IMPLEMENTATION OF A TUNING SYSTEM FOR HELMHOLTZ RESONATOR ARRAYS IN A HVAC DUCT

摘要

Onsite tuning is mandatory to utilize Helmholtz resonators for HVAC ducts. However, no tuning device or general-use system is yet available, and engineers have thus been avoiding the use of such resonators. The objective of this study is to develop a tuning system for resonator arrays for HVAC ducts. We employed the cavity volume, resonator neck resistance and neck open area as control parameters to tune the resonance frequency, resonance sharpness and sound dissipation factor, respectively. To control the cavity volume, resistance and neck open area, respectively, a cylinder with a screwed shaft, a spiral spring with adjustable gaps between the spring plates, and a camera aperture were used. These were controlled by individual stepper motors, which were driven by signals supplied by a PC. An experimental resonator array tuning system composed of six prototype tuning devices was build and installed in a section of a 250-mm diameter duct. The eighteen parameters of the six resonators were tuned successively through a feedback approach allowing the transmitted traveling plane wave to reach its target spectrum with reasonable precision. When a resonator tuner was inactive at its target resonance frequency, this target resonance frequency was switched to that of the next inactive tuner.