jats:p This paper investigates the novel possibility of utilising the structural concrete floor slab as a means of providing additional mid- to low-frequency sound absorption through the addition of cavities on the ceiling side, formed using flexible formwork, acting as Helmholtz resonators. Mid- to low-frequency sound absorption in rooms is typically achieved through the use of perforated plasterboard or a suspended tile-in-grid system. Such an approach can separate the room from the thermal mass of the ceiling above, leading to higher peak temperatures or increased cooling load. Suspended ceilings can also increase the embodied energy of the building and limit the potential for stack effect ventilation by reducing room height. In this work, frequency-dependent absorption coefficients of perforated concrete samples were measured using an impedance tube test. The results were found to agree with a theoretical analysis, suggesting that it would be relatively easy to predict the performance of perforations of other depths and diameters including those targeted at absorbing higher frequencies. </jats:p>jats:p Practical application: The measurements indicate that such a slab could be used as a practical replacement for perforated plasterboard or a tile-in-grid system. This would allow the slab to be tuned to the building’s acoustic performance and structural requirements. The approach has the potential to: (1) reduce the embodied and operational energy of buildings; (2) improve thermal comfort and (3) create a better acoustic environment in situations where surface robustness or longevity is important, for example public stairwells, pathways under roads and metro stations. </jats:p>