Guidelines for selecting silencers

The following information is needed to determine silencer Insertion Loss (IL) and Pressure Drop (PD) performance:

• Insertion Loss (IL) requirements
• Forward (supply) or reverse (return) airflow direction

Forward flow: airflow in the silencer is in the same direction as the noise propagation
Reverse flow: airflow in the silencer is in the opposite direction to the noise propagation

• Maximum allowable silencer PD
• Airflow (cfm)
• Length, width and height restrictions for where the silencer is to be installed, connecting duct dimensions.

The IL requirements, quoted for octave bands 1 through 8 may be determined by:

• Comparison to an existing specification
• Duct system analysis.
• Application-dependent requirements, such as elimination of low frequency or tonal noise

Example of Web-based Silencer Analysis

By incorporating the most up-to-date design analysis algorithms recognized by ASHRAE, this example from a leading manufacturer of a no-cost software service provides a complete eight-octave band acoustic analysis The program produces a report that displays whether or not a design meets the required noise level within the critical space. If the sound levels are not met, the program will automatically choose a duct silencer that meets the required attenuation while still meeting the user specified constraints such as the application’s allowable height, width, and length and pressure loss.

Conclusion

Proper acoustic analysis of an HVAC duct system is an important part of any design. Design professionals should always set specific acoustic requirements and analyze the duct system design to determine how much unwanted acoustic energy (noise) is produced by the system. A correctly performed acoustic analysis will determine exactly how much noise treatment is required to provide a quiet system with the lowest initial and operating costs.

Celebrating over 55 years, Kinetics Noise Control has extensive experience in designing and manufacturing innovative products to control sound and vibration. Established in 1958 as engineers focusing on sound and vibration control, Kinetics pioneered development of pre-compressed, molded fiberglass pad isolators that would be incorporated into an innovative new floor isolation system. Previous trade names of Kinetics Noise Control include Consolidated Kinetics and Peabody Noise Control. www.kineticsnoise.com