Why

Every ventilation duct product attenuates noise that propagates through it. The noise under consideration may originate from the ventilation system itself (fan noise, flow noise), from outside (environmental noise), or from an adjacent space (shared duct system).

A straight duct attenuates sound very little, and its effect is usually not considered in ventilation noise calculations. Control devices and bends attenuate sound more, but their effect is also typically disregarded. Significant sound attenuation occurs in terminal devices and silencers. Sound attenuation values must be based on laboratory measurements.

Products to be tested

• Terminal devices
• Silencers
• Filters
• Transfer air devices
• Grilles and screens
• Other components containing sound-absorbing materials

Test method

Sound attenuation (insertion loss) is determined according to ISO 7235 (with airflow) or ISO 11691 (without airflow) using the reverberation room method.

The measurement laboratory consists of three structurally isolated reverberation rooms and a workshop. The test system requires, in addition to the rooms, sound-insulated test ducts, other duct components, and transfer air paths. The system is designed customer-specifically according to the products to be tested. Available test duct sizes include 125 mm, 200 mm, 315 mm, and 500 mm. The appropriate test duct size is selected based on the product to be tested.

Figure 1 shows a schematic diagram of the sound attenuation test system. Sound pressure level measurements are conducted in Room 3. The test sound is generated into the duct system by a loudspeaker located in Room 1. The dashed line indicates the location for the terminal device and silencer.