ARCHITECTURAL ACOUSTICS

Architectural acoustics is the study of sound in homes and other buildings and the design of
those structures for optimal acoustic performance, including control of sound transmission
throughout the building, maintaining conditions for good speech intelligibility, and maintaining
sound isolation for speech privacy.

All of the sounds we hear on a daily basis can contribute to a host of problems. Environmental
noise in particular, is an area of focus for European researchers who have recently measured the
health complications it can present. In addition to negatively affecting the occupants’ energy
level, those complications can include everything from heart disease and tinnitus to sleep
deprivation and cognitive impairment, with the potential to take years off the average person’s
life.

Environmental noise includes transportation noise – road traffic, railway and aircraft – wind
turbine noise and leisure noise. Leisure noise refers to all noise sources that people are exposed
to during activities such as attending nightclubs, restaurants, fitness classes, live sporting events
or live music venues, and listening to loud music through personal listening devices.

Within the built environment, it would be easy to think that indoor noise might not have any
adverse impact compared to environmental noise. However, even within the confines of a
building, architectural acoustics play a significant role in the occupant’s experience (e.g.
environmental noise can be periodic and decrease during evening hours and overnight, while
excessive reverberation inside a room is always present, interfering with every word spoken).

Every element of a building’s construction contributes to its acoustical characteristics. It’s more
than just walls and ceilings: its shapes, surfaces, furniture, light fixtures, mechanical systems and
materials used in construction all have an impact on a building’s acoustics. When the acoustical
properties of materials are not considered during the specification process, the result is too often
a poor acoustical environment. The conversation around healthier buildings often focuses on
light and air quality, but the noise levels also significantly impact health and wellbeing.
Increasingly, though, many industry standards, guidelines and building rating systems now have
acoustic criteria sections, elevating the importance of acoustics in building occupant wellbeing.

In 2018, the World Health Organization (WHO) updated its Environmental Noise Guidelines for
the first time since 1999, with new research confirming that noise has negative impacts on
human health and is becoming a growing concern. The data shows that improving indoor
environmental quality (IEQ) results in a substantial benefit for occupants. That’s why
ROCKWOOL supports including health and wellbeing as criteria for how we evaluate, renovate,
and develop buildings – especially our homes, schools, offices, and hospitals.

The risks of poor acoustical building design

Depending on the type of structure, the potential complications from poor acoustical design can
vary greatly. Let’s take a look at the range of possible negative consequences that noise can
produce in different built environments. In healthcare settings, noises can range from irritating to
harmful for patients and caregivers.

SOUND TERMINOLOGY - THE BASIC DEFINITIONS OF BUILDING ACOUSTICS

Understanding acoustics means becoming familiar with many of the common sound terms used
by industry professionals. This next section will provide an overview of the fundamentals of
acoustics - the acoustics basics you need to know including definitions of the most common
terms sorted alphabetically.

TERM, DEFINITION, EXAMPLE/ SITUATION

Acoustic attenuation/ sound attenuation- When the intensity of a sound diminishes as it passes
through a medium. A sound’s intensity will always diminish with distance, but the type of
medium it passes through will affect how quickly it happens. In built environments, an ideal
attenuation is usually achieved with a combination of sound blocking and sound absorption
strategies.
Day-night average sound level (DNL)- This is the sound level in a space averaged over 24
hours, but with 10dB added to all sound between 10 pm and 7 am before the average is done.
This average level is thus usually greater than the true energy average level over the day. DNL is
used to assess the appropriateness of a potential building site relative to the function of the
building planned for it. High DNL values can mean a more massive and sound-attenuating
envelope is required to protect occupants from environmental noise.
HVAC background noise- The noise generated by a building’s heating, ventilation and air
conditioning (HVAC) equipment. Noise from HVAC equipment and systems needs to be
controlled through proper equipment selection, system design and routing, noise control
measures and physical barriers such as walls and slabs.
Impact sounds (impact isolation class - IIC)- The airborne sound or noise arising from the
impact of an object making direct contact with a surface. These sounds travel because the impact
creates vibrations in the construction elements (e.g. wood joists and beams) that connect walls,
floors and ceilings as part of the overall acoustics system. The easiest way to control impact
noise is to use carpet and pad on floors or to use a sound control underlayment beneath hard floor
finishes.
Noise level reduction (NLR)- The amount of attenuation provided by construction to reduce the
noise level on the other side than the source. Requirements for NLR vary by regional and local
regulations. To increase NLR the envelope of a building often needs to become more massive.
Noise pollution - Unwanted sounds that can have a negative impact on health and the quality of
an environment. Not just an outdoor phenomenon; noise pollution can be experienced in built
environments with negative consequences on health and productivity.
NRC and NRC rating- Noise reduction coefficient (NRC) is a rating of how much sound an
acoustic surface or material can absorb. Acoustic NRC sound ratings use a scale of 0 to 1, with 0
being the least absorptive (or reflective) of a sound, and 1 meaning the material absorbs a lot of
sound.
Outdoor-indoor transmission class/ OITC sound rating- The OITC sound rating provides a
single number rating for roofs, facades and facade elements that are subjected to transportation
noises. The higher the number the better the noise isolation; calculated over the frequency range
of 80 to 4,000 hertz. Created to test exterior walls and their elements (windows and doors);
because of the larger range in expected sound, OITC values are determined for lower frequencies
as well and are often lower than STC ratings for the same construction assembly.
Reverberation- The sound that reflects around inside a room even after the source has become
silent until it (the sound) eventually loses energy. Less reverberation means that it is easier to
understand speech in a given space. Reverberation is characterized by reverberation time
(which is further explained below) and can often be reduced through careful consideration of a
room’s surfaces.
Reverberation time- The time it takes for a sound to decay 60dB after the source has become
silent. Reverberation time is mostly affected by the volume and extent of sound absorbing
surfaces inside the room. As the room gets smaller or as more sound absorption is added, the
reverberation time decreases. In order for speech to be intelligible in most rooms, the
reverberation time should be no longer 0.60 seconds.
Sound isolation/insulation or noise isolation, sometimes referred to as sound blocking-
Sound isolation is the ability to block sound transmission from one room or area to another
(between the source and the receiver) by separating, or decoupling, assembly materials to stop
the transfer of sound energy. This soundproofing technique is often used in ”floating” walls or
floors.
Sound masking- When one sound, often intentional, is introduced into an environment to make
another undesirable sound less audible. Often confused with “white noise,” sound masking can
be provided by electronic systems, water features, nature or HVAC systems in buildings.
Sound pressure level (SPL)- The measure of a sound’s pressure relative to the pressure around
it; in its simplest form, quiet sounds produce waves with relatively small pressures. Loud noises
produce sound waves with large pressures. In architectural acoustics it is typically the goal to
attenuate noise with absorption and blocking in order to decrease the sound pressure level at the
ears of listeners or amplify desired sounds with reflections to increase sound pressure level at the
ears of listeners.
Sound transmission class/ STC rating- One of the standard metrics that quantifies an
assembly's ability to decrease airborne sound transfer between rooms. STC ratings between
rooms are most often required to be in the 40-50 range. Some situations require even higher
ratings. To increase STC, the assembly such as a wall or floor needs additional mass, insulation
inside cavities or resilient breaks between the layers of the construction.
Soundproofing- Soundproofing is a general term used to describe reducing sound pressure
between a source and the receiver. There are different ways to “soundproof” a space – the
most common are blocking and absorption; they work differently but have the same desired
effect of reducing noise and should ideally be used in conjunction with one another.
Speech intelligibility- Speech intelligibility is the ability to hear and understand conversation. It
is related to the sound power and directivity of the speaker, the background noise level and the
sound attenuation between the source and the receiver. Sentence understanding of 90-95% is
usually desired for clear understanding of the conversation in a room. To increase speech
intelligibility, block noise that would make the speech harder to hear, attenuate HVAC
background and environmental noise from the exterior and utilize sound-absorbing surfaces in
the room to decrease reverberation time.
Speech privacy- The inability to understand someone else’s speech – essentially the opposite of
speech intelligibility. Speech privacy relates to sound blocking by physical barriers such as
walls, slabs and doors and the background sound level. As the sound blocking capacity of the
barrier increases and as the background sound increases, the speech privacy also increases.

INTRODUCTION TO CONTROLLING NOISE POLLUTION

Creating a built environment with good acoustics includes controlling noise pollution. Exterior
sounds can infiltrate a building affecting the acoustic environment for its occupants. Building
system noise and occupant noise can transmit through the building affecting functionality. The
best way to control this noise pollution is with a “source-path-receiver” model – identifying
strategies at each point of sound transmission that can reduce the impact of the sound.

This concept for architectural acoustics design may be simple to understand, but it is often
difficult to apply. For example, road traffic noises outside of a building (the “source” in the
above image) are out of the control of architects and other construction professionals. Likewise,
noise pollution would not be a nuisance in an empty building where there is no “receiver” to hear
the sound. The most effective approach for architects, then, in managing noise pollution in a
building’s acoustic design is controlling the sound path.

Source:
https://www.rockwool.com/north-america/advice-and-inspiration/blog/fundamentals-of-
architectural-acoustics/#:~:text=Architectural%20acoustics%20is%20the%20study,sound
%20isolation%20for%20speech%20privacy.

BUILDING ACOUSTICS
Building acoustics is the science of controlling noise in buildings. This includes the minimization
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 and wellbeing, 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.

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.
 Impact noise.

CHARACTERISTICS OF SOUND
Sound intensity is measured in Decibels (dB). This is a logarithmic scale in which an increase of
10 dB gives an apparent doubling of loudness.
Sound pitch is measured in Hertz (Hz), the standard unit for the measurement for frequency.
The audible range of sound for humans is typically from 20 Hz to 20,000 Hz, although, through
ageing and exposure to loud sounds the upper limit will generally decrease.

As well as intensity and frequency, sound also transmits information. For example, music or
speech, transmit information which people may perceive differently from other sounds.

REVERBERATION TIME
The ‘reverberation time’ of a space changes the way the space ‘sounds’ and can affect the
intelligibility acoustic information. A high reverberation time can make a room sound muffled,
loud and noisy. Rooms designed for speech typically have a low reverberation time, whereas a
higher reverberation time can add depth, richness and warmth to music.

The reverberation time of a room is defined as the time it takes for sound to decay by 60 dB after
an abrupt termination. It is linked to the total quantity of soft treatments and the volume of the
room.

SOUND ABSORPTION
Sound absorption is the loss of sound energy when sound waves come into contact with an
absorbent material such as ceilings, walls, floors and other objects, as a result of which, the
sound is not reflected back into the space. Acoustic absorption can be used to reduce
reverberation times.

Absorbent materials are sometimes categorised from A to E, where A is highly absorbent and E
is almost fully reflective.

Sound absorbers can be divided into three main categories:

 Porous absorbents, such as fibrous materials or open-celled foam.

 Resonance absorbents, which consist of a mechanical or acoustic oscillation system, such
as membrane absorbers.
 Single absorbers such as tables, chairs or other objects.
SOUND INSULATION
Sound transmission paths can be interrupted by sound insulation and by blocking air paths. The
sound insulation of a single leaf of a material is governed by its mass, stiffening and damping.

The sound insulation across a good conventional, lightweight, office to office construction is
typically in the order of 45 dB Dw. This means that if the sound level in the source room is
around 65 dB (a typical level for speech), the sound level in the adjacent room, the receiver
room, will be approximately 20 dB (barely audible).

If sound levels are increased in the source room however, to 75 dB (raised voice), sound levels
within the adjacent room will also increase to around 30 dB (audible). Sound insulation therefore
describes the level of sound lost across a partition and not the level of sound within an adjacent
room.

Dw represents the sound insulation between rooms on-site. Rw represents the lab tested sound
insulation of an element making up a partition wall/floor type. Standards achieved in labs may
not be possible on site because of the quality of workmanship and due to sound ‘flanking’
acoustic elements, that is, travelling around them through an easier path, rather than only directly
through them as under lab conditions.

The building regulations part E sets minimum standards for design and construction in relation to
the resistance to the passage of sound.

NOISE NUISANCE
Building acoustics can help to mitigate the effects of noise disturbance which can have negative
effects on health, wellbeing and general quality of life.

The Noise Policy Statement for England (NPSE) defines noise pollution as:
 Environmental noise – which includes noise from transportation sources.
 Neighbour noise – which includes noise from inside and outside buildings.
 Neighbourhood noise – which includes noise arising from industrial and entertainment
premises, trade and businesses, construction sites and noise in the street.
This can be an important consideration for the location, design and construction of new
developments.

Source:
https://www.designingbuildings.co.uk/wiki/Building_acoustics