A circular saw makes more noise because of the type of motor it uses. The circular saw has a universal motor in it, and this type of motor is extremely noisy.

Universal motors are called "universal" because they are happy to run either off of AC or DC electric power. Circular saws use brush-type universal motors. Vacuum cleaners, routers and electric drills also use universal motors. These motors produce so much noise because the brushes rub on the slotted armature. In circular saws and drills, you also have gear train noise.

Something like a radial arm saw or a table saw uses an induction motor instead. Induction motors run only on AC power and do not use brushes -- that is the main reason they are so quiet. They also run slower and usually use a belt drive instead of a gear train.

Manufacturers use universal motors because they are smaller and much lighter than induction motors. According to AMETEK Specialty Motors:

a 3/4 Hp induction motor runs at 1075 - 3450 RPM, is about 6" long x 6" diameter and weighs about 19 pounds. If we compare this with a universal motor with 3/4 horsepower output, we see a speed increase of about 15,000 RPM, a size reduction to about 6" long x 3" diameter {1/4 of the volume} and a weight reduction of greater than 85%.

The weight difference is huge -- a circular saw would be almost unusable if it contained an induction motor.

If you have a quiet appliance, it probably has an induction motor. Ceiling fans and refrigerator compressors use induction motors.

It is always a good idea to wear ear protection when using loud power tools -- even the quiet radial arm saw gets noisy as soon as it starts chewing through a piece of wood.

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