Study of noise levels at the workplace

Customer: Confidential
Country: France
Application: Defense

The Challenge

Metravib was consulted by a defense industrial customer regarding noise and vibration issues at the workplace, and more specifically concerning :

  • Reduction of noise and vibration levels inside military vehicles
  • Improvement of the intelligibility inside such vehicles.

The Solution

To answer the questions raised by our customer, we carried out a test campaign on board a military vehicle in different operational configurations (static, dynamic, with ventilation and without ventilation).

The evaluation of the acoustics onboard the vehicle can lead to propose palliative measures to control the measured noise levels:

  • Reduction of noise levels at the source
  • Organization of the working day so that the workers remain exposed to levels below 85 dB(A) in an equivalent 8-hour daily exposure (which represents the threshold of danger beyond which, according to the WHO, damage can occur).
  • Use of hearing protection at the workplace whenever levels exceed 80 dB(A).
  • To control vibration levels, it may be necessary to modify the damping characteristics of vehicles or to set-up suspended seats (seats mounted on a shock absorber).

Concerning the second issue, we carried out intelligibility measurements in the presence of a noise source. The purpose of these measurements is to verify that a spoken message is audible and interpretable by all the vehicle occupants without persons having to raise their voice. We rely on the Speech Transmission Index (STI) and RASTI to determine the level of intelligibility inside the vehicle in an operational situation.

To get as close as possible to the STI index we can recommend the following measures :

  • Reduce noise levels at the source
  • Improve internal acoustics of the cabin
  • Use dual function headsets: they combine an active/passive noise reduction function and dedicated microphones. The use of these headsets must comply with the maximum noise levels to which vehicle users may be exposed.

At the end of the various works carried out, our customer was able to ensure that the acoustic and vibratory levels of his vehicle remain moderate for the majority of the uses. He will be able to use these outcomes as an attractive selling point with his customers.