3.0 ACOUSTIC PROPERTIES OF BUILDINGS
3.1 Introduction
Sound is caused by mechanical vibrations transmitted through a solid, liquid and gas
and travel as a wave.
The term acoustics can be used to describe the study of sound in general but the
subject of room acoustics is concerned with the control of sound within an enclosed
space. The general aim is to provide the best conditions for the production and the
reception of desirable sounds.
Building acoustics is the complex science of controlling noise in buildings. This
includes the minimisation of noise transmission from one space to another and the
control of the characteristics of sound within spaces themselves.
Building acoustics are an important consideration in the design, operation and
construction of most buildings, and can have a significant impact on health,
communication and productivity. They can be particularly significant in spaces such
as concert halls, recording studios, lecture theatres and so on, where the quality of
sound and its intelligibility are very important.
The general requirements for good acoustics are;
• Adequate levels of sound
• Even distribution to all listeners in the room
• Rate of decay (reverberation time) suitable for the type of room
• Background noise and external noise reduced to acceptable levels
• Absence of echoes and similar acoustic effects
3.1.1 Factors affecting building acoustics
Building acoustics can be influenced by:
▪ The geometry and volume of a space.
▪ The sound absorption, transmission and reflection characteristics of surfaces
enclosing the space and within the space.
▪ The sound absorption, transmission and reflection characteristics of materials
separating spaces.
▪ The generation of sound inside or outside the space.
▪ Airborne sound transmission. Airborne sound (or airborne noise) is sound that
is transmitted through the air. Typically, airborne sound might be generated
by: Speech, Television and radio, Animal sounds such as dogs barking and
Transport.
, ▪ Impact noise.
In most cases, the acoustics of a room will be satisfactory if a proper balance
between sound-absorbing and sound-reflecting materials is created. In achieving
this, reverberation as a factor should be taken into consideration.
Optimal control of noise in buildings can be achieved by understanding the basics of
how sound moves through solid objects and air. Building materials will have the
most impact on controlling sound in interiors, but strategic placement of absorptive
materials in finished areas can also be very effective.
3.2 The science of sound
Acoustics is the science of sound, including its production, transmission, and effects.
When we hear sound, it is actually our eardrums vibrating due to sound energy in
the air. Sound waves can travel through many different types of material, including
air, water, wood, and metals. The first part of understanding the science of sound
is finding the sound paths-sound's sources and modes of transmission.
There are two types of sound paths: airborne sound and structure-borne sound.
Airborne sound is what we hear when sounds radiate from a source directly into the
air. Examples emanating from a building's exterior include passing traffic, aircraft,
highway, and industrial noise.
On the interior of a building, depending on individual decibel levels, voices, music,
motors, machinery, and office equipment are often sources of airborne noise.
Another leading cause of unwanted interior airborne noise is conditioned airflow
through un-insulated HVAC ductwork.
Structure-borne sound, also known as "impact noise," is sound that travels through
solid building materials. Examples are the sound of footsteps on floors, door knocks
and slams, plumbing and mechanical equipment vibrations, and the impact of rain
on a building. Think of the disturbances created by steady rain on a metal roof over
a typically quiet building, such as a church or library, and one can understand what
a disruption structure-borne noise can be.
How is sound transmitted through a building?
Sound waves propagate, or spread, in three dimensions as expanding spheres of
pressure waves. Imagine blowing a soap bubble, and then another inside it, and then
another inside of the second, and so on, until they expand out infinitely through the
air.
Sound waves radiate directly around the source and decrease in amplitude, or
loudness, as they get farther from the source. Sound energy is reduced by half as
the distance from the source doubles.
, 3.2.1 Characteristics of sound
Period: the time required to complete a full cycle, T in seconds/cycle
Frequency: also known as pitch, is the number of cycles/sec. produced by a sound
wave generated by a sound source. Its unit of measurement is the hertz, and the
human hearing range is 16 to 20,000 Hz.
Amplitude: the maximum displacement from equilibrium A
Velocity of propagation: velocity is the distance moved per second in a fixed
direction
Wavelength: repeat distance of wave λ. It is the distance between the start and the
end of a sound-wave cycle. Amplitude could be referred to as loudness of sound.
The motion relationship "distance = velocity x time" is the key to the basic wave
relationship. With the wavelength as distance, this relationship λ = vT. Then using
f=1/T gives the standard wave relationship
3.2.2 Measuring Sound
To specify the strength of a sound, it is usually easiest to measure or describe some
aspect of its energy or its pressure.
3.2.2.1 Sound power
Sound power is the rate at which sound energy is produced at the source. It is
measured in watts. Sound power is a fundamental property of a sound source but it
is difficult to measure it directly.
3.2.2.2 Sound intensity
Sound intensity is the sound power distributed over unit area. It is a measure of the
rate at which energy is received at a given surface
3.1 Introduction
Sound is caused by mechanical vibrations transmitted through a solid, liquid and gas
and travel as a wave.
The term acoustics can be used to describe the study of sound in general but the
subject of room acoustics is concerned with the control of sound within an enclosed
space. The general aim is to provide the best conditions for the production and the
reception of desirable sounds.
Building acoustics is the complex science of controlling noise in buildings. This
includes the minimisation of noise transmission from one space to another and the
control of the characteristics of sound within spaces themselves.
Building acoustics are an important consideration in the design, operation and
construction of most buildings, and can have a significant impact on health,
communication and productivity. They can be particularly significant in spaces such
as concert halls, recording studios, lecture theatres and so on, where the quality of
sound and its intelligibility are very important.
The general requirements for good acoustics are;
• Adequate levels of sound
• Even distribution to all listeners in the room
• Rate of decay (reverberation time) suitable for the type of room
• Background noise and external noise reduced to acceptable levels
• Absence of echoes and similar acoustic effects
3.1.1 Factors affecting building acoustics
Building acoustics can be influenced by:
▪ The geometry and volume of a space.
▪ The sound absorption, transmission and reflection characteristics of surfaces
enclosing the space and within the space.
▪ The sound absorption, transmission and reflection characteristics of materials
separating spaces.
▪ The generation of sound inside or outside the space.
▪ Airborne sound transmission. Airborne sound (or airborne noise) is sound that
is transmitted through the air. Typically, airborne sound might be generated
by: Speech, Television and radio, Animal sounds such as dogs barking and
Transport.
, ▪ Impact noise.
In most cases, the acoustics of a room will be satisfactory if a proper balance
between sound-absorbing and sound-reflecting materials is created. In achieving
this, reverberation as a factor should be taken into consideration.
Optimal control of noise in buildings can be achieved by understanding the basics of
how sound moves through solid objects and air. Building materials will have the
most impact on controlling sound in interiors, but strategic placement of absorptive
materials in finished areas can also be very effective.
3.2 The science of sound
Acoustics is the science of sound, including its production, transmission, and effects.
When we hear sound, it is actually our eardrums vibrating due to sound energy in
the air. Sound waves can travel through many different types of material, including
air, water, wood, and metals. The first part of understanding the science of sound
is finding the sound paths-sound's sources and modes of transmission.
There are two types of sound paths: airborne sound and structure-borne sound.
Airborne sound is what we hear when sounds radiate from a source directly into the
air. Examples emanating from a building's exterior include passing traffic, aircraft,
highway, and industrial noise.
On the interior of a building, depending on individual decibel levels, voices, music,
motors, machinery, and office equipment are often sources of airborne noise.
Another leading cause of unwanted interior airborne noise is conditioned airflow
through un-insulated HVAC ductwork.
Structure-borne sound, also known as "impact noise," is sound that travels through
solid building materials. Examples are the sound of footsteps on floors, door knocks
and slams, plumbing and mechanical equipment vibrations, and the impact of rain
on a building. Think of the disturbances created by steady rain on a metal roof over
a typically quiet building, such as a church or library, and one can understand what
a disruption structure-borne noise can be.
How is sound transmitted through a building?
Sound waves propagate, or spread, in three dimensions as expanding spheres of
pressure waves. Imagine blowing a soap bubble, and then another inside it, and then
another inside of the second, and so on, until they expand out infinitely through the
air.
Sound waves radiate directly around the source and decrease in amplitude, or
loudness, as they get farther from the source. Sound energy is reduced by half as
the distance from the source doubles.
, 3.2.1 Characteristics of sound
Period: the time required to complete a full cycle, T in seconds/cycle
Frequency: also known as pitch, is the number of cycles/sec. produced by a sound
wave generated by a sound source. Its unit of measurement is the hertz, and the
human hearing range is 16 to 20,000 Hz.
Amplitude: the maximum displacement from equilibrium A
Velocity of propagation: velocity is the distance moved per second in a fixed
direction
Wavelength: repeat distance of wave λ. It is the distance between the start and the
end of a sound-wave cycle. Amplitude could be referred to as loudness of sound.
The motion relationship "distance = velocity x time" is the key to the basic wave
relationship. With the wavelength as distance, this relationship λ = vT. Then using
f=1/T gives the standard wave relationship
3.2.2 Measuring Sound
To specify the strength of a sound, it is usually easiest to measure or describe some
aspect of its energy or its pressure.
3.2.2.1 Sound power
Sound power is the rate at which sound energy is produced at the source. It is
measured in watts. Sound power is a fundamental property of a sound source but it
is difficult to measure it directly.
3.2.2.2 Sound intensity
Sound intensity is the sound power distributed over unit area. It is a measure of the
rate at which energy is received at a given surface
