This paper is based on findings resulting from ASHRAE Research Project RP-1335.

Building air distribution terminal system designers and system installers require accurate quantitative information on the noise performance of the installed system to achieve optimum system efficiency while maintaining preferred levels of human comfort. This research project, covered in three papers, establishes the diffuser baseline performance and then determines the field installation adjustment values. The first paper covers baseline performance. The second paper documents the field conditions difference in throw and pressure loss from ideal conditions of six types of ceiling diffusers, each with three different inlet sizes at three different inlet velocities. This paper documents the field conditions difference in sound performance from ideal conditions of the same variety of diffusers and inlet velocities. Full-scale laboratory testing of typical field installation variations was completed with variations in damper installation, duct approach angle, duct type, duct vertical height above the diffuser and close coupling duct installation. A predictive model for sound generation was developed and used to create a set of look-up tables that can be used to easily predict how the installation configuration would affect room sound levels compared to published data.