Which one of the following is correct? A concrete wall generally,

A concrete wall interacts with sound waves through reflection, absorption, and transmission. While dense concrete is primarily known as a superior sound reflector—often reflecting up to 99% of sound energy [t2]—it also possesses inherent properties that allow for both absorption and transmission. Concrete masonry effectively blocks airborne sound transmission due to its mass and rigidity, but some sound energy still passes through, a phenomenon measured by Sound Transmission Class (STC) ratings [t4][t5]. Additionally, concrete can absorb noise, diminishing its intensity; the degree of absorption depends on the material's porosity and the presence of open pores [t1][t9]. Modified or lightweight concretes are specifically designed to enhance these sound-absorbing qualities [t1][t8]. Therefore, a standard concrete wall does not exclusively reflect sound; it simultaneously absorbs a portion of the energy and transmits the remainder through the structure [t2][t3].

Sources

1. [1] https://pmc.ncbi.nlm.nih.gov/articles/PMC7830111/
2. [2] https://www.sciencedirect.com/science/article/abs/pii/S2352710222008282