Requirement for Low-Frequency Reverberation in Spaces for Music: Part 1: Smaller Rooms for Different Uses

(ProQuest: . denotes formulae omitted)Space is an intrinsic aspect of both music production and consumption: For musicians (instrumentalists as well as singers), it has a strong impact on their self-control and ensemble playing; for sound engineers with their audio equipment, as well as audiences with their listening ears (and watching eyes! ), the environment in which music or any other communication takes place has an equally powerful influence on their electronic outcome and resulting respectively complex sensations. The acoustical measure that plays a prominent role in these physical and psychological interactions is what W. C. Sabine (1922), more than a hundred years ago, defined as "reverberation time," a simple characteristic derived from the overall volume and sound absorption included in the room. The various reflections off surfaces in the environs of the sound source propagating toward the listener generate the acoustic signature of the space. The superposition of the energy and spectrum, the sequence in time, and the direction of reflections with the (most relevant! ) direct sound waves arriving at a listener contribute to whether a subjectively beneficial or negative effect is created in any enclosure, on a stage, or in an auditorium.As far as noise control tasks are concerned, there are many standards and regulations setting the goals for the abatement of external noises. The room-acoustics conditions in free-field and diffuse-field measurement enclosures are prescribed in detail, for example, in International Organization for Standardization (ISO) 3745, 10140, 23741, and 354. Concerning the sounds of the voices of users of rooms, their desirable or unwanted interaction with the respective enclosure is by far less clear. It is in this fairly complex field of how a space responds to various enclosed technical or human sound sources and how human sources intuitively react to their acoustic environment where the authors gained their technical and aural experience from their applied research and development activities at the Fraunhofer Institute (Fuchs, 2013). A novel practical approach is described by Fuchs and Lamprecht (2013) of how to limit reverberation times according to the German Institute for Standardization (DIN) 18041 and international norms in order to get rid of unwanted low-frequency (lf) sounds and achieve the necessary acoustical transparency, that is, intelligibility of speech and clarity of music in small to medium-sized rooms. In these, room resonances ("modes") are excited below the Schroder frequency (fS, in Hz),. (1)a simple derivative from volume (V, in m3) and absorption, respectively reverberation time (T, in s) of the room, where the constant varies between 1,200 (Vorlander, 2008), 2,000 (Kuttruff & Mommertz, 2013), and 4,000 (Cremer & Muller, 1982) and the number of resonance frequencies below fS may be estimated according to (Kuttruff & Mommertz, 2013) as. (2)Modes can heavily distort any sound emitted by severely modifying the energy and spectra transmitted from the sources and "masking" the higher frequencies that carry the bulk of useful information in music and speech.Effect of Resonances in Small Spaces on Sound SourcesAny source of speech or music is a transmitter of mechanical energy from human muscles into vibrational energy in strings, cavities, and membranes normally radiated as airborne sound with a characteristic, more or less discrete or broadband frequency spectrum. At a certain distance from the source, these primary waves may interact with secondary and higher order waves reflected from various obstacles or boundary surfaces of an enclosure. The resulting lf interference effects are most obvious and best covered in the standard literature on spatial acoustics as "standing waves" or "mode structures" at the resonance frequencies of smaller rooms (see, e.g., Fuchs, 2013, Chap. 2). When looking at the sound that is self-generated by users communicating in a room, its A-weighted spectrum typically exhibits a broad maximum between 500 and 1,000 Hz and a steep descent toward 63 Hz (Qin, Kang, & Jin, 2012). …