Understanding Sound Waves: Intensity, Frequency, and Quality, Slides of Architecture

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Acoustics and

sound insulation

GENERAL INTRODUCTION

 Sound is generated in the air when a surface is vibrated.  The vibrating surface sets up waves of compression and rarefaction.

 To understand it let us take example of tuning fork

GENERAL INTRODUCTION

• As a tuning fork's prongs move apart because of a vibration.
• The molecules ahead of it are crowded together.
• They look like they are being pushed together. They bump each other.

GENERAL INTRODUCTION

• As the tuning fork's prongs come back together, it leaves a region that has fewer molecules than usual.
• The region of a sound wave in which the molecules are crowded together is a compression.
• The region of a sound wave in which particles are spread apart is a rarefaction.

GENERAL INTRODUCTION

 And these compression and rarefactions sets the

ear drum vibrating.

 The movements of ear drum are translated by the

brain into sound sensation.

 So, we really don't hear with our ears - we hear

with our brains!

GENERAL INTRODUCTION

Shape (dish

type) of the

outer ear is

helpful in

receiving

sound waves.

GENERAL INTRODUCTION

 Which carry the vibrations to a fluid-filled tube

called the cochlea in the INNER EAR

 The fluid inside the cochlea vibrates a series of

tiny hairs called cilia, which are attached to

auditory nerves.

 The movement of these cilia stimulates the

nerves.

 And they send signals to the brain, which, in

turn, processes these signals into the sounds we

hear.

GENERAL INTRODUCTION

Intensity and loudness of sound

 Intensity of the sound is defined as the amount or

flow of wave energy crossing per unit time

through a unit area taken perpendicular to the

direction of propagation.

 Intensity of sound is purely a physical quantity

which can be accurately measured and is

independent of the ear of the listener.

Intensity and loudness of sound

 Loudness of a sound corresponds to the degree of sensation depending upon the intensity of sound and sensitivity of ear drums.  It may also happen that the same listener might give different judgments about the loudness of sound of the same intensity but of different frequencies as the response of the ear is found to vary with the frequency of vibration.

Frequency and pitch of sound

 The audio range falls between 20 Hz and 20,000 Hz. This range is important because its frequencies can be detected by the human ear.  A frequency is expressed in terms of Hz(Hertz) and it determines pitch of sound source. They can be categorized as:  Low tones –sound of urban road traffic.  Mild tones –sound of piano notes.  High tones –sound of single tea kettle.

Quality or timbre of sound.

 The quality of sound is that characteristics which enables us to distinguish between two notes of the same pitch and loudness played on two different instruments or produced by two different voices.

 It is to be noted that it is that tonal quality which enables us to recognize a large number of different sounds.

The behavior of sound propagation

 The viscosity of the medium also affects the

motion of sound waves.

 It determines the rate at which sound is

attenuated.

 For many media, such as air or water, attenuation

due to viscosity is negligible.

 Sound cannot travel through a vacume.

The behavior of sound propagation

 It travels much faster in solids and liquids then in

air.

 The velocity of sound in atmospheric air at 20

degree centigrade is 343 meter per second.

 The velocity of sound in pure water is 1450 meter

per second.

 The velocity of sound in bricks is 4300 meter per

second.

 The velocity of sound in concrete is 4000 meter

per second.