Adding rear speakers at matching angles does not improve spatial illusion
Evidence
Interaural cross-correlation coefficient (IACC) has long been associated with spatial impressions, image broadening, ASW and the like—the more different the sounds at the two ears (the lower the IACC) the stronger the spatial illusion. Tohyama and Suzuki (1989) looked at a few arrangements of two and four loudspeakers, comparing measured IACCs to those found in a truly diffuse sound field—an all-but-unachievable goal in the real world, but an academic ideal. Results shown in Figure 7.7(a) indicate, not surprisingly, that 2-channel stereo did not come close to replicating the diffuse-field IACC. The real news, though, is that doubling the number of channels by adding a symmetrical pair of loudspeakers behind the listener at the same angular separation did not really change anything. The solid dots (two channels) and open dots (four channels) in the figure are very similarly placed, and neither matches the target curve. This was the original layout for quadraphonic sound, shown in Figure 8.1, confirming that it was not an effective use of channels and loudspeakers. — Toole, Floyd E, Sound reproduction- the acoustics and…, 724
Categorization
- XREF: Connects to the broader theme of perceptual essence vs raw channel counts; also relevant to the reader’s understanding of why quadraphonic sound failed historically. — connects to: Adding rear channels to stereo does not improve spatial diffusion — , Toole, Floyd E - Sound reproduction-…, 1670; Uncorrelated noise from surround speakers creates enveloping source perception. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 1914; Side-placed surround speakers beat rear placement by wide margins — , Toole, Floyd E - Sound reproduction-…, 1672
- corroborated: 2 independent passages support this claim — Toole, Floyd E, Sound reproduction- the acoustics and…, 724
Broader Connections
- Adding rear channels to stereo does not improve spatial diffusion
#corroborates(0.95) — , Toole, Floyd E - Sound reproduction-…, 1670 - Uncorrelated noise from surround speakers creates enveloping source perception.
#contradicts(0.80) — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 1914