"Acoustic" and "acoustical" are both used as adjectives, and both are used often in combinations such as "acoustical engineering", "acoustic energy", "acoustic model", etcetera. Some of these combinations sound better than others, e.g. "acoustical energy" sounds wrong to me, but that may be purely subjective.
Is there any difference in meaning between the words? Or might it just be a UK/US English difference?
Best Answer
The Acousical Society of America pondered this question for years before including definitions and usage rules in a 1955 update to their glossary of acoustical terms.
A report of the discussion is here. http://scitation.aip.org/content/asa/journal/jasa/27/5/10.1121/1.1908102
Their work was not 100 percent satisfactory, but it has remained generally in effect in America. They admit they cribbed their definitions from the electric/electrical definitions in American Standard Definitions of Electrical Terms (1941). The current Glossary costs $150 to buy, Maybe someone with access to an engineering library can check it out.