Stuart Stephens, UK sales and product engineer at Shure Systems, explains why acoustic treatments in boardrooms are not as hard as you think.
Modern conference and boardrooms are notorious for poor acoustics. Everyone prefers working in environments that are light and open, but they also need to sound good to foster collaboration and support productivity.
Architects and interior designers create incredibly inspiring working environments, however these spaces are often rife with highly reflective materials like glass and metal. Every material, including people, contributes to the Reverberant Field of a room. Windows, glass partitions, tables, computers and tablet screens, hardwood floors and ceilings are the main culprits, offering little to no absorption of audio waves.
This can be a nightmare for the AV technician who is trying to optimise the audio equipment in a space that is not fit for purpose.
Whilst professional recording studios are free to successfully treat room acoustics with baffles, bass traps or diffusers, these solutions would rarely meet the approval of an architect or interior designer. Many companies are now offering baffles in various shapes, sizes and colours in order to meet strict visual requirements.
Reflections and Reverb
Sound within a room is comprised of direct sound, early reflections and reverberation. Direct sound passes straight from the loudspeaker to the listener’s ear but, as mentioned previously, sound emitted from a loudspeaker also bounces off walls, windows, floors, tables or any other surface in the room, before arriving at the listener. Any reflections arriving at a listener’s ear within 50ms are known as early reflections and are almost indistinguishable from the original sound source. Later reflections arriving beyond 50ms are considered part of the Reverberant field of the room.
For example, if you are in a video conference listening to the far-end caller through loudspeakers at the front of the room, you will hear the direct sound from the loudspeaker before any early reflections and lastly the reverberant field. If a room is too reflective the level of the reverberant field can smear or cloud consonants, making it harder to distinguish between words, which decreases the productivity of the meetings.
Another common acoustical problem in meeting rooms that can degrade the intelligibility of speech is flutter echo, which occurs when two reflective surfaces within a room are parallel (e.g. glass partitions and windows), causing sound waves to bounce back-and-forth. In contrast to reverb, even if the reflections arrive at the listener in under 50ms, the repetitive nature of the reflections make them audible as a flutter.
Flutter echo primarily contains mid-to-high frequency content, but at lower frequencies. A similar phenomenon occurs known as standing waves, or room modes. Room modes are naturally occurring resonant frequencies that are dependent on the dimensions of your room. The three room modes are Axial, occurring between two parallel surfaces; Tangential, where sound reflects off of four surfaces and Oblique, where sound reflects off of all six surfaces within a room (floor and ceiling, front and back, left and right).
If we focus on Axial modes, as the direct sound hits a surface and is reflected back, the reflection combines with the direct sound to reinforce peaks within the signal. The sound energy bounces back and forth between the two parallel walls, causing large peaks or cancellations within the frequency response of the room.
Fortunately, as room modes are dependent on the room dimensions, it is possible to calculate the fundamental frequency at which the standing wave will occur within a room. It is important to remember that additional standing waves will also occur at multiples of this fundamental wave (e.g. second harmonic, third harmonic, etc.).
Treating reflective rooms
When looking at room treatment we should consider both absorption and diffusion. Absorption reduces the amount of sound energy that is reflected back into the room by absorbing energy from a sound wave as it passes through. Absorption helps to reduce the reverberant field and minimise the impact of flutter echoes or standing waves. Absorbers are typically manufactured from high-density foam or fibreglass in various shapes, sizes and colours.
There are no rules on how much absorption you can add to a room: the greater the absorption, the lower the reverberant field. However, we are all familiar with a certain amount of reverberant noise in our day-to-day lives and if the reverberant noise is taken away entirely, it can lead to rooms that sound unnatural or ‘dead’.
The available space and cost are typically the limiting factors when treating a room with absorption but, as a guide, covering approximately 20% of the surface area of a room is a good starting point for controlling the reverberant field. Where wall space is unavailable or a limiting factor, acoustic ceiling tiles can be used to supplement the absorption within a room. A dropped or secondary ceiling can also serve as an additional source of sound transmission that contributes to the noise pollution in a room if not properly addressed.
Although rarely seen in conference rooms, diffusers are common in auditoriums where we might want to eliminate flutter echo but still conserve the overall sound energy within the room. As mentioned, too much absorption can lead to ‘dead’ sounding rooms without any, or a heavily dampened, reverberant field.
In some instances, it might be desirable to retain the acoustic qualities of the reverberant field but treat specific issues such as flutter echo. Diffusers prevent flutter echo by causing the initial sound waves to scatter evenly in a number of different directions, creating a diffuse sound field with an even frequency response.
Whether absorption or diffusion is used to tackle acoustic problems within a room, it is important that they have minimal impact on the original architecture and are visually pleasing to the client.
The good news
The good news is that there are ways to improve room acoustics without filling a clean and open space with obtrusive acoustic materials. Products like Primacoustic Cloud panels can be hung on ceiling structures more discreetly than wall mounted panels. These panels are also available with a paintable covering, allowing designers to match the colour scheme of the room.
Offered as ceiling clouds or wall panels, Cloud Paintables allow for absorption without impacting on aesthetics, effectively reducing reverberation and improving intelligibility in boardrooms, conference centres, educational facilities, performance spaces and more.
Cloud Paintables enable architects, designers and installers to design creative spaces without limitation. For larger spaces, a selection of hanging hardware allows Cloud Paintables to be suspended horizontally or vertically from the ceiling, absorbing sound energy on both sides for maximum efficiency, or wall-mounted using Surface Impalers to create a distinctive wall treatment.
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