There are two different types of sound which are important for us.
...is the sound which spreads in solid bodies such as walls of houses, heaters, pipes, etc. Transmission occurs particularly by tremors which are conducted by vibrations, for example, via the masonry or in machines, which conduct the structure-borne sound perfectly mainly because of the large proportion of metal (metals are very good conductors!). In contrast to airborne sound, one can also feel structure-borne sound. Example: A car with a powerful bass system passes us in traffic - the windows are vibrating (or the whole car) - here, the low frequencies in particular are responsible for the palpable vibrations! The structure-borne sound is transferred from the surface of the objects to airborne sound - only then can our ears actually hear it (for example, a neighbour listens to techno music - the walls vibrate and then one hears, for example, the loud base in the bedroom).
... is ultimately the sound which can spread only via the air. This can be detected, at least by the human ear, from 20Hz - 20000Hz.
Structure-borne sound and airborne sound thus merge - and namely at the limits of object surfaces and air space