Field testing of wood joist floor/ceiling assemblies and comparison with laboratory test results

Abstract

New construction of multifamily living units often includes noise insulation performance testing. The degree and source of deviation of field test (FSTC and FIIC) values from those of the prototype laboratory specimen are generally not predictable. Field testing according to ASTME336‐77 (FSTC) and ISO140 VII‐78 (FIIC) were performed. In this test series, flanking and the site background noise was controlled and octave‐band data was used to reduce test time [A. J. Campanella, J. Acoust. Soc. Am. Suppl. I 69, S8 (1981)]. Testing was conducted in partially completed units including wood framing, windows, doors, wiring, limited HVAC ducting. Wall FSTC tests generally agreed with laboratory tests, but the wood floors of rooms of reduced dimensions exhibited serious FSTC and impact sound level deficiencies amounting to as much as 10 to 14 dB in the 125‐Hz octave band. Additional 63‐Hz octave‐band data indicated that the floor/ceiling structures exhibited low TL values in either the 63‐ or 125‐Hz octave bands. This phenomenon was linked to bar‐like resonance in short joist lengths (8 to 10 ft vs 14 ft in the lab test). Accelerometer measurements on exposed joists showed significant joist vibration in the free‐end mode for the 125‐Hz band under impact excitation. A layer of gypsum board was added to the subfloor sandwich to effect mass loading and added damping of the free‐bar joist vibrational mode so that the 125‐Hz FTL was greater than that of the 63‐Hz octave band. Acceptable FSTC values were achieved by in addition placing the ceiling gypsum board on separate 2×4 subjoists with an added layer of R‐11 insulation.