Sound width perception depends on signal type, not physical source size

Evidence

White water, or waves hitting the seashore, forms a wide sound source from the perspective of an observer. A listener, indeed, perceives such sound to be wide. … Humans are at their best in this task when the sound from different sources is noise-like or impulsive, or if different parts of the source emit different frequency content. On the other hand, if all the parts of the source emit sinusoids with equal frequency, the subject perceives a very narrow auditory event that does not depend on the actual width of the source. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 1485

White water, or waves hitting the seashore, forms a wide sound source from the perspective of an observer. A listener, indeed, perceives such sound to be wide. The ability to perceive the spatial distribution of a spatially extended sound source is not very accurate, especially if the type of sound signal is not optimal. Humans are at their best in this task when the sound from different sources is noise-like or impulsive, or if different parts of the source emit different frequency content. On the other hand, if all the parts of the source emit sinusoids with equal frequency, the subject perceives a very narrow auditory event that does not depend on the actual width of the source. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 1485

Categorization

• XREF: Connects to my soundscape reading — the perceptual gap between physical sound fields and auditory events echoes how lo-fi/hi-fi environments shape what listeners detect.
• QUESTION: Why do equal-frequency sinusoids collapse perceived width? Is this an auditory grouping/capture phenomenon worth tracing further?
• corroborated: 2 independent passages support this claim — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 1485