Acentech’s RH Lyon Division conducted a noise audit of component noise sources and contributors on powered toothbrushes for a major manufacturer. Powered toothbrushes include several components: a battery, a small high speed electric motor, reduction gears, and a mechanical linkage that converts the rotational motion from the motor to a reciprocating motion of the brush. All of the design components are housed within the compact, handheld device. The goal of the noise audit was to determine which components are responsible for the noise radiated by the device that might be objectionable to the user and others nearby.

1/3 octave band spectra in Figure 1 show that noise radiated by the handle that houses the motor and gears is greater than noise radiated at the brush head. Peak noise levels occur in the 1600 Hz band and are due to housing vibration generated by fl uctuating forces at the mesh frequency of the reduction gears. Brush noise is likely to be more acceptable to the user as it relates to the primary function of the toothbrush. Gear noise is tonal in character which is generally less acceptable.

We achieved substantial overall noise reductions of ~5.4 dBA by focusing on gear induced vibration and radiation. The gears attach rigidly to the top of the housing, so we recommended incorporating soft rubber at the attachment to isolate the gearing and reduce vibration transmission into the housing, as shown in Figure 2. The connection of the motor/gear assembly at the base of the housing did not require modification.