Paurobally R.

Vacuum cleaners are noisy and disruptive appliances. Safety regulations, personal comfort and consumer demand are motivation to lower sound emissions from such products. The noise generated from a typical vacuum cleaner mainly consists of broadband random noise and tonal noise. Traditional passive control methods involving absorptive materials are unsuitable for reducing low frequency noise from vacuum cleaners since the bulk of such materials would disrupt airflow thus deteriorating performance. Conversely, active noise control (ANC) can be installed without decreasing airflow rate. Active noise control has been implemented in an industrial backpack vacuum cleaner. The aim is to attenuate a low frequency tonal component to reduce the annoyance while reducing the overall noise level. Experiments conducted in the feasibility study show that the tonal component can be reduced by about 15 dB to broadband level at the error microphone. Importantly, global attenuation can be achieved when the control system is confined to a duct around the lower body of the vacuum cleaner. However, the overall noise level is only reduced by about 2 dBA. Sound intensity measurements show that although random flow noise is a major contributor, structural vibration of the upper body and lid outside the duct also contributes to structure-borne noise radiation at the tone. To reduce the overall sound level, the noise control strategy must therefore include passive control methods such as absorptive materials and structural redesign to address structure-borne and flow noise.