In developing retrofit noise controls for mobile mining equipment, it is critical to document their effectiveness. In our particular work, we need to know first how the controls affect noise levels by the operator ear and second how the controls affect levels inside hearing protectors. While scientific experiments demand repeatability, a true evaluation would assess actual working conditions, which, in the case of mining, is not very repeatable.To obtain data, the following procedure has been developed. After discussions with the operator, a course is set up to simulate the actual operation of the machine. This is fairly repeatable. Then two miniature microphones connected to a dual track tape recorder are put into place - one at the entrance to the operator's ear canal, the other on his shoulder. The operator next puts on a set of muff type protectors over one microphone and as he operates his untreated machine through the predetermined course, noise is recorded simultaneously through both microphones. A noise control or set of controls is installed’ on the machine which is then run through the same course. This process is repeated until all desired controls and combinations are tested.In the laboratory, the tapes are first played through an X-Y plotter to obtain a time history of the recorded noise levels, Then a real-time analysis is made of the different segments of the simulated operator tramming, loading, dumping, etc. Comparisons of these frequency plots gives three pieces of information: 1. how the controls are affecting levels at the operator ear 2. how the controls are affecting levels inside the ear protector 3. how effective the ear protectors are Analysis will determine which controls are most effective and a cost benefit analysis will determine which should be used.In developing retrofit noise controls for mobile mining equipment, it is critical to document their effectiveness. In our particular work, we need to know how these controls reduce the noise levels both at the operator ear and inside hearing protectors. This paper describes the techniques used in gathering and analyzing this data and presents a specific example.