Motion vibrations occurring in a motor are propagated from the motor surface as airborne noise, and at the shaft and the motor’s fixed base as structure-borne noise, which to some extent is transformed into airborne noise for further propagation into the environment. In order to reduce the noise, a general approach is to interrupt the noise chain from the source to the transmission path to the ear, or to reduce the noise generation directly at the source. If this is not possible, one can at least try to make the noise pleasant or less objectionable.
Insulation and soundproofing
Sound barriers can be realized by sound insulation and vibration isolation. The insulation must be clearly distinguished from the damping layer, in which the vibration energy is converted into frictional heat. In solids, this frictional heat is caused by molecules or relatively large particles moving against each other in the body, but can also be caused by materials mounted on the outside of the device (e.g. foams, non-woven materials, elastomers) and exhibit a great deal of internal friction. In order for this material to also have a damping effect, it must be attached to the surface at the belly of the vibration wave. In other words, attached at the point where the vibration causes the greatest deformation of the material, this material is often referred to as an insulating material, and even if it is not insulating, it also acts as a damping agent.