WK9 Acoustic Comfort and Sound Insulation Principles

Acoustic Comfort

A concept that can be characterized by absence of unwanted sound and opportunities for acoustic activities without annoying other people.

Room Acoustics

Room acoustics is concerned with the control of sound within an enclosed space.

General Acoustic Requirements

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 defects.

Speech Reception

The overall requirement for the good reception of speech is that the speech is intelligible, depending upon the power and the clarity of the sounds.

Music Acoustic Requirements

Music consists of a wide range of sound levels and frequencies which all need to be heard, with qualities including fullness of tone, definition of sounds, blend of sounds, and balance of sounds.

Multi-purpose Auditoria

These auditoria have multi requirements of music and speech, which leads to compromises in design.

Sound Paths

A sound path is the directional track made by the wave vibrations as they travel through a material such as air.

Reflection

Sound is reflected, and reflecting surfaces in a room are used to help the even distribution of sound and to increase the overall sound levels by reinforcement of the sound waves.

Echoes

An echo is a delayed reflection that can cause blurring and confusion of the original sound, with a risk if a strong reflection is received later than 1/20th second (50 ms) after the reception of the direct sound.

Sound Transmission

The behaviour of sound paths inside an enclosed space can be affected by reflection, absorption, transmission, and diffraction.

Acoustic Design of Auditoria

The acoustic design of auditoria is particularly important, with detailed acoustic requirements varying with the purpose of the space.

Reverberation Time

The rate of decay (reverberation time) suitable for the type of room is a key acoustic requirement.

Background Noise

Background noise and external noise must be reduced to acceptable levels for good acoustics.

Absence of Echoes

Good acoustics require the absence of echoes and similar acoustic defects.

Sound Quality in Auditoria

The sound quality of a large auditorium such as a concert hall can be difficult to get right, and acoustics has sometimes been described as an art rather than a science.

Intelligibility of Speech

Intelligibility of speech is crucial in spaces like conference halls, law courts, theatres, and lecture rooms.

Loud Music Perception

When music is loud, it is usually perceived as being livelier and more intimate.

Examples of Music Auditoria

Examples of auditoria designed exclusively for music include concert halls, opera houses, recording studios, and practice rooms.

Sound Behaviour

Sound behaviour in a room can be affected by the size and shape of the enclosure and the nature of the materials used for the surfaces.

Acoustic Defects

Unwanted reflections of sound are called echoes.

Path Difference

At a velocity of 340 m/s, a time difference of 1/20th second (50 ms) corresponds to a path difference of 17 m.

Late reflections

Can be minimised by the use of absorbers on those surfaces that cause the echoes (materials).

Good acoustics

A direct sound is an important feature of good acoustics.

Hall Shapes

The aspects of shape affect the acoustics of an auditorium.

Rectangular hall shape

One of the hall shapes that can be used for good acoustics

Wide fan hall shape

One of the hall shapes that can be used for good acoustics

Horseshoe hall shape

One of the hall shapes that can be used for good acoustics.

Terracing (terraces)

At some designs, the audience and furnishings in these tiers also act as absorbers.

Sound absorption

A reduction in the sound energy reflected from a surface.

Sound absorption vs sound insulation

Sound absorption is distinguished from sound insulation because the two concepts have different effects and applications.

Absorption coefficient

It is a measure of the amount of sound absorption provided by a particular type of surface.

Absorption coefficient formula

The amount of sound energy not reflected is compared with the amount of sound energy arriving at the surface.

Perfect absorber

Has an absorption coefficient of a = 1.

Poor absorber

Has an absorption coefficient of a = 0.

Absorption coefficient example

A surface that absorbs 40% of incident sound energy has an absorption coefficient of 0.4.

Surface absorption coefficient

The coefficient of 'absorption' is a surface consideration and is not affected by what actually happens to the sound energy that is not reflected.

Total absorption

The effective absorption of a surface depends on the absorption coefficient of the surface material and the area of that surface exposed to the sound.

Total absorption calculation

Absorption of surface = area of surface × absorption coefficient of that surface.

Total absorption units

Measured in m2 sabins or 'absorption units'.

Sum of total absorption

Total absorption = Σ(area × absorption coefficient), which is the sum of the absorptions provided by each surface in the room.

Sound absorption by people and furnishings

People and soft furnishings absorb sound, and air also absorbs sound at higher frequencies.

Noise

Unwanted or disruptive sound that negatively impacts the acoustic comfort of a space.

Environmental factors of noise

Factors that affect human tolerance of noise.

Technical aspects of noise

Understanding how noise exposure is assessed in the workplace, and in recreation.

Noise exposure levels

Levels of noise exposure that cause hearing loss.

Noise annoyance assessment

Understanding how noise annoyance is assessed for contexts such as road noise and construction site noise.

Principles of noise control

The foundational concepts that guide the management and reduction of noise in various environments.

Sound transmission in buildings

The process by which sound travels through different materials and spaces within a building.

Airborne sound

Sound that travels through the air before reaching a partition.

Impact sound

Sound generated on a partition, typically from sources like footsteps or machinery.

Sound insulation performance

How effectively walls, floors, and other building elements reduce sound transmission.

Common measurements of sound insulation

Standard metrics used to quantify the effectiveness of sound insulation in buildings.

Building regulations and codes for sound insulation

The typical requirements that dictate the acceptable levels of sound insulation in construction.

Acceptance of noise

The degree to which individuals tolerate noise, influenced by personal sensitivity and preferences.

External factors affecting noise acceptance

Elements such as environment type, activity, frequency structure, and duration that influence how noise is perceived.

Noise limiting curves

Standard curves used to specify acceptable sound levels at different frequencies based on human ear sensitivity.

Noise criterion (NC)

A single-figure rating for noise obtained from NC curves.

Preferred noise criterion (PNC)

A single-figure rating for noise obtained from PNC curves.

Noise rating (NR)

A single-figure rating for noise obtained from NR curves.

Acceptable background noise levels

Standard indices for background noise levels in various environments, such as 40 for general offices and 20 for concert halls.

Sources of noise in buildings

Origins of sound that may be external or internal to the building, affecting noise levels.

Sound path

The route sound takes from its source to the receiver, which may include air or structural components.

Receiver of sound

The entity that perceives sound, which could be the building itself, a specific room, or a person.

Impact sound sources

Common origins of impact sound, including footsteps, doors, and vibrating machinery.

Airborne sound sources

Common origins of airborne sound, including voices, radios, and traffic.

Sound insulation

The reduction of sound energy transmitted into an adjoining air space.

Insulation in sound control

The primary method used to manage both airborne and impact sound in buildings.

Overall sound insulation performance

The effectiveness of a structure in reducing airborne and impact sound through all sound paths.

Assessment of sound insulation

The initial evaluation of sound insulation that considers one type of sound transfer at a time.

Sound Reduction Index (R or SRI)

R is a measure of the insulation against the direct transmission of airborne sound.

Measurement of SRI

The sound levels in the rooms on each side of the partition are measured and a normalised SRI obtained by adjusting for the area of the partition and for the absorption in the receiving room.

Laboratory Measurement of SRI

The measurement of an SRI can be made in a special laboratory where no flanking sound paths are possible around the partition under test.

Frequency Variation in Insulation

Insulation varies with frequency; the sound reduction index needs to be measured and considered for different frequency bands, such as specified octave intervals.

Insulation Curve

Results of measurements can be plotted against frequency on a graph.

SRI Formula

A working value for the SRI of a partition, at a frequency of 500 Hz, can be obtained by using the formula R = 14.5 log10 M + 10, where M = mass per unit area of the partition (kg/m2).

Heaviness in Sound Insulation

Heavyweight structures with high mass transmit less sound energy than lightweight structures.

Density and Sound Vibrations

The high density of heavyweight materials restricts the size of the sound vibrations inside the material.

SRI Increase Example

The average SRI of a brick wall increases from 45 dB to 50 dB when the thickness is increased from 102.5 mm to 215 mm.

Completeness in Sound Insulation

Areas of reduced insulation or small gaps in the construction of a wall have a far greater effect on overall insulation than is usually appreciated.

Airtightness

The presence of gaps is more significant; for example, if a brick wall contains a hole or crack which in size represents only 0.1% of the total area of the wall, the average SRI of that wall is reduced from 50 dB to 30 dB.

Porous Materials

Some materials may be also porous enough to pass sound through the small holes in their structure; brick and blockwork should therefore be plastered or sealed.

Flexibility in Sound Insulation

Stiffness is a physical property of a partition; it depends upon factors such as the elasticity of the materials and the fixing of the partition.

Isolation in Sound Insulation

Discontinuous construction can be effective in reducing the transmission of sound through a structure.

Energy Loss in Sound Transmission

As the sound is converted to different wave motions at the junction of different materials, energy is lost, and a useful amount of insulation is gained.

Air Cavities

This principle behind the effectiveness of air cavities in windows, floating floors, carpets etc.

Sound Insulation Regulations

UK - The Building Regulations 2010 - Resistance to the passage of sound. Regulations cover new buildings and materials change or renewed buildings.

Building Types Requirements

Building types requirements are included in the sound insulation regulations.

Building Components Requirement

Building components requirement like wall, floor roof etc. are included in the sound insulation regulations.

Dividers Between Dwellings

Dividers between dwellings and different types of adjacent, etc. are covered under sound insulation regulations.

Building envelope

The parts of buildings such as the roof, external walls, and windows which separate a dwelling from external sources such as noise from industry, road traffic, trains, and aircraft.

Separating walls

Walls that are between dwellings and within the same dwelling.

Separating floors

Floors that are between dwellings.

Typical target sound levels for internal noise

Standards set for acceptable sound levels within a building.

Sound insulation properties of ventilators

The ability of ventilators to minimize sound transmission.

Heavyweight walls

Walls that generally provide high levels of airborne sound insulation.

Cavities in walls

Spaces within walls that can increase sound insulation.

Lightweight walls

Walls that can provide adequate levels of airborne sound insulation.

Mass enhancement methods for floors

Recent methods include the use of thick layers of composite floorboard or multiple layers of plasterboard.

Natural mass of concrete floors

Provides insulation against airborne sound but can transfer impact sound.

Resilient layer in floors

Needed to provide insulation against impact sound.