As a method of rating sounds with respect to the expected community response, ISO(1971). ISO R 1996, "Assessment of noise with respect to community response" (International Organization for Standardization, Switzerland), recommends the measurement of the Aweighted equivalent sound level Leq. The usefulness of Leq for road-traffic sounds has been demonstrated in various studies. For impulse sounds, however, research into the adequacy of Leq has been very limited. The present laboratory study provides a further test of the adequacy of Leq as a descriptor of annoyance. in one condition, all impulse sounds had the same level, whereas in the other eight conditions the levels of the impulses could differ either by 6 or by 12 dB. The proportions of the impulses with high or low sound levels were 90% vs 10%, 75% vs 25%, and vice versa. Sixteen subjects compared the annoyance caused by the impulse sounds (G) with the annoyance due to road-traffic sounds (T). They adjusted the level of either T or G in such a way that these sounds were just as annoying as the standard G [Leq = 40 dB(A) ] or T [Leq = 45 dB(A) ] sounds. The results from one group of subjects showed that the degree of annoyance was about the same for all conditions, whereas the results from another group of subjects showed that Leq may overestimate the annoyance in at least some conditions. The present data, therefore, mildly support the effectiveness of Leq as a predictor of annoyance.
A laboratory experiment has been conducted to assess the noise annoyance of individual vehicle pass-bys as a function of sound level. Vehicle type varied from passenger cars to heavy tanks. Results showed that for each individual vehicle type, the A-weighted sound exposure level (SEL) was the most important predictor of the annoyance. However, at a given annoyance, the difference in level between different vehicle types could be as high as 11 dBA SEL. The difference in level between the high-frequency part and the low-frequency part of the spectrum seemed to play a role in the annoyance, in that sounds containing relatively much high-frequency energy (e.g., passenger cars) were judged as being more annoying than those having relatively much low-frequency energy (such as tanks). [Work supported by the Ministry of Defence.]
As an alternative to the A-weighted sound exposure level (ASEL) Schomer et al. [J. Acoust. Soc. Am. 110, 2390–2397 (2001)] used the equal-loudness level contours as a dynamic filter to determine the loudness-level-weighted sound exposure level (LLSEL). From their analyses they concluded that the LLSEL better orders and assesses traffic and impulsive sounds than the ASEL does. In the present study LLSELs were determined for a great variety of shooting sounds investigated by Vos [J. Acoust. Soc. Am. 109, 244–253 (2001)]. It was concluded that for the assessment of shooting sounds, the use of loudness-level weightings is less adequate than the use of A- and C-weighted sound exposure levels as proposed in Vos’s article.
Two laboratory experiments were performed to study the effect on annoyance of noise concentration in time. The first (rating-scale) experiment dealt with the influence on annoyance of short-time silent periods (varying from 0 to 160 s) in pass-by vehicle noise of 240-s total duration. Results showed that, at a fixed equivalent sound level, and with the number of vehicles kept constant, annoyance hardly depended on the duration and position in time of the silent period. In the second experiment subjects had to compare the annoyance of road traffic sounds with that of sounds from heavy vehicles (such as tanks). In deciding which fragment was more annoying, the subjects had to imagine that they were exposed to the road traffic sounds throughout the year, whereas the sounds of heavy vehicles were only audible during a certain part of the day, week, or year. Results indicate that, at a given equivalent sound level, concentration of the sounds in time reduces annoyance. [Work supported by the Ministry of Defence.]
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