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A manufacturer of automated countertop and wall-mounted soap and hand sanitizer dispensers, which work by sensing the presence of a hand to activate a motor and gear drive mechanism to pump out a small amount of liquid cleanser, was concerned about the noise made by these units. Acentech carried out a series of evaluations aimed at determining and characterizing the main sources and mechanisms of radiated noise, evaluating how effective various alternate designs could be at generating less noise, and quantifying how the units compared to others in the marketplace. The end-goal was to gain a better understanding of the primary sources of noise in this manufacturer’s line of touch-free dispensers, and to use that knowledge to come up with recommendations for design changes that can result in quieter products.

Acentech’s noise audit method and reverberant room were first used to characterize the total noise radiated by the various components and parts making up these dispensers. Paying special attention to the transient nature of the dispensing noise, we developed and implemented analysis procedures that could be used to consistently characterize these transient sounds across a range of different samples and models. We also used vibration measurements and analysis to determine that much of noise was due to certain gear mesh forces being transmitted to the covers of the device, which then could efficiently radiate noise.

Acentech’s main recommendation was to change one of the higher speed gearsets from having straight-cut gear teeth to having helical-cut teeth. The manufacturer did this and we were able to verify that units incorporating their production helical gears resulted in the overall A-weighted noise levels dropping by about 5 to 6 dB, with noticeably reduced gear “whine” noise. The results and recommendations obtained from this project will be applied to the design of current and future dispenser models.

Download the PDF project summary here.

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