On-axis flatness alone fails without controlled off-axis directivity.

Evidence

The DM12 had good on-axis response, but exhibited the classic 6-inch (150 mm) two-way off axis misbehavior. The Infinity (c) had good directional control but a mid-frequency hump determined the tonal balance of the product. — Toole, Floyd E, Sound reproduction- the acoustics and…, 1945

Categorization

• XREF: Directly instantiates the causal chain: driver size/geometry → off-axis response → reflected sound coloration in rooms.