Obtaining adequate speech privacy in modern buildings is one of the important goals of the architect and consultant. This paper deals with the development of a rating method which takes into account the several factors influencing speech privacy. Our work in this area began with a brief laboratory study. The results indicated that speech privacy is related to speech intelligibility rather than to level. The initial experiments were supplemented with an analysis of about 40 case histories representing about 400 pairs of spaces in different kinds of buildings. There appears to be good correlation between the articulation index of intruding speech sound and the reactions of building occupants.
This paper describes a single wall which, by proper distribution of massive elements on light, stiff plates, provides higher transmission loss than predicted by mass law for limp constructions. With sufficiently low damping, the masses and the unloaded plate areas will, at resonance, oscillate 180° out of phase. With uniform spacing of the masses, the average displacement of the wall would be zero, thus theoretically providing infinite TL at one frequency. A random mass distribution gives improved TL over a wider range of frequencies. At higher frequencies, mass law predictions will not be reached. The behavior of this construction can be represented by an inductance (mass) coupled in parallel with a capacitor (stiffness). Prototypes have been constructed and measured to corroborate the theory and the data are given.
Open planning in office buildings and in schools has presented a new range of problems in the control of the acoustical environment. Several case histories are described, including objective measurements and subjective reactions of the occupants. A preliminary scheme for the systematic analysis and evaluation of privacy and communication problems in these types of spaces is presented. The analysis technique utilizes the widely known AI concept in developing an objective rating for privacy (or communication) and corresponds reasonably well with observed subjective reactions in field situations.
Studies on speech privacy problems in buildings at Bolt Beranek and Newman begun in the mid 1950s showed convincingly that a person’s sense of acoustical privacy was directly related to the intelligibility of the intruding speech over the continuous ambient sound present [Cavanaugh et. al., J. Acoust. Soc. Am. 34, 475–492 (1962)]. Both in laboratory and in real-world settings people feel they have confidential privacy when the articulation index (AI) of the intruding speech is 0.05 or less. Higher values of AI are acceptable for less demanding tasks, i.e., normal privacy. The method quantifies each of the significant variables involved and compares a summary of these metrics with response data for prior case histories both to predict, and, in the case of existing situations, to evaluate speech privacy conditions. R. W. Young reviewed the analysis method and showed that sufficient accuracy was preserved if simple, commonly used A-scale sound levels were used in place of more cumbersome frequency-based metrics [R. W. Young, J. Acoust. Soc. Am. 38, 524–533 (1965)]. Later in the 1960s the method was successfully applied to open plan offices which were becoming more prevalent [Hirtle et. al., J. Acoust. Soc. Am. 46. 91A (1969)]. The lessons learned in applying the speech privacy calculation over the years are discussed.
The notion of a single number rating for speech privacy problems in buildings [B. G. Watters, J. Acoust. Soc. Am. 32, 917 (1960)] has been developed further. The resulting system rates both the measured noise reduction of the isolating construction and the background (masking) noise levels. It also takes into account those other factors that determine the acceptability of speech privacy between spaces such as the size of the rooms, the level of speech effort in the spaces, and the degree of privacy needed by the occupants. The ratings calculated, using this system, are compared with observed subjective evaluations of the occupants in a large number of field situations.
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