Although strides of progress have been made in source noise reduction, some types of industrial and manufacturing equipment such as hammer mills, power presses, plastic grinders, diesel engines, etc., are still quite noisy. In addition, there are many equipment installations where the cost to develop noise reduction measures for old vintage equipment is prohibitive. In these situations, the acoustical engineer must consider enclosing the equipment in either a partial or total enclosure. The thought of an enclosure is initially repulsive to the plant engineers, the maintenance staff, and the operator because of the anticipated nuisance associated with the loss of visibility, accessibility, and added maintenance. These penalties are not inherent, and a well-designed enclosure can provide bonus features such as mist and smoke control. In summary, the disadvantages of total enclosures are obvious; costly additional floor space is generally required, and some production penalties associated with machine operation and maintenance must be anticipated.