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4 ways to achieve effective noise reduction:

Sound Insulation. With this approach to noise control, the goal is to introduce a solid barrier to the environment that helps lessen the reverberation of the sound waves. Much like the insulation of a house helps keeps warm air in and cold air out (and vice versa depending on the seasons), this approach effectively mitigates the transference of sound within a defined area by adding materials which block the transfer of sound waves. High-density materials such as concrete, steel, and stone are often used in this application because of they are difficult to penetrate.

Sound Absorption. This concept is based on a basic law of physics which states that energy can neither be created nor destroyed. However, it can be converted into another form. In this case, the energy found in sound waves is converted into heat. By extension, this process then minimizes the amount of noise in the environment by reducing the amount of remaining energy in the sound wave. As a result, the amplitude of each sound wave cycle is diminished, thus causing the associated sound to trail off, as well.

As the name implies, this method of noise reduction relies on using porous materials that actually “soak up” the sound. Permeable materials such as polyurethane foam and materials are among the most popular material choices to accomplish this.

Vibration Damping. This form of noise control applies more to vibrating surfaces rather than air-borne sound waves. In effect, a damping mechanism is employed to extract the energy from the vibration and convert it into heat. As with sound absorption, this approach relies on converting the energy present in the original vibration into another form of energy (heat), thereby diminishing the amount of energy available for the original action (vibration). The end result is that the impact of the vibration on the surrounding environment is controlled.

Vibration Isolation. This form of noise control is based on protecting an object (or individuals) from a vibration. This is accomplished by introducing some form of physical impediment to the environment which produces an effective barrier between the object or individual being protected and the vibration source. An easy way to visualize this concept is to consider the suspension system of an automobile. In this example, a system of springs, brackets and shock absorbers are used to protect (isolate) the occupants inside the vehicle from the impact of the outside environment.