- Michael Fay
Parametric Acoustics, 2nd Edition*
Updated: Aug 23, 2022
The Case for the Parametric Method of Acoustic Treatment
The topic of architectural acoustics has been documented and carefully studied for more than a century. Historically, most acoustic treatment products and schemes have offered a relatively “broadband” approach to managing reverberation in a room. While this fundamental approach has changed little, acoustical goals, priorities, training, and materials need updating; each needs to incorporate and correlate a broader range of frequencies, while addressing their unique, quantitative relationship to one and other.
Why? Because of the massive amounts of full-bandwidth energy being pumped into rooms deploying our modern loudspeaker technologies.
The Parametric Acoustics thesis does not challenge the physics underlying traditional acoustic theory. Rather, it offers a fresh perspective on how new materials can and should be deployed.
This paper expands my T60 Slope Ratio thesis by providing methodology, commentary, and examples for specifying acoustic treatments as band-limited tools. The T60 Slope Ratio (TSR) is represented symbolically as T60SR6. The calculation delivers a relational score (Figure 1) using the two extreme time values - from the six octave centers - between 63 Hz and 2 kHz. The score is calculated by dividing the longest T60 by the shortest T60, regardless of octave.
Figure 1 - The TSR Mean Opinion Score Grading Matrix
This discourse outlines how a “Good” to “Optimum” TSR score can be achieved in any performance venue. To that end, the next level of architectural acoustic refinement is proposed: PMAT - the Parametric Method of Acoustic Treatment.
While the best practitioner’s in architectural acoustics already understand, and may implement similar principles, the PMAT concepts are not widely considered or applied.
* Following its original publication in May of 2021, I was notified of an error in tabulation regarding the data in Fig. 12. This second edition provides the corrected values in Fig. 3 below. Also, five new sections have been added or updated: The Wave/Ray Duality of Sound; two real-world reports on TSR and PMAT applications at work; and commentary on the ideal T60 and variable acoustics. In addition, several sections have been rewritten to provide better clarity.
The full paper pdf can be downloaded via the link below.