- Project number: F 2443
- Institution: Federal Institute for Occupational Safety and Health (BAuA)
- Status: Completed Project
Description:
The trend towards multi-person offices is continuing. At the same time exposure to noise has been identified as a major stressor in office work. This is true in particular of unwanted but intelligible speech noise in the work environment. If collective protective measures, such as room acoustics or organisational solutions, are not implemented consistently or are insufficient, employees often seek to protect themselves by wearing headphones that isolate them from noise and/or mask it with other kinds of sound. Such headphones are increasingly equipped with active noise control (ANC) technology.
In this project, objective measurement methods were used to investigate the extent to which headphones of this type can actually suppress unwanted speech noise during office work. The headphones’ sound attenuation was measured using a standardised method (DIN EN ISO 4869-3:2007). This involves the use of an artificial head located in a diffuse sound field. In addition, the transmission path for speech signals from outside through the headphones to the microphone of the artificial head was determined by measuring its influence on the Speech Transmission Index (STI). Both the active and passive noise attenuation features of the headphones were taken into account, as were different background noises. The STI is used - in office acoustics for example - as a measure with which to characterise the transmission quality of a speech signal from a source to the receiver, since there is a correlation between the STI and the expected speech intelligibility, defined as the proportion of the transmitted speech that is correctly understood.
Measurements taken with headphones from 2019/2020 found no evidence to suggest ANC technologies were particularly successful at suppressing ambient speech. Compared to headphones in passive mode, the ANC function leads to a moderate rise in the STI for most models and noise situations. Under certain circumstances, even greater increases in the STI were measured, with STI values under ANC headphones higher than for unimpeded transmission without headphones.
According to these first results, ANC headphones cannot at present be expected to ensure the targeted, highly effective suppression of unwanted speech noise in an office setting. It will remain desirable for annoying speech noise in the wearer’s surroundings to be considered as a scenario for the utilisation of ANC headphones when products are developed in future. Clear descriptions of the applications for which they are intended and instructions for their use are also to be recommended. It should be readily apparent from the product documentation, for example, whether a pair of headphones or one of its settings is intended to increase responsiveness if worn during office work, or whether it is intended to help suppress speech noise more effectively.