Smooth flat on- and off-axis response correlates with subjective preference.

Evidence

It had the best-looking set of measured data, confirming the perspective that there is value in smooth and flat frequency responses on and off axis. In subsequent subjective evaluations, this loudspeaker remained “king of the hill” for an extended period. — Toole, Floyd E, Sound reproduction- the acoustics and…, 73

Categorization

• XREF: Foreshadows the book’s central thesis that measured smoothness predicts subjective preference — the same claim later formalized in Spinorama and CEA-2034 work.