Category: (((—Acoustics Engineering—))))

6.13.1 Traffic Noise Index In an attempt to develop acceptability criteria for traffic noise from roads in residential areas, Griffiths and Langdon [45] produced a unit for rating traffic noise, the traffic noise index (TNI). They measured A‐weighted traffic noise levels at 14 sites in the London area and interviewed 1200 people at these sites in the process.…

In recent years some countries have continued to use NEF or NNI or similar noise measures or descriptors related to those that include a weighting based on the number of aircraft movements [29]. However, because they are much simpler to measure and seem to give adequate correlation with subjective response, there has been a move…

The noise levels around airports are of serious concern in many countries. Several attempts have been made to produce measures to predict and assess the annoyance caused by aircraft noise in the community. A study of rating measures in 1994 showed 11 different measures in use in the 16 countries studied [29]. The following measures…

The equivalent SPL discussed above accounts for the fluctuation in noise level of an unsteady noise by forming an average SPL resulting in an equivalent steady A‐weighted SPL. There is, however, some evidence that unsteady noise (e.g. from noise sources such as passing road vehicles or aircraft movements) is more disturbing than steady noise. To…

In the United States during the 1970s, the Environmental Protection Agency (EPA) developed a measure, from the equivalent SPL, known as the day–night equivalent level (DNL) or Ldn that accounts for the different response of people to noise during the night [31] given by (6.7) where Ld is the 15‐hour daytime A‐weighted equivalent SPL (from 07:00 to 22:00 hours) and Ln is the 9‐hour nighttime…

Although Leq measurements provide practical results for fluctuating noise, an Leq measurement does not remove ambiguity in the case of transient noise (e.g. aircraft flyover or a vehicle drive‐by). In such a case the SEL is very useful and corresponds to an equivalent SPL Leq normalized to one second, combining both loudness and duration in a single metric. Therefore, SEL is…

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…