Creating low-noise environments in communication rooms

As a research, development and consulting institute the IBP has frequently been confronted with external (intruding from outside) and internal (self-generated inside) noise in communication areas of one kind or another. As a fundamental discovery it has become obvious that the frequency range far below that covered by building and room acoustic standards is of the utmost importance for the sound generation and speech intelligibility process. A powerful new tool for tackling low-frequency problems was invented in the form of slender compound panel absorbers (CPA) to be mounted on (or integrated in) walls or ceilings as an efficient means to damp the, dominant eigenfrequencies of the room itself Since literature on the rather obscure phenomena observable below 125 or 100 Hz in real-life conversations was found to be very scarce, a large variety of acoustically unsatisfactory enclosures was investigated beyond the standard frequency limits and subsequently cured with some really convincing improvements experienced in acoustic comfort and sound quality. This paper was written as an advise and warning for acoustic consultants (not scientists) dealing with the often torturing acoustics in preferably hard-walled office, conference, foyer, restaurant or class rooms (not studios). The still growing problem of low-frequency room responses does not allow waiting for more academic studies and recognized extensions and adjustments of the valid measuring standards and regulations. Responsible acousticians should at least be aware that conventional single-number ratings for sound power, transmission and absorption are not of much help when dealing with this omnipresent problem which seems to have passed unnoticed even by experts in this field. (C) 2001 Elsevier Science Ltd. All rights reserved.