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Uncertainty of flanking transmission of metal stud walls by airborne measurement with shielding
Jochen Seidel1 1 Research and Development Knauf Group - Research Area Drywall Systems, Germany
ABSTRACT EN 12354 provides the means to predict the sound insulation between rooms. The required input is direct and flanking transmission of building elements. Here we consider drywall constructions made using metal studs. The work presented aims to adapt calculation and measurement to the needs of research and development of drywall junctions, which are high repeatability, acceptable effort of testing and low and known prediction errors. A series of more than 90 tests of junctions in a transmission suite for flanking transmission according to ISO 10848 were evaluated. The airborne method was applied. Shielding was used to separate transmission paths. The measured transmissions were combined arithmetically to predictions of the total transmission. These predictions are compared to measurements of the total transmission measured in the same setup but without any shielding. The error was evaluated. Special focus is on the verification of two assumptions. The first is that the flanking transmission of the flanking wall and interface is independent of the separating partition, at least in the scope of drywalls. The second assumption is that transmission on paths Fd and Df are negligible compared to transmission on path Ff and therefore the junction is sufficiently characterised by Dn,f,Ff. Keywords: Flanking transmission, metal stud walls, prediction method I-INCE Classification of Subjects Number(s): 51.5
1. INTRODUCTION Structure borne methods to assess the paths of flanking transmission are well established for
massive building elements. Extensions to drywalls are developed. They have to respect the frequency dependent radiation efficiency and the damping over distance. Both have to be estimated, calculated or measured, which increases uncertainty of results and effort of measurement.
Development of building solutions is usually done in small steps or small differences are detected analysed in order to increase them. Further an aim of development is a finely graduated range of solutions covering all demands.
Therefore at least for the time being airborne measurements are the first choice to generate flanking transmission data for development purposes and design of buildings. The drawback is an alternating sequence of airborne measurements and construction/ removal of shieldings which is necessary to assess a single junction. This article deals with the question if and how this sequence can be shortened.
2. TEST SETUP
2.1 Transmission suite The transmission suite is constructed in accordance with ISO 10848. As shown in Figure 1, the
sound insulation of the receiving room (on the left) is improved using additional linings in front of the 20-40 cm concrete building elements. The size of the source room is 4.71 x 4.04 x 2.86 m, the size of the receiving room within the linings is 5.26 x 3.88 x 2.59 m (length x width x height). The rooms are separated from each other and also from the concrete floor of the hall by an elastic break. Transmission suite and floor of the hall are in full contact with the ground. The maximum normalized flanking level difference measured in this suite is 88 dB.
The size S of the aperture between source and receiving room is 11.55 m² on the source side and
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10.05 m² on the receiving side. Throughout this article the smaller area of 10 m² on the receiving side is applied for the determination of the sound reduction R. This has two consequences. First values of sound reduction on the safe side (lower values) are used. Second because of the relation between the Dn,f and the R (equation 1), the value of both quantities is the same.
( ) ( )00, log10log10 ASRAADD fn −=−= (1) The fotograf of the transmission suite (Figure 1) shows on the left side the receiving room with
suspended ceiling, wall linings and floating dry screed. A fragment of a wall (blue) indicates the usual position of the separating partition. At its perimeter the surrounding acoustic break can be seen. The fix building elements of the sending room are separated from the separating partition and the receiving room by the break. The flanking wall is positioned at the front side.
Figure 1 Transmission suite for the measurement of flanking transmission
2.2 Shielding The shieldings used to exclude transmission paths from the airborne measurement had cavities of
approximately 15 cm filled with 80 mm mineral wool. They were clad with two layers of 12.5 mm board type “Diamant”. With a total of 25.6 kg/m², this results, for example, in a resonance frequency of 54 Hz in front of a single layer standard board or of 38 Hz in front of two layers of 12.8 kg/m². The end of the shielding was aligned with the edge of the interface forming an angle of approximately 45°. The end of the shielding rested on soft sealing tape on the separating partition.
2.3 Specimen Common properties of all specimen 2.3.1
Flanking and separating partitions consist of a single metal stud framework clad with gypsum boards. The details correspond to the common German construction method: The studs are German Knauf CW profiles with flange lengths of approximately 50 mm, the cavity of 100 mm is 80% filled with mineral wool (80 mm, density ≈ 15-20 kg/m³, r ≥ 5 kPas/m²), stud spacing (= half board width) is 625 mm.
Varying parameters 2.3.2Four different types of boards were applied. Standard gypsum boards with a mass per unit area of
8.5 kg/m² is coloured grey in the drawings. Blue is used for board type “Diamant”. With thickness 12.5 mm the weight is 12.8 kg/m² and 18 mm corresponds to a weight of 18 kg/m². Brown is the color of board type “Silentboard” with a weight of 17.5 kg/m². The critical frequency of the 12.5 mm boards is approximately equal. For the 18 mm board it is lower.
The flanking walls were clad with one or two layers. Some of the separating partitions were clad with three layers. Predominantly, the construction of flanking and separating wall are the same. Still there are also some cases of the separating partition being clad with double of total mass per area.
Five types of interfaces were realized. The design principles and their names can be seen in the drawings of column “Interface” of Table 4.
If not otherwise stated, the joint between the gypsum boards on the edge were filled with rigid gypsum based filler after applying a separation strip of waxed paper (see left side of Figure 2). In one
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case, an elastic joint was realized. It is called “modified” and denoted by footnote 3). The modified version of the junction was created by cutting the filler along the edge on the source and receiving side with a saw and sealing the joint elastically (see right side of Figure 2).
Figure 2 Interface type with break on separate studs. Left: Standard in this article. Right: Modified
3. INFLUENCE OF THE SEPARATING PARTITION It is desirable to get an estimator of the flanking transmission from the measurement of a junction
with different separating partition but with the same flanking wall and interface that is as similar as possible. To test this estimation, measurements of flanking transmission were repeated after changing the separating partition. In all cases, the change was doubling the total mass per area of the cladding. This was in some cases achieved by adding an additional layer of boards. In other cases, the cladding was changed completely. In one case even the studs were replaced by M-shaped acoustic studs. In an early stage of the project, an initial result showing a large deviation (line 1 of Table 3) was published (1). Smaller deviations were observed with the next 3 junctions and 6 paths or path-combinations. Also, the weighted single number quantity Dn,f,w as the third octave band values Dn,f of these pairings differed by between 0 dB and 4 dB. The sound protection is underestimated as long as the measure-ment with lightweight partition is used as an estimator for the heavy partition. An improvement of the separating construction can yield a reduction of flanking without changing the flanking construction.
Table 1 Comparison of flanking transmission when the separating partition varies
4. SIGNIFICANCE OF PATHS OTHER THAN Ff The transmission on the pure flanking path Ff is compared to the transmission on mixed paths Fd
and Df. The available pairs are listed in Table 2. Corresponding drawings in the subsequent figures can be identified by the number given in the column with the heading “number of drawing”. Additionally to the differences in Table 2 some absolute curves of Ff, Fd and Df are compared at Figure 5, Figure 10 and Figure 12.
The transmission on a mixed path ij is negligible if the difference Dn,f,ij-Dn,f,Ff is more than 10 dB. Accepting an error of 1 dB, a path could be neglected even with a difference of just 6 dB. But only some junctions fulfill even this soft condition and only at some third octave bands. In the range from
number of
layers
weightper
layer[kg/m²]
number of
layers
weightper
layer[kg/m²]
Dn,f,w
[dB]
number of
layers
weightper
layer[kg/m²]
Dn,f,w
[dB]
Difference(wall 2
-wall 1)
Pathsincluded
inmeas.
1 2 12,8 2 12,8 69,8 21
17,518 2) 74,8 5,0 dB Ff&Fd
2 2 8,5 2 8,5 70,7 21
8,517,5 71,4 0,7 dB Ff
3 67,3 68,3 1,0 dB Ff
4 67,9 71,5 3,6 dB Df
5 66,4 70,9 4,5 dB fD1)
6 58,5 58,8 0,3 dB Ff
7 56,3 57,7 1,4 dB Ff&Df
1) same as Df, but source room and receiving room switched2) additional difference: acoustic M-studs instead of C-studs
12,8
Partition wall 2
8,5
Dn,f,w
1 8,5 continous cladding 1 8,5 2
break on separate
studs
2 8,5
break bridged
byprofile-flange
2 8,5 3
sym
bol
line
Flanking wall Interface Partition wall 1
-15
-10
-5
0
5
10
15
63 125 250 500 1000 2000 4000
Dn,
f,wal
l2-D
n,f,w
all1
[dB
]
Frequency [Hz]
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400 Hz to 1600 Hz, the absolute value of the difference of all cases is less than 3 dB. There are plenty of cases with negative values, i.e. more transmission on the mixed path than on Ff. On the other hand, higher differences are observed around the critical frequency. This frequency range is of major importance since it is the one most likely to be dominated by flanking transmission. In case that the total flanking transmission is negligible compared to the direct transmission, disregarding Fd and Df will still be tolerable even though transmission on Fd and Df are not small compared to transmission on Ff.
Table 2 Comparison of transmission on path Ff to other paths
5. PREDICTED VERSUS MEASURED VALUES As part of this project the total transmission, i.e. without any shielding, was measured. Within this
article the corresponding apparent sound reduction index is denoted as R’. RDd of the separating partitions were available, too. In 17 cases, R’ was calculated disregarding Fd and Df. Contrary to this simplification for three cases, all paths were determined and used as input for the calculation. The configurations and results are summarized in Table 4. Here “+” means energetic summation of the transmission and “&” means measured together within a single airborne measurement with appropriate shielding.
The simplified and detailed model were applied. In many cases, the calculation with the weighted single number quantity resulted in the same value than the calculation in the third octave bands with subsequent weighting procedure according to ISO 717. Deviations greater than 0.1 dB were only observed with continuous cladding. Even then, the deviation was only limited to an 0.5 dB overestimation by the simplified model.
Disregarding Fd and Df always caused an overestimation of the prediction (higher predicted R’ than measured R’). It ranged from 0 dB to 4 dB. An attractive test setup is to apply only one shielding on one side of the separating partition. This means disregarding only one of Df or Fd. Still this does not reduce the overestimation significantly. On the other hand, the results including all paths after separate measurement are also unconvincing: In two of three cases when the overestimation was already small without Fd and Df, the error became smaller than 0.6 dB, but in the third case it dropped only from 4.2 dB to 2.6 dB.
Figure 3 to Figure 22 show the frequency dependant results and the drawings of the respective junction without shielding. It can be seen, that in most of the cases the direct transmission is dominating the result. Only with continuous cladding and close to the critical frequency is the result dominated by flanking transmission. And in that case, it has an effect on R’w.
Interface Ff
sym
bol
Num
ber o
f dra
win
g
num
ber o
f lay
ers
wei
ght p
er la
yer
[kg/
m²]
num
ber o
f lay
ers
wei
ght p
er la
yer
[kg/
m²]
Dn,
f,Ff,w
[dB
]
Dn,
f,ij,w
-Dn,
f,Ff,w
[dB
]
ij
85 1 8,5 2 8,5 58,8 7,2 Fd
51 2 12,8 2 12,8 54,8 8,0 Df
0,8 Df
-0,1 Fd
0,6 Df
-0,9 fD1)
3,2 Df
2,6 fD1)
32 2 12,8 2 12,8 73,0 -3,2 Df
41 23) 12,8 23) 12,8 73,9 -1,5 Df1) same as Df, but source room and receiving room switched3) additional modification of interface see text
93 2 8,5 3 12,8 68,3
75
67,38,528,5286
58,58,518,51
break on separate
studs
continouscladding
break bridged
byprofile-flange
other Path ijFlankingwall
Partitionwall
-15
-10
-5
0
5
10
15
63 125 250 500 1000 2000 4000
Dn,
f,ij-D
n,f,F
f[d
B]
Frequency [Hz]
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Table 3 Weighted apparent sound reduction indices - measured value and prediction error
Figure 3 Measured and calculated sound reductions to drawing 61 (line 1)
line number
oflayers
weightper
layer[kg/m²]
numberof
layers
weightper
layer[kg/m²]
Dd+Ff
Dd +
Ff&Fd
Dd+Ff+
Fd+Df
Dd+Ff
Dd +
Ff&Fd
Dd+Ff+
Fd+Df
1 61 2 8,5 2 8,5 54,0 0,2 - - 2,2 - -
2 75 1 8,5 1 8,5 48,6 -0,5 -0,3 -0,5 0,3 0,2 -0,6
3 85 1 8,5 2 8,5 55,2 0,1 0,3 - 0,5 0,1 -
4 51 2 12,8 2 12,8 54,1 0,2 0,2 - 0,3 0,5 -
5 55 1 12,8 1 12,8 48,1 0,0 - - 1,4 - -
6 86 2 8,5 2 8,5 56,4 -0,1 - -0,1 1,4 - 0,4
7 93 2 8,5 3 12,8 60,7 -0,1 - 0,0 4,2 - 2,6
8 64 2 8,5 2 8,5 56,5 -0,1 - - 1,6 - -9 74 1 8,5 1 8,5 49,2 -0,1 - - 0,6 - -10 32 2 12,8 2 12,8 60,1 0,0 0,1 - 2,7 2,3 -11 41 2 12,8 23) 12,8 60,3 0,0 0,1 - 2,5 2,0 -12 57 2 17,5 2 17,5 65,7 0,0 - - 3,1 - -
13 68 2 8,5 2 8,5 57,4 0,0 - - 0,8 - -
14 69 1 8,5 1 8,5 49,4 0,0 - - 0,5 - -
15 48 2 12,8 2 12,8 59,7 -0,1 0,0 - 3,2 2,8 -
16 50 2 12,8 2 12,8 59,8 0,0 - - 3,2 - -
17 59 2 17,5 2 17,5 65,2 -0,1 - - 4,1 - -
Num
ber o
f dra
win
gDescription of the junction
embe
dded
pa
rtitio
n w
all
Weighted appearant sound reduction index R'w [dB]PredictedMeasured
brea
k br
idge
d by
pro
file-
flang
ebr
eak
on se
para
te st
uds
inte
rrup
ted
Error of prediction>0 means overestimation
by the prediction
cont
inou
scl
addi
ng
Flanking wall Interface Partition wallDetailed model
minusSimplified model
0
10
20
30
40
50
60
70
80
90
63 125 250 500 1000 2000 4000
Soun
d re
duct
ion
inde
x R
[dB]
Frequency [Hz]
Dd measured58,4dB
Ff measured59,7dB
R' calculated56,2dB
R' measured54,0dB
ref. curve54,0 dB
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Figure 4 Measured and calculated sound reductions to drawing 75 (line 2, Ff only)
Figure 5 Measured and calculated sound reductions to drawing 75 (line 2, all paths)
Figure 6 Measured and calculated sound reductions to drawing 85 (line 3)
0
10
20
30
40
50
60
70
80
90
63 125 250 500 1000 2000 4000So
und
redu
ctio
n in
dex
R [d
B]Frequency [Hz]
Dd measured50,0dB
Ff measured58,5dB
R' calculated48,9dB
R' measured48,6dB
ref. curve48,6 dB
0
10
20
30
40
50
60
70
80
90
63 125 250 500 1000 2000 4000
Soun
d re
duct
ion
inde
x R
[dB]
Frequency [Hz]
Dd measured50,0dB
Ff measured58,5dB
Df measured59,3dB
Fd measured58,4dB
R' calculated48,0dB
R' measured48,6dB
ref. curve48,6 dB
0
10
20
30
40
50
60
70
80
90
63 125 250 500 1000 2000 4000
Soun
d re
duct
ion
inde
x R
[dB]
Frequency [Hz]
Dd measured58,4dB
Ff measured58,8dB
R' calculated55,7dB
R' measured55,2dB
ref. curve55,2 dB
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Figure 7 Measured and calculated sound reductions to drawing 51 (line 4)
Figure 8 Measured and calculated sound reductions to drawing 55 (line 5)
Figure 9 Measured and calculated sound reductions to drawing 86 (line 6, Ff only)
0
10
20
30
40
50
60
70
80
90
63 125 250 500 1000 2000 4000So
und
redu
ctio
n in
dex
R [d
B]Frequency [Hz]
Dd measured63,2dB
Ff measured54,8dB
R' calculated54,4dB
R' measured54,1dB
ref. curve54,1 dB
0
10
20
30
40
50
60
70
80
90
63 125 250 500 1000 2000 4000
Soun
d re
duct
ion
inde
x R
[dB]
Frequency [Hz]
Dd measured53,2dB
Ff measured51,9dB
R' calculated49,5dB
R' measured48,1dB
ref. curve48,1 dB
0
10
20
30
40
50
60
70
80
90
63 125 250 500 1000 2000 4000
Soun
d re
duct
ion
inde
x R
[dB]
Frequency [Hz]
Dd measured58,4dB
Ff measured67,3dB
R' calculated57,8dB
R' measured56,4dB
ref. curve56,4 dB
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Figure 10 Measured and calculated sound reductions to drawing 86 (line 6, all paths)
Figure 11 Measured and calculated sound reductions to drawing 93 (line 7, Ff only)
Figure 12 Measured and calculated sound reductions to drawing 93 (line 7, all paths)
0
10
20
30
40
50
60
70
80
90
63 125 250 500 1000 2000 4000
Soun
d re
duct
ion
inde
x R
[dB]
Frequency [Hz]
Dd measured58,4dB
Ff measured67,3dB
Df measured67,9dB
Fd measured66,4dB
R' calculated56,8dB
R' measured56,4dB
ref. curve56,4 dB
0
10
20
30
40
50
60
70
80
90
63 125 250 500 1000 2000 4000
Soun
d re
duct
ion
inde
x R
[dB]
Frequency [Hz]
Dd measured67,7dB
Ff measured68,3dB
R' calculated64,9dB
R' measured60,7dB
ref. curve60,7 dB
0
10
20
30
40
50
60
70
80
90
63 125 250 500 1000 2000 4000
Soun
d re
duct
ion
inde
x R
[dB]
Frequency [Hz]
Dd measured67,7dB
Ff measured68,3dB
Df measured71,5dB
Fd measured70,9dB
R' calculated63,3dB
R' measured60,7dB
ref. curve60,7 dB
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Figure 13 Measured and calculated sound reductions to drawing 64 (line 8)
Figure 14 Measured and calculated sound reductions to drawing 74 (line 9)
Figure 15 Measured and calculated sound reductions to drawing 32 (line 10)
0
10
20
30
40
50
60
70
80
90
63 125 250 500 1000 2000 4000So
und
redu
ctio
n in
dex
R [d
B]Frequency [Hz]
Dd measured58,4dB
Ff measured70,7dB
R' calculated58,1dB
R' measured56,5dB
ref. curve56,5 dB
0
10
20
30
40
50
60
70
80
90
63 125 250 500 1000 2000 4000
Soun
d re
duct
ion
inde
x R
[dB]
Frequency [Hz]
Dd measured50,0dB
Ff measured65,1dB
R' calculated49,8dB
R' measured49,2dB
ref. curve49,2 dB
0
10
20
30
40
50
60
70
80
90
63 125 250 500 1000 2000 4000
Soun
d re
duct
ion
inde
x R
[dB]
Frequency [Hz]
Dd measured63,2dB
Ff measured73,0dB
R' calculated62,8dB
R' measured60,1dB
ref. curve60,1 dB
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Figure 16 Measured and calculated sound reductions to drawing 41 (line 11)
Figure 17 Measured and calculated sound reductions to drawing 57 (line 12)
Figure 18 Measured and calculated sound reductions to drawing 68 (line 13)
0
10
20
30
40
50
60
70
80
90
63 125 250 500 1000 2000 4000So
und
redu
ctio
n in
dex
R [d
B]Frequency [Hz]
Dd measured63,2dB
Ff measured73,9dB
R' calculated62,8dB
R' measured60,3dB
ref. curve60,3 dB
0
10
20
30
40
50
60
70
80
90
63 125 250 500 1000 2000 4000
Soun
d re
duct
ion
inde
x R
[dB]
Frequency [Hz]
Dd measured70,3dB
Ff measured74,3dB
R' calculated68,8dB
R' measured65,7dB
ref. curve65,7 dB
0
10
20
30
40
50
60
70
80
90
63 125 250 500 1000 2000 4000
Soun
d re
duct
ion
inde
x R
[dB]
Frequency [Hz]
Dd measured58,4dB
Ff measured72,4dB
R' calculated58,2dB
R' measured57,4dB
ref. curve57,4 dB
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7
Figure 19 Measured and calculated sound reductions to drawing 69 (line 14)
Figure 20 Measured and calculated sound reductions to drawing 48 (line 15)
Figure 21 Measured and calculated sound reductions to drawing 50 (line 16)
0
10
20
30
40
50
60
70
80
90
63 125 250 500 1000 2000 4000So
und
redu
ctio
n in
dex
R [d
B]Frequency [Hz]
Dd measured50,0dB
Ff measured67,5dB
R' calculated49,9dB
R' measured49,4dB
ref. curve49,4 dB
0
10
20
30
40
50
60
70
80
90
63 125 250 500 1000 2000 4000
Soun
d re
duct
ion
inde
x R
[dB]
Frequency [Hz]
Dd measured63,2dB
Ff measured75,7dB
R' calculated62,9dB
R' measured59,7dB
ref. curve59,7 dB
0
10
20
30
40
50
60
70
80
90
63 125 250 500 1000 2000 4000
Soun
d re
duct
ion
inde
x R
[dB]
Frequency [Hz]
Dd measured63,2dB
Ff measured75,7dB
R' calculated62,9dB
R' measured59,7dB
ref. curve59,7 dB
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Figure 22 Measured and calculated sound reductions to drawing 59 (line 17)
6. CONCLUSIONS Testing the junction only with the setup with two shieldings that singles out the path Ff leads to
overestimation of 0 dB to 4 dB. Using only one shielding either in front of D or in front of d reduces the testing effort. But even though a further path now is included there is only a minor improvement of the prediction. There is not enough evidence to recommend accepting the maximal possible testing effort, i.e. singling out all the paths Ff, Fd and Df one after the other with appropriate placed shieldings. In all of three cases the prediction error was reduced by approximately 1 dB, but in one case an overestimation of 2.6 dB remained (see Figure 12). Still this may simply be in the statistics of reproducibility of a drywall being built in two different transmission suites (ISO 10140 and ISO 10848).
Thanks to nowadays available heavy gypsum boards shieldings can easily be realized that achieve resonance frequencies below 30 Hz in front of a heavy massive wall. Still in front of single layer standard board partition the resonance frequency can be in the 50Hz band and in front of a heavy wide-cavity drywall the interaction of the resonances of partition and shielding is hardly predictable. The following proposal overcomes these drawbacks and reduces the testing effort. Usually when it is decided to test the flanking transmission of a junction there has already a measurement of the direct sound reduction RDd of the separating partition being done. If now the junction is tested in a single measurement without any shielding a value Dn,f,all is retrieved that includes all paths (Dd, Ff, Fd and Df). From that an effective normalized flanking level difference Dn,f,eff including Ff, Fd and Df can be calculated.
−−= −− Ddallfn RlabD
efffn ASD 1.0
0
1.0,, 1010log10 ,, (2)
Herein Slab is the surface area of the separating partition in the ISO 10848-Setup and A0 = 10 m². Remainders of flanking transmission in the measured value of RDd will cause overestimated Dn,f,eff and are to be avoided.
The findings support the simplified model of EN 12354 very well. Many parameters of the drywalls in this project were kept constant. The parameters most
interesting to further studies appear to be the rigid joint filler and the separation strip at the perimeter.
REFERENCES 1. Seidel, Jochen und Hengst, Klaudius. The Influence of the Design of Metal Stud Wall Junctions on the
Flanking Transmission. Proc. Forum Acusticum 2014.
0
10
20
30
40
50
60
70
80
90
63 125 250 500 1000 2000 4000So
und
redu
ctio
n in
dex
R [d
B]
Frequency [Hz]
Dd measured70,3dB
Ff measured76,5dB
R' calculated69,3dB
R' measured65,2dB
ref. curve65,2 dB
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