Humans are least sensitive to delayed sounds emerging from the same speaker

Evidence

Another surprise in Figure 6.6 is that delayed sounds originating in the same loudspeaker are more difficult to hear—the threshold here is consistently higher than for sounds arriving from the side or above, slightly for short delays, and much higher (10+ dB) at long delays. Burgtorf (1961) agrees, finding thresholds for coincident delayed sounds to be 5–10 dB higher than those separated by 40°–80°. Seraphim (1961), used a delayed source that was positioned just above the direct-sound source (~5° elevation difference) and found that, with speech, the threshold was elevated by about 5 dB compared to one at a 30° horizontal separation. The relative insensitivity to coincident sounds appears to be real, and the explanation seems to be that it is the result of spectral similarities between the direct sound and the delayed sound. These sounds take on progressively greater timbral differences as they are elevated (or, one assumes, lowered) relative to the direct sound. For those readers who have been wondering about the phenomenon of “comb filtering”, it is worthy of note that this evidence tells us that the situation of maximum annoyance from comb filtering, when the direct and delayed sounds emerge from the same loudspeaker (as happens when the comb filtering is in the program itself), is the one for which we are least sensitive (Clark, 1983). — Toole, Floyd E, Sound reproduction- the acoustics and…, 627

Categorization

• DEFINE: Connects the perceptual insensitivity to coincident delayed sounds with the comb-filtering phenomenon, clarifying why program-embedded comb filtering is least detectable even though it is characterized as most annoying.
• XREF: Echoes the later discussion of comb filtering in the loudspeaker itself and relates to audibility thresholds typical of the psychoacoustics-of-reflections literature. — connects to: The human voice best indicates poor sonic quality at a natural site. — Almo Farina, Soundscape Ecology: Principles,…, 2271