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The foremost source of noise in open-plan offices comes from telephone calls and discussions between co-workers. Conversations are particularly disturbing because of the information content. Speech recognition notoriously distracts much more than other noises of a similar level.

However, if numerous people are speaking at the same time at a sufficient distance, we are no longer able to recognize what they are saying, and the noise generated has a beneficial masking effect on speech nearer to us.

Privacy and distraction

The most important acoustic parameters in open-plan offices are the amount of sound absorption material (usually in the ceiling), the use of screens and background noise.

Whereas room acoustics are usually characterized by the reverberation time (that is, the persistence of sound in an enclosed space after the original sound is produced), ISO 3382-3 introduces different acoustic parameters. These are the spatial decay rate of noise for a typical speech spectrum, and speech intelligibility as a function of distance.

These, in turn, help calculate two important measurements : privacy and distraction distances.

Privacy refers to the distance from a source at which speech is no longer intelligible due to attenuation and background noise. In some offices, however, this is longer than the total length of the office, which means privacy is not possible.

Distraction refers to the distance where speech is only partly intelligible, but mostly contributes to the background noise.

The ideal solution is to bring together people who want to share information, preferably within the distraction distance, and to keep further away those belonging to other groups.