)
pressure (pascals)
freqency (hertz)