Home Cinema Acoustics - The Bonello Criteria - January 11th, 2009
In home cinema installations, 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 dedicated home cinema systems, which sound good, this increase in mode density with frequency is smooth. This is the rationale behind a method for accessing the modal behaviour in a home cinema, known as the Bonello criteria.
These criteria try to ascertain how significant the modal behaviour of a home cinema room is in perceptual terms. It does this 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 then there is a good chance that we will perceive the dedicated home cinema room as having a ’smooth’ frequency response despite the resonances.
If the number of resonances found in a home cinema installation per third octave drops as the frequency rises, then there will be a perceptually noticeable peak in the frequency response. Coincident modes are also another way of creating a perceptually noticeable frequency response peak, and the Bonello criteria do further stipulate that there should be no modal coincidence within a third octave band, unless there are at least three additional non-coincident resonances to balance the two that are coincident.