StAB - Structural Acoustics Loads and Transmission Facility

Structural Acoustics Loads and Transmission Facility

Photograph of the transmission loss window from the inside of the reverberation chamber of the Structural
Acoustic Loads and Transmission facility Photograph of the microphone array in the anechoic chamber of the Structural
Acoustic Loads and Transmission facility

The Structural Acoustic Loads and Transmission (SALT) facility consists of an anechoic chamber, a reverberation chamber, and a transmission loss (TL) window.

The anechoic chamber is 4.57-m high, 7.65-m wide and 9.63-m long, measured from wedge tip to wedge tip for a volume of 337 cubic meters. The double walls of the chamber (concrete and sheet rock) were designed to provide 54 dB of sound attenuation at 125 Hz. Two 0.21-m thick, 1.65-m wide and 3.13-m high swinging door assemblies, with reinforced metal facings and interior absorptive materials provide access to the room. More than 4850 open-cell, polyurethane acoustic wedges cover the walls, the ceiling and the floor in the anechoic chamber. The 0.914-m tall wedges have a 0.3048-m by 0.3048-m by 0.3048-m base with a 0.610-m long, tapered section for a weight of 1.69 kg per specimen. Absorption coefficients range from 1.19 at 100 Hz to 2.80 at 5000 Hz. The movable partition in front of the TL window is covered with an arrangement of 90 wedges. An hemi-anechoic environment can be obtained by removing the wedges from the floor of the anechoic chamber. The anechoic and hemi-anechoic chambers provide a free-field or a partly free-field environment for sound power, sound pressure level, sound intensity and directivity measurements of acoustic sources.

The 278 cubic meters reverberation chamber is structurally isolated from the rest of the building and measures approximately 4.5 m by 6.5 m by 9.5 m. The chamber walls and ceiling are splayed to diminish the effects of standing waves between opposite surfaces and are separated by a 30-inch air gap from the surrounding 0.46-m thick concrete building walls. The total surface area of the walls, floor and ceiling is approximately 290 meters squared.

The TL window accommodates 1.41-m by 1.41-m test structures to allow for sound radiation and sound transmission loss measurements. The TL window frame was installed on four isolators in the wall of the reverberation chamber. The reverberation and anechoic chambers are only connected by a rubber slab to prevent structural vibrations from being transmitted into the anechoic chamber. Concrete supports with steel fairings and multiple layers of lead provide high noise attenuation.

For a report on the calibration of the SALT facility click here.