Volume 122, Issue 4, October 2007
Index of content:
- NOISE: ITS EFFECTS AND CONTROL 
122(2007); http://dx.doi.org/10.1121/1.2769972View Description Hide Description
The effects of vehicle speed variation on road traffic noise are analyzed. The steady speed motion is replaced by deceleration, cruise, and acceleration. Because of a relatively loud accelerationnoise, such a speed variation results not only in the noise decrease zones, but in the noise increase zones as well. The location of these zones depends slightly upon the ground covering (grass, concrete, etc.). Conversely, their boundaries change dramatically with the parameters describing noise emission during deceleration, cruise, and acceleration. For example, the Japanese and Polish models of noise emission have been applied. The critical length of the cruise segment of the road is introduced: for the sound energy decline (due to speed reduction) compensates the sound energy growth (due to acceleration). The results obtained could be useful for road administrators.
122(2007); http://dx.doi.org/10.1121/1.2756973View Description Hide Description
Attenuation of high-level acoustic impulses (noise reduction) by various types of earmuffs was measured using a laboratory source of type impulses and an artificial test fixture compatible with the ISO 4869-3 standard. The measurements were made for impulses of peak sound-pressure levels (SPLs) from 150 to . The rise time and duration of the impulses depended on their SPL and were within a range of (rise time) and ( duration). The results showed that earmuff peak level attenuation increases by about when the impulse’s rise time and the duration are reduced. The results also demonstrated that the signals under the earmuff cup have a longer rise and duration than the original impulses recorded outside the earmuff. Results of the measurements were used to check the validity of various hearing damage risk criteria that specify the maximum permissible exposure to impulse noise. The present data lead to the conclusion that procedures in which hearing damage risk is assessed only from signal attenuation, without taking into consideration changes in the signal waveform under the earmuff, tend to underestimate the risk of hearing damage.