Acoustical materials alter reflection spectra, invalidating broadband measurements for audibility

Evidence

All of this is especially relevant in room acoustics because acoustical materials, absorbers and diffusers, routinely modify the spectra of reflected sounds. Whenever the direct and reflected sounds have different spectra simple broadband ETCs or impulse responses are not trustworthy indicators of audible effects. — Toole, Floyd E, Sound reproduction- the acoustics and…, 678

Categorization

• QUESTION: What measurement alternatives do account for spectral differences between direct and reflected sound? This points toward a gap worth chasing in later chapters.
• XREF: Connects to signal processing knowledge about matched filters and why narrowband vs broadband correlation matters.