Projects

Sound masking floor-standing luminaire

© Fraunhofer IBP

Prototype of the sound-masking floor-standing luminaire, detail of the luminaire body with integrated loudspeaker.

Sound-masking floor-standing luminaire for open-plan offices, example workplace layout.
© Fraunhofer IBP

Sound-masking floor-standing luminaire for open-plan offices, example workplace layout.

Prototype of the sound-masking floor-standing luminaire for workplaces in open-offices, detail of the luminaire body.
© Fraunhofer IBP

Prototype of the sound-masking floor-standing luminaire for workplaces in open-offices, detail of the luminaire body.

Introduction
Everyone working in an office shared by a number of people is familiar with the scenario: phones blare out their ring tones, speech fragments buzz around, continually disturbing our thoughts and distracting us from working efficiently. In short, it takes a lot of inner calmness and power of concentration to be able to work successfully in such an office.

Many people can testify to what this means in the daily working routine: In Germany, around 10,5 million people work in offices, and most of them in open-plan offices. The high noise level in these offices not only impacts the well-being but also influences the cognitive performance of the employees, which investigations in office buildings performed by the Fraunhofer Institute for Building Physics IBP confirm. The measurement results can be quantified even more precisely in the laboratory. 

The researchers tested, among others, the cognitive basic functions of the test persons, using the established “Serial Recall” test: A number of digits appeared on the computer screen which the participants had to memorize and, after a certain time, had to enter into the computer again. This test was carried out by the researchers first in a quite environment, similar to the environment of an individual office. Then they carried out the same test with a high ambient noise level, comparable to the ambient noise of an office shared by numerous people.

Result: In an open-plan office the verbal short-term memory works 10% less efficiently as compared to a quiet environment, i.e., people forget things they have been told faster. Looking at the average work profile of office or administrative staff, this issue gets particularly relevant. The proportion of silent work amounts to 60% in comparison to 25% of work time spent for phone calls and meetings at the workplace. Without appropriate measures those employees, that are working in silence, feel disturbed almost constantly by the speech noise of their colleagues, which they cannot avoid hearing.

Intelligible speech is more distracting
The extent to which phone calls and meetings affect the concentration of the other employees is less dependent on loudness than on speech intelligibility. No matter how considerately the colleague whispers as quiet as possible in the phone – as long as his sentences are still intelligible for his colleagues sitting next to him, they will feel disturbed. A measure for the intelligibility of speech is provided by the “Speech Transmission Index” (STI). This index assigns the value of one to perfect intelligibility, and the value of zero to unintelligible speech. How strong the own ability to concentrate is disturbed by the voices and conversations of the colleagues that you can't avoid hearing, is also demonstrated by tests carried out at the Fraunhofer Institute for Building Physics IBP. The error rate of the test persons in tests with intelligible speech emitted from the environment was 10% higher (STI of 0,6) than with tests performed in a quiet office. The error rate dropped down to 2% with an STI of 0,3, compared to a quiet environment. Shielding measures and sound absorbing walls are only of limited help for masking disturbing sentences and conversations of the colleagues. It is a package of sound absorbing and sound shielding measures applied in combination with the so-called sound masking that helps significantly reduce this disturbing effect. In this respect, masking means: A further noise is emitted, that does not reduce the loudness of the original noise but overlays the disturbing speech sound. Thus, the conversations of the colleagues become unintelligible and the cognitive basic functions of the individual employee are hardly affected anymore.

Individual masking systems enhance people’s concentration
Masking systems are already quite common in open-plan offices in the USA. These systems consist of a grid of loudspeakers mounted below the ceiling, emitting consistently a monotone wide-area noise throughout the entire open-plan office, comparable to the sound of a ventilation system. This system is often perceived as a constant “sprinkling from above”. In Europe, however, it could not prevail. The office users feel to have no longer a personally controllable workplace and see their need for privacy reduced – which is why they rated the system negatively.

A sound-masking floor-standing luminaire for office workplaces is designed to overcome these problems. It has been developed by engineers and psychologists of the Fraunhofer Institute for Building Physics IBP in collaboration with their colleagues of the Nimbus Group in Stuttgart. The background noise does not emit immutably from above. Each workplace is equipped with a floor-standing luminaire which offers two advantages at the same time: On the one hand, the noise is focalized only to the individual workplace by the integrated loudspeakers, i.e. the employee can personally control the loudness he considers to be comfortable. On the other hand, the noise significantly masks the conversations and phone calls of the colleagues even if they raise their voices or if the masking sound is quiet. The floor-standing luminaire is sure to meet with high acceptance . Meanwhile, a prototype of the luminaire is available and has received an award already. The featuring of the sound-masking LED workplace luminaire at the industry's leading international trade fair for modern working environments ORGATEC 2014 attracted a lot of attention.