Communication is a key function to being human. Without it people’s functionality will be compromised. Our ability to hear, an important communication tool, is one of the most crucial means of survival in the world, and speech is one of the most distinctive characteristics of human development and culture. It is no surprise then that the science of acoustics spreads across many facets of society like music, medicine, industrial production and architecture.
Acoustic engineering needs to play an integral part in designing an office building, even more so in commercial projects like hospitals, theatre and convention centres and churches.
Controlling sound through walls
There are various materials that can be incorporated to control the sound that goes through walls. Pick materials that are heavy, dense and massive, such as concrete, brick, drywall or sheetrock, to block the sound.
Look out for a wall cavity that is hollow, which acts like a drum. If one wall is vibrating from sound, the sound will travel through the air and vibrate on the other side of the wall and be heard in the next room.
According to a research paper, Green acoustics for interior construction: The challenges and benefits of modular walls, done by David Atwood and Jeff Fullerton, LEED AP, walls made from studs and drywall have been used for many years to divide space, and provide visual and acoustical privacy. “With the emergence of sustainable design, building professionals are looking at new ways to improve the performance and flexibility of fixed wall construction while maintaining its benefits,” states the paper. “To improve their bottom line and remain nimble for changing workplace configurations, many companies are finding modular wall solutions, such as moveable and demountable walls, as a high-performance alternative to fixed interior wall construction.”
The paper states that there is a common misconception about demountable and moveable walls that these products do not provide the same acoustical separation and performance as closed offices and divided rooms. “If teams utilise appropriate design, correct background sound and insure proper installation, this misconception can be easily corrected.”
The research paper further notes that a modular wall system is not suitable to use in any building project. “Highly complex technical environments, which might require more stringent sound and air control, are a case in point.”
According to the paper, many industries that traditionally opt for hard interior construction may be surprised by the benefits and applicability of modular wall systems.
Creating acoustical privacy
The paper further states that acoustical privacy can be achieved by balancing four key factors.
The first factor to consider is the loudness of a noise source, such as a neighbouring office nearby the building project that emanates loud noises or an animated discussion in an adjacent conference room in an office space or conference centre. The second factor to keep in mind is the ability of the demising constructions like the walls, windows and doors to reduce noise. The background sound level where the listener is located is also at play and is the third factor. The sensitivity of the listener also plays a role in acoustical privacy and is the fourth factor in the equation.
Dr Ben van Zyl, an acoustic engineer at Acusolv, says the acoustic characteristics of a space will ultimately create or downplay acoustical privacy. To achieve acoustical privacy, a professional acoustic engineer needs to be involved in the design process of an office space or building from the beginning, as it is difficult to change the acoustics of a building after it is designed and constructed.
Various elements can be incorporated in the design of the building to achieve the level of sound privacy that a client wants. Van Zyl says that in an office space, the form of the building is not that important, but the selection of building material could make a huge difference in the acoustics of a building. “Adequate wall sound insulation, selecting appropriate ceiling boards and treating some of the wall surfaces will play a role in the end result,” he says. Floor tiles or materials with a hard finish will create footstep noise and aggravate airborne noise and reverberation. Softer floor covers on the other hand can be employed to dampen footstep (impact) noise in an office space. “If you have a long walkway, opt for softer material like a carpet to dampen footstep noise. Using tiles in conjunction with other hard wall and ceiling finishes will increase reverberation, elevating work activity, traffic and air-conditioning noise levels and resulting in an unpleasant acoustic environment with poor speech intelligibility. It also tends to cause a hollow sound when someone walks on the tiles, while the occupants in the offices on opposite sides of the hallway will be heavily disturbed.”
According to the research paper, using blocking or covering up techniques in the design will help to mitigate acoustical privacy concerns normally associated with modular wall construction. “The first acoustical design strategy called blocking means increasing the acoustical effectiveness of the barrier between neighbouring spaces. In traditional wall construction, materials form a continuous barrier that runs from the floor to the ceiling. With floor-to-ceiling modular wall constructions, it remains important to use panels that effectively block sound and seal well to each other for reducing sound transmission that might otherwise pass between the panels.”
The intelligibility of speech refers to the accuracy with which a normal listener understands a spoken word or phrase. Given the fact that some of the information communicated through speech is contained within contextual, visual and gestural cues, it is still possible to understand meaning even if only a fraction of the discrete speech units are heard correctly.
In a large auditorium and places where reproduced speech is used, the listener has limited access to these cues and must rely more heavily upon the sound actually produced by the mouth. This is where speech intelligibility plays a huge role by implementing the right acoustic elements to improve it.
The website www.gold-line.com states that for speech to be intelligible, it must have adequate audibility (sound pressure level) and clarity. For audibility, one should look at the signal-to-noise ratio. A voice is highly modulated and while intelligibility measurements do incorporate audibility, it comes into play when measuring the distances and reverberations of the sound that bounces off various platforms like the walls, floor and ceiling of a room.
When one wants to optimise speech intelligibility, you also need to look at the clarity of the sound that reaches a listener’s ear. Clarity is the property of sound that allows phonemes to be distinguished by a listener. According to www.gold-line.com, clarity is the freedom of these sound units from distortion introduced by any part of the sound system or environment.
Clarity can be reduced by amplitude distortion caused by electronics, frequency distortion caused by either the electronics or the acoustic environment, and time domain distortion due to reflection and reverberation in the acoustic environment.
According to an online course in acoustics posted on the website www.kemt.fei.tuke.sk, there are several methods of predicting speech intelligibility within an enclosure. These include the articulation index (AI), the speech interference level (SIL), the A-weighted signal-to-noise ratio (Lsa), useful/detrimental sound ratios (U80 and U95) and the speech transmission index (STI).
Each of these methods is based on the same fundamental principle, determining a ratio between the received speech signal and the level of interfering noise. It is this basic signal-to-noise relationship upon which speech intelligibility is deemed to depend – the higher the ratio, the greater the intelligibility.
There are basically three measurable factors which influence these signal-to-noise ratios: the level and manner of the speech output, the level and spectrum of background noise, and the nature and duration of the room response.
Highly specialised acoustic techniques are required in the design of a theatre. Van Zyl worked on the acoustic design of one of South Africa’s most prestigious theatres.
The Atterbury Theatre was built to create a superb classic concert hall and yet at the same time should be optimally “tuned” in respect of the spatial acoustical properties required for good functioning of sound systems employed in modern shows and conferences.
Some of the latest technical equipment available on the market was used to make the theatre the ideal venue for musical theatre productions, drama productions, performing bands, solo artists, dance productions, choirs and school productions. The theatre also includes a production and sound studio that can be utilised for the recording of shows, as well as CDs and DVDs. The Atterbury Theatre is further equipped with the latest audio-visual technology that makes it perfect for conferences.
“In a theatre, there has to be no audible sound interference from outside,” says Van Zyl. The theatre is situated on top of a gym, next to a busy highway intersection and in the middle of a busy shopping centre environment. “Insulation requirements for this project were extreme,” says Van Zyl. “The background noise from the buzz in the centre and the gym had to be managed optimally so that not the faintest sound from outside would reach the audience in the theatre.”
According to Van Zyl, a double floor construction with buffer space was specifically designed to prevent transmission of gym noise into the theatre. This was done by creating a sandwich-layered floor with a large sound absorbent space in-between the layers. Concrete was used for the floor layers.
Cavity walls with sound absorbing glass wool infill were also used to insulate sound..
As part of the design development and evaluation, Van Zyl acoustically modeled the theatre to quantify and assess its acoustical performance in terms of various acoustical quality ratings, such as reverberation times, loudness, clarity, transparency, intimacy and speech intelligibility. In this way it could be verified that every seat occupied during a show will be able to enjoy the performance on stage. Various acoustic elements were then incorporated in the design of the theatre to ensure that the sound quality is controlled optimally.
A lot of planning and measuring needs to be done in the design phase of building project to apply acoustics correctly. If it is not done properly, it will be difficult to change the acoustic properties of a space at a later phase of construction or after the project is completed. This is why it is crucial for an acoustic engineer to be involved in the process from the beginning, especially when acoustics plays an important role in the functioning of a building, like a hospital or theatre.
Full acknowledgement and thanks are given to Dr Ben van Zyl from Acusolv for the information given to write this article.