Heavy machinery such as AG and SAG mills generate a significant amount of noise due to the processes that are occurring inside them._x000D_
From an environmental perspective, the level of noise generated is a significant occupational safety hazard._x000D_
However from a technical perspective the noise presents an opportunity to determine some details of the processes occurring inside the mills._x000D_
The noise generated is not random and can be attributed to a range of events that occur inside these mills, consequently non-contact acoustic determinations of in-mill behaviour provide powerful insights into the operation of the primary comminution tumbling mills._x000D_
Traditionally, the use of perfect mixing has been assumed when modelling the operation of AG/SAG mills. If this were true then the acoustic emissions from AG/SAG mills would be uniform along the length of the mill. Experimentally this has been found not to be the case. From another perspective it should not be the case because of the different conditions existing at the feed end compared to the discharge end. This paper presents the results determined by non-contact acoustics and their analysis in terms of understanding of the mechanisms occurring inside a mill._x000D_
FORMAL CITATION:Pax, R A, 2011._x000D_
Non-contact acoustic measurement of dynamic in-mill processes for SAG/AG mills, in Proceedings MetPlant 2011, pp 163-175 (The Australasian Institute of Mining and Metallurgy: Melbourne).