Psychologists have found that noise reduces human efficiency. This effect may be considerable even for the most phlegmatic individuals. Moreover, almost everyone objects to unnecessary noises. In recent years there has arisen a very insistent demand for quieter electrical apparatus. This applies particularly to household apparatus such as refrigerator motors, vacuum sweepers and the like. Practically noiseless motors are also required for various drives ( refrigerating plants, circulation pumps of hot water systems, big ventilating systems for rooms, organ bellows etc. ) in non industrial plants such as storerooms, business houses, hotels, hospitals, churches, theatres etc> where all noise should be suppressed. It must also be noted that the stage has been reached where it is taken for granted that the products of the better known manufacturers will give entirely satisfactory performance, and often, the deciding factor between various makes is only the quietness with which the equipment operates. However,noise and vibration are not merely annoyances which may affect the sale of a product or lower the efficiency of a worker. They are often evidences of defects in design and manufacture which seriously affect the life of the equipment and, in many cases, the safety of the user.[...]

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