Real-time method for measurement of noise exposure from sources in close proximity to the ear

Sound sources close to the ear, such as communication headsets present a special challenge when it comes to the measurement of the sound exposure. This is due to two facts: firstly, it is very difficult to obtain precision measurements of the sound field in a person's ear, secondly, noise exposure standards refer to sound measured in a `free' field, i.e., in the place where the ear would normally be found, but with the listener removed. In order to obtain data for exposure that can be interpreted in terms of conventional standards and codes, the authors developed a method based on an accurate acousto-mechanical model of the human head (ATF, Acoustic Test Fixture) (Kunov, Giguere and Simpson, 1989; Kunov, 1989). With the help of the ATF, a sound level meter, and an attached filter it is possible to read the equivalent free-field sound levels from a communications headset or any other source in close proximity to the ear, including any environmental noise that finds its way into the ear canal. This can be done for any type of device, including insert headsets. In particular there was an interest in obtaining a sample of measurements of the noise exposure of workers who use communication headsets under very different working conditions, and with different headsets, environmental noise, etc