People draw rounded shapes for steady interior drone sounds.

Evidence

The fact that numerous people tested (in Canada) also produced rounded drawings in response to steady-state drones such as those produced by air-conditioners is perhaps explained by my remarks to follow about the taming of natural sounds as man retreats into artificially controlled interior environments. — Schafer, Murray R, The Soundscape- Our Sonic Environment…, 910

Categorization

• QUESTION: Worth pinning down whether this sound-visualization test was formally published, since only an anecdotal attribution appears here.
• corroborated: 2 independent passages support this claim — Schafer, Murray R, The Soundscape- Our Sonic Environment…, 910