Passage:
In 2007, acoustical physicists Nico Declercq and Cindy Dekeyser analyzed the structural properties responsible for the exceptional sound clarity of the ancient Greek theater at Epidaurus. For decades, scholars had advanced competing conjectures: some argued that prevailing daytime breezes carried vocal sounds up the hillside, while others posited that Greek performers wore specialized masks that acted as rudimentary acoustic horns. Declercq and Dekeyser established that the theater's exceptional acoustics stem directly from the geometry and material of its stepped rows. The fluted limestone seats act as a natural acoustic filter, scattering and attenuating sound waves with frequencies below 500 hertz—the frequency range characteristic of ambient background noise such as rustling foliage and audience murmurs. Concurrently, the stone surfaces reflect and preserve frequencies above 500 hertz, which carry the consonant sounds essential to human speech intelligibility. This selective filtering significantly reduces acoustic masking, allowing unamplified voices from the central stage to be heard clearly even in the uppermost tiers. Furthermore, their calculations disproved the prevailing breeze hypothesis, showing that the theater retains its distinct acoustic performance under calm atmospheric conditions.
Based directly on the passage above, match each physical element or hypothesis with the corresponding explicit finding or role described by the researchers.
- Stepped limestone seat rowsThe physical structure that functions as a natural acoustic filter to reduce acoustic masking and preserve speech clarity
- Frequencies below 500 hertzThe acoustic frequency band associated with ambient noise that is scattered and attenuated by the stone surfaces
- Prevailing daytime breeze hypothesisAn explanation disproved by calculations showing the theater maintains its acoustic clarity under calm atmospheric conditions