Modal density rising smoothly with frequency predicts perceptually smooth room response

Evidence

In general, the number of resonances within a given frequency bandwidth increases with frequency. In fact, it can be shown that they increase proportionally to the square of the frequency, and in large well-behaved acoustical spaces, which sound good, this increase in mode density with frequency is smooth. This is the rationale behind a method for assessing the modal behavior in a room known as the “Bonello criteria.” These criteria try to ascertain how significant the modal behavior of a room is in perceptual terms. This is done by dividing the audio frequency spectrum into third-octave bands as an approximation of critical bands and then counting the number of modes per band. If the number of modes per third-octave band increases monotonically, there is a good chance that we will perceive the room as having a “smooth” frequency response despite the resonances. If the number of resonances per third octave drops as the frequency rises, there will be a perceptually noticeable peak in the frequency response. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1981

Categorization

• DEFINE: Defines the Bonello criteria, a diagnostic method for judging a room’s perceptual evenness from modal counts per third-octave band.
• SEED: Article angle: using the monotone density principle to evaluate one’s own listening room or studio acoustics by ear’s critical bands.

Related

• Room mode density rising smoothly with frequency signals good acoustics (similarity 0.84)
• Monotonic mode growth predicts perceptually smooth room response (similarity 0.83)
• Three-dimensional rooms yield denser mode distributions at higher frequencies (similarity 0.81)
• Exciting multiple room modes instead of one reduces frequency and spatial sound variation (similarity 0.81)
• Room acoustical behavior changes across a broad transition region, not at one frequency (similarity 0.81)
• Hard-walled rooms behave as three-dimensional resonators with many audible modal frequencies (similarity 0.81)
• Spatially proportional room dimensions create coincident resonant modes (similarity 0.80)
• Axial mode frequencies are computable from room dimensions by a simple formula (similarity 0.80)
• Room acoustics shift from standing waves to irregular interference as frequency rises (similarity 0.80)
• Modal density scales with spatial dimension, from flat in 1D to squared in 3D. (similarity 0.79)
• Modal behavior intensifies as wavelength approaches the room’s mean free path (similarity 0.79)
• Room modes are determined by the linear dimensions of opposing surfaces (similarity 0.79)
• Room standing waves cause sound pressure to vary with listening position (similarity 0.79)
• On-axis frequency response cannot predict in-room measurements but does predict perceived sound. (similarity 0.79)
• Steady-state frequency response is the reliable indicator of audible room resonances (similarity 0.78)