Category: 6. Description, Criteria, and Procedures Used to Determine Human Response to Noise and Vibration

For noise that fluctuates in level with time it is useful to define the equivalent continuous SPL, LAeq, which is the A‐weighted SPL averaged over a suitable period, T. This average A‐weighted SPL is also sometimes known as the average sound level LAT in ANSI documents, so that LAeq = LAT. The equivalent SPL is defined by (6.5) where pA is the instantaneous sound pressure…

In 1989, Beranek [23, 24] modified the NC curves to include the 16‐ and 31.5‐Hz octave bands and changed the slope of the curves so that it is now −3.33 dB/octave between 500 and 8000 Hz. He also incorporated the A and B regions as specified by Blazier [25] in the RC curves. The rating number of a balanced…

NC curves are not defined in the low frequency range (16‐ and 31.5‐Hz one-octave bands) and are also generally regarded as allowing too much noise in the high‐frequency region (at and above 2000 Hz). Blazier based his derivation of the RC curves on an extensive study conducted for the American Society of Heating, Refrigeration, and Air‐Conditioning Engineers (ASHRAE)…

The NR curves are similar to the NC curves (see Figure 6.7). They were originally produced to develop a procedure to determine whether noise from factories heard in adjacent apartments and houses is acceptable [26]. The noise spectrum is measured and plotted on the family of NR curves (Figure 6.8) in just the same way as…

The NC curves (Figure 6.7) were developed from the results of a series of interviews with people in offices, public spaces, and industrial spaces [21, 22]. These results showed that the main concern was the interference of noise with speech communication and listening to music, radio, and television. In order to determine the NC rating of…

The SIL is mainly used to evaluate the effect of noise on speech in situations outdoors or indoors where the environment is not too reverberant. The A‐weighted SPL can be used as a guide for the acceptability of noise in indoor situations, but it gives no indication about which part of the frequency spectrum is…

The SIL is a measure used to evaluate the effect of background noise on speech communication [17]. The SIL is the arithmetic average of the SPLs of the interfering background noise in the four octave bands with center frequencies of 500, 1000, 2000, and 4000 Hz (see ANSI S3.14–1977(R‐1986)). If the SIL of the background noise…

The articulation index (AI) is a measure of the intelligibility of speech in a continuous noise. The AI was first proposed by French and Steinberg [16] and was extended later by Beranek and Ver [17]. Speech has a dynamic range of about 30 dB in each one‐third octave band from 200 to 6000 Hz, and the long‐term root…

6.4.1 Noisiness Although the level of noise or its loudness is very important in determining the annoyance caused by noise, there are other acoustical and nonacoustical factors that are also important. In laboratory studies, people were asked to rate sounds of equal duration in terms of their noisiness, annoyance, or unacceptability [9, 10]. Using octave bands…

As discussed in Section 4.3.2 which contains an in‐depth description of the loudness of sound, the human ear does not have a uniform sensitivity to sound as its frequency is varied. Figure 4.6 in Chapter 4 shows equal loudness level contours. These contours connect together pure‐tone sounds that appear equally loud to the average listener. Recently, slightly modified contours have been…