Theory of Vibration Isolation and Transmissibility [PDF]

High vibration levels can cause machinery failure, as well as objectionable noise levels. A common source of objectionable noise in buildings is the vibration of machines that are mounted on floors or walls.

Obviously, the best place to mount a vibrating machine is on the ground floor. In this article, I am going to explain What is the theory of vibration Isolation and transmissibility in a detailed manner.

Vibration Isolation Theory:

• Unfortunately (but fortunately for noise control consultants), this is not always possible.
• A typical problem is a rotating machine (such as a pump, AC compressor, blower, engine etc) mounted on a roof, or on a floor above the ground floor.
• The problem is usually most apparent in the immediate vicinity of the vibration source.
• However, mechanical vibrations can transmit for long distances, and by very circuitous routes through the structure of a building, sometimes resurfacing hundreds of feet from the source.
• A related problem is the isolation of vibration-sensitive machines from the normally occurring disturbances in a building (car or bus traffic, slamming doors, foot traffic, elevators).
• Examples of sensitive machines include surgical microscopes, electronic equipment, lasers, MRI units, scanning electron microscopes and computer disk drives. 

Transmissibility Theory:

   Transmissibility is the ratio of output to input.

    Transmissibility (T) = output/input

• T>1 means amplification and maximum amplification occurs when forcing frequency (ff) and natural frequency (fn) of the system coincide.
• There is no unit designation for transmissibility, although it may sometimes be referred to as the Q-factor.

The transmissibility is used in the calculation of passive compensation efficiency.

Some FAQ related to Theory of Vibration Isolation and Transmissibility:

References [External Links]:

• Vibration Isolation
• (PDF) Vibration Isolation: A Review
• Vibration isolation and force transmissibility - Nptel