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Analysis of the acoustical environment of urban dwellings
Applied Acoustics Z9 (1990) 273-287
Analysis of the Acoustical Environment of Urban Dwellings Liu Xiaotu Department of Architecture, Southeast University. Nanjing, Jiangsu Province, People's Republic of China (Received 13 September 1989; accepted 15 December 19891
A BSTRA CT A n investigation is reported in which more than 900families in two residential areas were interviewed and acoustical measurements were made at several representative locations. From these interviews and measurements, it was possible to describe the current situation, to identify trends in development, and to find the relationship between values o f L,q and a high degree o f annoyance during sleep, work and rest. The noise level in dwellings facing the road at a given distance can be estimated with a simplified equation. Two examples o f the layout o f a residential area and design of the dwellings, taking into account the requirements o f the acoustical environment, are introduced, and some conclusions are summarised.
1 INTRODUCTION Dwelling construction has developed quickly in recent years in China. The completed areas o f new dwellings have been about i00 000 000 m 2 every year in urban areas, and the scale o f the construction has been developed from scattered to conjoined residential areas. According to the new Five-year Plan of China, more new dwellings will be constructed. The 'Standard of environmental noise o f urban areas' (GB-3096-82) was published in China in 1982 (see Appendix 1), so the quietness o f a dwelling's environment is included as one o f the criteria o f its quality. In fact, investigations and considerations o f the quality o f the residential acoustical environment were 273 Applied Acoustics 0003-682X/90/$03.50 © 1990 Elsevier Science Publishers Ltd. England. Printed in Great Britain
Liu Xiaotu
274
not taken into account during the process of planning and design in m a n y cases as much as the appearance of the city, the limited area for each family, and the cost of every square metre, which thus led to some undesirable consequences. For example, some teachers preparing their lessons at home have to insert earplugs; in one residential area 30 families (accounting for nearly 6-30 of the total number) have to close the windows of their rooms without air-conditioning when they stay at home in the summer though the weather is very hot. We have recently interviewed 905 families in two residential areas and made separate acoustic measurements at each of 10 representative locations in the first quarter o f every hour over the same 24-h period in accordance with the 'Measurement method of c o m m u n i t y noise' of China (GB-3222-82) (see Appendix 2). Figure 1 shows the distribution of the measurement positions in one of them. F r o m these interviews and measurements, we have been able to describe the current noise situation, to identify internal and external noise sources and their relative proportions, to identify trends in development, and to find the relationship between Leq and a high degree of annoyance. This paper first determines the relationship between sleeping, working, resting and a high degree of annoyance. It then puts forward a prediction method for estimating the environmental noise level of dwellings along the traffic route under simplified conditions. Lastly, it sums up some planning and design measures for obtaining an adequate acoustic environment for the inhabitants.
/ l/
uu
-,/ Traffic
! road
i/ //
Fig. 1. The distribution of the measurement positions in one of the residential areas in which 479 families were interviewed.The data for the two 'Q' positions are shown in Fig. 4.
The acoustical environment o f urban dwellings
275
2 ANALYSIS OF T H E RESULTS OF T H E SURVEYS A N D MEASUREMENTS The total number of vehicles per hour and the noise levels listed in Table 1 show the changes between 1976 and 1986 on the Changjiang River Bridge in Nanjing City. The conditions for motor vehicles, including the width of the road, the side branches of the road and the speed limit for the vehicles, etc., did not change here. The only thing that did change was the number of vehicles per hour. From a comparison of measurements between 1976 and TABLE 1 Comparisons Between the Total Number of Vehicles/Hour and the Noise Levels in 1976 and 1986 (the measurement positions were on the pavement of the bridge) Time o1" statistics and measurements
Number of vehicles/hour Heavy
Light
Motor.car
Number
%
Number %
0800-09O0 8 October 1976
264
80-5
62
19
2
0-5
O8O0-O900 18 October 1986
797
81"1
148
15
49
4-9
Total number
Number %
Traffic-noise level li'om the center of flow or nearside earriageway !dB{A}~ Lto
Lso
L,~o
L,q
328
78-5
63
51
75
995
78.0
72
64
75-3
Note: Heavy vehicles are motor lorries, trucks, buses, car dumpers, mail cars, etc. Light vehicles are saloon cars, baby cars, open cars. etc.
1986, we can see that, owing to the increase in traffic flow, the Ls0 noise level rose on average by 1 dB per year. On the other hand, the various household appliances (especially sound appliances) owned by residents increased rapidly and resulted in obvious changes in the composition of noise inside the residential area. Figure 2 shows the net increase in the number of household appliances in a residential area in each two-year period over a decade. Figure 3 shows the composition of the noise that was perceived or of which the people were aware inside the residential area. Figure 4 shows the pattern of A-weighted sound level in bedrooms with windows open at an urban site over a 24-h period. There were two kinds of questionnaire for interviewing the residents (see Appendix 3). The first questionnaire asked people to answer eight questions about their living circumstances, but did not mention the word "noise' in order to avoid inducing people to say that noise annoyed them, with the result that the noise problem might appear more serious than it was. After the first questionnaire was completed, the residents were asked to evaluate the noisiness of their neighborhood by using a crude three-point scale (i.e. satisfactory, fair and highly annoying) in the second questionnaire. Because
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83-84
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Fig. 2. The increasing number of household appliances in every two-year period from 1974 to 1985 (total numbers of various household appliances owned by residents over a decade are the accumulation of the individual items in every two years shown in this figure). existing a v e r a g e s t a n d a r d s for dwellings in C h i n a are still lower (for instance, the n u m b e r o f s q u a r e meters o c c u p i e d by a p e r s o n in the a p a r t m e n t s is less a n d the living r o o m in m o s t o f the a p a r t m e n t s m u s t also be used as a b e d r o o m , etc.), these c r u d e r a n k s c o u l d r e m o v e the effects o f o t h e r n o n acoustical factors in the class o f ' h i g h l y a n n o y i n g ' . 50 4O Ip
3o c 4;
u 2o a.
lO
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.-
Fig. 3. The composition of the noise inside a residential area in accordance with the survey results by using the questionnaire in Appendix III. (Note: The noise of daily life includes flushing of toilets, activities in the kitchen, etc. The noise of furniture includes dragging or running furniture on the concrete floor-slabs, etc.)
The acoustical environment of urban dwellings
277
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Fig. 4. The pattern of dB(A) at an urban site over a 24-h period (the microphones were inside the bedrooms). , Bedroom near the road (the contribution of the traffic flow to the overall noise level is dominant). - - - , Bedroom away from the road (the contribution of the internal noise of the residential area is dominant). Figure 5 shows the relationship between the percentages o f a high degree o f a n n o y a n c e d u r i n g sleep and the value o f Loq(S~at night time (from 10 p m to 6 am). H e r e the responses are o f the s t r a t a p o p u l a t i o n with different extents o f noise e x p o s u r e in the residential area that was c o v e r e d by interviews and m e a s u r e m e n t s . Regression analysis shows that the c o r r e l a t i o n coefficient reaches 0.961. " 80-
~
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7~,8 10
/
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=
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50 60 Leq (8)dB(A)
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Fig. 5. The relationshi p between percentage of people suffering a high degree of annoyance during sleep and the noise level.
278
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60
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Fig. 6.
The relationship between percentage of people suffering a high degree of annoyance during work and the noise level.
Figure 6 shows the relationship between the value of Leq(16) and a high degree of annoyance during work. The subjective responses were based on 385 families (accounting for nearly 43% of the total number of families in the two residential areas surveyed and measured). They were teachers, engineers, newspaper reporters and editors, whose educational level and occupational classification were more or less the same. Their activities and work at home in general had similar requirements of quietness in their acoustical environment, so the correlation coefficient of the regression analysis reached 0.995. Figure 7 shows the relationship between Leq(16) and a high degree of annoyance during rest, conversation and musical appreciation. Because the requirements and interest of the residents in these fields were different, for example the range of loudness of the sound listened to, the level of unavoidable room noise to be expected, etc., it was found that the requirements for noise control were lower than those for work, the correlation coefficient also being lower. In comparison with the research results of Schultz ~ on the interference by noise with sleep, work, conversation and radio/television listening, we find some differences. The following proposals were made. (1)
Heavy vehicles should be allowed on some major routes in urban areas in China only at night. Owing to the tendency for total traffic flow to decline, the passage of individual very noisy vehicles becomes an insistent and directly perceptible source of annoyance, and the relationship between the percentage of people highly annoyed during
The acoustical environment of urban dwellings o~
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The relationship betweenpercentage of people sufferinga high degree of annoyance during rest, conversation, etc., and the noise level. sleep and the noise level L=q(8~ at night time may include some annoyance, especially the effect of sudden awakening produced by heavy vehicles that are disproportionately greater than their contribution to the overall noise level. The differences in the percentages of highly annoyed people during rest, conversation and radio/television listening may be due to the fact that some people think they can adjust the voice and the sound level emitted from radio and television sets for good listening. 3 P R E D I C T I O N OF T H E T R A F F I C - N O I S E LEVEL IN D W E L L I N G S A L O N G ROADS
In general, under conditions of free flow, the traffic-noise level transmitted to the dwelling depends on the total number of vehicles per hour, the percentage of heavy vehicles, the distance from the noise source, and the extent of the road that comes into the view of the residents. We note that the speed limit of the vehicles is roughly the same in urban areas and the measurement positions on the pavement are generally 15 m away from the carriageway; that is to say, the contribution of the individual vehicles to the overall noise level is not dominant, so the noise level in dwellings facing the route at a distance D could be estimated from the following simplified equation: LD = Lo -- 10 l o g ( D / X o ) + 10 log(OD/180)
dB(A)
In this equation, the first term is the traffic-noise level at a given distance Xo (outside the dwellings).
Liu Xiaotu
280
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I
140
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Degree
Fig. 8.
Relationship between correction and viewing angle.
The second term considers a stream of road vehicles as a 'line source', since the emission of noise from each vehicle varies considerably and the vehicles are seldom equally spaced, so a value of 3 dB is taken as the average rate of reduction for the doubled distance, where D is the distance from the traffic flow to the external wall facing the road, in meters. The third term is an adjustment depending on 0, 0o being the extent of the road that comes into view at the position o f the measurement or observation, expressed in degrees. Figure 8 shows the corrections for different values-of 0 o under the same traffic flow on the same road and compares the result with measurements. Table 2 shows the noise levels measured at the same time at the receiving positions on different floors of a dwelling facing the road. Generally speaking, because the distance from the traffic flow to the receiving points on the different floors above source height are greater than the horizontal distance, lower outdoor-noise levels would be expected in the upper storeys of a multi-dwelling rather than at road level. However, this reduction in outdoor-noise levels is offset by the dependence TABLE 2
Noise Levelsin Bedroomswith the WindowsOpen on Different Floors Measured at the Same Time Floor
Noise level Lg0 (dB(A)) (average values over 4 h)
I 2 3 4 5 6 7
54.5 52'5 54.5 53'0 54.3 53.1 54.5
The acoustical environment of urban dwellings
281
of the building's noise insulation on the angle from which traffic sound arrives. For this reason it seems that the distance correction is based only on the horizontal distance between the dwelling and the traffic-noise source if the ground surface is hard. 2 This view needs further proof with more measurements and analysis of the theory. If it was a high-rise building, or on the other side of the road opposite to a multi-floor dwelling, there were strong reflections, so different results could be predicted.
4 PLANNING AND DESIGN MEASURES FOR PROVIDING A QUIET RESIDENTIAL ENVIRONMENT (1) Owing to irrational traffic systems and the distribution of industry in some cities, people living in urban areas suffer from severe noise pollution. For example, there are two main railroads passing through the urban area of a provincial capital city, the closest distance between the railroad and the external walls of the dwellings facing the railroad is less than 20 m, and the average number of trains coming and going is five per hour during the night. The ambient noise level is often 37-43 dB(A) in the quietness of the night, but the noise level increases rapidly to more than 80dB(A) when a train passes. In another medium-sized city, the number of small airplanes from a nearby flying school involved in training flights above the city is 60-120 per hour, and the area affected by high levels ofaircraft noise is about 12 km:. With the development of cities and the increase in population in urban areas, the state of noise pollution is worsening. If there were national regulations of noise
Section
Fig. 9. A good example of shop-housing.
282
Liu Xiaotu
control, the 'Standard of environmental noise of urban areas' (GB-3096-82) would be put into effect forcefully, and the problems of noise pollution would be sure to be solved by the replanning and reconstruction of the cities. (2) The layout of a new residential area and the design of the dwellings themselves must take into account the requirements of the acoustical environment after the site is chosen. Figure 9 shows shops and housing. Most dwelling units in this building are arranged above the shops and pulled back 20m. The first floor of the market acts as a barrier. From the comparison of measurement with the remaining small portion of the building shown in Table 3, we can see that the noise level emitted by the traffic flow obviously decreased. It should also be noted that, since the
TABLE 3 Comparisons of the Noise Levels of the Dwelling Units Between the Different Parts of the Building levels in the bedrooms Floors and condition ~ - - - ~ of the measurements Second floor
Fourth floor
h the windows open ~,4t~tJ))
Dwelling units above the shops and drawn back 20m Dwelling units set on other parts of the building The effects of the barrier Dwelling units above the shops and drawn back 20 m Dwelling units set on other parts of the building The effects of the barrier
L90
L50
Lt 0
L~q
51'0
56"0
66-0
59-8
54.0 3-0
62'0 6'0
73.0 7.0
68"0 8.2
58"8
64.5
72.8
68"8
60.0 1.2
68'0 3'5
78-0 5"2
73.4 4-6
energy in the diffracted waves has been extracted from the uninterrupted waves, in the bedroom on the fourth floor there is a small reduction in intensity even outside the sound shadow. Another good example, shown in Fig. 10, is a new residential area in Nanjing City? The main characteristics of site planning and housing design are as follows. As a barrier the arrangement of the shops and housing could obstruct traffic noise, so the acoustical environment inside the residential mass could improve considerably. Owing to the serrated form of the external wall of the shops and housing facing the road, the extent of the road that came into view at the positions of
The acoustical environment of urban dwellings
283
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i=:= i ~---l!]
r
r.,
Lt~,
Aiii~ ili=~ll IF' la)
(b) Fig. 10.
(a) An example of a residential area (still under construction). (b) A model of the area (photo by Li Guoqiang).
284
Liu .Viaotu
observation was reduced, so the disturbance from traffic noise inside the building along the road could be further reduced. Noise disturbance due to the activities in the open space could be reinforced by reverberation, so the site planning of this area avoids the enclosure on all four sides. (3/ Auxiliary rooms (such as the toilet, kitchen, etc.) or" the dwelling unit can be placed near the road, in order to reduce interference by noise from traffic. According to the results of measurements, a corridor with glass windows can decrease the noise level from the outside environment by more than 20dB(At. Fricke's investigation shows that the maximum attenuation obtainable is approximately 6 dBIA) at the face of the building behind the balcony (with a white-noise source used). -~ Owing to the application of hollow concrete floor-slabs (I~>80dB) without any carpet and various light partitions (in general, I~ < 45 dB/in new Chinese dwellings, the acoustic privacy between two adjacent units in the dwellings has also become increasingly important. The flanking transmission of speech sound, due not only to the selection of partitions but also to large holes or windows installed on the interior wall separating two cheaper dwelling units, is serious. Acoustic privacy can be improved if it is considered at the initial stage of the design by the architects and will not necessarily add too much to engineering costs.
5 CONCLUSIONS (1) Owing to total traffic flow in urban areas in China, which is on the increase, the average noise level has been increasing by nearly 1 dB per year. (2) The simplified equation L D = L o -
10 log(D/Xol + 10
log(Oo/180)
could be used for estimating the noise level in dB{A) at ground level in urban areas. If the ground surface of the area between the carriageway and the dwelling is hard, this equation could be used for multi-storey dwellings. (3) A good acoustical environment in all cities depends largely on the rational functional division of cities. This is the most effective and economic way of providing noise control. A number of the cities are now being replanned, so this offers an opportunity for improving the acoustical environment of urban dwellings. (41 If a site in a mixed-function area were selected for developing public housing, then the number of dwellings could be fewer, allowing for more expensive acoustic measures to provide a satisfactory environment.
The acoustical environment of urban dwellings
285
REFERENCES I. Schultz, T. J., Community' Noise Rating, 2nd edn. Applied Science Publishers, London, 1982. 2. CMHC, Road and rail noise: effects on housing, 77. Central Mortgage and Housing Corporation, 1977. 3. Fan Hua et aL, Discussion on some problems of planning for reconstruction of old residential areas in the city. In Proceedings of IYSH--lnternational Conference on Housing (Nanjing, China), Vol. !, pp. 2-24/2-33, 1987. 4. Fricke, F. R., The protection of building against traffic noise. Noise Control Engng, 8(1) (1977) 30-1.
A P P E N D I X 1: S T A N D A R D O F E N V I R O N M E N T A L N O I S E O F U R B A N A R E A S O F C H I N A (GB-3096-82) ( E X T R A C T )
The areas to be covered
The equivalent sound levels outside the walls or the windows away f r o m 1"0 m
(dB(A))
The special housing areas Areas for residents, culture and education The first kind of mixed areas The second kind o f mixed areas and commercial-centre areas The concentrated industrial areas Both sides of the main traffic routes
Day time
Night time
45 50 55
35 40 45
60 65 70
50 55 55
Notes 1. The special housing areas denote areas that require special quietness. 2. Areas for residents, culture and education refer to residential areas and cultural and educational institutions. 3. The first kind o f mixed areas are areas where residents are mixed with general commerce. 4. Commercial-centre areas are the d o w n t o w n districts. 5. The concentrated industrial areas are the industrial areas delineated clearly in the city. 6. Both sides o f the main traffic route indicate roads in which the traffic flow is more than 100 vehicles per hour.
286
Liu Xiaotu
A P P E N D I X 2: M E A S U R E M E N T M E T H O D OF C O M M U N I T Y NOISE OF C H I N A (GB-3222-82) (EXTRACT) 1. The microphone supplied with the precision sound-level meter is the basic instrument for measuring the community noise and the instruments have to meet the precision requirements of IEC 651 (1979). The calibrations should be made before and after each use of the measurement equipment. 2. The microphone should also be kept out of any appreciable wind. If it is not possible to avoid wind on the microphone, a wind screen should be used. Measurement should never be made, even with a wind screen, in winds exceeding the speed limit. 3. The height of the microphone above the ground or supporting surface is 1.2 m, and far away from the reflective surface of the buildings. 4. Set the precision sound-level-meter weighting switch to the 'A' position and the meter-response switch to the 'Slow' position. Read the instantaneous A-weighted sound level every 5 seconds. 5. After the appropriate number of samples has been taken (such as 200 samples), calculate the Lto, Ls0, L9o and Leq values. A P P E N D I X 3(A) The survey questionnaire on housing (1) Name: Occupation:
Sex:
Date:
Age: Address:
1. Could you concentrate your attention on working, reading and thinking at home? If you could not, what are the main reasons? 2. Do you have difficulty in getting to sleep? If so, what are the main reasons? 3. Do you wake up from a deep sleep? If so, what are the main reasons? 4. What do you do to help you to have a good sleep? 5. Do you sleep with windows open or closed in summer? What is the main reason for that? 6. Do you sleep with windows open or closed in winter? What is the main reason for that? 7. How long have you been living in here? In comparison with the past conditions in which you lived, are there obvious differences?
The acoustical environment of urban dwellings
287
8. The features of the materials and the constructions (such as exterior walls, the partitions separating two family units, floor-slabs, the doors and the windows, etc.) of the dwelling unit. Your suggestions and opinions about improvement of the living conditions.
APPENDIX 3(B) The survey questionnaire on housing (2) Name:
Sex:
Age:
Address:
Date:
No. of bldg:
Floor:
No. of family units: The synopsis of the surroundings and a sketch of the measurement positions: The type of housing (strip form, spot form, the number of the household sharing a staircase, the materials and the structure, etc.): The internal and external noise sources (perception or awareness of noise) and the noisy circumstances reported by the residents: The overall ratings on the acoustical environment of the residents: 1. On working, study, thinking, reading, etc. much interference fair
quiet
2. On rest, conversation much interference
quiet
fair
3. On enjoying music, watching TV much interference fair L
4. On sleep at night impossible I
t
difficult I
non-interference I
satisfactory I
The main noise sources and the results of the measurements: The household appliances, etc. (such as radio, tape-recorder, TV set, washing-machine, sewing-machine); the power consumption of the appliances and the date of purchase:
Analysis of the Acoustical Environment of Urban Dwellings Liu Xiaotu Department of Architecture, Southeast University. Nanjing, Jiangsu Province, People's Republic of China (Received 13 September 1989; accepted 15 December 19891
A BSTRA CT A n investigation is reported in which more than 900families in two residential areas were interviewed and acoustical measurements were made at several representative locations. From these interviews and measurements, it was possible to describe the current situation, to identify trends in development, and to find the relationship between values o f L,q and a high degree o f annoyance during sleep, work and rest. The noise level in dwellings facing the road at a given distance can be estimated with a simplified equation. Two examples o f the layout o f a residential area and design of the dwellings, taking into account the requirements o f the acoustical environment, are introduced, and some conclusions are summarised.
1 INTRODUCTION Dwelling construction has developed quickly in recent years in China. The completed areas o f new dwellings have been about i00 000 000 m 2 every year in urban areas, and the scale o f the construction has been developed from scattered to conjoined residential areas. According to the new Five-year Plan of China, more new dwellings will be constructed. The 'Standard of environmental noise o f urban areas' (GB-3096-82) was published in China in 1982 (see Appendix 1), so the quietness o f a dwelling's environment is included as one o f the criteria o f its quality. In fact, investigations and considerations o f the quality o f the residential acoustical environment were 273 Applied Acoustics 0003-682X/90/$03.50 © 1990 Elsevier Science Publishers Ltd. England. Printed in Great Britain
Liu Xiaotu
274
not taken into account during the process of planning and design in m a n y cases as much as the appearance of the city, the limited area for each family, and the cost of every square metre, which thus led to some undesirable consequences. For example, some teachers preparing their lessons at home have to insert earplugs; in one residential area 30 families (accounting for nearly 6-30 of the total number) have to close the windows of their rooms without air-conditioning when they stay at home in the summer though the weather is very hot. We have recently interviewed 905 families in two residential areas and made separate acoustic measurements at each of 10 representative locations in the first quarter o f every hour over the same 24-h period in accordance with the 'Measurement method of c o m m u n i t y noise' of China (GB-3222-82) (see Appendix 2). Figure 1 shows the distribution of the measurement positions in one of them. F r o m these interviews and measurements, we have been able to describe the current noise situation, to identify internal and external noise sources and their relative proportions, to identify trends in development, and to find the relationship between Leq and a high degree of annoyance. This paper first determines the relationship between sleeping, working, resting and a high degree of annoyance. It then puts forward a prediction method for estimating the environmental noise level of dwellings along the traffic route under simplified conditions. Lastly, it sums up some planning and design measures for obtaining an adequate acoustic environment for the inhabitants.
/ l/
uu
-,/ Traffic
! road
i/ //
Fig. 1. The distribution of the measurement positions in one of the residential areas in which 479 families were interviewed.The data for the two 'Q' positions are shown in Fig. 4.
The acoustical environment o f urban dwellings
275
2 ANALYSIS OF T H E RESULTS OF T H E SURVEYS A N D MEASUREMENTS The total number of vehicles per hour and the noise levels listed in Table 1 show the changes between 1976 and 1986 on the Changjiang River Bridge in Nanjing City. The conditions for motor vehicles, including the width of the road, the side branches of the road and the speed limit for the vehicles, etc., did not change here. The only thing that did change was the number of vehicles per hour. From a comparison of measurements between 1976 and TABLE 1 Comparisons Between the Total Number of Vehicles/Hour and the Noise Levels in 1976 and 1986 (the measurement positions were on the pavement of the bridge) Time o1" statistics and measurements
Number of vehicles/hour Heavy
Light
Motor.car
Number
%
Number %
0800-09O0 8 October 1976
264
80-5
62
19
2
0-5
O8O0-O900 18 October 1986
797
81"1
148
15
49
4-9
Total number
Number %
Traffic-noise level li'om the center of flow or nearside earriageway !dB{A}~ Lto
Lso
L,~o
L,q
328
78-5
63
51
75
995
78.0
72
64
75-3
Note: Heavy vehicles are motor lorries, trucks, buses, car dumpers, mail cars, etc. Light vehicles are saloon cars, baby cars, open cars. etc.
1986, we can see that, owing to the increase in traffic flow, the Ls0 noise level rose on average by 1 dB per year. On the other hand, the various household appliances (especially sound appliances) owned by residents increased rapidly and resulted in obvious changes in the composition of noise inside the residential area. Figure 2 shows the net increase in the number of household appliances in a residential area in each two-year period over a decade. Figure 3 shows the composition of the noise that was perceived or of which the people were aware inside the residential area. Figure 4 shows the pattern of A-weighted sound level in bedrooms with windows open at an urban site over a 24-h period. There were two kinds of questionnaire for interviewing the residents (see Appendix 3). The first questionnaire asked people to answer eight questions about their living circumstances, but did not mention the word "noise' in order to avoid inducing people to say that noise annoyed them, with the result that the noise problem might appear more serious than it was. After the first questionnaire was completed, the residents were asked to evaluate the noisiness of their neighborhood by using a crude three-point scale (i.e. satisfactory, fair and highly annoying) in the second questionnaire. Because
276
Liu Xiaotu 180
160 140 120 100 80 E 7= SO 401 2O 0
R. Before
]Hn.I I !1, [H 75-76
77-78
Date
1974
79-80
i Sewing
machine
81-82
83-84
purchase
of
i
i
i
i
Radio i i Television
Tape-recorder
Fig. 2. The increasing number of household appliances in every two-year period from 1974 to 1985 (total numbers of various household appliances owned by residents over a decade are the accumulation of the individual items in every two years shown in this figure). existing a v e r a g e s t a n d a r d s for dwellings in C h i n a are still lower (for instance, the n u m b e r o f s q u a r e meters o c c u p i e d by a p e r s o n in the a p a r t m e n t s is less a n d the living r o o m in m o s t o f the a p a r t m e n t s m u s t also be used as a b e d r o o m , etc.), these c r u d e r a n k s c o u l d r e m o v e the effects o f o t h e r n o n acoustical factors in the class o f ' h i g h l y a n n o y i n g ' . 50 4O Ip
3o c 4;
u 2o a.
lO
b--n IlJ ell 171
.~
=:~
~ ° o
"o 2
~ ~
.-
Fig. 3. The composition of the noise inside a residential area in accordance with the survey results by using the questionnaire in Appendix III. (Note: The noise of daily life includes flushing of toilets, activities in the kitchen, etc. The noise of furniture includes dragging or running furniture on the concrete floor-slabs, etc.)
The acoustical environment of urban dwellings
277
70
60
m
50
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30
7
i
I
i
i
9
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i
i
19
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21
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I
I
2.3
1
I
3
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day
Fig. 4. The pattern of dB(A) at an urban site over a 24-h period (the microphones were inside the bedrooms). , Bedroom near the road (the contribution of the traffic flow to the overall noise level is dominant). - - - , Bedroom away from the road (the contribution of the internal noise of the residential area is dominant). Figure 5 shows the relationship between the percentages o f a high degree o f a n n o y a n c e d u r i n g sleep and the value o f Loq(S~at night time (from 10 p m to 6 am). H e r e the responses are o f the s t r a t a p o p u l a t i o n with different extents o f noise e x p o s u r e in the residential area that was c o v e r e d by interviews and m e a s u r e m e n t s . Regression analysis shows that the c o r r e l a t i o n coefficient reaches 0.961. " 80-
~
70
x
4o
._m
~ 3o g
7~,8 10
/
r =0-961
n
C!
20
'
ll.,
I
30
40
1
I
=
I
50 60 Leq (8)dB(A)
=
1
70
r
I
80
Fig. 5. The relationshi p between percentage of people suffering a high degree of annoyance during sleep and the noise level.
278
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F
0 r-
7ol--
"E 6O c
5O 0
4O tO
3O
x
x
2O L n
-140.1
10 0
3O
¢ V°?? 4O
50
60
70
80
Leq (~)d B (A)
Fig. 6.
The relationship between percentage of people suffering a high degree of annoyance during work and the noise level.
Figure 6 shows the relationship between the value of Leq(16) and a high degree of annoyance during work. The subjective responses were based on 385 families (accounting for nearly 43% of the total number of families in the two residential areas surveyed and measured). They were teachers, engineers, newspaper reporters and editors, whose educational level and occupational classification were more or less the same. Their activities and work at home in general had similar requirements of quietness in their acoustical environment, so the correlation coefficient of the regression analysis reached 0.995. Figure 7 shows the relationship between Leq(16) and a high degree of annoyance during rest, conversation and musical appreciation. Because the requirements and interest of the residents in these fields were different, for example the range of loudness of the sound listened to, the level of unavoidable room noise to be expected, etc., it was found that the requirements for noise control were lower than those for work, the correlation coefficient also being lower. In comparison with the research results of Schultz ~ on the interference by noise with sleep, work, conversation and radio/television listening, we find some differences. The following proposals were made. (1)
Heavy vehicles should be allowed on some major routes in urban areas in China only at night. Owing to the tendency for total traffic flow to decline, the passage of individual very noisy vehicles becomes an insistent and directly perceptible source of annoyance, and the relationship between the percentage of people highly annoyed during
The acoustical environment of urban dwellings o~
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279
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7.
(2)
r=0.92 I
[
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t
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60 70 80 Leq 06)riB(A)
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The relationship betweenpercentage of people sufferinga high degree of annoyance during rest, conversation, etc., and the noise level. sleep and the noise level L=q(8~ at night time may include some annoyance, especially the effect of sudden awakening produced by heavy vehicles that are disproportionately greater than their contribution to the overall noise level. The differences in the percentages of highly annoyed people during rest, conversation and radio/television listening may be due to the fact that some people think they can adjust the voice and the sound level emitted from radio and television sets for good listening. 3 P R E D I C T I O N OF T H E T R A F F I C - N O I S E LEVEL IN D W E L L I N G S A L O N G ROADS
In general, under conditions of free flow, the traffic-noise level transmitted to the dwelling depends on the total number of vehicles per hour, the percentage of heavy vehicles, the distance from the noise source, and the extent of the road that comes into the view of the residents. We note that the speed limit of the vehicles is roughly the same in urban areas and the measurement positions on the pavement are generally 15 m away from the carriageway; that is to say, the contribution of the individual vehicles to the overall noise level is not dominant, so the noise level in dwellings facing the route at a distance D could be estimated from the following simplified equation: LD = Lo -- 10 l o g ( D / X o ) + 10 log(OD/180)
dB(A)
In this equation, the first term is the traffic-noise level at a given distance Xo (outside the dwellings).
Liu Xiaotu
280
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I
140
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100
,
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Degree
Fig. 8.
Relationship between correction and viewing angle.
The second term considers a stream of road vehicles as a 'line source', since the emission of noise from each vehicle varies considerably and the vehicles are seldom equally spaced, so a value of 3 dB is taken as the average rate of reduction for the doubled distance, where D is the distance from the traffic flow to the external wall facing the road, in meters. The third term is an adjustment depending on 0, 0o being the extent of the road that comes into view at the position o f the measurement or observation, expressed in degrees. Figure 8 shows the corrections for different values-of 0 o under the same traffic flow on the same road and compares the result with measurements. Table 2 shows the noise levels measured at the same time at the receiving positions on different floors of a dwelling facing the road. Generally speaking, because the distance from the traffic flow to the receiving points on the different floors above source height are greater than the horizontal distance, lower outdoor-noise levels would be expected in the upper storeys of a multi-dwelling rather than at road level. However, this reduction in outdoor-noise levels is offset by the dependence TABLE 2
Noise Levelsin Bedroomswith the WindowsOpen on Different Floors Measured at the Same Time Floor
Noise level Lg0 (dB(A)) (average values over 4 h)
I 2 3 4 5 6 7
54.5 52'5 54.5 53'0 54.3 53.1 54.5
The acoustical environment of urban dwellings
281
of the building's noise insulation on the angle from which traffic sound arrives. For this reason it seems that the distance correction is based only on the horizontal distance between the dwelling and the traffic-noise source if the ground surface is hard. 2 This view needs further proof with more measurements and analysis of the theory. If it was a high-rise building, or on the other side of the road opposite to a multi-floor dwelling, there were strong reflections, so different results could be predicted.
4 PLANNING AND DESIGN MEASURES FOR PROVIDING A QUIET RESIDENTIAL ENVIRONMENT (1) Owing to irrational traffic systems and the distribution of industry in some cities, people living in urban areas suffer from severe noise pollution. For example, there are two main railroads passing through the urban area of a provincial capital city, the closest distance between the railroad and the external walls of the dwellings facing the railroad is less than 20 m, and the average number of trains coming and going is five per hour during the night. The ambient noise level is often 37-43 dB(A) in the quietness of the night, but the noise level increases rapidly to more than 80dB(A) when a train passes. In another medium-sized city, the number of small airplanes from a nearby flying school involved in training flights above the city is 60-120 per hour, and the area affected by high levels ofaircraft noise is about 12 km:. With the development of cities and the increase in population in urban areas, the state of noise pollution is worsening. If there were national regulations of noise
Section
Fig. 9. A good example of shop-housing.
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Liu Xiaotu
control, the 'Standard of environmental noise of urban areas' (GB-3096-82) would be put into effect forcefully, and the problems of noise pollution would be sure to be solved by the replanning and reconstruction of the cities. (2) The layout of a new residential area and the design of the dwellings themselves must take into account the requirements of the acoustical environment after the site is chosen. Figure 9 shows shops and housing. Most dwelling units in this building are arranged above the shops and pulled back 20m. The first floor of the market acts as a barrier. From the comparison of measurement with the remaining small portion of the building shown in Table 3, we can see that the noise level emitted by the traffic flow obviously decreased. It should also be noted that, since the
TABLE 3 Comparisons of the Noise Levels of the Dwelling Units Between the Different Parts of the Building levels in the bedrooms Floors and condition ~ - - - ~ of the measurements Second floor
Fourth floor
h the windows open ~,4t~tJ))
Dwelling units above the shops and drawn back 20m Dwelling units set on other parts of the building The effects of the barrier Dwelling units above the shops and drawn back 20 m Dwelling units set on other parts of the building The effects of the barrier
L90
L50
Lt 0
L~q
51'0
56"0
66-0
59-8
54.0 3-0
62'0 6'0
73.0 7.0
68"0 8.2
58"8
64.5
72.8
68"8
60.0 1.2
68'0 3'5
78-0 5"2
73.4 4-6
energy in the diffracted waves has been extracted from the uninterrupted waves, in the bedroom on the fourth floor there is a small reduction in intensity even outside the sound shadow. Another good example, shown in Fig. 10, is a new residential area in Nanjing City? The main characteristics of site planning and housing design are as follows. As a barrier the arrangement of the shops and housing could obstruct traffic noise, so the acoustical environment inside the residential mass could improve considerably. Owing to the serrated form of the external wall of the shops and housing facing the road, the extent of the road that came into view at the positions of
The acoustical environment of urban dwellings
283
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i=:= i ~---l!]
r
r.,
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Aiii~ ili=~ll IF' la)
(b) Fig. 10.
(a) An example of a residential area (still under construction). (b) A model of the area (photo by Li Guoqiang).
284
Liu .Viaotu
observation was reduced, so the disturbance from traffic noise inside the building along the road could be further reduced. Noise disturbance due to the activities in the open space could be reinforced by reverberation, so the site planning of this area avoids the enclosure on all four sides. (3/ Auxiliary rooms (such as the toilet, kitchen, etc.) or" the dwelling unit can be placed near the road, in order to reduce interference by noise from traffic. According to the results of measurements, a corridor with glass windows can decrease the noise level from the outside environment by more than 20dB(At. Fricke's investigation shows that the maximum attenuation obtainable is approximately 6 dBIA) at the face of the building behind the balcony (with a white-noise source used). -~ Owing to the application of hollow concrete floor-slabs (I~>80dB) without any carpet and various light partitions (in general, I~ < 45 dB/in new Chinese dwellings, the acoustic privacy between two adjacent units in the dwellings has also become increasingly important. The flanking transmission of speech sound, due not only to the selection of partitions but also to large holes or windows installed on the interior wall separating two cheaper dwelling units, is serious. Acoustic privacy can be improved if it is considered at the initial stage of the design by the architects and will not necessarily add too much to engineering costs.
5 CONCLUSIONS (1) Owing to total traffic flow in urban areas in China, which is on the increase, the average noise level has been increasing by nearly 1 dB per year. (2) The simplified equation L D = L o -
10 log(D/Xol + 10
log(Oo/180)
could be used for estimating the noise level in dB{A) at ground level in urban areas. If the ground surface of the area between the carriageway and the dwelling is hard, this equation could be used for multi-storey dwellings. (3) A good acoustical environment in all cities depends largely on the rational functional division of cities. This is the most effective and economic way of providing noise control. A number of the cities are now being replanned, so this offers an opportunity for improving the acoustical environment of urban dwellings. (41 If a site in a mixed-function area were selected for developing public housing, then the number of dwellings could be fewer, allowing for more expensive acoustic measures to provide a satisfactory environment.
The acoustical environment of urban dwellings
285
REFERENCES I. Schultz, T. J., Community' Noise Rating, 2nd edn. Applied Science Publishers, London, 1982. 2. CMHC, Road and rail noise: effects on housing, 77. Central Mortgage and Housing Corporation, 1977. 3. Fan Hua et aL, Discussion on some problems of planning for reconstruction of old residential areas in the city. In Proceedings of IYSH--lnternational Conference on Housing (Nanjing, China), Vol. !, pp. 2-24/2-33, 1987. 4. Fricke, F. R., The protection of building against traffic noise. Noise Control Engng, 8(1) (1977) 30-1.
A P P E N D I X 1: S T A N D A R D O F E N V I R O N M E N T A L N O I S E O F U R B A N A R E A S O F C H I N A (GB-3096-82) ( E X T R A C T )
The areas to be covered
The equivalent sound levels outside the walls or the windows away f r o m 1"0 m
(dB(A))
The special housing areas Areas for residents, culture and education The first kind of mixed areas The second kind o f mixed areas and commercial-centre areas The concentrated industrial areas Both sides of the main traffic routes
Day time
Night time
45 50 55
35 40 45
60 65 70
50 55 55
Notes 1. The special housing areas denote areas that require special quietness. 2. Areas for residents, culture and education refer to residential areas and cultural and educational institutions. 3. The first kind o f mixed areas are areas where residents are mixed with general commerce. 4. Commercial-centre areas are the d o w n t o w n districts. 5. The concentrated industrial areas are the industrial areas delineated clearly in the city. 6. Both sides o f the main traffic route indicate roads in which the traffic flow is more than 100 vehicles per hour.
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Liu Xiaotu
A P P E N D I X 2: M E A S U R E M E N T M E T H O D OF C O M M U N I T Y NOISE OF C H I N A (GB-3222-82) (EXTRACT) 1. The microphone supplied with the precision sound-level meter is the basic instrument for measuring the community noise and the instruments have to meet the precision requirements of IEC 651 (1979). The calibrations should be made before and after each use of the measurement equipment. 2. The microphone should also be kept out of any appreciable wind. If it is not possible to avoid wind on the microphone, a wind screen should be used. Measurement should never be made, even with a wind screen, in winds exceeding the speed limit. 3. The height of the microphone above the ground or supporting surface is 1.2 m, and far away from the reflective surface of the buildings. 4. Set the precision sound-level-meter weighting switch to the 'A' position and the meter-response switch to the 'Slow' position. Read the instantaneous A-weighted sound level every 5 seconds. 5. After the appropriate number of samples has been taken (such as 200 samples), calculate the Lto, Ls0, L9o and Leq values. A P P E N D I X 3(A) The survey questionnaire on housing (1) Name: Occupation:
Sex:
Date:
Age: Address:
1. Could you concentrate your attention on working, reading and thinking at home? If you could not, what are the main reasons? 2. Do you have difficulty in getting to sleep? If so, what are the main reasons? 3. Do you wake up from a deep sleep? If so, what are the main reasons? 4. What do you do to help you to have a good sleep? 5. Do you sleep with windows open or closed in summer? What is the main reason for that? 6. Do you sleep with windows open or closed in winter? What is the main reason for that? 7. How long have you been living in here? In comparison with the past conditions in which you lived, are there obvious differences?
The acoustical environment of urban dwellings
287
8. The features of the materials and the constructions (such as exterior walls, the partitions separating two family units, floor-slabs, the doors and the windows, etc.) of the dwelling unit. Your suggestions and opinions about improvement of the living conditions.
APPENDIX 3(B) The survey questionnaire on housing (2) Name:
Sex:
Age:
Address:
Date:
No. of bldg:
Floor:
No. of family units: The synopsis of the surroundings and a sketch of the measurement positions: The type of housing (strip form, spot form, the number of the household sharing a staircase, the materials and the structure, etc.): The internal and external noise sources (perception or awareness of noise) and the noisy circumstances reported by the residents: The overall ratings on the acoustical environment of the residents: 1. On working, study, thinking, reading, etc. much interference fair
quiet
2. On rest, conversation much interference
quiet
fair
3. On enjoying music, watching TV much interference fair L
4. On sleep at night impossible I
t
difficult I
non-interference I
satisfactory I
The main noise sources and the results of the measurements: The household appliances, etc. (such as radio, tape-recorder, TV set, washing-machine, sewing-machine); the power consumption of the appliances and the date of purchase: