Revised noise criteria for design and rating of HVAC systems

Abstract

This paper reviews current methods of rating the noise produced by HVAC systems and explains why these ratings fail to be correlated with subjective opinion in many cases. An entirely new method of assigning noise ratings is proposed which is expected to provide a significantly better correlation between objective measurements and subjective response. The proposed new rating method makes use of a revised set of noise criterion curves (RC curves) which appeared for the first time in Chap. 35 of the 1980 Systems Volume of the ASHRAE Handbook. This paper also discusses the technical considerations leading to the development of the RC curves as a replacement for the NC curves which have been used in the past.

Effects of room acoustics on the intelligibility of speech in classrooms for young children

“…Noise with a -5 dB per octave spectrum shape was produced and radiated incoherently from all 8 loudspeakers in the sound field simulation system. This spectrum shape has been shown to approximate typical indoor ambient noise such as that from ventilation systems and is often referred to as a 'neutral' spectrum [21,22]. The binaural noise recordings were corrected for the response of the headphones and mannequin as described for the speech sounds.…”

Psycho-acoustic evaluation of the indoor noise in cabins of a naval vessel using a back-propagation neural network algorithm

“…The primary reason given is that if there are strong fluctuations or surging in the HVAC noise, the specified low-frequency octave-band levels for the RC curves ought to be low enough so that the noise is not disturbing. Even though RC was revised to RC Mark-II (Blaizer, 1997), original RC (Blaizer, 1981) is used in this paper. In addition, PSIL (ANSI, 1977) should be used for evaluations in a naval vessel because speech interference is an important potential hindrance when a command is given.…”

Some spatial and temporal effects on the speech privacy of meeting rooms

“…This is often referred to as "neutral" sounding and is representative of typical indoor noise spectra. 14,15 To focus on the main differences between the two previous studies, in these tests only speech intelligibility scores were obtained. A number of spatially different combinations of speech and noise sources were compared as well as differences in added reflected sounds.…”

“…Random noise, which was equalized to have an approximately −5 dB/octave spectrum shape representative of typical ventilation noise, 14,15 was used. The ambient noise levels were measured using a single microphone at the location of the listener's head.…”

“…Only a few studies have included the effects of room reverberation and usually the term reverberation has been used loosely to include all types of reflected sound. Most often the interfering signal has been speech 14,15 and not typical room noises such as that from ventilation systems.…”