객석바닥 경사각 변화가 장방향실의 객석 흡음률에 미치는 영향 = The effect of raked floor on the sound absorption of audience area in a shoe-box shaped hall

다국어 초록 (Multilingual Abstract)

A raked audience area has been used in various places to help audience have good sight-lines without significant direct sound energy losses. In particular, a vineyard shaped concert hall, which consists of various raked seating area, has been known to offer the possibility of providing early reflections to majority of audience and steeply raked balcony make it possible for audience to be close to stage. Although chairs and human body in raked audience area would be well exposed to the sound field, sufficient information to meet requirements about absorption of raked audience area is not available for initial acoustic design. Eventually, inaccurate absorption of audience area can cause a significant disagreement between predicted acoustic values and evaluated acoustic conditions after constructed, especially, for reverberation time which is once regarded as the predominant indicator of its acoustical properties in a room.

Beranek and Kuttruff have stated with logical reasoning that the sound absorption by seating area would increase as the floor slope gets higher. Also, Hegvold has shown similar results after a series of 1/10 scale model experiments. However, Beranek and Kuttruff’s hypothesis needs a precondition in that exposed audience and chair to direct sound should be highly absorptive, such as mid-season clothes as are used in Hegvold’s experiment. Strict dress code is not mandatory in recent year while clothes restriction for audience was prevalent in most of theatres and concert halls in the past. Moreover, the amount of clothing worn by audience tends to change depending on the weather condition. Therefore, it seems to be unavoidable that audience area absorption is highly dependent on the weather condition, since lightly clothes and human skin are rather reflective while mid-season clothing tends to be absorptive. Several studies on audience body and skin in seating area have been published. Kirkegaard has stated that seasonal clothing is critical in concert halls and other rooms, and Katz has demonstrated that human skin is acoustically rigid, with absorption coefficient"(α)= 0.03" , Mommretz and Tahvanainen have described that audience shoulder and knee indeed reflect sound. In other words, absorption of raked seating area might not be increased compared to absorption of flat seating area, if audience skin and summer clothes were exposed to direct sound.

This study tried to provide a practical research data for initial acoustic design process through a series of 1/15 scale model experiments. Three variables for audience area, changes in floor rake angle (0 to 35 degrees, 5 degrees steps), the amount of sound absorption of chairs, and seasonal changes in audience clothing were considered. In order to evaluate the subjective effect of absorption change caused by audience area condition, this study defined new 1 JND of absorption coefficient by using 1 JND of reverberation time based on the ISO-3382. Any change in sound absorption coefficients by varying experimental condition of audience area which exceeds 1 JND was regarded as having significant subjective effects on audience in the present work.

The results from this work suggested that the audience area consisted of low absorption of chair and summer clothes seems not to be influenced by the change in floor rake angle, which is due to the reflective area of back rest, seat pan and human skin. On the other hand, absorption coefficient of the audience area consisted of high absorption chair and spring/autumn clothes is getting higher as the floor rake is increased up to 20 or 25 degrees. This result proposed that the effect of porous absorbing material of chair and clothes on the sound absorption, exposed to direct sound, tends to be stronger as the floor rake gets steeper. The change in absorption coefficient of audience area larger than 1 JND was not observed, and decreasing tendency by more than 1 JND was found in some cases, when the floor rake exceeds 20 or 25 degrees.

The analysis of direct sound distribution on the cross-section of audience area suggests that the under space of chair and audience knee are begun to be exposed to the direct sound as the floor rake is larger than 20 or 25 degrees. Furthermore, when floor degree is larger than 20 degrees, absorption coefficient at 4 kHz of occupied high absorption chair with audience in summer clothes gets lower than those of unoccupied high absorption chair. This can be explained that audience wearing summer clothes is well exposed to direct sound relative to heavily absorbing materials of chair, it is so called ‘shadowing effect’. Therefore, absorption of raked seating area depends on the portion of chair which are exposed to the incident sound and its degree of absorptive treatment.

목차 (Table of Contents)

• 1. 서론 1
• 1.1 연구 배경 및 목적 1
• 1.2 연구 범위 및 방법 4
• 2. 이론적 배경 7
• 2.1 경사객석 흡음률 변화에 대한 선행연구 및 고찰 7
• 2.2 흡음 10
• 2.2.1 흡음재 10
• 2.2.2 흡음률 측정 방법 11
• 2.2.3 흡음률의 JND(just noticeable difference) 14
• 3. 측정 개요 15
• 3.1 측정 대상 15
• 3.2 축소모형 실험 16
• 3.2.1 객석바닥의 경사각 변화 17
• 3.2.2 객석의자의 흡음력 변화 18
• 3.2.3 청중의 흡음력 변화 23
• 3.3 대상 공간 개요 26
• 3.2 측정 방법 35
• 4. 측정 결과 38
• 4.1 공석 시 경사객석 흡음률 변화 38
• 4.2 만석 시 경사객석 흡음률 변화 43
• 4.2.1 의자 흡음력 차이에 따른 영향 48
• 4.2.2 청중 흡음력 차이에 따른 영향 52
• 4.3 소결 56
• 5. 종합토의 58
• 6. 결론 및 향후 과제 70
• 부록 A 72
• 부록 B 74
• 참고문헌 76