Anna Wilczura, Acoustic Engineer, Nowy Styl Group
Acoustics in the workplace is a problem that most employees encounter. Intense and unwanted sounds, which we call noise, contribute significantly to a drop in effectiveness and concentration. In order to mitigate the adverse impact of noise in the office, we must accurately determine its source and choose measures to prevent and if possible eliminate it from our environment. One of the effective ways of ensuring a good acoustic environment in an office space is suitable furniture arrangements.
In terms of interior acoustics in offices, it is important to maintain a low level of speech intelligibility, with an appropriate background noise level and general noise level. What does that really mean? We understand background noise in the office as sounds propagated in the room, both from the outside and from the devices located inside, without the employee's presence. The requirements as to the maximum background noise levels are laid down in standard PN-B-02151-2:2018-01. In offices where administrative work is performed and there are internal noise sources, this level should not exceed 45 dB. However, if background noise is much lower than the level of the sound generated by employees' conversations and there are no room dividers provided in the room to limit its propagation, speech will be easily intelligible, even in remote parts of the office. This situation impedes concentration because employees' sounds will not be masked by other sounds, thus preventing their colleagues from performing their duties effectively.
One possible solution is the use of an electronic sound masking system comprised of a network of loudspeaker devices. The devices generate noise at a suitable level so that it does not affect employees adversely and reduces the distance at which conversations heard from adjacent workstations cause distraction. The loudspeakers can be used to play music, the sound of the sea or forest, or other pleasant sounds. However, if no such experiments are welcome, it is still worth investing in suitable interior arrangements that will improve acoustic conditions and allow employees to work effectively.
The main source of undesirable sounds in the office is obviously our co-workers. A human being is naturally adapted to ‘eavesdropping on’ other people; therefore, even subconsciously we often try to analyse the content of distant conversations. The human voice is one of the most distracting noise sources. Hence, if we can hear colleagues talking on the phone at the other end of the room we have less chance to work effectively.
Aside from employees, there is a wide range of other undesirable sound sources in offices: phones ringing, printers, copiers, shredders, keyboard and mouse sounds, or colleagues' heels pattering against the floor.
The room itself may contribute to an increase in the noise level generated by other sources. If it has not been designed with sound-absorbing finishes and suitable equipment that acoustically insulates workstations and office devices, an acoustic wave will spread freely and the reflections from all confining surfaces will overlap and create so-called reverberation noise.
If there are few sound-absorbing surfaces in a room, reverberation time and noise may be reduced by sofas or modular systems with enhanced sound absorption properties. However, the principle of ‘the more, the better’ does not work here. Sound-absorbing materials should not be excessive: despite the fact that they will contribute to a decrease in reverberation noise, too many may lead to the creation of a ‘deaf’ office, where the conversation of nearby colleagues will be even more intelligible, and thus more distracting. The frequency characteristics of the sound absorption coefficient are also important and are often provided by manufacturers even in the case of furniture. Thus, an acoustician will select products characterised by appropriate parameters, determine their number necessary to meet standards, and indicate where to place the products so that they best fulfil their function.
Besides sound-absorbing furniture, acoustics may even be improved by the ubiquitous office cabinets, which can be an alternative to office partitions. If they are at least 1.4 m tall, the cabinets can have a favourable impact on limiting noise propagation between adjacent rows of desks. In addition, blinds or perforated doors may be fitted to the cabinets. Hence, instead of reflecting sound, they become a sound-absorbing trap, which is more effective than sponge-covered furniture and wall or desk panels filled with porous materials. This is particularly significant in rooms where there is no acoustic suspended ceiling, which is often the only surface capable of absorbing to a large extent an acoustic wave with frequencies below 500 Hz.
Another significant aspect, which mainly pertains to open space offices, is to limit the propagation of direct sound between workstations. Desk panels or partitions may be used for this, and the most essential parameter here is the height. Walls or panels of height 1.2 m or lower will not help here, because the average height of human ears is 1.2 m when they are sitting at a desk. Furthermore, an acoustic wave bends at the edges of barriers, which further reduces the effectiveness of such a baffle. Because an acoustic wave is also transferred by being reflected from a surface, in the case of desk panels it penetrates into further parts of the room, passing under the desk. Therefore, the optimal solution to separate workstations is partitions of 1.4 m or higher, and if an office lacks sound-absorbing surfaces, we can use panels filled with sound-absorbing materials. However, we must remember that they should be characterised by sound absorption coefficients adjusted to the room being furnished. Moreover, it is necessary to consider that without acoustic adaptation of the ceiling even high partitions will be barely effective as an acoustic wave will be reflected from the ceiling and will come back to the person on the other side, just as light reflects from a mirror. An important parameter to consider while choosing partitions is the effectiveness of a noise barrier provided in decibels: the higher the value, the less sound will penetrate into the other side.
If informal meeting zones are to be placed in our open space, it is worth applying modular seating systems with high backs, which will isolate the sounds of conversations inside. Such upholstered furniture may also have good sound-absorbing properties, and it is important these booths have sound absorption characteristics in the frequency range relevant to human speech (125–2000 Hz), which will enable us to prevent the unpleasant feeling of ‘blocked ears’ while inside.
As with furniture, each surface in the room affects the quality of its acoustics. Floor coverings suppress the unwanted sounds from steps, moving chairs, etc., and they also absorb other sounds to a certain extent and may contribute to a decrease in reverberation noise. Some floor coverings manufacturers specify sound absorption coefficients in their product data sheets: due to the thinness of the materials these values are not very high, but compared to smooth concrete for example the difference will be relatively large.
There are solutions aimed controlling the acoustics in an interior space by absorbing an acoustic wave within the desired frequency range or scattering it in a suitable way. Nowadays offices are primarily equipped with sound-absorbing elements in the form of panels mounted on the walls, islands, or panels suspended vertically under the ceiling – so-called baffles. Such panels are most often filled with foam, or nonwoven or mineral wool covered with breathable upholstery. Located in suitable places, the panels help to reduce adverse sound reflections from the surface of walls or the ceiling. Furthermore, they reduce reverberation time, so that the room is quieter. In the office acoustic products market, free-standing elements are also starting to appear in the form of columns or corner elements that provide sound absorption within a range of lower frequencies. This type of product can be an effective solution in small rooms, such as meeting rooms, where flutter echo or unpleasant ‘rumbling’ may hinder conversations, including those conducted through videoconference systems.
Nevertheless, one should be aware that the mere arrangement of an office – the appropriate layout of furniture as well as the choice of materials and finishes – may exert a significant influence on the noise level. The application of even some of these elements and modifications in the layout of furniture will help control noise. It is worth doing this in cooperation with an acoustician, who will treat this issue appropriately.