The In’s and Out’s of Office Acoustics
Posted in Acoustic Consultants News on Jul 11, 2018
For many of us, more hours are spent in the office than in our own homes. For this reason, it is imperative that intelligent design incorporates the key considerations of office acoustics, and in this blog we will go into some of the important factors when it comes to getting noise exactly right in a professional work environment.
If there is one goal which is central to design when planning acoustics in office spaces, it is achieving a desirable level of background noise, while also controlling the intrusive noise level between areas. In offices, people need to concentrate so minimising disturbance will always be an important aim.
Speech Intelligibility is a key parameter when incorporating office acoustics into design plans. It is quantified by the Speech Transmission Index, between the source of the speech and the receiver. Where some designers miss a trick is looking at the Reverberation Time as the 'be all and end all', but Reverberation Time is just one factor which adds up to make up the Speech Transmission Index.
Speech Levels are another of these important factors. These decrease when the receiver moves away from the source, and it is the Reverberation Time - that is, the extent to which the sound energy is absorbed in the room - which the Speech Levels are dependent on.
Sound absorption can be controlled by intelligent placement of 'treatment' - small screens between desks for example, or glazed partitions and bookcases. In this way, a designer or acoustic consultant is able to control Reverberation Time, and thus Speech Levels, as well as add to the layout of the room.
The right reverberation
Reverberation Time influences both the acoustic characteristics of office features, as well as the room volume. Acoustic consultants are able to lower reverberation time with the addition of soft finishes, such as walls, ceilings and floors. There can be several disadvantages to higher reverberation in an office environment.
Firstly, inhabitants could be faced with a build-up of noise due to the longer absorption time, and then an unwanted 'snowball effect' as workers raise their voices to be heard over the noise of their fellow workers in different parts of the room. The direct sound is blended with multiple reflections of sound, meaning sound in rooms which are full of harder, rather than softer surfaces, takes longer to die down.
The importance of containing sound and lowering reverberation is even more pertinent in offices such as call centres, when a number of workers are likely to be talking concurrently. In these situations, screens can be ideal, but it should be noted that there are some potentially negative consequences of installing screens, such as the possibility that lines of sight are cut, communication becomes harder, and interactions are more seldom. Ultimately, the acoustic consultant's job is often a balancing act which is conducted in line with the priorities of the organisation which inhabits the office.
Hitting your targets
While there are few formal acoustic standards which a consultant can refer to when inputting into the design plans of an open plan office, there are some useful guidelines which can be taken into account. For instance, BS8233:2014 ‘Guidance for sound insulation and noise reduction for buildings’ sets out advice that if ceilings are higher than 3m in open plan offices a background noise level of between 45 – 50 dB Laeq,T is recommended. Then there is the British Council for Offices' 'Guide to Specification', which concurs that the range should be around a similar 45 dB Laeq,T.
Acoustics consultants can advise when it comes to Speech Intelligibility, to ensure you hit a Good or Excellent rating means speech can only be heard in the immediate vicinity of the speaker - i.e. when sat next to or in front of. Fair is classed as speech which can be heard in the "general vicinity" or on the same desk or the desk behind. Poor refers to speech which can be heard at a distance of over 5m, while finally, Bad means noise from a speaker can even be heard on other floors and in other rooms.