Loren Cook Sound Laboratory

Loren Cook Company in Springfield, Missouri is a major manufacturer of HVAC fans and related equipment. Their recently completed acoustics laboratory represents the state of the art in sound testing laboratories designed to conduct sound power testing of fans using the AMCA 300 test method. The facility consists of a 1,018 cubic meter (35,900 cu.ft.) reverberation chamber with a large control room equipped to handle up to 16 observers to witness equipment tests. The facility is designed to test inlet, discharge, and casing radiated fans of all types and sizes from 20 CFM to 40,000 CFM at static pressures up to 10 inches of water.

There are several unique features to this lab. First, the reverberation chamber ceiling has two different heights. The ceiling height in the majority of the room is 22 feet, but the 8" thick concrete ceiling drops to 14 feet above the floor along the entire east side of the room to facilitate testing of rooftop units with supply and return air openings in the floor. Another unique feature is the use of two microphones on the same rotating boom. One microphone is 10 feet from the center of rotation, and the other is at the opposite end of the boom 5 feet from the center. Sampling the sound field in the room with both microphones simultaneously results in greater precision than one can get with a single rotating microphone. The facility also includes a sound monitoring system which permits the user to monitor (through headphones or via ceiling mounted loudspeakers in the control room) remote areas during a sound test from the control room.
The all-concrete reverberation chamber weighs a total of 922 tons, and it floats 4 inches above the at-grade slab on 9,817 Mason bridge-bearing Super W neoprene pads. The outer building shell is constructed from 8" thick pre-cast concrete wall panels and 4" thick concrete roof panels to isolate the facility from exterior noise. A total of 13 gypsum board and 17 aluminum panels of various sizes are mounted on the walls and ceiling of the reverberation chamber to provide added low frequency absorption (LFA). The LFA panels are necessary to meet the pure tone qualification limits specified in AMCA 300 and ISO 3741. The reverberation time and pure tone qualification charts show the impact of the LFA panels as they were added to the chamber. The values in parentheses represent the percentage of the interior surface area that is covered by LFA panels.