insulation A fresh look at acoustics By Andrew Parkin, BEng (Hons) CEng FIOA FIHEEM, director of Cundall Acoustics
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coustic guidance for offices has been avail- able in many forms, from many publishers, for many years. A review of research into
office acoustics shows that since designers started to omit partitions back in the 1940s, inter- nal finishes, screens and space planning have been used to try to emulate the levels of acoustic privacy that had been otherwise lost. It is inter- esting to note that almost all the available acoustic guidance for offices (e.g. BS 8233: 1999, BREEAM, BCO etc.) takes this approach and assumes that everyone in an open plan office wants and needs privacy at all times. However, is this how we need the modern
office to operate? Are we still working in our own little silos or have our working practices evolved? I would suggest that there are much greater demands on our workspaces now, with a need for flexibility and adaptation. People on the same floor plate now need to be able to communicate freely with their co-workers, whilst not causing undue disturbance to others seated not far away. The acoustics of the space therefore need to support and facilitate this shift in work- ing trends. The workplace market is very different to that pre-recession (i.e. before 2008). Outside London, speculative office developments, or those without significant pre-lets or anchor tenants, are now few and far between. There is a growing trend towards refurbishment of old and tired buildings, often the only affordable option for businesses. Acoustically, this can offer much better solutions, more able to accommodate the varying demands of the end user. The method of procurement for speculative offices (i.e. shell & core, Cat A fit-out, Cat B fit-out) is incredibly wasteful and unsustain- able, with significant amounts of internal finishes scrapped between each stage; by refurbishing an existing office and going straight to Cat B, a more focused and best-fit approach can be achieved, with the needs of the end use at the very heart of the design.
So, how do we go about designing acoustic
flexibility into open plan workspaces? It all boils down to intelligibility of speech, i.e. whether it can be understood as well as heard. Where speech communication is needed, then co-workers need to be able to clearly hear and understand what each other are saying; this will involve a good signal-to-noise ratio (i.e. the level difference between the speech signal and background noise) and relatively calm reverberant conditions (i.e. not too much echo or too many reflections that may otherwise ‘muddy’ speech). Where speech pri- vacy is required, the signal-to- noise ratio needs to be low and some muddying of unwanted speech is an advantage. There are a number of design factors at our disposal that can facilitate these diametrically opposed require- ments within the same open workspace, includ- ing the following:
Background noise due to building services This will depend very much on the method of ventilation. For example, fan coil units are rela- tively noisy and will provide better masking of speech than a quiet system such as chilled beams or displacement ventilation. Where ventilation is particularly quiet, noise can be introduced into a space by means of noise masking systems.
Background noise due to external noise ingress Natural ventilation is often perceived as the more ‘sustainable’ solution, although this is not always the case (e.g. controlling heat loss through open- ings in a façade). The level of external noise will determine the corresponding internal level, result- ing in potentially better conditions for internal privacy in urban environments where traffic noise and the like is prevalent.
‘The move straight to Cat B fit out enables us to create effective
environments that best meet the requirements of the building occupants’
Using internal finishes to control sound Sound in an open plan workspace can either be absorbed, reflected or diffused. Absorption of sound limits its propagation that can help to ‘contain’ sound as well as provide a calm envi- ronment. Reflections can be used construc- tively to help transmit sound from one part of an office to another, enhancing com- munication, although care needs to be taken to avoid unwanted reflections that can create echoes that are unpleasant and particularly prevalent between parallel reflective surfaces. Diffusion, or scattering, can be used to
prevent unwanted reflections without deadening the sound (a factor used extensively in concert hall design), helpful in promoting good intel- ligibility; this can be achieved by using irregu- larly shaped fixtures and fittings or randomly tex- tured surfaces.
Use of furniture, fixtures and equipment (FF&E) and space planning This can be used to good effect to set out zones for communication and privacy. Having clusters of seating and desks that face towards a common point promotes communication, whereas spacing desks apart from each other by the use of other office furniture and equipment can effectively facilitate privacy. FF&E can also be used to control the other factors discussed above.
So, there are many factors that need to be con- sidered in the acoustic design of workspaces. The move straight to Cat B fit out enables us to create effective environments that best meet the requirements of the building occupants. The new Guide to Office Acoustics, published by the Association of Interior Specialists, provides more information and guidance on these issues.
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