A leading manufacturer of consumer household appliances was seeking to gain a better understanding of the sources of acoustic noise in their line of blenders and food processors. Acentech was retained to help gain a better understanding of the acoustical challenges of these products. After a comparison of the noise from three representative models, Acentech completed a comprehensive noise audit of one model, chosen by the manufacturer.
A noise audit is a thorough investigation of all elements of a product in order to identify and quantify the levels and sources of the noise that product creates. Acentech performs these tests in a special reverberant room, which provides a diffuse field for the noise, allowing for the accurate capture of the total sound power being produced. The “window” method, whereby the unit is enclosed within a highly effective barrier while parts of the barrier are then removed to expose just one component, was utilized as part of the noise audit.
Acentech’s measurement revealed that the blender noise consisted of broadband noise plus some prominent tones centered around the motor and blade rotation rates. Further testing utilizing vibration indicated that the source of some of these tones lay within the planetary gearbox. The main finding was that most of the noise contributing to the high sound levels is relatively high frequency broadband airborne noise from the motor, radiated out through the cooling vents in the base of the units.
Acentech’s findings led to recommendations of a short term solution of investigating the feasibility of adding sound absorption to the interior of the base while still allowing fo the necessary cooling airflow. A recommended longer term solution was to determine the specific sources of motor noise and to consider a redesign of the drive system in which the motor does not need to rotate faster than the blades when some containers are attached.