FprEN ISO 10534-2
(Main)Acoustics - Determination of acoustic properties in impedance tubes - Part 2: Two-microphone technique for normal sound absorption coefficient and normal surface impedance (ISO/FDIS 10534-2:2023)
Acoustics - Determination of acoustic properties in impedance tubes - Part 2: Two-microphone technique for normal sound absorption coefficient and normal surface impedance (ISO/FDIS 10534-2:2023)
Akustik - Bestimmung der akustischen Eigenschaften in Impedanzrohren - Teil 2: 2-Mikrofontechnik für Standardschallabsorptionsgrad und Standardoberflächenimpedanz (ISO/FDIS 10534-2:2023)
Dieses Prüfverfahren behandelt die Bestimmung des Schallabsorptionsgrades von schallabsorbierenden Werkstoffen bei senkrechtem Schalleinfall unter Anwendung eines Impedanzrohres, zweier Mikrofonorte sowie eines Frequenzanalysesystems. Es kann auch zur Bestimmung der akustischen Oberflächenimpedanz oder Oberflächenadmittanz von schallabsorbierenden Werkstoffen angewendet werden. In Erweiterung kann es auch angewendet werden, um intrinsische Eigenschaften von homogenen akustischen Werkstoffen, wie z. B. deren charakteristische Impedanz, die charakteristische Wellenzahl, die dynamische Massendichte und den dynamischen Kompressionsmodul, zu beurteilen.
Das Prüfverfahren ist dem in ISO 10534 1 [1] festgelegten insofern ähnlich, als ein Impedanzrohr verwendet wird, an dessen einem Ende eine Schallquelle angeschlossen ist und in dessen anderem Ende der Prüfkörper befestigt wird. Das Messverfahren ist jedoch ein anderes. Bei diesem Prüfverfahren werden mit Hilfe einer Schallquelle ebene Wellen im Rohr erzeugt und die Zerlegung des Interferenzfeldes durch Messung des akustischen Druckes an zwei festen Orten erreicht, wobei an der Wand befestigte Mikrofone oder ein im Rohr verfahrbares Mikrofon verwendet werden bzw. wird; anschließend werden die komplexe akustische Übertragungsfunktion und die vorstehend genannten Größen berechnet. Dieses Prüfverfahren soll ein alternatives und im Vergleich zu dem in ISO 10534 1 [1] behandelten im Allgemeinen viel schnelleres Messverfahren bereitstellen.
Die sich bei Impedanzrohrmessungen mit senkrechtem Schalleinfall ergebenden Absorptionsgrade sind nicht mit den in Hallräumen bei zufälligem Schalleinfall nach ISO 354 [2] gemessenen Absorptionsgraden vergleichbar. Mit Hilfe des Hallraumverfahrens wird (unter Idealbedingungen) der Schallabsorptionsgrad bei diffusem Schalleinfall bestimmt. Für das Hallraumverfahren werden jedoch verhältnismäßig große Probekörper benötigt. Das Impedanzrohrverfahren ist auf Untersuchungen bei senkrechtem und ebenem Schalleinfall begrenzt und erfordert Proben des Prüfgegenstandes, die die gleiche Größe wie der Querschnitt des Impedanzrohres besitzen. Bei ausschließlich lokal wirkenden Werkstoffen können die Schallabsorptionsgrade bei diffusem Einfall aus den Messergebnissen geschätzt werden, die mit dem Impedanzrohrverfahren gewonnen wurden (siehe Anhang E).
Im gesamten Dokument wird eine e^(+jωt)-Zeitkonvention verwendet.
Acoustique - Détermination des propriétés acoustiques aux tubes d’impédance - Partie 2: Méthode à deux microphones pour le coefficient d’absorption acoustique normal et l’impédance de surface normale (ISO/FDIS 10534-2:2023)
Akustika - Ugotavljanje akustičnih lastnosti v Kundtovi cevi - 2. del: Dvomikrofonska tehnika za določanje normalnega koeficienta absorpcije zvoka in normalne površinske impedance (ISO/FDIS 10534-2:2023)
General Information
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Standards Content (Sample)
SLOVENSKI STANDARD
oSIST prEN ISO 10534-2:2022
01-november-2022
Akustika - Ugotavljanje akustičnih lastnosti v Kundtovi cevi - 2. del:
Dvomikrofonska tehnika za določanje normalnega koeficienta absorpcije zvoka in
normalne površinske impedance (ISO/DIS 10534-2:2022)
Acoustics - Determination of acoustic properties in impedance tubes - Part 2: Two-
microphone technique for normal sound absorption coefficient and normal surface
impedance (ISO/DIS 10534-2:2022)
Akustik - Bestimmung der akustischen Eigenschaften in Impedanzrohren - Teil 2: 2-
Mikrofontechnik für Standardschallabsorptionsgrad und Standardoberflächenimpedanz
(ISO/DIS 10534-2:2022)
Acoustique - Détermination des propriétés acoustiques aux tubes d’impédance - Partie
2: Méthode à deux microphones pour le coefficient d’absorption acoustique normal et
l’impédance de surface normale (ISO/DIS 10534-2:2022)
Ta slovenski standard je istoveten z: prEN ISO 10534-2
ICS:
17.140.01 Akustična merjenja in Acoustic measurements and
blaženje hrupa na splošno noise abatement in general
oSIST prEN ISO 10534-2:2022 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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oSIST prEN ISO 10534-2:2022
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oSIST prEN ISO 10534-2:2022
DRAFT INTERNATIONAL STANDARD
ISO/DIS 10534-2
ISO/TC 43/SC 2 Secretariat: DIN
Voting begins on: Voting terminates on:
2022-09-15 2022-12-08
Acoustics — Determination of acoustic properties in
impedance tubes —
Part 2:
Two-microphone technique for normal sound absorption
coefficient and normal surface impedance
ICS: 17.140.01
This document is circulated as received from the committee secretariat.
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENT AND APPROVAL. IT IS
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oSIST prEN ISO 10534-2:2022
ISO/DIS 10534-2:2022(E)
DRAFT INTERNATIONAL STANDARD
ISO/DIS 10534-2
ISO/TC 43/SC 2 Secretariat: DIN
Voting begins on: Voting terminates on:
Acoustics — Determination of acoustic properties in
impedance tubes —
Part 2:
Two-microphone technique for normal sound absorption
coefficient and normal surface impedance
ICS: 17.140.01
This document is circulated as received from the committee secretariat.
COPYRIGHT PROTECTED DOCUMENT
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENT AND APPROVAL. IT IS
© ISO 2022
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ii
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PROVIDE SUPPORTING DOCUMENTATION. © ISO 2022
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oSIST prEN ISO 10534-2:2022
ISO/DIS 10534-2:2022(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Terms, Definitions and symbols . .1
3 Principle . 4
4 Test equipment .5
4.1 Construction of the impedance tube . 5
4.2 Working frequency range . 6
4.3 Length of the impedance tube . 6
4.4 Microphones . 7
4.5 Positions of the microphones . 7
4.6 Acoustic centre of the microphone . 8
4.7 Test sample holder. 8
4.8 Signal processing equipment . 8
4.9 Loudspeaker . 9
4.10 Signal generator. 9
4.11 Thermometer, barometer and hygrometer . 9
5 Preliminary test and measurements . 9
6 Test specimen mounting .10
7 Test procedure .11
7.1 Specification of the reference plane . 11
7.2 Determination of the sound velocity, wavelength and characteristic impedance . 11
7.3 Selection of the signal amplitude .12
7.4 Selection of the number of averages .12
7.5 Correction for microphone mismatch .12
7.5.1 Measurement repeated with the microphones interchanged .13
7.5.2 Predetermined calibration factor . 14
7.6 Determination of the transfer function between the two locations .15
7.7 Determination of the reflection coefficient . 16
7.8 Determination of the sound absorption coefficient . 16
7.9 Determination of the specific acoustic impedance ratio . 16
7.10 Determination of the specific acoustic admittance ratio . 17
8 Precision .17
9 Test report .17
Annex A (normative) Preliminary measurements .21
Annex B (normative) Procedure for the one-microphone technique .23
Annex C (informative) Theoretical background .24
Annex D (informative) Error sources .26
Annex E (informative) Estimation of diffuse sound absorption coefficient ast of locally
reacting absorbers from the results of this part of ISO 10534 .28
Annex F (informative) Estimation of intrinsic properties .29
Bibliography .31
iii
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oSIST prEN ISO 10534-2:2022
ISO/DIS 10534-2:2022(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non- governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
Draft International Standards adopted by the technical committees are circulated to the member
bodies for voting. Publication as an International Standard requires approval by at least 75 % of the
member bodies casting a vote.
International Standard ISO 10534-2 was prepared by Technical Committee ISO/TC 43, Acoustics,
Subcommittee SC 2, Building acoustics.
ISO 10534 currently consists of the following parts:
— Part 1: Method using standing wave ratio
— Part 2: 2-microphone technique for normal sound absorption coefficient and normal surface
impedance
Annexes A and B form an integral part of this part of ISO 10534. Annexes C to G are for information only.
iv
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oSIST prEN ISO 10534-2:2022
DRAFT INTERNATIONAL STANDARD ISO/DIS 10534-2:2022(E)
Acoustics — Determination of acoustic properties in
impedance tubes —
Part 2:
Two-microphone technique for normal sound absorption
coefficient and normal surface impedance
1 Scope
This test method covers the use of an impedance tube, two microphone locations and a frequency
analysis system for the determination of the sound absorption coefficient of sound absorbing materials
for normal sound incidence. It can also be applied for the determination of the acoustical surface
impedance or surface admittance of sound absorbing materials. As an extension, it can also be used to
assess intrinsic properties of homogeneous acoustical materials such as their characteristic impedance,
characteristic wavenumber, dynamic mass density and dynamic bulk modulus.
[1]
The test method is similar to the test method specified in ISO 10534-1 in that it uses an impedance
tube with a sound source connected to one end and the test sample mounted in the tube at the
other end. However, the measurement technique is different. In this test method, plane waves are
generated in a tube by a noise source, and the decomposition of the interference field is achieved by the
measurement of acoustic pressures at two fixed locations using wall-mounted microphones or an in-
tube traversing microphone, and subsequent calculation of the complex acoustic transfer function and
quantities reported in the previous paragraph. The test method is intended to provide an alternative,
[1]
and generally much faster, measurement technique than that of ISO 10534-1 .
Normal incidence absorption coefficients coming from impedance tube measurements are not
comparable with random incidence absorption coefficients measured in reverberation rooms according
[2]
to ISO 354. The reverberation room method will (under ideal conditions) determine the sound
absorption coefficient for diffuse sound incidence. However, the reverberation room method requires
test specimens which are rather large. The impedance tube method is limited to studies at normal and
plane incidence and requires samples of the test object which are of the same size as the cross-section
of the impedance tube. For materials that are locally reacting only, diffuse incidence sound absorption
coefficients can be estimated from measurement results obtained by the impedance tube method (see
Annex E).
+ jtω
Through the whole document, a e time convention is used.
2 Terms, Definitions and symbols
For the purposes of this part of ISO 10534 the following definitions apply.
2.1
sound absorption coefficient at normal incidence
α
n
ratio of the sound power entering the surface of the test object (without return) to the incident sound
power for a plane wave at normal incidence
Note 1 to entry: “Plane wave” here describes a wave whose value, at any moment, is constant over any plane
perpendicular to its direction of propagation. “Normal incidence” describes the direction of the longest axis of
the impedance tube.
1
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oSIST prEN ISO 10534-2:2022
ISO/DIS 10534-2:2022(E)
2.2
sound pressure reflection coefficient at normal incidence
r
complex ratio of the reflected wave sound pressure amplitude to that of the incident wave in the
reference plane for a plane wave at normal incidence
2.3
reference plane
cross-section of the impedance tube for which the reflection coefficient r or the impedance Z or the
admittance G are determined and which is usually the surface of the test object, if flat
Note 1 to entry: The reference plane is assumed to be at x = 0.
2.4
normal surface impedance
Z
ratio of the complex sound pressure p(x=0) to the normal component of the complex sound particle
velocity v(x=0) at an individual frequency in the reference plane defined as x=0. The particle velocity
vector has a positive direction pointing towards the interior of the tested object. Z is expressed in
-3
newton second per cubic meter (N.s.m )
2.5
normal surface admittance
G
3 -
inverse of the normal surface impedance Z. G is expressed in cubic meter per newton per second (m .N
1 -1
.s )
2.6
wave number in air
k
0
variable, expressed in radian per metre, defined by
kc==ω//2π fc
00 0
where
ω
is the angular frequency;
f
is the frequency;
c is the speed of sound in the air
0
Note 1 to entry: In general, the wave number is complex, so
kk=−′ jk"
00 0
where
k is the real component k =2πλ/ ;
()
0' 00
λ
is the wavelength in air;
0
k
is the imaginary component which is the attenuation constant, in radian per metre.
0"
2
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oSIST prEN ISO 10534-2:2022
ISO/DIS 10534-2:2022(E)
2.7
material characteristic wave number
k
c
variable, expressed in radian per meter, defined by
kc==ωπ//2 fc=ω pK/
ceqeq
where
c is the speed of sound inside the material;
p
is the material dynamic mass density (defined in 2.9);
eq
K
is the material bulk modulus (defined in 2.10)
eq
2.8
material characteristic impedance
Z
c
variable, expressed in newton. second per cubic metre, defined by
Zp= K
ceqeq
2.9
material dynamic mass density
p
eq
describes the visco-inertial dissipation inside the tested material. The dynamic mass density can differ
-3
from the static (volume-averaged) value. It is expressed in kg.m
2.10
material dynamic bulk modulus
K
eq
describes the thermal dissipation inside the tested material. The dynamic bulk modulus can differ from
-2
the static (volume-averaged) value. It is expressed in N.m (or equivalently in pascal)
2.11
complex sound pressure
p
frequency-domain spectrum of the sound pressure time signal
2.12
cross spectrum
S
12
product pp *, determined from the complex sound pressures p and p at two microphone positions
21 1 2
Note 1 to entry: * means the complex conjugate.
2.13
auto spectrum
S
11
product pp *, determined from the complex sound pressure p at microphone position one
11 1
Note 1 to entry: * means the complex conjugate.
3
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oSIST prEN ISO 10534-2:2022
ISO/DIS 10534-2:2022(E)
2.14
transfer function
H
12
transfer function from microphone position one to two, defined by the complex ratio pp//=SS
21 12 11
12/
or SS/ , or []()SS//()SS
22 21 12 11 22 21
2.15
calibration factor
H
c
factor used to correct for amplitude and phase mismatches between the microphones
Note 1 to entry: See 7.5.2.
2.16
local reaction
a material for which the pressure and velocity fields at a given point on the surface are independent
on the behaviour at other points of the surface is called a locally reacting material. This local reaction
behavior infers specific properties for a material: its surface impedance is independent on the
incidence angle of a plane wave impinging the material. Homogeneous honeycomb structures and
perforated plates are examples of possible locally reacting materials (see Figure 1, left). Note that for a
locally reacting material, its absorption coefficient depends on the angle of incidence as its reflection
coefficient does as well
Key
1 locally reacting material sample 4 plane wave impinging the sample
2 non-locally reacting material sample 5 plane wave impinging the sample with a different angle
3 rigid & impervious backing A locally reacting material sample
B non-Locally reacting material sample
Figure 1 — Propagation of plane waves inside a locally reacting material sample and
comparison to a non-locally reacting material sample
2.17
bulk or extended reaction
the assumption of bulk or extended reaction implies that the reaction inside the material does not
occur only normal to the surface. The reaction in each point is hence dependent on the reaction of the
neighbouring points. Examples of materials experiencing bulk reactions are foams made of multiple
pores and fibrous with fibres not parallel to each other's (see Figure 1, right)
3 Principle
The test sample is mounted at one end of a straight, rigid, smooth and airtight impedance tube. Plane
waves are generated in the tube by a sound source emitting a signal such as a random noise, pseudo-
random sequence, or a deterministic signal such as a chirp signal, and the sound pressures are measured
at two locations near to the sample. The complex acoustic transfer function of the two microphone
signals is determined and used to compute the normal-incidence complex reflection coefficient (see
4
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oSIST prEN ISO 10534-2:2022
ISO/DIS 10534-2:2022(E)
Annex C), the normal-incidence absorption coefficient, and the normal surface impedance of the test
material. From two distinct measurements, the intrinsic properties of the material (characteristic wave
number, characteristic impedance, dynamic mass density and dynamic bulk modulus) can be assessed
(see Annex G) assuming this material is homogeneous.
The quantities are determined as functions of the frequency (or frequency bands as detailed in
[3]
ISO 266 ) with a frequency resolution which is determined from the sampling frequency and the record
length of the digital frequency analysis system used for the measurements. The usable frequency range
depends on the lateral dimensions or diameter of the tube and the spacing between the microphone
positions. An extended frequency range may be obtained from the combination of measurements with
different lateral dimensions (or diameter) and spacings.
The measurements may be performed by employing one of two techniques:
1) two-microphone method (using two microphones in fixed locations);
2) one-microphone method (using one microphone successively in two locations).
Technique 1: requires a pre-test or in-test correction procedure to minimize the amplitude and phase
difference characteristics between the microphones; however, it combines speed, high
accuracy, and ease of implementation. Technique 1 is recommended for general test
purposes.
Technique 2: has particular signal generation and processing requirements and may necessitate more
time; however, it eliminates phase mismatch between microphones and allows the se-
lection of optimal microphone locations for any frequency. Technique 2 is recommended
for measurements with higher precision, and its requirements are described in more
detail in Annex B.
4 Test equipment
4.1 Construction of the impedance tube
The apparatus is essentially a tube with a test sample holder at one end and a sound source at the other.
Microphone ports are usually located at two or three locations along the wall of the tube (depending
on the chosen microphone spacing), but variations involving a centred mounted microphone or probe
microphone are possible.
The impedance tube shall be straight with a uniform cross-section (diameter or cross dimension within
±0,2 %) and with rigid, smooth, non-porous walls without holes or slits (except for the microphone
positions) in the test section. The walls shall be heavy and thick enough so that they are not excited to
vibrations by the sound signal and show no vibration resonances in the working frequency range of the
tube. For metal walls, a thickness of about 5 % of the diameter is recommended for circular tubes. For
rectangular tubes the corners shall be made rigid enough to prevent distortion of the side wall plates.
It is recommended that the side wall thickness be about 10 % of the cross dimension of the tube. Tube
walls made of concrete shall be sealed by a smooth adhesive finish to ensure air tightness. The same
holds for tube walls made of wood; these should be reinforced and damped by an external coating of
steel or lead sheets.
The shape of the cross-section of the tube is arbitrary, in principle. Circular or rectangular (if
rectangular, then preferably square) cross-sections are recommended.
If rectangular tubes are composed of plates, care shall be taken that there are no air leaks (e.g. by
sealing with adhesives or with a finish). Tubes should be sound and vibration isolated against external
noise or vibration.
5
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oSIST prEN ISO 10534-2:2022
ISO/DIS 10534-2:2022(E)
4.2 Working frequency range
The working frequency range is
ff<< f (1)
lu
where
is the lower working frequency of the tube;
f
l
f is the operating frequency;
is the upper working frequency of the tube.
f
u
f is limited by the accuracy of the signal processing equipment and the spacing between the 2
l
microphone positions.
f is chosen to avoid the occurrence of non-plane wave mode propagation. The condition for f is:
u u
df<<05,:80 λ ⋅dc,58 (2)
uu 0
for circular tubes with the inside diameter d in metres and f in hertz.
u
df<<05,:00 λ ⋅dc,50 (3)
uu 0
for rectangular tubes with the maximum side length d in metres; c is the speed of sound in metres per
0
second given by Equation (5).
The spacing s in metres between the microphones shall be chosen to avoid singularities when the
distance of the two microphone positions is equal to a multiple of half the operating wavelength. The
first singularity is avoided when ensuring that
fs⋅< 04, 5 c (4)
u 0
The lower frequency limit is dependent on the spacing between the microphones and the accuracy of the
analysis system but, as a general guide, the microphone spacing should exceed 1,5 % of the wavelength
corresponding to the lower frequency of interest, provided that the requirements of Equation (4) are
satisfied. A larger spacing between the microphones enhances the accuracy of the measurements for
these low frequencies but reduces the value of the upper working frequency.
Different microphone spacings can be used to cover a wider frequency range than the one allowed
for a single spacing. In this case, the working frequency ranges shall overlap by about one octave (as
described in ISO 266, “Acoustics — Preferred frequencies”). The averaging technique used to obtain the
averaged and combined result should be at least mentioned.
Different impedance tubes can also be used to cover a wider frequency range than the one allowed for a
single tube (see section 9.i).
4.3 Length of the impedance tube
The tube should be long enough to cause plane wave development between the source and the sample.
Microphone measurement points shall be in the plane wave field.
The loudspeaker generally will produce non-plane waves besides the plane wave. They will die out
within a distance of about three tube diameters or three times the maximum lateral dimensions of
rectangular tubes for frequencies below the lower cut-off frequency of the first higher mode. Thus, it is
recommended that microphones be located no closer to the source than suggested above.
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oSIST prEN ISO 10534-2:2022
ISO/DIS 10534-2:2022(E)
Test samples will also cause proximity distortions to the acoustic field. It is recommended to have a
minimum spacing between microphone and sample of ½ diameter or ½ maximum lateral dimension
but this spacing should be increased to 2 diameters or 2 times the maximum lateral dimension for
non-planar materials or materials with a few small perforations (as perforated plates with a single
millimetric perforation).
4.4 Microphones
Microphones of identical type shall be used in each location. When side-wall-mounted microphones are
used, the diameter of the microphones shall be small compared to cf/ .
0 u
For side-wall mounting, it is recommended to use microphones of the pressure type. For in-tube
microphones, it is recommended to use microphones of the free-field type.
4.5 Positions of the microphones
When side-wall-mounted microphones are used, each microphone shall be mounted with the diaphragm
flush with the interior surface of the tube. A small recess is often necessary to prevent the microphone
to be inserted inside the tube (see Figure 2); the recess should be kept small and be identical for both
microphone mountings. The microphone grid shall be sealed tight to the microphone housing and there
shall be a sealing between the microphone and the mounting hole.
Key
1 microphone
2 sealing
Figure 2 — Examples of typical microphone mounting
When using a single microphone in two successive wall positions, the microphone position not in use
shall be sealed to av
...
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