Material sound

Professional Definition

In construction and architectural acoustics, the distinction of the noise propagation path is crucial for effective insulation.

Material sound – sound propagating through a solid medium as a result of the interaction of airborne sounds or material vibrations with that medium.

This means that the carrier of energy is not air here, but the building structure (floors, walls, pipes). This sound becomes audible to us (as airborne sound) only when the vibrating structure radiates it back into the air in our room.

Acoustics in Simple Words

Imagine that you live in an apartment on the 3rd floor. A neighbor on the 8th floor is drilling a hole in the wall with a hammer drill. Even though five floors and many closed doors separate you, you hear that drilling as clearly as if they were standing right behind your wall. Why?

The drill bit striking the concrete causes the entire wall slab to vibrate strongly. These vibrations do not "search" for air – they rush directly through the rigid, interconnected building structure (concrete and steel conduct sound exceptionally well, much faster and with less loss than air). These vibrations travel down through the reinforcement and load-bearing walls until they reach your room. There, they vibrate your walls, which act like large speaker membranes, emitting noise directly into your ears.

Material sound occurs in two main ways:

1. Direct impact: Steps of a neighbor in high heels, a falling object, a drill, moving furniture. These are known as impact sounds (a subcategory of material sounds).

2. Excitation from air: Very loud music (especially bass) from a neighbor can make the wall vibrate, which will transmit through the structure to other apartments.

That's why sound insulation for material sounds is so difficult – sealing the doors is not enough. Often, you need to "cut off" the transmission path, for example, by using floating floors or expansion joints that interrupt the continuity of the structure and prevent vibrations from traveling further.

Summary

Material sound is noise "trapped in walls". It propagates within solid bodies – the building structure or plumbing pipes. It is the main culprit behind neighbor issues (thumping, drilling) because it can travel long distances in the building structure almost without energy loss, ultimately radiating as audible noise in a distant room.