Recently noise is closest to our life and is recognized as serious pollution. Especially the noise at work place is the second biggest noise source in the frequency of civil complaint except dailylife noise. Therefore, the importance of pleasant work place is getting more highlighted. This loud noise of working machinery affect laborers working in work place for a long time, causing temporary hearing loss(TTS, Temporary Threshold Shift) out of auditory fatigue. And this has a direct effect on production and quality of the products. Also it can cause the difficulty in hearing(Hearing Loss) resulting from excessive exposure to noise. Because permanent hearing loss(PTS, Permanent Threshold Shift) appears after decades of latent period, it led to class-action suits of laborers working in the loud noisy work place in the past, coming to the fore as a serious social problem. Therefore strategy for sound-proof and sound-reduction is urgently needed in order to reduce the damage from noise by minimizing the noise of machinery made in high-noisy work places.
From this point of view, this study investigated physical characteristics of 31 sorts of working machinery noise in 4 work places causing loud noise. With this, psychological evaluation was conducted through Zwicker Parameter which is physical indicator to evaluate sound quality. On the basis of this materials, sound absorbtion strategy using acoustic simulation technique and level of noise reduction through Auralization were predicted for noise reduction strategy by architectural method. Also subjective responses according to the patterns of wearing protective device were compared by conducting Jury Test according to patterns of wearing protective device as the noise reduction strategy of workers and by presenting average improvement ratio in loud noisy working machinery.
The result from this study is following.
1. The measured change of sound pressure level by noise time of working machinery in work places causing 31 sorts of loud noise showed characteristic of normal noise. It was repeated in constant section except number 14 "metal process saw" and number 18 "lapidary mill". Noise of working machinery was kept high level of sound pressure ranging 66dB(A)~105.6dB(A). As for characteristic of sound pressure level by frequency, irregular pattern was showed in low frequency and reached the peak in1kHz and then grew weakened gradually.
2. According to correlation analysis of dB(A)와 Zwicker Parameter, Loudness was 0.91, Unbiased Annoyance was 0.84, showing its high correlation. Therefore the noise of working machinery will be perceived as 'Loud, Annoying Sound'.
Judging from this result, more rational and more exact grasp of characteristic of working machinery noise will be possible if Loudness, Unbiased Annoyance items are evaluated together both by dB(A), which is physical evaluation standard of noise, and by Zwicker Parameter representing psychological aspect of human being.
3. The NR decision frequency of working machinery noise was decided in the middle-high frequency zone of 1,000Hz - 8,000Hz except number 4 "table middle circular saws" and number 12 "rock-cutting machine". According to the result of applying architectural sound absorbtion strategy to the grade decision frequency area of NR curve, sound pressure level after and before improvement was reduced in every frequency and jewelry processing plants showed improvement in the noise by 9.1dB(A) and model workshop showed improvement in noise by 3.7dB(A). Considering this result, it will be effective to select materials for sound absorbtion based on grade decision frequency in NR curve for the future noise reduction strategy using sound absorbtion.
4. In the result of Jury using auralization, before architectural sound absorbtion strategy, because of high level of sound pressure of working machinery, the average in every item by stage 13 measure was 8.55~11.25 in jewelry processing plants and 11.95~12.35 in model workshop. But after improvement, the improvement ratio by average of each item was declined by 1.05~2.95(8%~23%) in jewelry processing plants and by 1.55~2(12%~15%) in model workshop. Therefore noise reduction strategy through architectural sound absorbtion strategy for loud noisy work place will be very effective.
5. The improvement ratio in evaluation value of feeling the change of words through perception of sound reduction effect was above 2 at 104.8dB(A) when wearing earcap, at 97.4~104.8dB(A) when wearing earplug and at 97.4~104.8dB(A) when wearing earcap and earplug together.. Especially when wearing earcap and earplug together, the best effect of noise reduction was produced from 88.2dB(A) at above 3 and from 88.2dB(A) at above 4 of improvement ratio. Therefore considering that noise reduction effect gets better as it goes from loud noisy working machinery with low level of sound pressure to loud noisy working machinery with high level of sound pressure, wearing soundproof protective device(ear protector) will be very effective in loud noisy work places.