Acoustics Laboratory Facilities
Duct Noise Test Facility
Measuring Noise in Ducts
The ‘Duct Noise Test Facility’ in the Department of Mechanical Engineering is used to measure the insertion loss of ducts, duct linings and other sound attenuating devices which may be placed in a duct.
The facility meets the requirement of ISO 7235: - ‘Measurement procedures for ducted silencers - Insertion loss, flow noise and total pressure loss’. The method of calculating the insertion loss is based on measurements of the sound pressure level (SPL) before and after the test specimen has been inserted. The facility provides for the measurement of pressure loss due to a test specimen in the duct.
Test Facilities
Facility Environment
The room in which the ‘Duct Noise Test Facility’ is located is acoustically treated to reduce the surrounding noise field. The walls of the room are lined with sound absorbing material, the floor of the room is covered in cut-pile carpet on top of foam underlay and absorbers constructed of Quash, a closed-cell low-density polyethylene foam are suspended from the ceiling above the test facility.
Apparatus
A schematic of the facility can be seen below in Figure 1. A centrifugal fan provides a mean flow for testing. The fan has an impeller diameter of 690 mm consisting of 11 backwards inclined laminar (straight) blades. The volume flow rate being controlled by varying the fan speed via a variable speed AC drive unit connected to the 15 HP three-phase motor. The fan and drive motor can obtain a maximum volume flow rate of ~4 m3s-1.
Figure 1. Schematic of Duct Noise Test Facility
Ducts
Currently, there are two duct sizes available for testing: 540mm x 380mm and 270mm x 300mm.
Figure 2 . Duct Noise Test Rig