Physics of Musical Sound
Sound as Physical Motion
- Pressure--Pascals or Nm-1
- Density--kg m-3
- Velocity--m s-1
- Force--Newtons or kg m s-2
- Frequency--Hertz or Cycles per Second
- Loudness--decibels (dB) or sones
Sound as Music
- Rhythm--note values, time signatures
- Melody--sequence of sounds
- Harmony--relationships between sounds
- Intervals--relationships between notes
- Musical Notation
- Pitched and Unpitched sounds
- Scales and Tunings
Sound as Wave Motion
- Superposition--Beats, Interference,
Sound Perception and Acoustics
- Timbre--a fancy term for tone color
- Loudness--not as simple as it seems
- Just Noticeable Differences--volume and
- Reverberation--direct and indirect
- What Makes a Good Concert Hall?
Sources of Musical Sound
- Source of Energy--beat, pluck, blow
- Vibrator--generates the actual tone
- Resonator--amplifies, spreads, colors
- Pitch, Repetition, and Harmonic
- Plucked, Struck, and Bowed Strings
- Blown Pipes
- Faraday's Law
- Lorentz Force Law
- Tape Recording
- CD recording
- Hard/Floppy Disks
Physical Quantities we Need
- The normal everyday quantity that measures
how far apart two things are.
- Unit the Metre or Meter. 1m = 39+inches
- actually defined by the distance light
travels in a given length of time
- combines ideas of speed (how fast) and
direction into 1 quantity
- defined as distance traveled /time
- units metres per second, m
- important to us because sound travels at a
fixed speed of about 300ms-1
- how fast velocity changes
- defined as change in velocity/time
- units m s-2
- always caused by a force. We cannot feel
distance or velocity but we can feel a force and
so we can feel acceleration--rollercoaster.
- Most common is accel. due to gravity,
- a push or a pull, just what we usually
- Units Newtons. 1N = 1 kg m
- I.e. 1N will give a mass of 1kg an
acceleration of 1m s-2.
- Newton's First Law says that unless there is
a force then a body will stay still or move at
constant velocity for ever.
- Forces needed to make air move and give us
sound. Need to think where they come from.
- When you push something you do work.
- Defined as Force x Distance moved in
direction of force.
- Units Joules. 1J = 1N m = 1kg m2 s-2.
- Don't need it very often but it is a
fundamental quantity. Anything we do that is
useful requires work!
- The ability to do work or a measure of the
- Units are same as work, Joules.
- First Law of Thermodynamics says that the
Work done by a system is equal to the energy
that is lost from the system.
- We can detect sound only because of the
energy that the sound carries and we will
usually express the strength of sound using
- The rate at which work is done.
- Unit Watts. 1Watt = 1Joule per second = 1J
- Power is particularly important for sound.
Sound is a continuous process. If we look at one
plane in space then, as the sound goes by,
energy flows through the plane and we have a
power associated with the sound.
- We usually measure the strength of a sound
in energy/area/time or
W/m2/s or W m-2 s-1.
Numbers in Physics
- Enormous range of physical quantities
- energy in detectable sound ranges from about
1000W/m2 to 0.000000000001W/m2 a
range of 1,000,000,000,000,000:1
- Express in Scientific Notation
- pull out powers of 10 to express as a small
number x a power of ten.
- numbers less than 1 are expressed with