Study shows that active noise-cancelling headphones had no effect on work effiency

Work efficiency in open-plan office noise is not improved by active noise-canceling headphones, shows a recent study by a research group specialized in acoustics and psychology.

Headphones with active noise-canceling function are known to reduce noise more than conventional headphones. Their popularity has grown enormously.

− Companies can purchase active noise-canceling headphones for their offices, even for their entire staff. Such headphones are marketed with the promise that they improve work peace and work efficiency, describes Valtteri Hongisto, adjunct professor in noise control at Turku University of Applied Sciences in Finland.

The effects of active noise-canceling headphones during office noise had not previously been studied. The Built Environment research group led by Hongisto decided to investigate the effects.

According to the study, work efficiency was the same regardless of whether the subject was wearing noise-canceling headphones or not. Noise-canceling headphones did not even reduce the perceived annoyance of speech. Noise-canceling headphones were only beneficial if they were used to play a masking noise that covered up speech. This effect can also be achieved with conventional headphones that do not have an active noise-canceling function. The results apply to all types of active noise-canceling headphones, because they apply the same technology.

The result is explained by the fact that the active noise-canceling function only cuts through low- and mid-frequency sounds, i.e. frequencies below 600 Hertz. However, speech contains a wider frequency range, 200-10 000 hertz. The most important frequencies for speech intelligibility are above 600 Hertz. These frequencies contain the vowels and consonants of speech.

− According to the study, active noise-canceling headphones are not beneficial for work peace. However, they can be freely used, because they did not produce any disadvantages either. If you want to reduce speech noise using headphones, you can play, for example, the sound of creek or rapids through the headphones at the desired level. Speech is easily masked by it, says Hongisto.

56 subjects participated in the psychological experiment conducted in the laboratory. The experiment had five sound conditions, and they were created with different settings of the cup-shaped active noise-canceling headphones. The first condition was speech without headphones. In the second condition, the headphones were put on, which reduced the sound a little. In the third condition, the active noise-canceling function was turned on. In the fourth condition, the noise-canceling function was off and masking noise was played. In the fifth condition, masking noise was played and the active noise-canceling function was on. In each condition, the subjects performed work tasks and answered surveys.

The research team has previously shown that unnecessary speech noise during office work reduces work efficiency by up to 16 percent if the speech sounds are well distinguishable. The decrease in work efficiency can only be prevented by reducing the intelligibility of speech. This is best achieved by improving the room acoustics. However, speech intelligibility can only be reduced to zero by moving to a different room or phone booth.

Original research is available here