CEN/TS 16272-5:2014

SLOVENSKI STANDARD
01-junij-2014
äHOH]QLãNHQDSUDYH=JRUQMLXVWURMSURJH3URWLKUXSQHRYLUHLQSULSDGDMRþH
QDSUDYHNLYSOLYDMRQDãLUMHQMH]YRNDY]UDNX3UHVNXVQDPHWRGD]DXJRWDYOMDQMH
DNXVWLþQLKODVWQRVWLGHO3RVHEQHNDUDNWHULVWLNH7HUHQVNHYUHGQRVWLRGERMD
]YRNDSULXVPHUMHQHP]YRþQHPSROMX
Railway applications - Track - Noise barriers and related devices acting on airborne
sound propagation - Test method for determining the acoustic performance - Part 5:
Intrinsic characteristics - In situ values of sound reflection under direct sound field
conditions
Bahnanwendungen - Oberbau - Lärmschutzwände und verwandte Vorrichtungen zur
Beeinflussung der Luftschallausbreitung - Prüfverfahren zur Bestimmung der
akustischen Eigenschaften - Teil 5: Produktspezifische Merkmale - In-situ-Werte zur
Schallreflexion in gerichteten Schallfeldern
Applications ferroviaires - Voie - Dispositifs de réduction du bruit - Méthode d'essai pour
la détermination des performances acoustiques - Partie 5: Valeurs in situ de la réflexion
acoustique dans des conditions de champ acoustique direct
Ta slovenski standard je istoveten z: CEN/TS 16272-5:2014
ICS:
17.140.30 Emisija hrupa transportnih Noise emitted by means of
sredstev transport
45.020 Železniška tehnika na Railway engineering in
splošno general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

TECHNICAL SPECIFICATION
CEN/TS 16272-5
SPÉCIFICATION TECHNIQUE
TECHNISCHE SPEZIFIKATION
April 2014
ICS 93.100
English Version
Railway applications - Track - Noise barriers and related devices
acting on airborne sound propagation - Test method for
determining the acoustic performance - Part 5: Intrinsic
characteristics - In situ values of sound reflection under direct
sound field conditions
Applications ferroviaires - Voie - Dispositifs de réduction du Bahnanwendungen - Oberbau - Lärmschutzwände und
bruit - Méthode d'essai pour la détermination des verwandte Vorrichtungen zur Beeinflussung der
performances acoustiques - Partie 5: Valeurs in situ de la Luftschallausbreitung - Prüfverfahren zur Bestimmung der
réflexion acoustique dans des conditions de champ akustischen Eigenschaften - Teil 5: Produktspezifische
acoustique direct Merkmale - In-situ-Werte zur Schallreflexion in gerichteten
Schallfeldern
This Technical Specification (CEN/TS) was approved by CEN on 26 February 2013 for provisional application.

The period of validity of this CEN/TS is limited initially to three years. After two years the members of CEN will be requested to submit their
comments, particularly on the question whether the CEN/TS can be converted into a European Standard.

CEN members are required to announce the existence of this CEN/TS in the same way as for an EN and to make the CEN/TS available
promptly at national level in an appropriate form. It is permissible to keep conflicting national standards in force (in parallel to the CEN/TS)
until the final decision about the possible conversion of the CEN/TS into an EN is reached.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United
Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2014 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TS 16272-5:2014 E
worldwide for CEN national Members.

Contents
Foreword . 4
Introduction . 5
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 Symbols and abbreviations . 10
5 Sound reflection index measurements . 11
5.1 General principle. 11
5.2 Measured quantity . 11
5.3 Test arrangement . 12
5.4 Measuring equipment . 16
5.4.1 Components of the measuring system . 16
5.4.2 Sound source . 17
5.4.3 Test signal . 17
5.5 Data processing . 18
5.5.1 Calibration . 18
5.5.2 Sample rate . 18
5.5.3 Background noise. 18
5.5.4 Signal subtraction technique . 18
5.5.5 Adrienne temporal window . 19
5.5.6 Placement of the Adrienne temporal window . 21
5.5.7 Low frequency limit and sample size . 21
5.6 Positioning of the measuring equipment . 22
5.6.1 Maximum sampled area . 22
5.6.2 Selection of the measurement positions . 23
5.6.3 Reflecting objects . 27
5.6.4 Safety considerations . 27
5.7 Sample surface and meteorological conditions . 27
5.7.1 Condition of the sample surface . 27
5.7.2 Wind . 27
5.7.3 Air temperature . 28
5.8 Measurement uncertainty . 28
5.9 Measuring procedure . 28
5.10 Test report . 29
Annex A (informative) Measurement uncertainty . 30
A.1 General . 30
A.2 Expression for the calculation of sound reflection index . 30
A.3 Contributions to measurement uncertainty . 31
A.4 Expanded uncertainty of measurement . 31
A.5 Measurement uncertainty based upon reproducibility data . 32
Annex B (informative) Template of test report on sound reflection of railway noise barriers . 33
B.1 Template of test report . 33
B.2 Test setup (example) . 34

B.3 Test object and test situation (example) . 35
B.4 Results (example) . 37
B.4.1 Part 1 – Results in tabular form . 37
B.4.2 Part 2 – Results in graphic form . 38
Bibliography . 39

Foreword
This document (CEN/TS 16272-5:2014) has been prepared by Technical Committee CEN/TC 256 “Railway
applications”, the secretariat of which is held by DIN.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights.
CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
This Technical Specification is one of the series EN 16272 “Railway applications – Track – Noise barriers and
related devices acting on airborne sound propagation – Test method for determining the acoustic performance” as
listed below:
— Part 1: Intrinsic characteristics – Sound absorption in the laboratory under diffuse sound field conditions
— Part 2: Intrinsic characteristics – Airborne sound insulation in the laboratory under diffuse sound field
conditions
— Part 3-1: Normalized railway noise spectrum and single number ratings for diffuse field applications
— Part 3-2: Normalized railway noise spectrum and single number ratings for direct field applications
— Part 4: Intrinsic characteristics – In situ values of sound diffraction under direct sound field conditions
— Part 5: Intrinsic characteristics – In situ values of sound reflection under direct sound field conditions
— Part 6: Intrinsic characteristics – In situ values of airborne sound insulation under direct sound field conditions
— Part 7: Extrinsic characteristics – In situ values of insertion loss
It should be read in conjunction with:
EN 16272-1, Railway applications – Track – Noise barriers and related devices acting on airborne sound
propagation – Test method for determining the acoustic performance – Part 1: Intrinsic characteristics – Sound
absorption in the laboratory under diffuse sound field conditions
EN 16272-3-1, Railway applications – Track – Noise barriers and related devices acting on airborne sound
propagation – Test method for determining the acoustic performance – Part 3-1: Normalized railway noise
spectrum and single number ratings for diffuse field applications
EN 16272-3-2, Railway applications – Track – Noise barriers and related devices acting on airborne sound
propagation – Test method for determining the acoustic performance – Part 3-2: Normalized railway noise
spectrum and single number ratings for direct field applications
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to announce this Technical Specification: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech
Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece,
Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom.
Introduction
This Technical Specification describes a test method for determining the intrinsic characteristics of sound reflection
of noise barriers and claddings designed for railways in non-reverberant conditions (a measure of intrinsic
performance). It can be applied in situ, i.e. where the noise barriers are installed. The method can be applied
without damaging the surface.
The method can be used to qualify products to be installed along railways as well as to verify the compliance of
installed noise barriers to design specifications. Regular application of the method can be used to verify the long
term performance of noise barriers.
The method requires the average of results of measurements taken in different points in front of the device under
test and/or for specific angles of incidences. The method is able to investigate flat and non-flat products.
The measurements results of this method for sound reflection are not directly comparable with the results of the
laboratory method (EN 16272-1), mainly because the present method uses a directional sound field, while the
laboratory method assumes a diffuse sound field. The test method described in the present document should not
be used to determine the intrinsic characteristics of sound reflection of noise reducing devices to be installed in
reverberant conditions, e.g. claddings inside tunnels or deep trenches.
For the purpose of this Technical Specification reverberant conditions are defined based on the envelope, e, across
the rail formed by the barriers, trench sides or buildings (the envelope does not include the railway surface) as
shown by the dashed lines in Figure 1. Conditions are defined as being reverberant when the percentage of open
space in the envelope is less than or equal to 25 %, i.e.:
+ h )
Reverberant conditions occur when w/e ≤ 0,25, where e = (w + h
1 2
This criterion is applied also to the open space between the train body and the barrier surface.

(a) Partial cover on both sides of the railway;
(b) Partial cover on one side of the railway; e = w + h

envelope, e = w + h + h
1 2
(c) Deep trench envelope, e = w + h + h  (d) Tall barriers or buildings; envelope, e = w + h + h
1 2 1 2
(e) Train passing close to a noise barrier envelope, (f) Train passing close to a platform at the station,

e = w + h + h e = w + h + h
1 2 1 2
Key
TOR top of rail
w width of open space
Figure 1 — (not to scale) Sketch of the reverberant condition check in six cases.
This method introduces a specific quantity, called reflection index, to define the sound reflection in front of a noise
barrier or cladding, while the laboratory method gives a sound absorption coefficient. Laboratory values of the
sound absorption coefficient can be converted to conventional values of a reflection coefficient taking the
complement to one. In this case, research studies suggest that a quite good correlation exists between laboratory
data, measured according to EN 16272-1 and field data, measured according to the method described in the
present document.
This method may be used to qualify noise reducing devices for other applications, e.g. to be installed along roads
or nearby industrial sites. In this case the single-number ratings should be calculated using an appropriate
spectrum.
1 Scope
This Technical Specification describes a test method for measuring a quantity representative of the intrinsic
characteristics of sound reflection from railway noise barriers: the reflection index.
The test method is intended for the following applications:
— determination of the intrinsic characteristics of sound reflection of noise barriers to be installed along railways,
to be measured either on typical installations alongside railways or on a relevant sample section;
— determination of the in situ intrinsic characteristics of sound reflection of noise barriers and claddings in actual
use;
— comparison of design specifications with actual performance data after the completion of the construction
work;
— verification of the long term performance of noise barriers and claddings (with a repeated application of the
method).
The test method is not intended for the following applications:
— determination of the intrinsic characteristics of sound reflection of noise reducing devices to be installed in
reverberant conditions, e.g. inside tunnels or deep trenches.
Results are expressed as a function of frequency, in one-third octave bands between 100 Hz and 5 kHz. If it is not
possible to get valid measurements results over the whole frequency range indicated, the results should be given in
a restricted frequency range and the reasons of the restriction(s) should be clearly reported.
All noise reducing devices different from noise barriers and related devices acting on airborne sound propagation,
e.g. devices for attenuation of ground borne vibration and on board devices are out of the scope of this Technical
Specification.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for
its application. For dated references, only the edition cited applies. For undated references, the latest edition of the
referenced document (including any amendments) applies.
prEN 16272-3-2:2012, Railway applications – Track – Noise barriers and related devices acting on airborne sound
propagation – Test method for determining the acoustic performance – Part 3-2: Normalized railway noise
spectrum and single number ratings for direct field applications
EN 61672-1, Electroacoustics – Sound level meters – Part 1: Specifications (IEC 61672-1)
ISO/IEC Guide 98-3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in
measurement (GUM:1995)
3 Terms and definitions
For the purpose of this document the following definitions apply.
3.1
acoustic element
element whose primary function is to provide the acoustic performance of the device
3.2
Adrienne temporal window
the composite temporal window described in 5.5.5
3.3
background noise
noise coming from sources other than the source emitting the test signal
3.4
cladding
noise reducing device, which is attached to a wall or other structure and reduces the amount of sound reflected
Note 1 to entry: Claddings are generally made of acoustic and structural elements (see 3.3 and 3.4).
3.5
impulse response
the time signal at the output of a system when a Dirac function is applied to the input
Note 1 to entry: The Dirac function, also called δ function, is the mathematical idealisation of a signal infinitely short in time
that carries a unit amount of energy.
3.6
maximum sampled area
the surface area, projected on a front view of the noise reducing device under test for reflection index
measurements, which shall remain free of reflecting objects causing parasitic reflections
3.7
noise barrier
noise reducing device, which obstructs the direct transmission of airborne sound emanating from railways; it may
either span or overhang the railway
Note 1 to entry: Noise barriers are generally made of acoustic and structural elements (see 3.3 and 3.4).
3.8
reference height
a height h equal to half the height h of the noise barrier or cladding under test: h = h /2 (see Figures 2 and 3)
S B S B
3.9
rotation of the loudspeaker-microphone assembly
a set of nine measurement positions, including the reference position, reached rotating the loudspeaker-
microphone assembly, around the axis of rotation R (see Figure 2), on the same plane in steps of 10° (Figures 5, 6
and 7)
3.10
signal-to-noise ratio, S/N
the difference in decibels between the level of the test signal and the level of the background noise at the moment
of detection of the useful event (within the Adrienne temporal window)
3.11
sound reflection index
the result of a sound reflection test described by formula (1) (see 5.2)
3.12
structural element
element whose primary function is to support or hold in place acoustic elements
Key
1 reference circle
2 axis of rotation
3 loudspeaker front panel
4 microphone
Figure 2 — (not to scale) Sketch of the loudspeaker-microphone assembly in front of the noise reducing
device under test for reflection index measurements

Key
1 loudspeaker front panel
2 microphone
Figure 3 — (not to scale) Sketch of the set-up for the reference “free-field” sound measurement for the
determination of the reflection index measurement
4 Symbols and abbreviations
For the purposes of this document, the following symbols and abbreviations apply.
Table 1 – Symbols and abbreviations
Symbol or Designation Unit
abbreviation
a Major axis of the ellipsoid of revolution used to define the maximum sampled area at m
oblique incidence
a , a , a , a Coefficient for the expression of the Blackman-Harris window -
0 1 2 3
c Speed of sound in air m/s
d Horizontal distance from the microphone to the reference circle; it is equal to d = 0,25 m m
M S
d Horizontal distance from the loudspeaker front panel to the microphone projected on a m
p
vertical plane, placed between the microphone and the noise reducing device under
test, tangential to the reference circle when the loudspeaker-microphone assembly is
horizontal
d Horizontal distance from the reference axis of rotation to the loudspeaker front panel; it m
RS
is equal to: d = 0,15 m
RS
d Horizontal distance from the front panel of the loudspeaker to the reference circle; it is m
S
equal to: d = 1,50 m
S
d Horizontal distance from the front panel of the loudspeaker to the microphone; it is equal m
SM
to: d = 1,25 m
SM
DL Single number rating of sound reflection dB
RI
δ Any input quantity to allow for uncertainty estimates -
i
Δf Width of the j-the one-third octave frequency band Hz
i
f Frequency Hz
F Symbol of the Fourier transform -
f Low frequency limit of sound reflection index measurements Hz
min
f Sample rate Hz
s
f Cut-off frequency of the anti-aliasing filter Hz
co
h Noise barrier height m
B
h Reference height m
S
h (t) Incident reference component of the free-field impulse response -
i
h (t) Reflected component of the impulse response at the k-th angle -
rk
j Index of the j-th one-third octave frequency band (between 100 Hz and 5 kHz) -
k Coverage factor -
k Constant used for the anti-aliasing filter -
f
n Number of angles on which to average -
j
r Radius of the maximum sampled area at normal incidence m
RI Sound reflection index in the j-th one-third octave frequency band dB
j
t Time s or
ms
T Length of the Blackman-Harris trailing edge of the Adrienne temporal window ms
W,BH
Symbol or Designation Unit
abbreviation
T Total length of the Adrienne temporal window ms
W,ADR
u Standard uncertainty -
U Expanded uncertainty -
w (t) Reference free-field component time window (Adrienne temporal window) -
i
w (t) Time window (Adrienne temporal window) for the reflected component -
r
5 Sound reflection index measurements
5.1 General principle
The sound source emits a transient sound wave that travels past the microphone position to the device under test
and is then reflected on it (Figures 2, 3, 5 and 6). The microphone placed between the sound source and the
device under test receives both the direct sound pressure wave travelling from the sound source to the device
under test and the sound pressure wave reflected (including scattering) by the device under test. The power
spectra of the direct and the reflected components, corrected to take into account the path length difference of the
two components, gives the basis for calculating the reflection index.
The measurement shall take place in an essentially free field in the direct surroundings of the device, i.e. a field
free from reflections coming from surfaces other than the surface of the device under test. For this reason, the
acquisition of an impulse response having peaks as sharp as possible is recommended: in this way, the reflections
coming from other surfaces than the tested device can be identified from their delay time and rejected.
5.2 Measured quantity
The expression used to compute the sound reflection index RI as a function of frequency, in one-third octave
bands, is:
F[t× h (t)×w (t)] df
∫
rk r
n
j ∆f
j
(1)
RI = ∑
j
n k=1
j [ ]
∫ F t× h(t)×w(t) df
i i
∆f
j
where:
h (t) is the incident reference component of the free-field impulse response;
i
h (t) is the reflected component of the impulse response at the k-th angle;
rk
w (t) is the incident reference free-field component time window (Adrienne temporal window);
i
w (t) is the reflected component time window (Adrienne temporal window);
r
F is the symbol of the Fourier transform;
j is the index of the one-third octave frequency bands (between 100 Hz and 5 kHz);
is the width of the j-th one-third octave frequency band;
∆f
j
n is the number of angles on which to average (n ≤ 9 per rotation; see 5.5.2 and Table 1);
j
t is a time whose origin is at the beginning of the impulse response acquired by the measurement
chain.
NOTE The reflections from different portions of the surface under test arrive at the microphone position at different times,
depending on the travel path from the loudspeaker to the position of each test surface portion and back. The longer the travel
path from the loudspeaker to a specific test surface portion and back, the greater the time delay. Thus, the amplitude of the
reflected sound waves from different test surface portions, as detected at the microphone position, is attenuated in a manner
inversely proportional to the travel time. In order to compensate for this effect, t is included as a factor in both numerator and
denominator in Formula (1).
5.3 Test arrangement
The test method can be applied both in situ and on barriers purposely built to be tested using the method described
here.
For applications on barriers purposely built to be tested using the method described here the specimen shall be
built as follows:
— a part, composed of acoustic elements, that extends at least 4 m and is at least 4 m high.
The test specimen shall be mounted and assembled in the same manner as the manufactured device is used in
practice with the same connections and seals between components parts.
For in situ applications the test specimen shall be constructed as follows:
— for in situ applications using single acoustic elements to achieve full height:
• the test specimen shall be constructed as a single element which is representative of the in situ
application;
• where the test specimen cannot be constructed as a single element or where the in situ application is
lower than 4 m, the test specimen shall be centred on the loudspeaker axis (at reference height h
S
above the ground) and built up to 4 m high using smaller height acoustic elements at the base and
top as appropriate;
— for in situ applications using stacked elements to achieve full height:
• the test specimen shall be constructed as used in situ.
For the results to be valid on the full frequency range, the minimum dimensions of the sample shall be as follows
(see Figure 4):
— a part, composed of acoustic elements, 4 m wide and 4 m high;
— two posts 4 m high at both sides (if applicable for the specific noise reducing device under test).

Figure 4 — Sketch of the minimum flat sample required for reflection index measurements in the 200 Hz -
5 kHz frequency range (see 5.5.7). Thin circle: maximum sampled area (5.6.1)
(a) Reflected sound measurements, from 50° to 130° in step of 10° on the same rotation plane, in front of a
non-flat noise reducing device

(b) Reference “free-field” sound measurement
Key
1 axis of rotation
2 loudspeaker front panel
3 microphone
Figure 5 — (not to scale) Sketch of the set-up for the reflection index measurement (example for rotation in
vertical direction)
(a) Reflected sound measurements, from 50° to 130° in step of 10° on the same rotation plane, in front of an
inclined flat noise reducing device
(b) Reflected sound measurements, from 50° to 130° in step of 10° on the same rotation plane, in front of an
inclined non flat noise reducing device
Key
1 axis of rotation
2 loudspeaker front panel
3 microphone
Figure 6 — (not to scale) Sketch of the set-up for the reflection index measurement (example for rotation in
vertical direction)
(a) Reflected sound measurements, from 50° to 130° in step of 10° on the same rotation plane, in front of a
concave noise reducing device
(b) Reflected sound measurements, from 50° to 130° in step of 10° on the same rotation plane, in front of a
convex noise reducing device
Key
1 axis of rotation
2 loudspeaker front panel
3 microphone
Figure 7 — Sketch of the set-up for the reflection index measurement (example for rotation in vertical
direction)
Figure 8 — Sketch representing the essential components of the measuring system
5.4 Measuring equipment
5.4.1 Components of the measuring system
The measuring equipment shall comprise: an electro-acoustic system, consisting of an electrical signal generator, a
power amplifier and a loudspeaker, a microphone with its microphone amplifier and a signal analyser capable of
performing transformations between the time domain and the frequency domain.
NOTE Part of these devices can be integrated into a frequency analyser or a personal computer equipped with specific
add-on board(s).
The essential components of the measuring system are shown in Figure 8.
The complete measuring system shall meet the requirements of at least a type 1 instrument in accordance with
EN 61672-1, except for the microphone which shall meet the requirements for type 2 and have a diameter of 1/2”
maximum.
The measurement procedure here described is based on ratios of the power spectra of signals extracted from
impulse responses sampled with the same equipment in the same place under the same conditions within a short
time. Also, a high accuracy in measuring sound levels is not of interest here. Strict requirements on the absolute
accuracy of the measurement chain are, therefore, not needed. Anyway, the requirement for a type 1 instrument is
maintained for compatibility with other European Standards. The microphone should be sufficiently small and
lightweight in order to be fixed in front of the loudspeaker without moving: the signal subtraction technique
(see 5.5.4) requires the loudspeaker and microphone relative position be kept strictly constant. It is difficult to find
on the market type1 microphones meeting this requirement. For this reason, the microphone is allowed to meet the
requirements for type 2.
5.4.2 Sound source
The electro-acoustic sound source shall meet the following characteristics:
— have a single loudspeaker driver;
— be constructed without any port, e.g. to enhance low frequency response;
— be constructed without any electrically active or passive components (such as crossovers) which can affect the
frequency response of the whole system;
— have a smooth magnitude of the frequency response without sharp irregularities throughout the measurement
frequency range, resulting in an impulse response under free-field conditions with a length not greater than
3 ms.
NOTE As the sound reflection index is calculated from the ratio of energetic quantities extracted from impulse responses
taken using the same loudspeaker-microphone assembly within a short time period, the characteristics of the loudspeaker
frequency response are not critical, provided a good quality loudspeaker meeting the above prescriptions is used.
5.4.3 Test signal
The electro-acoustic source shall receive an input electrical signal which is deterministic and exactly repeatable.
The input signal has to be set in order to avoid any nonlinearity of the loudspeaker.
The S/N ratio is improved by repeating the same test signal and synchronously averaging the microphone
response. At least 16 averages shall be kept.
This Technical Specification recommends the use of a MLS signal as test signal. Alternatively, a different test
signal may be used (e.g. sine sweep) as long as the results have been demonstrated to be exactly the same. This
means that it shall be clearly demonstrated that:
— the generation of the test signal is deterministic and exactly repeatable;
— impulse responses are accurately sampled (without distortion) on the whole frequency range of interest (one-
third octave bands between 100 Hz and 5 kHz);
— the test method maintains a good background noise immunity, i.e. the effective S/N ratio can be made higher
than 10 dB on the whole frequency range of interest within a short measurement time (no more than 5 minutes
per impulse response);
— the sample rate can be chosen high enough to allow an accurate correction of possible time shifts in the
impulse responses between the measurement in front of the sample and the free-field measurement due to
temperature changes;
— the test signal is easy-to-use, i.e. it can be conveniently generated and fed to the sound source using only
equipment which is available on the market.
5.5 Data processing
5.5.1 Calibration
The measurement procedure here described is based on ratios of the power spectra of signals extracted from
impulse responses sampled with the same equipment in the same place under the same conditions. An absolute
calibration of the measurement chain with regard to the sound pressure level is therefore not needed. It is anyway
recommended to check the correct functioning of the measurement chain from the beginning to the end of
measurements.
5.5.2 Sample rate
The frequency at which the microphone response is sampled depends on the specified upper frequency limit of the
measurement and on the anti-aliasing filter type and characteristics.
The sample rate f shall have a value greater than 43 kHz.
s
NOTE Although the signal is already unambiguously defined when the Nyquist criterion is met, higher sample rates
facilitate a clear reproduction of the signal. This document prescribes the use of the signal subtraction technique (see 5.5.4),
which implies knowledge of the exact wave form. Therefore, with the prescribed sample rates errors can be detected and
corrected more easily, such as time shifts in the impulse responses between the measurement in front of the sample and the
free-field measurement due to temperature changes.
The sample rate shall be equal to the clock rate of the signal generator.
The cut-off frequency of the anti-aliasing filter, f , shall have a value:
co
f ≤ kf (2)
co s
where k = 1/3 for the Chebyshev filter and k = 1/4 for the Butterworth and Bessel filters.
For each measurement, the sample rate, the type and the characteristics of the anti-aliasing filter shall be clearly
stated in each test report.
5.5.3 Background noise
The effective signal-to-noise ratio S/N, taking into account sample averaging, shall be greater than 10 dB over the
frequency range of measurements.
NOTE Coherent detection techniques, such as the MLS cross-correlation, provide high S/N ratios.
5.5.4 Signal subtraction technique
After positioning the loudspeaker-microphone assembly as described in 3.9, the overall impulse response has to be
measured.
It consists of a direct component, a component reflected from the surface under test and other parasitic reflections
(Figure 9 (a)). The direct component and the reflected component from the device under test shall be separated.
This European Technical Specification requires this separation be done using the signal subtraction technique: the
reflected component is extracted from the overall impulse response after having removed the direct component by
subtraction of an identical signal (Figures 9 (c) and 9 (d)). This means that the direct sound component shall be
exactly known in shape, amplitude and time delay. This can be obtained by performing a free-field measurement
using the same geometrical configuration of the loudspeaker and the microphone. In particular, their relative
position shall be kept strictly constant. This requirement can be obtained by using a fixed and stable connection
between the source and the microphone. The direct component is extracted from the free-field measurement
(Figure 9 (b)).
This technique allows broadening of the time window, leading to a lower frequency limit of the working frequency
range, without having very long distances between loudspeaker, microphone and device under test.
The principle of the signal subtraction technique is schematically illustrated in Figure 9.

(a) Overall impulse response including: direct incident (b) Free-field direct component (i’)
component (i) reflected component (r), unwanted
parasitic components (u)
(c) Direct component cancellation from the overall (d) Result
impulse response using the free-field direct component
(i’)
Key
1 i
2 r
3 u
4 i'
Figure 9 — Principle of the signal subtraction technique
The measurement shall take place in a sound field free from reflections coming from objects other than the device
under test. However, the use of a time window cancels out reflections arriving after a certain time delay, and thus
originating from locations further away than a certain distance (see 5.6.3).
5.5.5 Adrienne temporal window
For the purpose of this Technical Specification, windowing operations in the time domain shall be performed using
a temporal window, called Adrienne temporal window, with the following specifications (see Figure 10):
— a leading edge having a left-half Blackman-Harris shape and a total length of 0,5 ms (“pre-window”);
— a flat portion having a total length of 5,18 ms (“main body”);
— a trailing edge having a right-half Blackman-Harris shape and a total length of 2,22 ms.
The total length of the Adrienne temporal window is T = 7,9 ms.
W ,ADR
NOTE A four-term full Blackman-Harris window of length T is:
W,BH
     
2πt 4πt 6πt
     
(3)
w(t)= a − a cos + a cos − a cos
0 1 2 3
     
T T T
W ,BH W ,BH W ,BH
     
where
a = 0,35875;
a = 0,48829;
a = 0,14128;
a = 0,01168;
0≤ t≤ T
W ,BH
If the window length T has to be varied (this occurs only in exceptional cases) the lengths of the flat portion
W ,ADR
and the right-half Blackman-Harris portion shall have a ratio of 7/3. As an example, when testing very large
samples the window length can be enlarged in order to achieve a better low frequency limit.
The point where the flat portion of the Adrienne temporal window begins is called the marker point (MP).

Key
X time [ms]
Y Adrienne window function w(t) [relative units]
1 marker point MP
Figure 10 — The Adrienne temporal window, with the marker point MP
5.5.6 Placement of the Adrienne temporal window
For the “free-field” direct component, the Adrienne temporal window shall be placed as follows:
— the first peak of the impulse response, corresponding to the direct component, is detected;
— a time instant preceding the direct component peak of 0,2 ms is located;
— the direct component Adrienne temporal window is placed so as its marker point corresponds to this time
instant.
In other words, the direct component Adrienne temporal window is placed so as its flat portion begins 0,2 ms before
the direct component peak.
For the reflected component, the Adrienne temporal window shall be placed as follows:
— the time instant labelled by the direct component Adrienne temporal window marker point is located ;
— the time delay τ= 2d / c is added to this time instant; the resulting time instant is assumed as the position of
M
the reflected component Adrienne temporal window marker point;
— the reflected component Adrienne temporal window is placed so as its marker point corresponds to this new
time instant.
In other words, the reflected component Adrienne temporal window is placed so as its flat portion begins 0,2 ms
before the first peak of the reflected component.
In computat
...