Rating of Sound Insulation of Wall Impact Sounds in Buildings. Shih-Pin Huang and Rong-Ping Lai. Reprinted from JOURNAL OF BUILDING ACOUSTICS

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1 Rating of Sound Insulation of Wall Impact Sounds in Buildings by Shih-Pin Huang and Rong-Ping Lai Reprinted from JOURNAL OF BUILDING ACOUSTICS Volume 13 Number 2 06 MULTI-SCIENCE PUBLISHING CO. LTD. 5 Wates Way, Brentwood, Essex CM15 9TB, United Kingdom

2 BUILDING ACOUSTICS Volume 13 Number 2 06 Pages Rating of Sound Insulation of Wall Impact Sounds in Buildings Shih-Pin Huang a and Rong-Ping Lai b a Department of Architecture, Kao-Yuan University No.1821, Jhongshan Rd, Lujhu Township, Kaoshiung County 82151, Taiwan (R.O.C) sphuanh@cc.kyu.edu.tw b Department of Architecture, National Cheng-Kung University, Taiwan (R.O.C) (Received January 06 and accepted 27 March 06) ABSTRACT The standards for rating airborne sound insulation of walls in buildings have been established. Refer to ISO 717/1, ASTM E413, JIS A1419-1, and CNS 8465 A1031. However, there is no standard for rating of sound insulation of wall impact sounds in building. This research has been conducted to develop it. At first, levels of wall impact sounds were measured by hitting lightweight walls in an acoustics laboratory and recording the resultant sound spectra. Those curves were divided in two groups, soft impact curves and hard impact curves. In addition to recording impact sound sources, people living in houses were invited to complete one questionnaire. Subjective responses were then compared with those of daily activities, including watching television, reading, listening, sleeping, and talking. Finally Soft Impact Curves (SIC) and Hard Impact Curves (HIC) were drafted for rating of sound insulation of wall impact sounds, and index of wall impact sound were recommended. Keywords: Wall impact sound; sound insulation; acoustic laboratory 1. INTRODUCTION Lightweight walls are increasingly used as part of building constructions. They have several advantages: they are lighter than concrete and involve a dry construction process, which is relatively quick. However, people living in houses are concerned about the sound insulation of lightweight walls. From previous studies of the noise environment in houses, in 1995, results show wall impact sound is ranked the fourth most annoying noise source according to a survey [1] (Figure 1). There are eight impact sources in real life, shown in Table 1. With regards to degree of annoyance, (Figure 2), type 1, nailing or decorating on the wall is the most frequent occurrence, which also causes the most serious annoyance. Type 3, furniture hitting the wall is rated second. Type 4, human body impacts on the wall had the lowest ranking. The performance of

3 128 Rating of Sound Insulation of Wall Impact Sounds in Buildings Wall impact noise Upper floor noise Neighboring noise Outdoor noise 0% % % 60% 80% Figure 1. Annoyance percentages of noise sources, after [1]. 50% % Percentages % % 10% 0% Wall impact sources Figure 2. Annoyance percentages of five impact sources, after [1]. Table 1: Types of wall impact sources Types Wall impact sources 1 Nailing or decorating the wall 2 Ball hitting the wall 3 Moving furniture and carelessly hitting the wall 4 Human body hitting the wall 5 Children throwing things at the wall 6 Door opening vibrations on the wall 7 Broom hitting the wall 8 Drainpipes vibrate in the wall

4 BUILDING ACOUSTICS Volume 13 Number Standards for rating airborne sound insulation of walls and partitions: ISO 717/1, BS5821/1, ASTM E413, JIS A1419-1,CNS 8465 A1031. Noise or impact sound from upper floor Sound insulation of floor Standards for rating floor impact sounds: ISO 717/2, ASTM E989, JIS A1419-2, CNS 8465 A1031. Standard for wall impact sounds is under development Neighbor noise or impact sound Sound insulation of wall Indoor environment Sound insulation of window Outdoor noise Sound insulation of floor Noise or impact sound from lower floor Figure 3. Impact sound Standards for indoor acoustic environments. Airborne sound insulation in lightweight walls for reducing impact noise is likely to have greater importance in future. In order to evaluate the insulation performance of lightweight wall to impact sound, a series of laboratory measurement investigations was initiated in 1995 [2 4]. Also considered was the work of Bowles and Gold, who suggested a rating procedure for impact noise transmission through walls [5]. A draft standard for laboratory measurement of wall impact sounds is proposed. In the draft, the impact source, impact system, laboratory conditions, and measuring positions are discussed. To provide a high quality of indoor sound environment, we require measurement standards to insure sound insulation of construction materials, including windows, walls, and floors. An idealised system of standards is shown in Figure 3. Already in place are national and international standards for rating airborne sound insulation of walls and partitions, such as ISO 717/1 [6], BS5821/PART1 [7], ASTM E413 [8], JIS A [9], and CNS 8465 A1031 [10]. Standards, for rating floor impact sounds, such as ISO 717/2 [11], ASTM E989 [12], JIS A [13], and CNS 8465 A1031 are also already established and have been in use for a number of years. The present research addresses the shortfall in standards for sound insulation classification of wall impact sounds. 2. CHARACTERISTICS OF WALL IMPACT SOUND The study simulates real life impacts in an acoustics laboratory, shown as Table 2. Impact sources include a basketball, fist, hammer, and chair. The lightweight walls tested are commonly used in the construction of houses. The walls in Table 3 include gypsum panels, hollow fiber cement, complex cement, and hollow gypsum brick. Simulated impacts were performed on each wall. The instrumentation involved, as shown in Figure 4, consisted of microphones, microphone pre-amplifiers, frequency

5 1 Rating of Sound Insulation of Wall Impact Sounds in Buildings Table 2: Laboratory simulations of real life impacts Real impacts Impact sources Weight (kg) Ball hitting the wall Basketball Human body hitting the wall Fist Nailing or decorating the wall Hammer Moving furniture and carelessly hitting the wall Chair 3.10 Table 3: Data on lightweight walls Thickness Weight Surface density Construction (cm) (kg) (kg -m2 ) A-0 Gypsum panel (single layer each side) A-1 Gypsum panel (single layer each side and glass wool filling) A-2 Gypsum panel (double layers each side and glass wool filling) B-1 Hollow fiber cement wall B-2 Hollow fiber cement wall B-3 Hollow fiber cement wall C-1 Complex cement wall D-1 Hollow gypsum brick Semi-anechoic room Reverberation room Specimen Microphone Frequency analyzer Impact Centre of room Source room Receiving room Opening Figure 4. Measurement system for impact sound levels. Computer

6 BUILDING ACOUSTICS Volume 13 Number Wall impact sound level (db) K 2K 4K 1/1 Octave band frequency (Hz) soft impact average curve Figure 5. Soft impact average curve. analyser, and a PC computer. Five measuring points were arranged in a reverberation room. The frequency range of measurement, in 1/3 octave bands, was Hz. Additionally a 1/32 second short-term peak value of impact sound level was measured and averaged over twenty measurements. The results are shown in Figures 5 and 6. The curves are classified in two groups. The basketball and fist were grouped as soft impacts. Their resultant sound levels displayed significant low-frequency components with a rapid decrease with increase in frequency, more than 125 Hz. The hammer and chair were grouped as hard impacts. The resultant spectra contained significant frequency components in the range Hz, above which a decrease with frequency is indicated. 3. SURVEYS To investigate residents reactions to wall impact sounds, reference were made to papers on experimental methods for noise response [14 17]. The instruments required included a digital recorder, sound level meter, and loudspeakers. Four impact sounds were played and 89 people were invited to answer a questionnaire. Topics included

7 132 Rating of Sound Insulation of Wall Impact Sounds in Buildings Wall impact sound level (db) K 2K 4K 1/1 Octave band frequency (Hz) hard impact average curve Figure 6. Hard impact average curve. discussion of the degree of annoyance of wall impact sounds to daily activities. These included watching television, reading, listening, sleeping, and talking. The participants answered questions on impact sound levels from 60 db(a) to 100 db(a). Results are shown in Figures 7 and 8. There were five classifications ranging from not annoying to very annoying. Tables 4 and 5 show the distributions in subjective response. Participants reported a greater annoyance when impact sound levels were more than 80 db(a). Hard impacts were more annoying than soft impact sounds. Table 6 shows that hammer sounds produce higher frequency components whereas the basketball and fist sounds produced a greater bass response. 4. DRAFT FOR SOUND INSULATION CLASSIFICATION OF WALL IMPACT SOUND Establishing a standard for sound insulation classification for wall impact sounds is the main purpose of this research. According to the two average curves in Figures 5 and 6 and referring to ISO 717/2, ASTM E989, CNS 8465 A11, and JIS A1419-2, a sound

8 BUILDING ACOUSTICS Volume 13 Number Seclecting Samples db(A) 70-80db(A) 80-90db(A) db(A) 1(Not annoying) (Very annoying) Figure 7. Annoyance aspect of soft impacts. Seclecting samples db(A) 70-80db(A) 80-90db(A) db(A) 1(Not annoying) (Very annoying) Figure 8. Annoyance aspect of hard impacts. insulation classification for wall impact sounds was drafted. There are two recommended curves. Soft Impact Curves (abbreviated to SIC ) are applied to evaluate sound insulation of walls or partitions by soft impacts in Figure 9. The correlation coefficient between the SIC and soft impacts average curve is R 2 = 0.98, showing SIC are representative. Hard Impact Curves (abbreviated to HIC ) are suitable for hard

9 134 Rating of Sound Insulation of Wall Impact Sounds in Buildings Table 4: Subjective responses to soft impact sounds Wall impact sound levels Not Low Fairly More Very db(a) annoying annoyance annoying annoying annoying (6%) 17 (47%) 12 (33%) 5 (14%) 0 (0%) (10%) 11 (28%) 12 (%) 12 (%) 1 (2%) (2%) 2 (4%) 16 (%) 21 (39%) 14 (25%) (0%) 4 (8%) 12 (24%) 17 (34%) 17 (34%) Table 5: Subjective responses to hard impact sounds Wall impact sound levels Not Low Fairly More Very db(a) annoying annoyance annoying annoying annoying (0%) 7 (19%) 13 (36%) 12 (33%) 4 (11%) (2%) 7 (18%) 7 (42%) 11 (28%) 4 (10%) (0%) 4 (7%) 8 (15%) (37%) 22 (41%) (0%) 3 (6%) 7 (14%) 10 (%) (60%) Table 6: Frequency components of impact sounds Low bass High bass Mid range Low treble High treble Hammer sound 16.8%.8% 25.9% 15.1% 11.4% Chair sound 12.4% 34.6% 31.4% 19.5% 2.2% Basketball sound 24.3% 36.2% 28.6% 8.1% 2.7% Fist sound 31.9% 36.2% 21.6% 7.6% 2.7% impacts as in Figure 10. The correlation coefficient between the HIC and hard impacts average curve is R 2 = 0.98 showing HIC curves are also representative. 5. COMPARISONS OF FOUR CURVES: SIC, HIC, L CURVE, IIC CURVE After recommending the standard for sound insulation classification of wall impact sound, we compared four curves: the SIC, HIC, L curve, and IIC curve. L curve is a single-number rating derived in accordance with ISO 717/2 and ASTM E989, IIC curve is also a single-number rating derived in accordance with CNS 8465 A11 and JIS A The results are shown in Figures 11 and 12. The HIC is close to the IIC curve. The SIC and L curve have slightly different trends in the high frequency domain.

10 BUILDING ACOUSTICS Volume 13 Number Wall impact sound level (db) SIC-75 SIC K 2K 4K 1/1 Octave band frequency (Hz) soft impact average curve Figure 9. SIC for soft impact sounds. 6. RECOMMENDATION OF INDOOR SOUND INDEX FOR WALL IMPACT SOUNDS To ensure the quality of indoor sound environment in houses, we analyzed the residents responses from Tables 4 and 5 and referred to JIS A1419 and CNS 8465 A1031. The recommendations for wall impact sounds in houses form four classes, in Table APPLICATION OF SIC AND HIC CURVES First, it is necessary to measure sound pressure levels of walls or partitions in an acoustics laboratory. The method for measuring wall impact sounds are as recommended in 1999 [4]. For example, we measured the wall impact sound levels of sandwich gypsum panels [18]. The results are shown in Table 8. The data then was processed as in Figures 9 and 10. The final evaluation curves are SIC55 and HIC65 for sandwich gypsum panels, which are the first class of wall impact sound from Table CONCLUSIONS Wall impact sources can be divided into soft impact and hard impact sources. The hard impact sources generate mid-frequency components, while soft impact sources have

11 136 Rating of Sound Insulation of Wall Impact Sounds in Buildings Wall impact sound level (db) HIC-95 HIC K 2K 4K 1/1 Octave band frequency (Hz) Figure 10. HIC for hard impact sounds. hard impact average curve Table 7: Indoor sound index for wall impact sounds Sound pressure levels Best class First class Second class Third class Soft impact sounds <SIC60 SIC60-SIC70 SIC70-SIC80 >SIC80 Hard impact sounds <HIC60 HIC60-HIC70 HIC70-HIC80 >HIC80 Table 8: Wall impact sound levels of sandwich gypsum panel 63Hz 125Hz 250Hz 500Hz 1000Hz 00Hz 00Hz Soft wall impact sound levels (db) Hard wall impact sound levels (db)

12 BUILDING ACOUSTICS Volume 13 Number Impact sound level (db) K 2K 4K 1/1 Octave band frequency (Hz) SIC-60 L-60 Figure 11. Comparison of SIC with L curve. significant components confined to low frequencies. When wall impact sound level raises more than 80 db(a) participants felt annoyed. This study referred to other international standards in order to draft sound insulation classification of wall impact sounds. Two evaluation curves for floor impact sound are proposed, the L curve applies to heavy impacts and the IIC curve applies to light impacts. Therefore, the two evaluating curves are recommended, SIC applies to wall soft impact source and HIC applies to wall hard impact source. Four curves were compared: the SIC, HIC, L curve, and IIC curve. The results show the HIC curve is close to the IIC curve. The SIC curve and L curve have marginally different trends in the high frequency domain. Applications of the SIC curve and HIC curve for wall impact sounds can evaluate any type of wall or partition. A sound index for wall impacts, therefore, is recommended in order to improve the acoustic environment in houses, and to provide the basic index for establishing the standard for codes. ACKNOWLEDGEMENTS Thanks to National Science Council of R.O.C. for sponsoring this research. The Project number is NSC E

13 138 Rating of Sound Insulation of Wall Impact Sounds in Buildings Impact sound level (db) K 2K 4K 1/1 Octave band frequency (Hz) HIC-60 IIC-60 Figure 12. Comparison of HIC with IIC curve. REFERENCES [1] Huang, S. P. and Lai, R. P., Characteristics of impact sound through lightweight walls in houses: Proceedings of WESTPRAC, [2] Huang, S. P., Huang, G. M., and Lai, R. P., Residential subjective responses on impact sound radiated from lightweight walls in housing (in Chinese), Journal of Architecture of the Republic of China, 1995, 14, 1 8. [3] Huang, S. P., Huang, G. M., and Lai, R. P., Characteristics of impact sound radiated from lightweight walls, Analysis of actual impact in acoustics laboratory(in Chinese), Journal of Architecture of the Republic of China, 1997, 21, [4] Huang, S. P. and Lai, R. P., Development of standardized impact sources for laboratory measurement of sound transmission through lightweight walls, Applied Acoustics, 1999, 58, [5] Bowles, S. J. and Gold, E., Development of a rating procedure for impact noise transmission through walls. Applied Acoustics, 1987, 21, [6] ISO 717/1: Rating of sound insulation in buildings and of building elements. Part 1: Airborne sound insulation in buildings and of interior building elements.

14 BUILDING ACOUSTICS Volume 13 Number [7] BS 5821: Rating of sound insulation in buildings and of building elements. Part 1: Airborne sound insulation in buildings and of interior building elements. [8] ASTM E413: Determination of sound transmission class. [9] JIS A1419-1: Acoustics Rating of sound insulation in buildings and building elements Part 1: Airborne sound insulation. [10] CNS 8465 A1031: Classification of air-borne and impact sound insulation for buildings. [11] ISO 717/2: Rating of sound insulation in buildings and of building elements. Part 2: Impact sound insulation. [12] ASTM E989: Classification for determination of impact insulation class. [13] JIS A1419-2: Acoustics Rating of sound insulation in buildings and building elements Part 2: Floor impact sound insulation. [14] JIS A1419: Explanation Experiment on rating of sound insulation (in Japanese) [15] Kozo Hiramatsu, Satoshi Kobayashi, and Toshihito Matsui, A rating scale experiment on the judgements of loudness, noisiness, and annoyance of various environmental noise (in Japanese), The Journal of the Acoustical Society of Japan, 1988, 44(5), [16] Kenji Furihata and Takesaburo Yanagisawa, Investigation on composition of rating scale possible common to evaluate psychological effects on various kinds of noise sources (in Japanese), The Journal of the Acoustical Society of Japan, 1989, 45(8), [17] Satoshi Shimai and Masatoshi Tanaka, Relationships between pleasantnessunpleasantness evaluation and sound levels of environmental sounds (in Japanese), The Journal of the Acoustical Society of Japan, 1993, 49(4), [18] Huang, S. P. and Lai, R. P., The characteristics of impact sound transmission through sandwich gypsum panels(in Chinese), Journal of the Acoustical Society of R.O.C, 1998, 5(2), 1 14.

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