SL-08-001 (RP-1314) -- Experimental Investigation of Reflection of Airborne Noise at Duct Terminations PDF

This paper is based on findings resulting from ASHRAE Research Project RP-1314.

This paper discusses the results from ASHRAE Research project RP-1314, which explored a number of issues pertaining to end reflection loss (ERL). A major focus of the work was to use the two-microphone impedance method to experimentally determine the ERL of a variety of rectangular duct configurations down to low frequency. This work also considered the impact that termination variations have on ERL and how experimental results correspond with analytic predictions and current ERL values in the 2003 ASHRAE Handbook—HVAC Applications (ASHRAE 2003). Major findings of the project include 1) the analytic ERLs for rectangular and circular ducts are equal for equal duct areas, 2) current ASHRAE ERL values differ from analytic values by approximately 1 dB, 3) experimental ERLs for flush terminations agree with analytic ERLs, 4) free-space ERL conditions probably do not exist in practice, 5) duct aspect ratio has no influence on ERL, 6) lay-in ceilings are not equivalent to free space, 7) flex duct causes ERL values to be dramatically reduced, 8) slot diffusers dramatically reduce ERL, and 9) blade diffusers and grilles have little impact on ERL.

Units: Dual