Basic principles of acoustic design from ISO 22955

"ISO 22955: Acoustic quality of open office spaces" was released earlier this year. It specifies clear guidelines for what constitutes acoustic quality in open office spaces. The task of designing open offices with satisfactory acoustic conditions can be quite difficult. ISO 22955 reduces this complexity in several ways. One of them is a clear definition of the most important principles of room acoustic design. Because of this, ISO 22955 has great potential for acousticians and sound enthusiasts, who finally have a standard to refer to when prescribing acoustic design interventions for open offices. So what are the basic principles of acoustic design from ISO 22955?

In this post, we bring you a list of simplified notes describing the basic principles of acoustic design from ISO 22955. These include:

• General principles
• Ceiling insulation
• Wall insulation
• Floor insulation
• Acoustic images
• Geometry of the room
• Sound masking systems

General principles:

Acoustic room design basically involves covering room surfaces with sound-absorbing materials to prevent sound reflections. The more sound is absorbed by the given material (ie higher coefficient of sound absorption) and the larger its surface, the better. Preference should be given to surfaces directly exposed to sound sources in the room.

Ceiling insulation

The ceiling is the most important surface of the room and should absorb as much sound as possible. A wall-to-wall sound-absorbing ceiling is preferred.

Wall insulation

In a typical open office, the wall area is relatively small compared to the ceiling area. However, wall absorbers are still a good way to reduce the reverberation time if the open office is furnished minimalistically. They also minimize echoes and sound reflections of workplaces located close to walls, especially in the corners of open offices. Wall absorbers should be installed at the height of the ears of the users of the room.

Floor insulation

In general, the impact of acoustic treatment on floor surfaces in open plan offices is not significant unless highly specialized solutions such as perforated cavity floors are installed. The soft floor contributes only very moderate absorption in the higher frequency ranges. The main spatial acoustic benefit of carpets is the minimization of footfall noise from stairs and furniture.

When designing office buildings with an access floor, special attention should be paid to facilitating the structural sound insulation properties of the structure.

Acoustic images

Acoustic images increase the privacy of conversations through an open office. They do this by minimizing sound propagation over long distances. The effect of acoustic curtains depends on the quality of the acoustic environment: the less sound-reflecting surfaces are present, the more privacy the acoustic curtains provide during conversations.

The height of acoustic images should be sufficient to block the direct path of conversation from one workplace to another. It should also be noted that acoustic screens extending above and below the table surface provide a higher degree of privacy during conversation.

Both absorption and sound attenuation determine the effectiveness of acoustic screens.

Furniture

As a rule, the furniture is not sufficient to satisfy the acoustic needs of open office spaces. Instead, in acoustic treatment, treatment of room surfaces with sound-absorbing materials should be preferred.

Geometry of the room

Open offices are generally characterized by a relatively low ceiling height in relation to their floor area. This dimensional relationship, in conjunction with the acoustic soffit, serves to minimize sound propagation and should therefore ideally be followed when designing open office spaces.

Particularly long and narrow room shapes should be avoided, as they amplify sound propagation through open offices.

Sound masking systems (not prescriptive)

The use of sound masking systems (ie increasing background noise levels with electronically amplified sound sources) is quite controversial. There is evidence both for and against the effectiveness of sound masking systems.

Both laboratory and field studies indicate that noise levels above 45 dB(A) are already too high. Above this level, sound masking systems can also trigger the Lombard effect.

Natural sounds seem preferable to digitally generated noise (white, pink, etc.).