In-plane excitation of reception plates according to EN 15657:2017
Ulrich SCHANDA(1) ; Michael HOSSFELD(2) ; Fabian SCHÖPFER(3) ; Andreas MAYR(4)(1) Technical University of Applied Sciences Rosenheim, Germany, ulrich.schanda@th-rosenheim.de(2) Technical University of Applied Sciences Rosenheim, Germany, michael.hossfeld@th-rosenheim.de(3) Technical University of Applied Sciences Rosenheim, Germany, fabian.schoepfer@th-rosenheim.de(4) Technical University of Applied Sciences Rosenheim, Germany, andreas.mayr@th-rosenheim.de

Abstract

EN 15657:2017 [1] describes methods for the determination of the characteristic structure-borne sound power ofbuilding service equipment. The so-called indirect method is based on the use of a reception plate. The method
is robust for the case when the mobility of the source (building service equipment) is significantly higher thanthe mobility of the reception plate. The source is mounted on the plane of the reception plate. Therefore theexcitation of the reception plate happens out-of-plane, the measurement is carried out by sensors sensitive to thecomponent of the out-of-plane movement of the plate. In practice however there are situations which require
the mounting of the source in wall openings, for example roller shutters in window openings or doors. In thesecases the excitation happens in the soffit of the structures, the excitation takes place in-plane. The assumption
then is that primarily quasi-longitudinal waves rather than bending waves are excited in the receiving building
elements, but then a fast conversion of energy from quasi-longitudinal waves to bending waves takes place. A
determination of the characteristic structure-borne sound power should then be possible as in the usual case of anout-of-plane mounting. To test this assumption the in-plane exitation of two reception plates was experimentallyinvestigated.
Keywords: Structure-borne Sound, Reception Plate, In-Plane Excitation

1INTRODUCTION

In the actual version of the German Standard on sound insulation in buildings DIN 4109-1:2018-01 [2] requirements on the A-weighted, maximum and normalized sound power level LAF,max,n caused by service equipment
are listed.
In order to predict this level in rooms of interest during the planning phase there is a model available in the harmonized European Standard EN 12354-5:2009 [3]. As input data the charateristic structure-borne sound power
Psn of the individual service quipment is needed. In the European Standard EN 15657:2017 [1] a measurement
procedure using a reception plate to obtain Psn is described. There the service equipment is installed directlyon the front of the reception plate, the exitation of the reception plate takes place out-of-plane.
In fact it is often the case that the service equipment is not installed on the front, but inside the building element
like e.g. windows or ventilators in walls or roller shutters in the soffit of the window-like opening within awall. Therefore one can assume that the exitation of the reception plate resp. building element takes placein-plane. In order to study the applicability of the reception plate method according to [1] a reception plate
test rig was set up in the new Rosenheim technology center for energy & buildings (roteg) at the Technische
Hochschule Rosenheim. The reception plates are in agreement with the example described in [1], but havediffering geometries. One of the recpetion plates has an opening with size of 1.50 m x 1.25 m. Within thisopening service equipment can be installed und run under realistic mounting conditions if the equipement has to
be installed in the soffit. The reception plate test rig is shown in figure 1; the test rig is built up in accordancewith the sketch of appendix F in [1].
In order to extend the measurement method of the charateristic structure-borne sound power Psn to an in-plane
exitation, several investigations were carried out. First of all the driving-point mobility was determined for1255

WinPlate

RefPlate

Figure 1. Reception plate test rig at roteg. The reception plate with an window opening is refererred to WinPlate in the text, thenormal reception plate according to [4] is named RefPlate.

in-plane and out-of-plane exitation of the reception plates. Secondly the balance of the input power at theexcitation point and the power of the reception plate was compared.

2RECEPTION PLATE METHOD

According to the Standard EN 15657:2017 [1] the reception plate method is called an indirect method to determine the characteristic structure-borne sound power of a device, since it is not determined directly at thedevice, but by the vibrational energy of the reception plate, where it is mounted on. The installation of thedevice on the recpetion plate is done as it is on the building site and the device is then driven under typicaloperation conditions. In parallel the spatial average of the square of the plate velocity ṽ2i , is measured using
N accelerometers on the reception plate. Taking into account the loss factor η and the toal mass m of thereception plate, the installed structure-borne sound power of the device can be determined according equation(1)1 NPs = m · η · ω · · ∑ ṽ2i(1)N i=1The loss factor is usally determined by a measurement of the structure-borne reverberation time, or in the low
frequency range with a low mode density by determining the width of the eigenmodes.
The characterisitic structure-borne sound power is calculated using equation (2), mutliplying the measured
structure-borne sound power of the reception plate Ps by the ratio of the single-euivalent driving-point mobility YR,low,eq of the plate from the mean of all excitation points and the charateristic mobility of an infinte
plate YR,∞,low .
YR,∞,lowPsn = Ps ·(2)Re(YR,low,eq )The recpetion plate method is rather robust in the case that the mobility of the reception plate is much smaller
than the mobility of the source. To emphasize this condition the index low is added.
Due to the normalization according to equation (2) the characteristic structure-borne sound power of different
devices of the same type can be compared, even when the devices have been measured on different reception
plates.

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100

loss factor ηmedian WinPlate
median RefPlate
10−110−231.5

63125250500
frequency f /Hz

1k2kFigure 2. Loss factors of the RefPlate and the WinPLate; presented are the median and the 25 % and 75 % quantils.

3LOSS FACTORS AND MOBILITIES OF THE RECEPTION PLATESThe loss factors of the reception plates have been measured by using the reverberation time method. Themeasurement results of the loss factos are shown in figure 2. The results are averaged from three exitation
positions, twelve randomly chossen measurement positions, the evaluation of the results was carried out using
Schroeder backward integration and evaluating T10 . The exitation was done by an impact hammer. Due tothe high damping of the elastomer layers supporting the two plates, the loss factors are quite high. By an
experimental modal analysis it was confirmed that at least one bending mode is within each 1/3-octave band.
The small spreading of the measurement results gives rise to be confident in the procedure and in the numbers.
The characteristic mobility of an infinite plate, exited out-of-plane is given by equation (3) with bending stiffness
B according to equation (4), density ρ and plate thickness t [5]. It is frequency indipendent and pure real. The
index oop indicates out-of-plane exitation. The reception plates have a thickness of 10 cm, the size of theRefPlate is 3,8 m x 2.7 m and of the WinPlate 4,0 m x 2.8 m, the density ρ was determined to 2600(1 ± 2%)
kg/m3 , the Poisson ratio ν was chosen to be 0.2, the used value for the elasticity modul E was determinedfrom a TOF-measurement of the longitudinal wave and from the first logitudinal eigenmode as 47(1 ± 12%)GPa. However for further comparisons values from literature are taken (E = 30 GPa, ρ = 2300 kg/m3 ). In theStandard EN 15657:2017 [1] the characteristic mobility of an infinite concrete plate of a thickness of 10 cm isgiven to YR,∞,low = 5 · 10−6 (m/s)/N. It can be calculated using equation (3).
1√
(8 · ρ · t · B)

(3)

E · t312 · (1 − ν 2 )(4)

Y∞,oop =
B=The values of the driving-point mobility of the different plates were obtained by an excitation of the plates
at three points, indicated in figure 4a for the RefPlate and in figure 4b for the WinPlate. The measurements
consisted of an average of approx. five hits at each excitation point, averaging the mobilities of the two accelerometers next to the hammer position as shown in figure 3. In fact the mobility at each individual excitation
point was determined from the cross spectrum of force and velocity and the autopower spectrum of the force.
The magnitudes of the complex narrow band mobilities had then be converted to one-third octave band values and averaged for all excitation points. The magnitudes YR of these averaged driving-point mobilities areindicated with an index av and an index oop for out-of-plane excitation and ip for in-plane excitation.
Looking at figure 5 it can be noticed that in the case of out-of-plane excitation the agreement of YR,av,oop with
Y∞,oop is quite good for both reception plates, especially above 100 Hz. On a logarithmic scale the deviation isless than 3 dB.

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Figure 3. Force excitation with an impact hammer and two accelerometers for the determination of the velocity. The situation
shown is the in-plane exitation, where the accelerometers are mounted in the middle plane of the plate.

The characteristic mobility of an infinite plate, excited in-plane, is given by equation (5) [6] with shear stiffness
G, longitudinal stiffness D, plate thickness d and the wave numbers for quasi-longitudinal and transverse waves
kL and kT . Parameter e corresponds to the radius of the indenter. It was measured by colouring the tip of theimpact hammer and determining the size of the imprint to e = 2 mm.
ω
2 kL · eω
2 kT · eY ∞,ip =1 − i ln+
1 − i ln
(5)8·t ·Dπ
28·t ·G
π2E
2 · (1 + ν)ED=
(1 − ν 2 )r
ρ · (1 − ν 2 )kL =·ωEr2 · ρ · (1 + ν))
kT =·ωE
G=

(6)
(7)
(8)
(9)

The values of the driving-point mobility for in-plane excitation of the plates were obtained at three resp. fivedifferent points distributed along the vertical face as shown in figure 6.
Figure 5a shows a comparison of the measured mobilities YR,av,ip and the theoretical curve according to equation(5). As in the case with out-of-plane excitation there is good agreement of the measured mobilities with themobility Y∞,ip of an infinite plate above 100 Hz. At lower frequency the mobilies tend to higher values. Thisis due to the elastic bearing of the reception plate, which together with the plate forms a mass-spring-system.
Its resonance is at approx. 30 Hz. The decline of the mobilities from the resonance towards higher frequeny
is the mass dominated part of the resonance. In the case of the WinPlate the in-plane excitation was carriedout in horizontal as well as vertical direction. For the vertical direction only one excitation point and one
accelerometer position could be measured since the coherence was bad between the one-third octave bands
160 Hz and 200 Hz. Therefore no results are shown in this frequency range. Also the mass-spring system isdifferent for horizontal and vertical in-plane excitation, this explains the difference in the low frequency range.

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(a) RefPlate(b) WinPlate

Figure 4. Excitation positions, marked with red crosses - positions 1..3 are out-of-plane exitations, positions 4..6/9 indicate
in-plane exitation. Measurement positions of the accelerometers are marked with black circles for out-of-planemeasurements and with red circles for in-plane measurements.

For the RefPlate the measured mobility shows a distinct resonance at approx.500 Hz, indicated as a black vertical line in figure 5a. This is the fundamental mode of the longitudinal waves. It can be identified also in thecase of the WinPlate with vertical excitation, but at a higher frequency due to smaller dimensions. It is not that
evident for the horizontal excitation of the WinPlate, since the window opening supresses this standing wave.

4POWER BALANCE

The basic assumption of the reception plate method is expressed in equation (1). The power of the plate Ps
equals the power input at the excitation point Pep . The latter is evaluated according to (10). It is calculated
from the real part of the cross spectrum of force and velocity. Figure 3 shows the measurement setup for thepresented investigations, where the source is realized by the impact hammer.
1 n ∗ oPep = Re F̂ · v̂(10)2In figure 6a and 6b level differences are shown for various combinations of excitation and measurement directions. The level differences ∆LWs indicate the difference between the direct measured power at the excitation
point Pep and the power of the reception plate Ps .
The level difference has been calculated as average of three individual excitation positions for out-of-planeexcitation. The standard deviation is indicated with error bars. The power balance does hold for the caseof out-of-plane excitation und measurement of the out-of-plane power of the reception plate Ps in both cases,
shown in figure 6a, graph a for the RefPlate and in figure 6b, graph a for the WinPlate. Level differences arebelow 3 dB.
The power balance does not hold in the case of an in-plane excitation und measurement of the out-of-plane
power of the reception plate Ps . In both cases level differences exceed values of 10 dB in a wide frequency
range, as can be seen in figure 6a, graph b for the RefPlate and in figure 6b, graph b for the WinPlate .
In-plane excitation was carried out at three excitation positions for each reception plate. Obviously the input
in-plane power is not converted to bending waves at all but remains as quasi-longitudinal waves in the plate,
at least within the measurement time intervall. The reason that the level differences are less for the WinPlate

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Magnitude of mobility in m/Ns

10−4

YR,av,oop
Y∞,oop10−5

10−6

YR,av,ipY∞,ip
10−7
31.5

63125

250500frequency f/Hz

1k2k(a) RefPlate

Magnitude of mobility in m/Ns

10−4YR,av,oop
Y∞,oop
10−5

10−6

10−7
31.5

YR,av,ipY∞,ipYR,av,vertical,ip
63

125250500frequency f/Hz

1k2k(b) WinPlate
Figure 5. Magnitude of the averaged driving-point mobilities for an excitation out-of-plane (oop) or in-plane (ip). Indicated withdashed lines are also the theoretically expected values for infinite plates. Dotted lines indicate the theoretical values,
when the calculation is performed with the measured material data. Error bars indicate the standard deviation of themagnitudes from different exitation positions.

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∆LWs in dB

20100a−1031.563125250500
frequency f/Hz

bc1k2k(a) RefPlate∆LWs in dB

20100a−1031.5

63125

250
500
frequency f/Hz

b1kc2k(b) WinPlate
Figure 6. Level difference ∆LWs of Pep and Ps ; mean value of three excitation positions together with their standard deviation,
indicated by error bars.
a: oop excitaion, oop measurment (standard case according to EN 15657:2017 [1])b: ip excitation, oop measurementc: ip excitation, ip measurement

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(approx. 10 dB over the whole frequency range) may be due to the fact, that the discontinuities at the window
opening contributes to a conversion of quasi-longitudinal waves into bending waves.
A much better power balance can be observed by comparing the input power of in-plane excitation with the inplane power of the reception plate determined by the accelerometers, which are sensitive to in-plane movementof the plate. This can be seen from the graphs in figure 6a, graph c for the RefPlate and in figure 6b, graphc for the WinPlate. Especially above the fundamental longitudinal mode, the power balance is quite good withdifferences within 3 dB. This supports the conclusion that energy is stored in longitudinal standing waves andis therefore not detected by out-of-plane measurement.

5SUMMARY

The reception plate method according to EN 15657:2017 [1] was investigated on the extension to an in-planeexcitation. The magnitudes of the measured driving-point mobilities show a very sensible behaviour, their spectral shape can be explained to a satisfactory extent.
The power balance between the input power at the excitation point and the reception plate power as the fundamental requirement for the application of the reception plate method is achieved for the case in which thereception plate is excited out-of-plane. In this case dominantly bending waves are excited, which can be measured by out-of-plane sensitive accelerometer.
However the power balance is not fulfilled to a satisfactory extent if the excitation of the reception plate isin-plane. The correct determination of the reception plate power in this case needs further investigations.

6ACKNOWLEDGEMENTS

The authors are greatful to Müller-BBM Vibroacoustic Systems GmbH for their support with measurement
equipment.

REFERENCES

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[1]

EN 15657:2017: Acoustic properties of building elements and of buildings - Laboratory measurement of structure-borne
sound from building service equipment for all installation conditions[2]

DIN 4109-1:2018-01: Schallschutz im Hochbau - Teil 1: Mindestanforderung[3]

EN 12354-5:2009: Building acoustics – Estimation of acoustic performance of building from the performance of elements.
Part 5: Sound levels due to the service equipment.

[4]

DIN EN 15657:2017-10: Akustische Eigenschaften von Bauteilen und von Gebäuden - Messung des Körperschalls vonhaustechnischen Anlagen im Prüfstand für alle Installationsbedingungen[5]Cremer, L.; Heckl, M. A.: Körperschall: Physikalische Grundlagen und Anwendungen. Berlin, Heidelberg, New York:
Springer Verlag, 1967

[6]Gardonio, P.; Brennan, M. J.: “Mobility and impedance methods in structural dynamics: Chapter 9”. In: Advanced Application in Acoustics, Noise and Vibration. Ed. by Fahy, F. J.; Walker, J. 2004