Acoustics
Sound blocking
Noise pollution
Sound absorption
Soundproofing

What is architectural acoustics?

Chad Holmes
Product Manager – EWI, Roofing & Core Solutions
Chad Holmes
15 August 2019

A 101 guide on the fundamentals of building acoustics - terms and definitions you need to know in the building industry

Illustrative image, office, meeting room, sound insulation, acoustics, multiple people, open plan office

Why do we need acoustics?

Acoustics affects everyone on a daily basis – from homeowners, office workers, students and hospital patients, to professionals working in the design and construction industries. Therefore, knowing the basics of architectural acoustics and the meaning of acoustical design and construction is essential; terms like sound transmission class (STC) and noise reduction coefficient (NRC) are only the beginning.

This is the first in a series of articles developed to establish a foundation of understanding in building acoustics. Let’s dive in!

Why acoustics matter in homes and buildings

Constructing new buildings – be they homes, schools, office towers or industrial workplaces – has become an increasingly sophisticated exercise. We know more today than ever before about the importance of building structures that are energy-efficient, safe and comfortable for occupants. Creating these high-performance buildings begins at the planning stage with design professionals and technical experts who consider all the factors that go into making spaces perform as they are intended – whether optimizing productivity for office workers, quiet recovery areas for patients, good acoustics in learning environments for students, or any number of other examples to bring the acoustical properties of a space in line with its intended use.

One of the factors that often gets overlooked at the planning stage is acoustics, yet the acoustic environment of a building can have a significant impact on the occupants’ experiences. For example, research has established that sound can negatively affect health and recovery periods in hospitals. Design trends that are driving the creation of open workspaces for collaboration may also have the effect of decreasing privacy and productivity. Construction practices and products selected to meet sustainability goals may, at times, inadvertently sacrifice the ability of a space to deliver occupant comfort by decreasing unwanted noise.

Considering the acoustic needs of a building at the start of the planning process can help save time and money by reducing the need for renovations or retrofits once construction is completed. Within this acoustics article series, we focus on rethinking the role of acoustical design and engineering. Increasing awareness and understanding of acoustics among industry professionals, including architects and designers, building owners, as well as the general population, will only help drive this shift. Occupants of these high-performance buildings will continue to demand that sound be a key consideration in new construction.

What is sound?

At its most basic level, sound is a very small and very rapid fluctuation in air pressure above and below atmospheric pressure. All sounds – an HVAC system, a vibrating cell phone on a desk, road traffic – operate using this principle. The ear is very sensitive to sound sources and the range of pressure vibration from the weakest to the loudest sound heard is extremely large.

The ear doesn’t experience sound in a linear fashion. Instead, it uses a logarithmic scale with a measure of energy in decibels (dB). To the ear, a sound heard at 60dB only needs to decrease to 50dB to experience this sound as being half as loud. Furthermore, a sound going from 60dB to 40dB (i.e. a busy street to a quiet library), would be experienced as an even more dramatic change. The potential for a sound to damage our hearing is proportional to its intensity, not its loudness as shown in the table below.

Facts about sound

  • Acoustical engineers use decibels (dB) to measure sound or quantify sound loudness.
  • The energy in the loudest sounds typically heard is one million times that in the weakest sounds audible.
  • The ear is a tremendously sensitive organ; the range of pressure variation from the weakest to loudest sounds heard is extremely large.
  • To make a sound twice as loud requires 10 times as much power. Inversely, to make it half as loud, 90 percent of the sound must be eliminated.
PNG - The potential for a sound to damage our hearing is proportional to its intensity, not its loudness. See the decibel level logarithmic scale.

The decibel logarithmic scale measuring sound shows that while a 3 dB change leads to a barely noticeable perceived difference to the human ear, a 20 dB swing is a very dramatic change.

How is sound measured?

Acoustical engineers use decibels to quantify sound loudness, but when it comes to acoustics design in buildings, that measure is just one way of evaluating its performance.

There are two primary metrics used in noise measurement for evaluating the acoustic performance in a building’s acoustical performance – acoustical absorption and sound transmission loss.

Acoustical absorption is the ability of a material to absorb rather than reflect sound (think about the difference between jumping onto a trampoline vs into a pile of pillows). Sound transmission loss refers to a material’s ability to reduce sound transfer from one space to another (i.e. blocking noise or sound between rooms). When you’re trying to find a solution to meet good architectural acoustics requirements for your next project, it is important to know the difference between the two.

When referring to sound absorption, you should look for products that absorb reverberation and echoes in a room. If you want a product that will stop or block a sound, you’ll need a heavier, denser material. Materials with high sound absorption are not great for stopping sound transmission. For example, concrete is great for sound transmission loss, but not great for sound absorption.

Stone wool ceiling tiles provide high absorption levels, whereas ROCKWOOL’s wall and roofing products as components of an assembly can help reduce sound between rooms as well as noise from the exterior environment. Depending on the application, the acoustical properties of the building materials you specify and use will play a significant role in overall soundproofing.

PNG - sound is measured on a logarithmic decibel scale and how loud things are is impacted both by the sound absorption and sound transmission loss of space and building materials used in construction.

While sound absorption is the ability of a material to absorb rather than reflect sound waves, sound transmission loss highlights the decrease in sound energy as it passes through the built environment. Both are important considerations in building design and the materials chosen for construction.

What is 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 real impact of noise

Studies have shown that children miss 25 percent of the words spoken by their teachers as a consequence of a noisy classroom. The WHO recommends a noise level of less than 35dB(A) in classrooms in order to support optimal teaching and learning conditions. This is significantly lower than in many urban locations.

Read this post

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.

For patients:

  • Sudden noises can set off startle reflexes, leading to injury, increased blood pressure and higher respiratory rates
  • Prolonged noise can contribute to memory problems, irritation, impaired pain tolerance and perceptions of isolation
  • Reduced noise levels in intensive care units have been found to promote better sleep and healing

Noise at all hours can lead to sleep deprivation which has been tied to longer recovery, falls, dementia, higher re-hospitalization and worse medical outcomes.

For caregivers:

  • Healthcare professionals can usually perform important tasks in high-stress situations, including high levels of noise; however, it may require greater energy to do so, contributing to fatigue.
  • The need to protect patient confidentiality is critical, so speech privacy – the ability to hold discrete conversations without being heard by unintended listeners – is essential.
  • Speech intelligibility is a very real risk in healthcare environments when noise is uncontrolled. Patient care teams require the ability to quickly and accurately understand and respond to auditory signals, be they care directives, equipment alarms, etc.

In an office or educational environment, the acoustical design can severely limit productivity and inhibit privacy when not properly considered. Open design concepts in the workplace are on the rise for quite some time, in part because they promote greater cooperation and collaboration among colleagues, decrease response times to requests, and enhance necessary communication. However, these types of environments may lead to louder working environments and frequent distractions, as there are fewer surfaces to absorb the noise from coworker conversations, mechanical systems, and other background sounds. Similar design trends are occurring in educational buildings.

The shift to open-concept spaces that allow for more natural light and warmth by incorporating glass walls, high ceilings and low partitions, can also contribute to increased distraction and lower productivity. Privacy can be non-existent in these designs, though in fairness, traditional floor plans with closed-door offices and classrooms often don’t include an adequate acoustical design and therefore provide a false sense of privacy. Specific short-term health problems related to poor acoustics include increased stress, anxiety, and higher heart and respiration rates, and muscle tension.

The bottom line is that now, more than ever, creating an optimal acoustics experience in any kind of building is as important as the look, feel and function of the space to ensure the health and wellbeing of occupants.

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.

TermDefinitionExample/ Situation
Acoustic attenuation/ sound attenuationWhen 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 noiseThe 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 ratingNoise 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 ratingThe 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.
ReverberationThe 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 timeThe 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 blockingSound 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 ratingOne 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 privacyThe 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.

ROCKWOOL and Rockfon both provide effective components in your designs and assemblies which will contribute to controlling sound at the path, including:

  • Control over vibrations – high-density stone wool has proven acoustic capabilities that allow it to isolate and control vibrations, thus efficiently absorbing sound and reducing noise
  • Installation of barriers, panels, or enclosures – for example: weather stripping (which stone wool can be used for) and double-paned windows
  • Control in the transmission path – stone wool insulation acts as an intervention in the path between source and receiver

The WHO defined five categories of noise pollution intervention types following decades of environmental noise management research, as outlined in the table below: 

PNG - how can you improve the acoustical comfort of a space using the source-path-receiver model? The World Health Organization (WHO) defines five categories of noise pollution intervention.

There are five categories of noise pollution intervention according to the World Health Organization (WHO) including source intervention, path intervention, new/closed infrastructure, other physical intervention, and behavior change intervention. These interventions are part of controlling the source-path-receiver model and designing for acoustic comfort.

Summary

The increasing awareness and understanding of the importance of acoustics in building design and construction is a positive, and essential, shift. Acoustics play a significant role in the building occupants’ experience, and the greater the knowledge around sound and architectural acoustics are among professionals, the better. It begins with recognizing and understanding the core terminology of the industry. 

We know that noise or sound, if not properly planned for, can contribute to a poor built environment, even having a negative impact on health and wellbeing. Conversely, professionals who consider architectural acoustics in planning new buildings, including how the structure supports optimal acoustic performance, can create a positive experience for occupants and enhance a building’s purpose.

What does that look like? Here are four strategies to improve acoustic comfort:

  1. Assess the environmental noise (DNL) of the site and plan the appropriate building envelope assemblies (roof and walls) including ROCKWOOL stone wool insulation to increase the noise reduction (OITC).
  2. Select quiet HVAC equipment and locate it away from spaces sensitive to sound, using interior partitions with ROCKWOOL insulation to boost the STC.
  3. Provide speech privacy between rooms by using full-height partitions with ROCKWOOL insulation to achieve the STC 40-50.
  4. Achieve speech intelligibility inside rooms by incorporating Rockfon's high-performing, sound-absorbing ceilings, islands and baffles.

Together, ROCKWOOL and building design and construction professionals can work to ensure that acoustics are a primary consideration in the planning process and that ultimately, architectural acoustics design and engineering is a key part of the foundation of a positive occupant experience.

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