Tuning the octave bands: A history of dividing the spectrum for acoustical measurements in the 20th century

Abstract

Standardized octave and one-third octave bands are ubiquitous in modern acoustical measurements, such that the particular way they divide the spectrum might reasonably be assumed to be self-evident. Yet when Hans Thilo was granted the patent for the first octave band analyzer in 1937, this division was anything but certain. In the ensuing years, many systems proliferated, with different center frequencies employed between airborne noise and vibration, source and absorption measurements, and even American and European practitioners. This presentation traces the multiple systems in play from Wallace Sabine’s early experiments with organ pipes up through the dominant standard today based upon preferred numbers. Though the large majority of these systems have long since been abandoned, their ghosts are still occasionally encountered, haunting compliance studies beholden to legacy noise ordinances, and muddling the definitions of metrics such as speech interference level (SIL), which were originally defined using older octave bands.