Two types of noise
Our daily life is overloaded with unwanted noise. Sound has two basic forms: acoustic energy and mechanical energy. Each type of sound has to be tackled in their own way.
1 Acoustic energy
Acoustic energy or sound is what we experience every day. It is in fact vibration of air (sound waves) which is transformed by the tympanic membrane in the ear of human to audible sounds.
Do you want to reduce this noise, then you will have to slow down or absorb the sound waves in the air. Classic absorbtion materials like thick curtains, carpets, acoustic panels, etc.
2 Mechanical energy
Mechanical energy is the source of acoustic energy. Everything what vibrates, brings the surrounding air in motion and thus creates acoustic sound. Sometimes in a desired shape as the speakers of a hi-fi system, but mostly it is undesirable (ambient) noise.
The body of an automobile which is exposed to a constant sources of sound of the motor, drive line, rolling noise of the tires and the road surface, the roughness of the road surface etc.
In ships is mechanically sound produced by waves and from the engine.
Cargo spaces of vans.
Transportation pipes used in petrochemical and food industries, etc.
Sound is produced in all of the above examples and passed through the structure. Specifically, you hear even the drop of a screwdriver 50 meters away on a steel oil platform.
To counter this you will have to do something to prevent the vibration of the structure. PYROTEK NC and VIBRAMOUNT develop products to reduce the vibration and resonance.