Wall mounting creates a comb-filter cancellation dip whose frequency scales with baffle size.

Evidence

Figure 13.8(b) shows what happens when the loudspeaker is simply mounted on the surface of a wall. For comparison purposes the half-space data from Figure 13.7 are repeated in (a). It can be seen that there is a strong acoustical interference dip at about 220 Hz. We saw this before, back in Figure 13.2, but at a lower frequency. This loudspeaker is smaller, and the round-trip distance from the woofer to the wall and back is shorter: about 31 inches (787 mm), which is one-half wavelength at about 220 Hz, the destructive-interference condition representing the first “tooth” in a comb filter. — Toole, Floyd E, Sound reproduction- the acoustics and…, 1483

Categorization

• DEFINE: Concrete instance of a comb filter’s first destructive-interference tooth tied to a specific physical dimension.