Acoustic Design in Open Plan Offices

January has been a very busy month for ParkerJones Acoustics! And much of this work, has been on the topic of acoustic design in offices. We’ve been helping to consult on the fit-out of offices in London, Birmingham, and Bristol this past month.

Open plan offices in London have been an area we have particularly been involved with recently. And with it, comes the opportunity to conduct acoustic modelling. These are able to be manipulated to show the changes in reverberation, build-up/control of noise levels, and the impact on speech intelligibility and speech privacy, throughout the entire open plan office, in a visual and easy to understand way.

Along with our acoustic modelling, we’ve been creating rendered images to demonstrate how acoustic treatment and screening products might look in the finished development. We understand that the aesthetic of the space is a critical part of the interior design and that acoustic solutions must fit seamlessly into this. This includes liasing with acoustic treatment suppliers/installers such Standapart to gauge the practical and cost implications of our proposed acoustic design solutions.

Optimal Acoustic Conditions in Offices

Achieving optimal acoustic design in an office-based working environment hinges primarily on achieving:

• A suitable level of reverberation for the intended use of the space, particularly in open plan areas and rooms with audio/video conferencing systems.
• A background noise level which is designed to be quiet enough in meeting rooms, but not too quiet in other areas such that noise from adjacent areas is more perceptible.
• A high level of speech intelligibility and in some areas, speech privacy, to ensure that speech is clear in conversations and phone calls in the area they are occurring, but not as clear for unintended recipients in surrounding spaces, where eavesdropping is usually unintentional but can be unavoidable.

However, the required balance of each factor above is very much dependent upon how the space will be used!

Cellular Offices

Small cellular offices are used in a straightforward manner, i.e. people sit working quietly at a desk, they may have a conversation with their neighbour, or over the phone. The workers in these offices tend to be part of a team, hence there is not much need for privacy between them. Therefore, achieving a moderate reverberation time and a moderate level of background noise should be adequate for occupants to be productive in their work.

Meeting/Conference Rooms

In a meeting room people are sat around a central table, talking directly to one another, hence there is a need to make sure that speech has clarity. If there is an audio/video conferencing system, then it’s important that the room acoustics lend themselves to a strong, clear audio signal, particularly if attendees cannot see each other on either end of the line, missing many of the visual cues which help with speech intelligibility. A much lower reverberation time and a low background noise level are important for optimum speech clarity in this case.

Open Plan Offices

An open plan office is different. How an open plan space is used is not necessarily straightforward. There may be those who work individually and silently; people who work individually but in constant conversation on the phone (such as a call centre), those who work in a team over a group of desks where regular communication is required; people using breakout spaces for an informal meeting; or groups using the same space for socializing at lunch. There is not necessarily a set pattern in many open plan spaces.

The removal of partitions also means the reduction of acoustic privacy. The distraction of hearing other people’s conversations and the consciousness that their own conversations can be heard by others can give rise to complaints by the occupants. Therefore, unlike cellular offices and meeting spaces, there is not necessarily a desire to achieve high levels of speech intelligibility throughout. Commonly, a high level of speech intelligibility is desired between users within the same team, and a low level of speech intelligibility is desired between different teams, such to keep distraction and noise nuisance to a minimum. I.e. good speech intelligibility is important to the person next to you, opposite you, behind you or on the same row of desks in your team, but speech privacy is more important from the person sat 3 rows of desks away.

This needs a slightly different design strategy to cellular offices, whereby a very low reverberation time is beneficial to reduce the spread of sound energy from speech, and a moderately high background noise level can actually be a good thing, to help mask the sound of others conversations and avoid unintentional eavesdropping.

Acoustic model of an informal meeting area

Rendered images showing how acoustic treatment may look like in the finished room

Comparison of speech intelligibility with no acoustic treatment, with a more suitable reverberation time, and then with acoustic screens. Enhancing speech privacy in an open plan office

Speech privacy between open plan areas after artificially increasing background noise levels through a speech masking system

Rendered images showing how acoustic treatment might look in a conference room