Architectural Acoustics: The Art of Sound Design
When you think of acoustics, you probably think of concert halls. But musicians aren’t the only ones who benefit from good acoustics. Architectural acoustics are essential in ensuring sounds are transmitted clearly and effectively. They matter when it comes to keeping things quiet in places like libraries or museums, or in making sure loud noises aren’t too loud, in places like casinos.
Loud noise can increase stress, anxiety, and blood pressure, and put people at greater risk of stroke and heart disease. Conversely, a well-designed building with the proper acoustics can influence a person’s mental health and overall sense of well-being for the better.
The fact is, good acoustics are important in almost any setting — that’s why it’s essential to get them right from the beginning. It’s a lot easier to build good acoustics into a project at the outset, from the design phase through construction, than it is to adjust things later on.
What is Architectural Acoustics?
Acoustics is actually a branch of physics that focuses on studying sound: how it’s produced, transmitted, controlled, and received, and the effects of this process. As it applies to architecture, acoustics is the process of using building design and construction methods to harness the properties of sound to their greatest effect.
Architectural acoustics involves designing a building to control how soundwaves reverberate off its interior in such a way as to maximize clarity, amplifying sound in areas where it’s appropriate to do so, and reducing noise levels where doing so is beneficial.
Doing this involves considering several factors, including the geometry of the room and the materials used in construction — specifically their sound-absorbing or enhancing qualities. Mechanical systems can play a role, too: Fans, motors, and other mechanical components can create noises that cause unwanted distractions and may interfere with the transmission of communication.
Architects take these factors into account when designing buildings with the proper surfaces, shapes, and mechanical systems to distribute and control sound effectively.
Interestingly, research has found there’s actually an optimal room shape for achieving perfect acoustics: it’s rectangular and constructed using the golden ratio (8 feet high by 12.8 feet wide and 18.64 feet long).
When it comes to materials, softer materials such as carpet, fiberglass insulation, and foam padding tend to absorb sound well, while harder materials such as concrete and brick tend to reflect it. Wood can reflect sound well, but if holes are drilled in it, it can also absorb it.
Mechanical components can be placed at a distance from rooms to minimize their impact on acoustics, and noise-controls such as insulation and technology can also be employed.
The Purpose of Acoustic Design
As we’ve already suggested, good acoustic design can serve multiple purposes, including the following:
- Decreasing stress and anxiety levels
- Preserving hearing
- Aiding in concentration
- Reducing or minimizing hypertension
- Improving speech communication
- Maximizing the enjoyment of musical performances
Communication, in particular, is helped by good acoustics through the interplay of several factors. Properly designed acoustics aid in the clear transmission of verbal communication while at the same time reducing unwanted noise, thereby reducing distraction and aiding in concentration.
The elimination of loud noises, moreover, can contribute to the preservation of hearing over time.
Architectural Acoustic Techniques
Whether you’re designing an auditorium, library, or music hall, it’s important to understand the qualities of sound, how it’s transmitted, and techniques that can be used to control that transmission.
Reverberation is to sound what reflection is to light. Also known as resonance, reverberation refers to the amount of time it takes a sound to dissipate.
As sound waves bounce off surfaces in interior spaces, such as ceiling tiles and wall panels, noise builds up and reflects back on itself, reducing its clarity and making it harder to understand. It’s different from an echo, in which there’s a delay between the original sound and its fainter answer.
An echo off a distant canyon wall may take a few tenths of a second to return to you. But since the original sound only persists in your memory for 0.1 of a second, there’s no confusion. With reverberation, the reflecting surface (such as an interior wall) is much closer to you, and the time between when the original sound is made and reflected is less than 0.1 of a second.
The combination of the two can create the perception of a single, prolonged sound wave, which bounces back on itself, creating distortion.
Reverberation time is the amount of time needed for a sound to decay by 60 db (decibels) after being abruptly terminated. The higher the reverberation time, the noisier and more muffled a room can sound.
Buildings With Reverberation
Sometimes, you want to design a space with a higher reverberation time. Doing so can add to the warmth and texture of music, so concert venues and symphony halls are likely to be constructed with higher reverberation times.
When high reverberation times are included in the design of a music venue, it can create a richer and more majestic experience. When they’re not, the music is likely to sound and feel smaller and more hollow.
Buildings Without Reverberation
By contrast, if your venue is used primarily for speaking, such as a lecture hall, you’ll want to create acoustics with a lower reverberation time to preserve clarity. Failure to do so can result in miscommunication and frustration among attendees trying to make out what’s being said.
When low reverberation is included in a venue such as a conference room, listeners will remain engaged longer because it will take them less effort to hear and understand the message. When it’s not, they may “tune out” from frustration or leave feeling exhausted from having to focus, not just on the message, but on making sure they’re hearing it.
Sound absorption is the quality found in different materials that reduce reverberation times by absorbing sound energy and reducing sound levels. By eliminating unwanted sound, these materials can improve sound quality in a room.
Buildings With Sound Absorption
It can be helpful to use sound-absorbing material in rooms designed for speaking, such as lecture halls and conference rooms.
As mentioned above, different types of materials either reflect or absorb sound to different degrees. For instance, smooth concrete may absorb just 2% of sound, while reflecting the remaining 98%. In contrast, an acoustic panel — a glass fiber wrapped in fabric and mounted to furring (wooden strips) — with airspace behind it might absorb 75% of the sound that hits it.
Including sound absorption in a building’s design can help create a clearer, less cluttered sound quality by reducing reverberation: absorbing sound before it has the chance to bounce back. It can create a quieter, more peaceful environment.
Buildings Without Sound Absorption
Buildings without sound absorption are vulnerable to excessive reverberation because there’s nothing to remove the sound from the room before it can bounce back — thereby creating a noisier, busier environment. This can make it more difficult to hear spoken communication, make it harder to focus, and add to stress levels as a result.
Sound insulation is the property in a wall that allows it to keep noise from passing from one side to the other by absorbing sound waves of different frequencies. It can impact acoustic design by blocking air paths between rooms or between a room and the building’s exterior.
The effectiveness of sound insulation is measured in terms of dB Dw, with dB referring to decibels and Dw signifying the difference between the noise level in the room where sound is being produced and the level in a second, adjacent room, where it’s being heard or received.
The term sound insulation refers to how much sound is lost when it travels between the source room and adjacent room. If the dB Dw between two rooms is 45, that might mean the sound level is 65 dB in the source room and 20 in the adjacent room during a typical speech.
But if the speaker were to raise his voice, or even start yelling — at, say, 85 db — that would double the sound level in the other room to 40 db. In other words, the number of decibels (sound level) would increase by the same number in both rooms, rather than according to a ratio.
Sound waves need a medium through which to travel, most typically air. As a result, sound can travel through vents and electrical outlets or under doors — anywhere air can go. Sealing such spaces and adding insulation to venting systems are therefore effective ways of reducing unwanted sound.
Buildings With Sound Insulation
When a building includes sound insulation, it can minimize distractions from sound that emanates from adjacent rooms, whether it’s music, speech, or mechanical noise.
Acoustic insulation boards consisting of fiberglass panels and wrapped in cloth, as mentioned above, can absorb sound and effectively insulate adjacent rooms from the sound created in each of them, reducing background noise and improving focus.
Acoustic boards (also known as acoustic panels) are specifically designed with materials that absorb sound. They can be used in a number of spaces, including on walls or ceilings — especially at points where sound is known to reverberate — to reduce unwanted noise and create added clarity.
Panels may be situated in a variety of ways. They may be freestanding, mounted on walls, or suspected from ceilings. They may also be inserted between two walls. Vertical panels prevent sound from moving across a room from one end to the other, while horizontal panels absorb sound directly.
Wall-mounted acoustic panels can be especially helpful in small rooms, where sound tends to reverberate off walls because they’re close to the source of the sound. By contrast, ceiling panels can be more useful in larger venues where the sound source is farther from any surface and may reverberate off ceilings.
Acoustic boards can also be made using other inexpensive materials such as packaging foam, but these may be less effective at reducing sound.
Buildings Without Sound Insulation
Buildings without sound insulation, on the other hand, can create problems for those occupying rooms that are side-by-side.
This is the kind of situation that leads people to complain about “thin” walls in motels and apartment buildings. But those aren’t the only places this problem can occur.
For instance, consider a school classroom with classrooms on both sides, and all are in session at the same time. Sound from both adjacent classrooms is likely to make it through the walls on both sides; if one class is a drama course in which students are reading from a script, loud voices could be particularly disruptive.
Or imagine if a classroom were adjacent to a basketball court during a physical education class. Without sound insulation, the bouncing of basketballs and squeaking of shoes on the hardwood floor could be extremely distracting in the classroom next door.
Acoustical design that utilizes acoustical boards not only minimizes human noise from adjacent rooms but also reduces noise created by HVAC units, whether they’re against exterior walls or on the roof.
Using acoustical panels can be highly effective. Fiberglass black acoustical ceiling and wall liners are inexpensive and effective ways to reduce noise while being integrated seamlessly into a structure.
Buildings With Acoustical Boards
Buildings with acoustical boards will be able to minimize artificial noise created by HVAC and other mechanical units. These mechanical systems can prove distracting when they switch on and off; thoughtful acoustic design using acoustical boards can help prevent or mitigate this annoying background noise.
Buildings Without Acoustical Boards
Buildings without acoustical boards are vulnerable to disruptions caused by HVAC units — especially during seasons that experience temperature extremes — when air conditioning units, in particular, can labor for long hours or repeatedly activate and shut off as temperature targets are met or exceeded.
Challenges of Architectural Acoustics
Architectural acoustics creates a number of challenges during construction, both as it relates to building acoustics — insulation from unwanted sound — and room acoustics, or maximizing sound quality.
The challenges take place both in the process itself and in reaching the intended goal.
They include controlling noise pollution, dealing with environmental noise, and predicting sound distribution.
Controlling Noise Pollution
Controlling noise pollution can involve dealing with noise from HVAC systems once they’re installed to minimize noise pollution from the construction process itself.
The Environmental Protection Agency defines noise pollution as “unwanted or disturbing sound,” adding that “sound becomes unwanted when it either interferes with normal activities such as sleeping, conversation, or disrupts or diminishes one’s quality of life.”
OSHA considers anything causing or exceeding 85 decibels over an eight-hour period to be noise pollution. Excessive noise over prolonged periods, as mentioned earlier, can cause stress, anxiety, sleep disturbances, hearing loss, and high blood pressure, among other negative effects.
Choosing low-noise machinery can help minimize noise pollution. So can creating noise barriers and scheduling high-volume work for times when fewer people are nearby.
Sound passing between walls of adjacent rooms isn’t the only challenge you’ll face in designing and constructing a building. Location matters, too: a lot. If your project is on a long driveway off a rural road, you’ll have a lot less environmental noise to deal with than if you’re building a convention center at the heart of downtown.
You’ll need to choose building materials and insulation to account for external noises such as heavy vehicle traffic, construction (if you’re in the middle of a developing area), pedestrian conversations, mobile food vendors, and ambulance or police sirens, depending on the location and its environment.
The challenges are different in North Dakota, for example, than they are in New York City.
The larger a room is, the bigger the challenge of measuring sound distribution. Doing so requires more than measuring reverberation because the sound quality is likely to be different at various points around the room.
Sound distribution refers to where sound travels in a room. This is particularly important in large venues such as theaters, where audience members are distributed at different angles and distances from the sound source.
In a concert hall, for instance, the acoustics are likely to be different in front of the stage than in the wings or in the balcony. To measure sound distribution, you can place a sound source in position (for example, where the stage will be) and measure sound pressure levels at different locations around the room.
Open Concept Spaces
Open concept spaces in office buildings are designed to foster collaboration and remove barriers between employees, such as office walls and cubicle barriers. Counterintuitively, however, Harvard University’s Business Review reports that face-to-face interactions actually fell by 70% when companies made the switch to open offices.
Sound can travel across entire open spaces in such offices, creating distractions that can be avoided if insulated walls are in place. Ringing phones, employee conferences, and noise from office machinery such as photocopiers can make employees want to hunker down rather than open up and interact more.
Removing sound isolation, ironically, can create a desire for more actual isolation in such offices.
Accounting for potential sound variations and acoustical challenges during the design phase of any construction project will make your job easier and maximize your chances of success in the long run.
It will allow you to design rooms in the proper shape to create the best possible architectural acoustics, as well as to select the best building materials to serve as sound absorbers and diffusers where necessary. You’ll also be able to select the proper equipment for the construction job you’re planning.
Whether you’re soundproofing walls for a recording studio, creating greater resonance in a concert hall, or improving the functionality of walls separating conference rooms or classrooms, you can be sure you’re on your way to a successful construction project if you consider the elements of good architectural acoustics.