Multi-purpose apparatus for evaluation of noise transmitted through air ducts

The noise generated in HVAC systems by fans or air turbulence is propagated along ducts and, through duct walls, can be irradiated in rooms; moreover duct lines can easily transmit the sound produced in noisy environments from one room to another, vanishing the sound insulation of walls which they are passing through. The knowledge of sound insulating properties of duct walls is fundamental for a good system design, including unitary attenuators and active noise control devices. In this work a multi-purpose apparatus for evaluation of noise transmitted through air ducts in a reverberant room is presented. This apparatus allows one to measure, with the same equipment, the sound power level emitted from a short length ducts specimen in a reverberant room, as well as linear sound attenuation and break-in and break-out transmission loss. A further application of the same apparatus is the measurement of sound insulation and normal incidence impedance of small plane elements of isotropic or composite materials.