Development of passive and active noise control for next generation locomotive cabs

The noise environment in a locomotive cab has been the focus of recent attention by the Federal Railroad Administration (FRA). In October 2006 the FRA established a new rule to amend its existing occupational noise standards for railroad employees whose predominant noise exposure occurs in locomotive cabs. The noise exposure rule is expressed in terms of the A-weighted noise level and is consistent with OSHA limits set for general workplace noise exposure. Recent studies have shown that low-frequency sound can be an important contributor to noise induced hearing loss as well as fatigue. Therefore the focus of the FRA rule on the A-weighted noise level may not be enough to guarantee a fatigue-free cab environment where low-frequency sound sources are dominant. This paper describes the research project sponsored by the FRA to demonstrate the feasibility of a combination of passive and active noise controls in the cab of next generation locomotives. A mock-up of a locomotive cab was used to demonstrate the feasibility of active noise control to reduce the low-frequency noise levels. The active noise control system focused on eliminating key pure tones that are typically found in the noise spectrum from a diesel engine.