CD Companion Introduction: Acoustics

What are we talking about when we use the word "acoustics"? For contemporary scientists and engineers, acoustics is the study of mechanical waves in solids, liquids and gases, thus including the phenomena of vibration, sound, ultrasound and infrasound. Wave phenomena-not all of it audible-is thus investigated, recorded, measured, analyzed, described, characterized and freshly synthesized, and in many cases, plausible explanations of these phenomena have been offered and generally accepted, and countless applications have been developed in a diversity of fields.

However, everyday use of the word is quite different: It is focused on audible sounds and is often casual and imprecise, qualitative rather than quantitative. A room or public space-whether for private, domestic, commercial, civil, military, or sacred use-gets praised or critiqued for its acoustics, a blanket term covering any number of qualities more or less associated with sound. We praise the acoustics of a home shower or the ancient theater at Epidaurus-spaces with strongly reflective surfaces and resonant characteristics. On the other hand, we may describe some spaces as having "no acoustics" when these characteristics are weak [1].

Acoustics is often a label used in conversation and writing for qualities about which we have decided not to be explicit, but implicitly it is rather reliably about bringing out (articulating, amplifying, resonating) the sounds-music and speech in particular-that we want to hear and attenuating, hiding or eliminating the sounds we don't want to hear. This selectivity about sounds may reflect a fairly reliable set of physical and physiological constraints, but it is essentially aesthetic in character, and the interaction between those constraints and aesthetics has a long history, a contentious present and an intriguing future. From a physical standpoint, every object that can vibrate, every wave that moves and every medium through which waves move has its acoustics-just as every building has its statics and every moving object its dynamics. But in everyday use, we are interested in particular arrangements that we consider good or bad, and artists working with sound-musicians among them-often find it useful to work with scientists and engineers specializing in acoustics, by defining parameters for sound-transversing spaces and sound-bearing technology that are musically optimal. These artists frequently also find it useful to adopt techniques and tools from the repertoire of science and engineering directly in their own musical productions.

The earliest known research in acoustics can be found in the fifth of Vitruvius's Ten Books of Architecture (1st century BC) and concerns itself more with an aesthetic theme than a pure scientific one: the design of classical theaters in a cooperative enterprise between mathematicians (acousticians) and musicians as architectural spaces in which voices onstage project with "greater clarity and sweetness" to the ears of the audience. To this end, Vitruvius describes the ideal physical placement of a theater, the plans and sections of Greek and Roman theaters-with the semi-circular auditorium rising to reflect the stage still the dominant model for modern theaters both in- and out-of-doors-and classifies the ways in which a space responds to a voice as dissonant, circumsonant, resonant and consonant-terms that a modern acoustic engineer or sound designer would understand. Most remarkably, Vitruvius details how large ceramic vases (which we now recognize as Helmholtz resonators) were tuned precisely to musical tones-he includes a small introduction to the Quadrivial art of Harmonics, a basis of tonal music theory-and positioned under the wooden stage of the theater. It is not entirely clear if the vessels were intended to serve as fixed pitch references for the vocalizing actors above or actually to amplify the voices through sympathetic vibration (if the latter were the case, the effect would have been fairly subtle in such a large space, particularly one filled with an audience). It is clear, however, that the intention was to enhance the acoustical experience through the emphasis on a selective set of tones.

As "acoustics" in a musical context can mean almost anything and everything, this CD does not attempt to represent the entire diversity of musical responses to and applications of acoustical...