acoustical

2.05  acoustic, acoustical. Qualifying adjectives meaning containing, producing, arising from, actuated by, related to, or associated with sound. Acoustic is used when the term being qualified designates something that has the properties, dimensions, or physical characteristics associated with sound waves; acoustical is used when the term being qualified does not designate explicitly something that has such properties, dimensions, or physical characteristics.

Annotation 1          Examples that should use the qualifying adjective acoustic are impedance, inertance, load (radiation field), output (sound power), energy, wave, medium, signal, absorptivity, and transducer.

Annotation 2          Examples not having the requisite physical characteristics and that therefore should use the qualifying adjective acoustical are: society, method, engineer, school, glossary, symbol, problem, measurement, point of view, end-use, device, and standard.

Annotation 3          Generic terms are usually modified by acoustical, whereas acoustic applies to terms with specific technical implication.