1. The Physics of Sound

2. The Nature of Sound
• SOUND is a longitudinal wave that is created by
vibrating objects that is capable of producing a sensation
in our auditory system.
• It is also called pressure wave because it consists of a
series of high pressure (compression) and low
pressure (rarefaction) regions.
• The audible range of sound frequency for humans is
from 20Hz – 20 000Hz. Sounds with frequencies below
20Hz are called infrasounds and the ones above
frequencies of 20 000Hz are called ultrasounds.

3. The Speed of Sound
• Since sound is a mechanical wave, then its
velocity is affected by the kind of medium that it
travels through.
• For every phase of matter, there is a
corresponding equation that describes the speed
of sound.
• through air: v = 331 + 0.6Tc
( Tc is temperature in C )
(in m/s)

4. Doppler Effect
The apparent change in pitch due to the
relative motion of the source and/or the
observer.

5. Characteristic of Sound
Sound may be described by 3 perceptual (as
perceived by human senses – auditory)
characteristics: pitch, quality, and loudness.
These 3 characteristics correspond to 3 physical
(scientific) characteristics: frequency,
waveform, and intensity.

6. Characteristics of Sound
Pitch
• PITCH refers to the highness or lowness of a
sound, and therefore depends on the frequency
of the sounding object. It is also related to the
wavelength and the energy that it carries.
high pitch -- high frequency -- short waves -- high energy
low pitch --- low frequency --- long waves --- low energy

7. Characteristics of Sound
Loudness
• This is scientifically described as sound
intensity, the greater the intensity, the louder
the sound, measured in decibels.
▫ Threshold of hearing – 0 db
▫ Threshold of pain – 120 db
• Sound Intensity ( I ) refers to the energy the
sound delivers to a unit area of a surface per unit
time.
▫ Proportional to amplitude
▫ Inversely proportional to distance from source

8. Characteristics of Sound
Quality
• QUALITY, a.k.a. timbre, is the property of a tone
that distinguishes it from another tone of the
same pitch and loudness produced by a different
musical instrument.
• It is described by the kind of waveform that
resulted from the impositions of its component
frequencies.

9. Sound as a Wave
• Refraction (bending) – sound bends due to temperature
difference
• Diffraction (scattering) –the sound wave scatters upon
passing through an opening
• Interference (meeting) – could be destructive or
constructive e.g. noise and sound
cancellation/reinforcement technology
• Reflection (bouncing) – reflection of sound is called an
ECHO, a series or multiple echoes is
REVERBERATIONS.

10. SONAR: Sound Navigation and Ranging

11. Altimeter (Altitude Meter)