Acoustics for Interior Designers & Architects
Introduction
Acoustics are an important part of design for functionality. Spaces such as commercial, education, retail, hospitality, childcare, and healthcare all require careful consideration when factoring in acoustics.
It is important to get it right. Understanding how sound reacts to different materials can allow for a beautiful and functional space!
Sound is indeed a powerful contributor to how humans perceive the quality of a space. It is often the case that if you get it right it will not be thought about, however, if you get it wrong it can be a disaster.
A good acoustic consultant can suggest an acoustical composition that can be balanced through many different combinations. This should provide the support to allow for the designer to have sufficient aesthetic freedoms, flexibility, and a variety of options to meet budget. Remember: Interior design and acoustics should be in congruence to ensure a successful project.
- An Acoustics Glossary that addresses some of the terms we will discuss can be found at the base of this article!
Importance of Acoustics
Every functional space should factor in acoustics, with the aim to make the occupants feel as comfortable as possible. Not only do poor acoustics cause annoyance, they can also directly impact productivity, health and well-being, learning and comfort.
Acoustics should support the aesthetic design and ultimately lead to greater productivity, concentration, job satisfaction and well-being. Acoustic comfort is paramount in achieving effective workplaces.
A study of over 100,000 workers shows that only 30% of office occupants are satisfied with the noise levels in their workplace [1]. Worksafe QLD states that excessive noise levels can: interfere with concentration and thought processes, cause fatigue and aggression, lead to heart disease and reduce immune response [2].
Office acoustics noise also causes distraction, which leads to negative performance in the workplace and makes us less productive [3, 4]. Furthermore, after distraction, it takes an average of 23 minutes and 15 seconds to get back to the task, leading to wasted time [5]. This implies that in a frequently noisy environment you may never be back to task!
Psychologists have also stated that distractions degrade the overall quality of people’s work [6]. Other Psychologists have shown that noise has an impact on ‘free recall’ or memory functions [7]. Furthermore, the Australasian Faculty of Occupational Medicine states that noise has the potential to give rise to direct compensable absence and indirect workplace absenteeism [8]. Another study indicated that noise is linked to stress in the workplace and can even lead to musculoskeletal disorder through noise exposed workers being less likely to correct their posture [9].
The Association of Australasian Acoustical Consultants (AAAC) states that “if adequate intelligibility and acoustic comfort were provided, concentration would be easier, and participants would be less frustrated and more productive” [10].
Good acoustics, equal good psychological and emotional balance. Acoustics though do not have to be ugly! With proper knowledge, advice and early engagement; inspired designs can often go unimpeded by the technical requirements.
Excellent acoustic spaces are usually only noticed by persons with trained ears; therefore, a little compromise is usually ok and is often the case when it comes to the acoustics. It is usually when good acoustic comfort is achieved that it is considered sufficient to the average occupant.
Acoustics should be versatile, and a great consultant can work with you to provide you with as much creative freedom as possible. All hard surfaces like a hard floor, glazing, plasterboard and a concrete soffit in the one place though usually poses a significant challenge, which we will address the reasons why in this blog.
How do we Assess Room Acoustics?
Acoustic design is complex and requires significant attention to detail and mathematical calculation and assessment. You will find that the design of a functional space is often more complex than meets the eye.
A room should be designed with acoustics in mind. Remember that the early stages are best to engage an acoustic consultant; as less time will be required, less money can be spent, and more options will be available for the designer to work with. It is a collaborative process.
The most important factors for measuring room acoustics are:
· Internal noise levels
· Construction & Floorplan
· Room size
· Geometry
· Characteristics of surfaces
· Positioning of surfaces
· Occupancy
All contribute to the overall acoustical quality of a space. When correctly balanced, the space can achieve an excellent acoustical outcome that ensures that it will function as intended.
In order to achieve this, calculations either on site or theoretically modelled need to be conducted. The data can then be used to provide suitable constructions and performances of each surface to meet the requirements and recommendations set out in the relevant Australian standards.
What is Sound & Frequency?
Sound is interesting as it is literally a series of vibrations that oscillate about atmospheric pressure. That rate of vibration is the frequency. Each frequency vibrates at a different rate and interacts with the environment in a different way.
· The low (or bass) frequencies are very large in size and travel through the air spherically like large waves. They are difficult to contain, often requiring larger air cavities and heavy constructions to control.
· High frequencies (treble) are very small in size and travel through the air more directionally like rays of light. They are much easier to contain than low frequencies often requiring less strategy to control.
Human speech does though contain frequencies from 80Hz (very low) all the way up to 12,000 Hz (very high). Other sources such as aircraft, traffic, impact and vibrations contain frequencies across and beyond the human range of hearing, which is generally accepted to be 20Hz to 20,000Hz. This means that balanced control across the frequency spectrum should be factored into any room acoustics application.
Infrasound is defined as sounds below 20Hz with Ultrasound defined as sound above 20,000Hz
Important Acoustic Parameters
It is important to know the definitions of the different room acoustics parameters as a guide to how sound will behave in a proposed space.
Reverberation Time is the time (in seconds) taken for the sound pressure level generated by a source to decay by 60 decibels following the conclusion of the source event. It provides relevant information for assessing the speech intelligibility and the acoustic quality of a space. It is sometimes referred to as the “echo” in a room.
Both excessive and lack of reverberation can lead to a poor acoustic environment depending on the function of the space. This means that in order to achieve the correct range of reverberation time for a space – it must be calculated.
Sound Absorption Coefficient is a single number rating between 0 and 1 that describes a materials ability to absorb sound at a particular frequency. The larger the number, the higher the absorption of the material at the described frequency. An absorption coefficient of 0.60 could be considered as absorbing 60% and reflecting 40%.
Sound absorption refers to the portion of a sound wave that is not reflected when meeting an object. This portion of the sound wave will not continue to travel and will be converted into thermal energy. 100% absorption is represented as “1” on the sound absorption coefficient rating. It is the opposite of reflection. Sound absorption reduces reverberation time
Reflection is the portion of a sound wave that is not absorbed when meeting an object. The portion of the sound wave will change direction and continue to travel. 100% reflection is represented as “0” on the sound absorption coefficient rating. It is the opposite of absorption.
Did you know that reflection can be used to reinforce speech in certain areas? (as below).
Strategy in presentation room utilising reflective ceiling and presentation wall as speech reinforcement. This must be calculated into the design!
NRC refers to the Noise Reduction Coefficient (NRC) value which is a single number rating between 0 and 1. It is the average of the mid-frequency octave-band sound absorption coefficients (250, 500, 1000 and 2000 Hz) rounded to the nearest 5%. The larger the number, the higher the absorption of the material.
Rw refers to the weighted noise reduction that roughly corresponds to the decibel scale. It is a measure of how much airborne sound is attenuated between a partition. This is the descriptor that would usually be described as “Soundproofing”
CAC refers to the Ceiling Attenuation Class (CAC) value which is a rating that describes a materials ability to prevent sound travelling between partitions through the ceiling cavity. It is usually required between private spaces when the walls do no go full height.
Different Acoustic Materials
A rule of thumb is that; soft furnishings usually dampen reflections and reduce the reverberation time and hard surfaces such as concrete, glazing, and plasterboard usually increase reverberation time.
This does not mean that plasterboard and glazing can’t be used – it does though suggest that other absorptive surfaces should be factored in.
Not all hard surfaces though are poor absorbers. Perforated, slotted and Slatted acoustic panels are a great hard surface that can be engineered to absorb sound. They can come in a variety of configurations, materials and finishes that should be conducive to many designs!
Acoustic designed materials can usually be designed in a way that allows for the quality of acoustic character to differ from each surface without affecting the aesthetic. Things like density of materials, air spaces, additional bulk insulations can all change the frequency of absorption and acoustic rating.
A chosen aesthetic in most cases be balanced to achieve the desired acoustic outcome – a good understanding of acoustic materials is paramount to achieving the design goals.
"Soundproofing" is a term often used to describe blocking sound out from disturbing your neighbours or blocking sound from entering your space.We refer to this as internal and external noise intrusions.
It is also the descriptor that relates to speech privacy. We would need to "soundproof" a private office to prevent conversations from being heard.
This part of acoustics is a separate issue to reverberation control. It is important to understand that; by controlling your reverberation issues it does not necessarily mean that you have created any "soundproofing" or speech privacy. It is though generally accepted that controlling reverberation times can lower internal noise levels by up to 5dB.
In order to "Soundproof" we would need to consider these 3 factors in design:
Mass
Air-tight construction
Resilience
This means that we need heavy (mass), sealed (airtight) and free from rigid contact (resilient) constructions in order to soundproof an area. This is important for any wall, floor or ceiling. Remember that any noisy mechanical services or ducting will also need to be looked at.
An acoustic consultant will recommend systems that can meet the requirements of your building and function of space. When guesswork is involved you run the risk of over specifying and affecting your budget or under specifying and not designing to the requirements of the project.
Conclusion
There is not a one size fits all solution to acoustics. Like interior design & architecture, every acoustic project is unique. Placing acoustic panels in a room without thought will very rarely create a solution without first understanding and calculating what is required. Every space will have its own set of unique challenges with its own solutions. In many instances, bespoke solutions can be designed.
Industry experts such as interior designers and architects should seek an acoustic consultant to assist with the support of acoustical design within any functional space.
Michael Phillips is an acoustic engineering consultant experienced in building, environmental, and aestheticacoustics solutions.
Get in touch to discuss your next design project!
Michael Phillips
Acoustic Engineering Consultant
M.A.A.S.
MArchSc (Audio & Acoustics), AssocDeg (Audio Eng.)
P: 0413 904 997