SOFTWARE FOR AUTOMATIC APPLICATION OF THE CALCULATION MODELS
OF EN 12354 IN BUILDING ACOUSTICS
António Xavier Gonçalves Frazão da Rocha Pinto
DECivil, Instituto Superior Técnico, Av Rovisco Pais, 1, 1049-001 Lisbon, Portugal
October, 2011
ABSTRACT
Knowing that the correct application of the calculation models presented in the standard series
EN 12354 demands an accurate management of a great amount of data and a meticulous
choice of some given calculation options, its automation ensures an error minimization and a
considerable decrease of the time spent in each project.
Based on some previous analyses developed in Instituto Superior Técnico on the assessment
of the detailed calculation models of parts 1 and 2 of the standard EN 12354 applied to casestudies, the present thesis aims to create a software for automatic application of the models.
The program was conceived in a CAD platform chosen for its important role in design and
communication between each entity involved in building design and construction. The program
validation was made using the same case-studies mentioned above.
The results obtained by automatic calculation prove to be equivalent to results obtained in the
previously mentioned studies, thus confirming the correct use of the calculation models. Impact
sound insulation prediction model seems to be more accurate than the airborne sound
insulation prediction model for the considered case-studies.
KEYWORDS: Estimation of sound transmission; EN ISO 12354; Automation; AutoCAD;
Software
_____________________________________________________________________
1. INTRODUCTION
Considering that the first Portuguese law concerning building acoustics is less than twenty five
years old, the study of this subject still has great relevance. More recently, the European
Standard series EN ISO 12354 presented the first calculation model in European, and therefore
Portuguese, legislation. The study of building acoustics itself is a rather new subject for which
there is yet no model capable of fitting to every construction solution nor a perfect adjustment
between the models and field results. Being so new these Standards are still incomplete and its
accuracy is not properly quantified. Therefore, the software developed throughout this thesis
aims, not only to ease the calculation model application, by reducing the time spent in the
calculation process as well as minimizing errors, but also to contribute to the study of the
mentioned model by increasing the number of available results.
Once it was proven that the detailed model gives better results than the simplified model, only
the first one was implemented. Although the Standards EN ISO 12354-1 [1] and EN ISO 123542 [2] give primacy to the use of experimental data regarding construction elements and
junctions, the developed software calculates its behavior using theoretical models hence it only
allows the introduction of material properties and element dimensions. This option lays on the
absence of information regarding the most used elements and junctions in the National scene.
The validation of the software was made by calculating the case-studies used by Dias [3] and
Galante [4] in their previous papers - which compared the results of the detailed model with
several simplified models and field results.
2. STATE OF THE ART
Four commercial computer programs were analyzed when conceiving the presented software:
Cypevac Acoubat, CAEd and SONarchitect. Although many of these computer programs also
verify other Standards from the EN ISO 12354 series, only the first two standards verification
were taken into account.
Cypevac is the simplest. It has no visual representation of the building, nor does it spatially
relate the construction elements. The results are obtained simply by applying the empirical
expression as function of the mass per unit area to each element. The elements can be chosen
from a lot of preset elements or introduced by the user. The results are shown in a Portuguese
written report with graphic representation of the element’s section.
Acoubat has a tridimensional graphic interface that can represent one, two or four rooms in the
same floor or in adjacent floors. The calculation is based on laboratory measurements so that it
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is only possible to use elements from the database provided. The database has about 3000
entries.
The CAEd has a similar structure to Acoubat’s. It also has a tridimensional graphic interface but
this one can only represent two rooms at a time. Although the database has the most common
elements used in Portuguese construction, its 100 entries prove to fail at more original
solutions. The management of the database is less intuitive than Acoubat’s.
SONarchitect is the high-end software in building acoustics. It is the only software capable of
calculating the entire building at once, identifying the sound reduction index corresponding to
each transmission path. It is also the only software capable of importing .dwg drawing files
although it also includes a drawing tool. The building is represented in two or three dimensions,
allowing almost any type of architectural variation.
3. CALCULATION MODEL
The first step before using the calculation model presented in the Standards is the
homogenization of the constructive solution. It is required that each element has a single value
for its dimensions, density, Poisson ratio and Young’s modulus. In case of additional lining or
floating floors the structural element should be considered independently from any other layer.
Since there is no specification concerning heavy double leaf walls, this type of element was
considered as a single leaf heavy element.
(1)
Once the element is homogenized some parameters must be calculated: the critical frequency
(fc), phase speed of longitudinal waves (cL), and the frequencies fp and f11, as the following
formulae expose:
(2)
(3)
(4)
(5)
Where E is the Young’s modulus, l1 and l2 are the element dimensions and t is the element
thickness.
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The junction vibration reduction index is obtained using the Annex E from the Standard EN ISO
12354-1 [1]. For each junction type and each sound path there is an equation which describes
its behaviour, as it is shown in the image bellow for the case of heavy cross junction:
2
K13 = 8,7 + 17,1 M + 5,7 M dB; 0 dB / octave
2
K12 = 8,7 + 5,7 M (= K23) dB; 0 dB / octave
(6)
(7)
(8)
It is then calculated the absorption coefficient for bending wave field at each border k of an
element:
(9)
Being fref the reference frequency (1000 Hz) and fc,j the the critical frequency of the element j in
the sound transmission path ij.
Finally the sound reduction index and the normalized sound pressure level for direct
transmission are defined by:
(10)
(11)
These formulae are the result of a sequence of complex calculations described in Annex C of
the EN ISO 12354-1 which, for its complexity and length will not be described here.
Other transmission paths are considered through the following expressions:
(11)
;
(12)
(13)
All the previous values are calculated for all the one third octave bands. The single number
value is obtained by shifting a reference curve towards the measured curve until de sum of
unfavourable deviations is as large as possible but not more than 32,0 dB, as defined in ISO
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717-1 [5] and ISO 717-2 [6] for airborne and impact sound insulation respectively. The single
number value is the 500 Hz value of the reference curve.
In the case of airborne sound insulation, the additional linings are considered as a single
number value, for each of the considered transmission paths as listed in the following table:
Table 1 – Weighted sound reduction index improvement by a lining,
depending on the resonance frequency [1].
Resonance frequency f0
of the lining
(Hz)
≤80
100
125
160
200
250
315
400
500
ΔRw
630 - 1600
(dB)
35-Rw/2
32-Rw/2
30-Rw/2
28-Rw/2
-1
-3
-5
-7
-9
-10
>1600
-5
Where f0 is
(14)
(15)
For elastic or rigid connections to the heavy element, as explained in annex C of EN ISO
12354-1.
In the case impact sound insulation thecontribution of the additional layers is considered as a
single number in the direct path and spectrum distributed in flanking paths.
(dB)
(16)
If elements are constructed of several parts (in parallel), its sound reduction index should be
summed:
(dB),
(17)
Finally, to provide the user a quantity that can be compared with legally required values,
standardized level difference and normalized sound pressure level are computed:
(dB);
(18)
5
(dB).
(19)
4. PROGRAM STRUCTURE
The developed software stands out from other computer programs for its interaction with a CAD
platform and its independence from databases. Unlike what happens with other programs, the
developed software is not based on a sender-receiver pair. In fact, it relies on the construction
of an element network so that elements may be part of different sender-receiver pairs.
To begin with, the user must define the elements involved, its dimensions and materials. There
are three types of elements: walls, homogeneous floors and floating floors. The second step is
defining the junctions. For each element, four junctions should be defined. Since there is no
coordinate system implemented in the program, the position of any lining must be defined at this
point.
Finally, the calculation of the sound reduction index or impact sound pressure level only needs
the designation of the separating element and the volume of the receiving room.
In order to reduce the minimum time needed to get the first results, it was allowed a
simplification of the calculation method. Thus instead of demanding the definition of the four
junctions per element in contact with the separating element, these definitions are optional. For
each element whose junctions are not defined the program assumes the laboratory values as
equivalent to field values. The quantification of the effect this abridgement has in the final result
can be observed in the results chapter bellow. The user is always informed on the number of
transmission paths that were subject to this simplification.
5. RESULTS
The program was submitted to four validation tests, two for the airborne sound insulation and
two for the impact sound insulation. The first test for either procedure was the calculus of the
example given in annex H and E of the standards EN ISO 12354-1 [1] and EN ISO 12354-2 [2],
respectively. In addition to the results provided by the program were also considered the results
of manual calculation, the results given in the annex and, in the case of airborne sound, the
results of Cypevac.
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Table 2 – Results from manual and automatic calculation of the example
given in Annex H of EN 12354-1 [1].
Example 1
DnT,w (dB)
Annex H of EN 12354-1
55
Manual Calculation
58
Automatic Calculation
57
Cypevac Results
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Table 3 – Results from manual and automatic calculation of the example
given in Annex E of EN 12354-2 [2].
Example 2
L’nT,w (dB)
Annex E of EN 12354-2
41
Manual Calculation
40
Automatic Calculation
40
The difference between automatic and manual calculation in airborne sound level difference is
due to rounding errors in all sound reduction indexes of each frequency band in each of the
transmission paths. The difference between the value obtained with the program and the value
given in the standard cannot be properly explained for the calculation method is not extensively
described in the annex. Nevertheless, the results prove to be satisfactory.
The second test for either of the calculation models was made by comparison of the results
obtained with the results given by Dias [3] and Galante [4] in their thesis. Five of the seven
elements (four slabs and one internal wall) studied in Dias’s work were included in the analysis
as well as three of the four elements (three slabs) analyzed by Galante.
Some aspects must be taken into account to fully understand the meaning of the results
exposed above. In Graphics 1 and 2 the references LA(4T) and LA(2X+2T) correspond to the
same element, only in Dias’s work were considered four T junctions which, in the author’s
opinion, is not the best approach to the real architecture. In Graphics 3 and 4 the calculation for
impact sound pressure level for slabs LB and LC was made considering two different volumes
in the receiving room: first only the volume limited by the analyzed slab and second the volume
corresponding to the whole receiving room. The first results prove to be more accurate.
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Graphic 1 – Difference between the results of two automated methods compared to manual method by
Galante [4], given in dB (percussion sound)
dB
9
8
7
6
5
4
3
2
1
0
Detailed automatic forecast
Fast automatic forecast
Graphic 2 – Difference between the results of two automated methods and the manual method by Galante
[4] against the results of measurements in situ, given in dB (percussion sound)
dB
12
11
10
9
8
7
6
5
4
3
2
1
0
Detailed manual forecast
Detailed automatic forecast
Fast automatic forecast
Graphic 3 – Difference between the results of two automated methods compared to manual method by Dias
[3], given in dB (airborne sound)
dB
6
5
4
Detailed automatic forecast
Fast automatic forecast
3
2
1
0
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Graphic 4 – Difference between the results of two automated methods and the manual method by Dias [3]
against the results of measurements in situ, given in dB (airborne sound)
dB
10
9
8
7
6
5
4
3
2
1
0
Detailed manual forecast
Detailed automatic forecast
Fast automatic forecast
In general, when compared to the results calculated by Dias [3] and Galante [4], the results
prove to be accurate enough (with a difference below 3 dB) – Graphics 1 and 3. The simplified
method has a bigger impact in the sound reduction index which was predictable for its greater
number of flanking paths. These results are not to be trusted as a precise description of the
element’s behaviour.
When compared to field results, the impact sound insulation gives more accurate results
proving to be trustworthy. These conclusions are only valid to elements similar to the ones
tested. Therefore no precise conclusions can be taken, for instance, on floating floors (rather
than what the first validation test may allow to assume).
6. CONCLUSIONS
Several aspects should be taken into account so that conclusions can be taken. Starting with
the results it is clear that the ones given by the software are equivalent to the ones calculated
by other authors, proving the correct implementation of the calculation model. As for its
accuracy, more cases should be studied before a correct quantification can be made. The
Standards estimate a standard deviation of 1,5 dB to 2,5 dB for airborne sound. As for impact
sound, it is said that the results are in a range of ±2 dB in 60% of the predicted values and ±4
dB in 100% of the predicted values. The standard deviation obtained is of 6,3 dB in airborne
sound insulation and 1,5 in impact sound insulation.
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The program reveals several improvement opportunities naturally inherent to any software or
thesis. First of all the introduction of a coordinate system. This would allow a great reduction in
the time spent in the definition of junctions and would automatically locate the position of the
lining. An upgrade on the graphic interface would also be important, especially in the definition
of the junctions so that, for instance, horizontal junctions would be represented differently from
vertical junctions.
Although one of the main goals of the present thesis was to conceive a program independent of
any kind of database, the introduction of a data structure, at least for the most common building
elements, might reduce the operating time.
Furthermore, one unavoidable weakness of the developed software is its dependence of the
host software. Therefore, for each version of AutoCAD, there must be a different version of the
software. There is also some liability on Microsoft Excel used for data storage. This could be
minimized by using CVS system.
7. REFERENCES
[1]
EN ISO 12354 – 1 (2000): Building acoustics – Estimation of acoustic performance of
buildings from the performance of elements – Part 1: Airborne sound insulation between
rooms, British Standard.
[2]
EN ISO 12354 – 2 (2000): Building acoustics – Estimation of acoustic performance of
buildings from the performance of elements – Part 1: Impact sound insulation between
rooms, British Standard.
[3]
Dias, R (2010). Análise comparativa dos métodos normalizados de previsão da
transmissão sonora por via aérea. Instituto Superior Técnico.
[4]
Galante, R. (2010). Análise comparativa dos métodos normalizados de previsão da
transmissão sonora por via estrutural. Instituto Superior Técnico.
[5]
EN ISO 717 – 1 (1996) Acoustics – Rating of sound insulation in buildings and of
building elements – Part 1: Airborne sound insulation; British Standard
[6]
EN ISO 717-2 (1996), Acoustics – Rating of sound insulation in buildings and of building
elements – Part 2: Impact sound insulation, British Standard.
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