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BANKEN UND BEHÖRDEN • BANKS AND AUTHORITY BUILDINGS TECHNISCHER AUSBAU • TECHNICAL SOLUTIONS

Foto: Annica Feuss, Projekt: Mercer Deutschland GmbH in Frankfurt am Main, Entwurf: conceptsued, München

Foto: Kinnarps, Projekt: NCC Suomi Oy in Oulu, Entwurf: Tytti Nevalainen/Kinnarps

Zwei Tipps zur akustischen Optimierung von Büroräumen: Arbeitsplätze im Großraumbüro immer in Reihe anordnen. In kleinen Büros oder Besprechungszimmern verhindern Wandabsorber die Entstehung von Flatterechos.

D esigning acoustics correctly is an exciting task. The Japanese acoustician Ya- The sound-absorption surfaces of all the products are then added up and are the
suhisa Toyota has even become a star with his design of some worldwide fa-
overall result for the room. This calculation has to be done for each frequency!
mous concert halls. Good sound is also decisive in the office! Even though the de- Which absorbers are most effective? It turns out that acoustic ceilings absorb a lot
mands are different since it is here not about music but speech. The spatial sur- of sound across all frequencies. For achieving this, a ceiling offers the largest sur-
roundings have an essential influence on the quality of our work. If the acoustics face available for installing acoustic elements. Walls are often used to put up ca-
are attuned to the tasks, the first basic conditions for a successful office routine binets and had thus better be kept free. Carpet, on the contrary, only becomes ef-
are established. Empty offices in the shell state are reverberant since sound is re- fective starting at 2,000 Hz. It is thus less suitable for absorbing speech than for
flected on the smooth surfaces. A solution is the installation of absorption surfaces footfall sound absorption. It depends on the carpet’s structure height. A thin pro-
on ceilings, walls and floors since they reduce reverberation time. Recommenda- duct such as a carpet can only absorb the short, high frequencies whereas a sus-
tions are found in the technical guidelines for workspaces ASR A3.7, VDI 2569 and pended ceiling also manages to absorb long, deep frequencies. The combination
DIN 18041. The main cause of reverberation in offices is the communicating human of the two measures may thus result in a good basic equipment of rooms. For a
being. Our speech consists of many frequencies and the recommendations are rough classification of extensive absorbers, the so-called absorber classes A to E
thus directed at all the frequencies in the relevant range between 250 to 2,000 has been introduced. Since here a single value classifies the whole product, ho-
Hertz (Hz). Depending on how a room is used, different reverberation times are re- wever, it is a strong simplification where deviations of individual frequencies are
commended (see [1]). Generally it can be said: The better speech is to be under- not clearly identifiable and thus not suitable for acoustic overall concepts!
stood, the shorter reverberation time should be! This for instance means for mee-
ting rooms – depending on their size – 0.4 to 0.5 seconds. In offices where concen- Wall- and movable-wall absorbers serve for optimization
trated individual work is in the foreground, it is more of a disturbance if speech is
understood. Reverberation of 0.5 to 0.8 seconds is here the goal. Ideally, the voice Besides reverberation time, in large offices acousticians also test how the volume
contents are then lost in the diffuse noise level. The arrangement of the absorbers decreases with the distance in the room. Mobile walls, cabinets and partitions as-
in the room also plays a role. The guidelines thus also have advice in this respect: sist in shielding workstations and zones in larger rooms. This decreases sound pro-
In offices and lounges, the absorption surfaces are evenly distributed whereas in pagation. The goal is to restrict speech intelligibility to the immediate environment
training rooms the wall behind the lecturer and the centre of the ceiling should be and thus avoid disturbing other persons. Mobile walls or attachment on top of
left free of absorbers (see [2]). These areas then function as reflection surfaces. desks are recommended where concentrated work has to be done in larger offices.
Thus even medium-sized rooms can dispense with a loudspeaker system. If A part of the sound can thus already be absorbed at the source while the remai-
speech is hard to understand in a room or distorted, it indicates that reverberation ning reflected sound is then absorbed by the ceiling. When planning workstations,
time is too long. If, on the contrary, speech can be very clearly understood, it it is important to know that sound spreads spherically around the head, hence
points to a reverberation time which is too short. The goal is to create a balanced also to the sides and towards the back. It is thus best to arrange the workspaces
relationship between room volume and absorption surfaces (see [3] and [4]). one behind the other. In this way, a wall is able to absorb the sound of two per-
sons. For classic double workstations where the employees sit opposite each other,
Acoustically effective ceilings and floors form the basis a mobile wall or a cabinet at the back is recommended. Team workspaces are to
make coordinating among the members possible. It therefore does not make sense
Ceilings and floors are the first possible absorbers. Acoustically effective products to inhibit this but rather to separate complete teams with cabinets or partitions.
are usually tested according to ISO 354. The test certificates list their sound-absor- In small offices or meeting rooms, the wall surfaces are in the focus. Wall absor-
bing qualities as so-called coefficients, individually for every frequency (see [5]). bers are used to avoid flutter echoes between parallel walls. They can at the same
The 0 sound-absorption degree means that a product completely reflects sound; a time be used for decorative design purposes or as pinboards as long as there are
1 sound-absorption degree means that the product completely absorbs sound. The sufficient other absorption surfaces. For interior designers focused on acoustics, it
coefficients are mostly in between. A product’s sound-absorption surface thus cor- is always a pleasure if the absorbers are from one product family, a large choice
responds to its surface multiplied with the sound-absorption coefficient (see [6]). of fabrics is available and the surfaces can be coordinated as to their forms and

152 • AIT 12.2019