The key issue with the S12.2-1995 standard is not the differences in the assessment of sound quality, particularly at the low frequencies, but rather the use of octave-band data to describe low-frequency equipment misbehavior. Unfortunately, the "NCB vs RC" controversy leads research efforts and technical discussions in the wrong directions, disregarding serious economic and technical considerations. This conflict can be resolved by: (1) avoiding the use of octave-band data to rate noise with abnormal (spectral and/or temporal) characteristics, (2) addressing the widespread need for the room noise criteria as a practical design tool for general use in architectural spaces, and (3) developing adequate descriptor/procedures to qualify, quantify, and determine the impact of "rumble" on human response. A further goal should be to develop integrated criteria that would apply to both HVAC and computer noise sources.

Fans used in the cooling of mechanical and electrical equipment are often the major sources of noise. This paper reviews the past and current noise control activities in the fan industry and related trade and professional organizations. Technology trends are discussed. Research needs and priorities are identified. The impact of fan design (blade, housing, and motor) and fan manufacturing (materials and processes) on fan noise and system acoustical quality are discussed. This paper illustrates with examples that fan noise control is more a challenge for design, application, and manufacturing than an investigation of fundamental aeroacoustic mechanisms. The approach is multi-disciplinary and comprehensive in its treatment of each integration level—from bearings and windings to motor, housing, and end-use equipment, thereby integrating noise control into fan design and manufacturing to achieve total quality for tomorrow's market.

A series of direction determination experiments has been performed to evaluate the extent to which automobile drivers can locate audible warning devices of emergency vehicles. Blindfolded subjects were required to indicate the perceived position of a siren, first in an open space and, secondly, while seated in an idling automobile with the windows both open and closed. For the open-air control case, the direction of the siren was correctly indicated to be in the appropriate 45° sector for 91% of the test presentations. With the subject seated in the automobiles, the identification of the correct location fell to 37.6% with the passenger window open and 26% with the windows closed. Based on an analysis of the results and the magnitude of the errors, it is concluded that aural localization for the directional identification of emergency vehicles is not practicable. [Work supported by the Society of Automotive Engineers, Inc.]

With the general consensus of practicing noise control consultants that the two different sets of criterion curves for evaluating room noise contained in ANSI S12.2-1995 [room criterion (RC) and balanced noise criterion (NCB)] should be replaced with a single set of criterion curves, the authors believe that lessons can be learned from the computer industry, especially in accounting for noises with abnormal characteristics. This industry realizes that the noise emissions from their products should be compatible with the acoustical requirements of the environment in which the products are installed. The types of computer products cover a wide range with respect to functionality, size, sound power level, and spectral and temporal characteristics of their emissions. The rooms in which these products are installed also cover a wide range, including many types with significantly different levels of acceptable noise. In addition to using A-weighted descriptors (sound power level to describe product emissions and sound-pressure level to describe room noise levels), the computer industry has recognized the need to take into account and to characterize abnormal features of the noises, such as prominent discrete tones (ECMA-74-1996 or ANSI S1.13), tonal modulation or beating, and impulsive or fluctuating sounds. This paper presents some of these experiences from the computer industry in the context of establishing room noise criterion curves. [See NOISE-CON Proceedings for full paper.]