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Journal of the Acoustical Society of America, 36, 4, pp. 725-728, 1964-04
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Sound insulation and the apartment dweller
Northwood, T. D.
Ser
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no. 185
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Nerorunl Reseencn
CANADAD I V I S I O N O F B U I L D I N G
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R E S E A R C H
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N R C A O a Ts64168
SOUND
INSULATION
AND THE APARTMENT
DWELLER
BY
T. D. NORTHWOOD
A N A L Y Z E D
R E P R I N T E D F R O M
T H E J O U R N A L O F T H E A C O U S T I C A L S O C I E T Y O F A M E R I C A voL. 36. NO. 4, P. 725 - 72A, APR|L 1964
T E C H N I C A L P A P E R N O . I A 5 O F T H E
DIVISION OF BUILDING RESEARCH
B U I L D I N G R E S E A R C H. L I B N A R Y .
sEP 1? 1964
N A T I O N A L R E S E A R G H C O U N C I LOTTAWA
AUGUST 1964
P R I C E 1 0 C E N T SSOMMAIRE
pour €valuer lrieolation du bruit dang les habitatione'
Reprinted from Tne Jounu.e,r, oF rrrn Acousucer- Socnrv ol Aunmce, Vol. 36, No. 4,725-728, April 1964
Copyright, 1964 by the Acoustical Society of Amerrca. Printed in U. S. A.
s2
Sound Insulation and the Apartment Dweller
T. D. Nonrnwooo
Divi,sion oJ Buil'di,ng Research, National Ruearch Counci.l, Oltawa, Ontorio, Canad.a
Most of the existing sound-insulation requirements are based on experience with traditional construction, and this is reflected in the shape of the standard grading curve. Since nontraditional constructions frequently have quite different sound-insulation characteristics, the desired shape of insulation curve, i.e., the relative importance of the various frequency bands, becomes an important consideration. To gain insight on this point, the problem was approached by considering directly the activities and needs of apartment dwellers. The tentative conclusion is that the most common type of grading curves, including the ASTM Sound Transmission Class curve, are of approximately the correct shape for rating sound insulation between dwellings,
f N the preceding paper,l Professor Brandt described I the assortment of sound-insulation requirements used in continental Europe and Great Britain. He has emphasized the empirical basis of these requirements, aimed simply at keeping new construction as good as the best of old construction. My intention is to try another approach, based not on the properties of buildings old and new, but on the properties of people. How much noise do the inhabitants of buildings make? How much intruding noise will they tolerate? There-fore, how much sound insulation is required?
These questions are ditrcult to answer in the case of dwellings, because human domestic activities vary tremendously and erratically in noise output. Cor-respondingly, the sound-insulation requirement varies from almost nil, when everybody is doing tle same thing at the same time, to an impractically high value, when there is a cocktail party next door to a man trying to sleep. A practical objective would be to satisfy most of the people most of the time.
As a preliminary, we might note that many of ttre existing requirements are based on the performance of a 9-in. brick wall, which formerly was widely used for tle separation of dwelling units. Incidentally, it was used primarily as a fire wall, and it was only when 1 O. Brandt, "European Experience with Sound-Insulation Requirements," J. Acoust. Soc. Am. 36,719 (964),
lighter, thinner, and cheaper fire walls became accepted that the need for sound-insulation requirements be-came pressing. As many people have lived in multi-dwelling structures, over the years we have accumulated some subjective information, mostly rather qualitative, about the performance of traditional buildings. In particular, tenant surveys about noise have been made in Great Britain, Sweden, and the Netherlands.2+ These surveys indicate that about two-thirds of tenants separated by a 9-in. brick wall are reasonably satisfied with the sound insulation that it provides. Taking this as a definition of "soundproofness," it may seem a simple matter to determine the acceptability of alterna-tive structures by comparing their transmission losses with that of the brick wall.
But if you attempt such a comparison for a typical modern wall, it turns out to be something of a problem. In Fig. 1, for example, are shown transmission-loss characteristics for a brick wall and two other structures. Perhaps intuition will tell you that the brick wall is
2 O. Brandt and I. Daldn, Byggmiistaren 31, 145 (1952). a C. Bitter and P. Van Weeren. "Sound Nuisance and Sound Insulation in Blocks of Dwellings, f," Res. Inst. Public Health Eng. Rept. No.24, TNO (1955).
I P. G. Gray, A. Cartwright, and P. H. Parkin, "Noise in Three Groups of Flats with Difierent Floor Constructions," Natl. Building Studies Res. Paper No. 27 (Her Majesty's Sfationery Ofrce, 1958).
7
7 2 6
B R A N D T , N O R T H W O O D , S C H U L T Z , A N D R O S EThere is surprisingly little quantitative information available on domestic noises generally, but the spectra of typical household noises are shown in Fig. 2. The bottom one is a well-desigted room air-conditioner in good condition. Next is a vacuum cleaner-not usually a problem because it is rarely used at critical times of day. Most household appliances produce noise in the range between tlese two curves. The next curve shows the peak levels occurring, in a typical room, because of normal conversational speech. There is considerable variation in speech level, depending on the speakers and on the number of participants in a conversation' A curve showing peak levels of radio noise is also in-cluded, but this is dealt with more fully later. I have ventured to sum all tlese up in the curve labeled "standard household noise." This is intended to denote something close to the maximum levels that commonly occur in dwellings. P E R C E N T O F T I M E L E V E L E X C E E D E D s * / 50 lo0 ?00 400 800 1600 3150 63 M t o - B A N o F R E o u E N c Y , c v c l e s / s e c Frc.3. Distribution ol sound levels o{ radio programs. fAfter Van den Eijk.6l
Radio noise has been examined in a more systematic way by J. Van den Eijk of the Netherlands.5 (In-cidentally, I am told that they do not have commericals on Nethlilands Radio; this might affect the*applica-bility of the results to the American scene' but we shall use them anyway.) Van den Eijk, with the assistance of suitable electronic gadgetry, set up a continuous watch on radio programs, and determined for each octave band the distribution of peak levels as a function of time. Thus, he could determine, for example, the octave-band levels exceeded 5/6 or 10/6 of. the time. Some of his data are shown in Fig. 3.
So much for the noisv noises. Now, we have to
con-60 @ ( 4 5 0
t
a 4 0=
z z ? 0 9 r N E R | C K AVG 50 08 C L A S S 5 4--, ^--/
\ \ c a v t T Y t ^ , a L L A V G 4 9 D 8 , C L A S S 4 7 r 0 r25 250 500 t000 2000 4000 F R E Q U E N C Y , C Y C L E S / S E C o N 0 Frc. 1. Sound insulation of three walls.the best, yet if you examine various frequency ranges you may begin to wonder. At high frequencies, the cavity wall is definitely the best and the brick wall is poorest. If you take the average, either the traditional 9-frequency average or a full ll-frequency average, tlere is only a decibel or two to choose among them. We shall return to these curves after an examination of the questions that I posed earlier.
First, Iet us consider the sort of domestic noises that may be troublesome. Again, the tenant surveys provide a qualitative guide. High on the list of obnoxious noises from next door are voices and radio and television noises, and, fortunately, there is quantitative inJorma-tion available on both kinds of noise. (Another equally important category is impact noises such as footsteps, which are initiated as a vibration in the structure itself, and are thus already half-way to their destination next door or downstairs. I leave this topic, however, to Dr. Schultz in Paper S3.)
..\
" "
-' - -' R A D r 0 N 0 r s E . . . vAcuuM C L E A N E R \ . . - - s P E E c H - P E A K L E V E L s \ . . , _ . . A I R C O N D I T I O N E R \ , . - S T A N O A R O H O U S E H O L O N O I S E t ? 5 2 5 0 5 0 0 1 0 0 0 2 0 0 0 4 0 0 0 M r D - B A N D F R E Q U E N c Y , c v c l r s , / s r c Fro. 2. Half-octave-band spectra of typical household noises.8 0 6 - 7 0 =t 60 @ F ] U o 4 0 : a 7 0 > @ z = A n @ N o . o > : ; o 5 0 L @ - z a i
6 T. Van den Eiik, in Prcceedings of the Tbiri], Intrernal,ionol Coisress on Acotiti.cs, Stuttgart, 1959, e&ted by L. Cremer (Eljevier Publishing C6., Amsterdam, 1961), VoI. 2, p. 1041.
S O U N D - I N S U L A T I O N R E Q U I R E M E N T S F O R sider the people on the quiet side of the partition. The intruding noise will not be heard at all if in each
fre-quency band it is always below the ambient level in the 70 quiet area (or alternatively below the thresholds of
attention and thus disturb him. ?o
M U L T I D W E L L I N G B U I L D I N G S 7 2 7
/ / - - -
- - \ \
S T A N D A R D H O U S E H O L O N O I S E ( J/2 ocTAVE ) GE R IUAN G R A D I N G C U R V E C A L C U L A T E D I N S U L A T I O N R E Q U I R E I V E N T- -
- - ,.,r-r,
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Frc.4. Derivation of sound insulation required to reduce standard household noise (Fig. 2) to a level corresponding to NC-25.
I might note, however, that the German method of comparing test curves with the grading curve tends to diminish the importance of the shape of the standard curve. An average deficiency of 2 dB is allowed, without limit on the deficiency in any one band. The dashed curve in Fig. 4 and 5, assuming a 2-dB deficiency across the board, still looks pretty good, but very commonly the total deficiency may be concentrated as a sag of 6 or 8 dB in the crucial middle-frequency range between
N C - 2 5 E X C E E D E D 5 % O F T I M E N C - 2 5 E X C E E O E D I O ' / . O F T I M E
Consequently, my inclination is to assume that one should try to ensure that the probability of intruding sound being heard at all is reduced to a reasonably small number. To determine this, all we need are some
level with location and time of day, but we will assume an average value in the range NC-20 to NC-30. Let us consider this quiet ambient level in coniunction with the noisy noises discussed earlier.
Figure 4 shows the curves of standard household noise and the NC-25 contour (the latter adjusted to the same half-octave series as the upper curve). Sub-tractirrg these gives the sound insulation required to reduce standard household noise to the NC-25 level in each band. There is, of course, a random ffuctuation in both these levels, with the result that the curve found. here probably corresponds to about a S0/o probability of intrusion.. To get down to a reasonable -value, say 10/6 to 2O/6, would. require that the sound. insulation
Fig. 4 is a sound-level difference, but for med,ium-size domestic rooms the level difierence is nearlv the same as the sound-transmission loss.
A similar result is obtained if one uses Van den Eijk's data for radio noise (Fig. 5). Here, the crucial impor-tance of the middle-frequency range is still more evident, but again the general form of the German curve is app,"opriate. @ o 5 0 o z A 6 O 1 v z a ^ F z
-o 2 d 125 250 500 1000 2000 4000 F R E Q U E N C Y , C Y C L E S / S E C o N DFrc.S. Sound insulation required to reduce radio noise to NC-25. [After Van den Eijk.rl
-7 2 8
250 and 1000 cps. The current ASTM rating system uses a family of curves of tle same shape as the German curve, but allows no deficiencies in the middle-frequency range and no more than 3 dB in the outer segments. Ilence, for many structures, an ASTM Class 50 or so would be roughly equivalent to the German requirement. From these rather sketchy data, our tentative con-dusion is ttrat a requirement similar to the German curve, possibly 3 or 4 dB lower, is an appropriate mini-mum requirement for dwelling separation. It is also concluded, however, that deficiencies in the middle-frequency region should be severely limited. In terms of the ASTM rating system, the requirement might be a sound-transmission class 50 or so.
With ttris criterion in hand, let us return again to Fig. 1. We can now see at a glance tlat the low- and middle-frequency transmission losses of two of these walls are inadequate. It will be noted that both walls have a sound-transmission Class 47 as compared to Class 54 for tle brick wall. Using the Class 50 criterion that I suggested earlier, the brick waII would be
com-B R A N D T , N O R T H W O O D , S C H U L ^ I Z , A N D R O S E
fortably above the requirement, whereas the other two would be rejected.
Finally, I must emphasize again the rather specula-tive nature of this analysis, based as it is on very sketchy information about both noisy and quiet dwel-ling conditions. A more comprehensive survey of the distribution of dwelling noises is being organized and this should ultimately enable us to be more quantitative about these matters.
It should be realized, however, that the practical results will not be greatly different: we rnay become slightly more sophisticated in defining the insulation requirements, thus providing tle building designer with a more precise objective. But the real impetus toward better desiga and construction will only begin after a definite requirement has been adopted. I am therefore impelled to echo Professor Brandt's closing comment: our present approximate answers are needed nmtt, to arrest tle steady downward trend in sound-insulation performance being brought about by new building techniques.
T h i s p u b l i c a t i o n i s b e i n g d i s t r i b u t e d b y t h e D i v i s i o n o f B u i l d i n g R e s e a r c h o f t h e N a t i o n a l R e s e a r c h C o u n c i l . I t s h o u l d n o t b e r e p r o d u c e d i n w h o l e o r i n p a r t , w i t h o u t p e r m i s -s i o n o f t h e o r i g i n a l p u b l i s h e r . T h e D i v i s i o n w o u l d b e g l a d t o b e o f a s s i s t a n c e i n o b t a i n i n g s u c h p e r m i s s i o n . P u b l i c a t i o n s o f t h e D i v i e i o n o f B u i l d i n g Re s ear ch may b e o b t a i n e d b y m a i l i n g t h e a p p r o p r i a t e r e m i t t a n c e , ( a Bank, E : r p r e s s , o r P o s t O f f i c e M o n e y Order o r a c h e q u e m a d e p a y -a b l e -a t p -a r i n O t t -a w -a , t o t h e R e c e i v e r G e n e r a l o f C a n a d a , c r e d i t N a t i o n a l R e s e a r c h C o u n c i l ) t o t h e N a t i o n a l R e s e a r c h C o u n c i l , O t t a w a . S t a m p s a r e n o t acceptable.
A c o u p o n s y s t e r n has been introduced t o m a k e p a y -m e n t s f o r p u b l i c a t i o n s r e l a t i v e l y s i m p l e . C o u p o n s a r e a v a i l -a b l e i n d e n o m i n -a t i o n s o f 5 , 2 5 a n d 5 0 c e n t s , a n d r n a y b e o b -t a i n e d b y r n a k i n g a r e m i t t a n c e a s i n d i c a t e d a b o v e . T h e s e c o u p o n s r n a y b e u s e d f o r t h e p u r c h a s e o f a l l N a t i o n a l R e s e a r c h C o u n c i l p u b l i c a t i o n s i n c l u d i n g s p e c i f i c a t i o n s o f t h e C a n a d i a n G o v e r n m e n t S p e c i f i c a t i o n s B o a r d . A l i s t o f all publications o f t h e D i v i s i o n o f B u i l d i n g R e s e a r c h i s a v a i l a b l e a n d m a y b e o b t a i n e d f r o m t h e p u b l i c a -t i o n s S e c -t i o n , D i v i s i o n of Building Research, Na-tional Research C o u n c i l , O t t a w a , C a n a d a .
