Assessment of the helicopter cabin noise impact on mental calculation and memory performance

Helicopters passengers are more and more demanding in terms of acoustic comfort inside the cabin. They wish to work, read, or relax, without the need of wearing a noise cancelling headset. Recently, active noise control has made considerable progress, and systems can be embedded in the passengers' seats. Yet, this technique requires to carefully design filters that target the frequencies that are the most annoying. However, predict and characterise the discomfort and the negative impact of noise on passengers can be difficult for manufacturers, the effects of noise on cognitive functioning and emotional state is complex. In this study, the impact of various helicopter cabin noises was evaluated on perceived acoustic comfort, cognitive performance and physiological activity. 20 volunteers were asked to perform the "TNT", a task combining mental arithmetic and memory load, while they were submitted to 5 different noises and a silent condition. These five noises varied in terms of tonal frequencies amplitude: raw, filtered, low-frequency, high-frequency and isophonic. Subjective results showed that the silent condition was less stressful than all noises. More importantly, the raw sound was evaluated as the most annoying. No difference of task performance across the different noises were found, which is consistent with the literature. Cardiac and brain activities were measured during the experiment via electroencephalography and electrocardiography and showed an effect of time on workload and fatigue. Ultimately, these results will allow to define filters for an active noise control system to optimize acoustic comfort. Filters might be tuned according to the type of task performed by the passengers and as a function of their actual physiological activity.