SIST EN ISO 10534-1:2002

Acoustics - Determination of sound absorption coefficient and impedance in impedances tubes - Part 1: Method using standing wave ratio (ISO 10534-1:1996)

Specifies a method for the determination of the sound absorption coefficient, reflection factor, surface impedance or admittance of materials and objects. The values are determined by evaluation of the standing wave pattern of a plane wave in a tube, which is generated by the superposition of an incident sinusiodal plane wave with the plane wave reflected from the test object.

Akustik - Bestimmung des Schallabsorptionsgrades und der Impedanz in Impedanzrohren - Teil 1: Verfahren mit Stehwellenverhältnis (ISO 10534-1:1996)

Anwendungsbereich
1.1 Dieser Teil von ISO 10534 legt die Bestimmung des Schallabsorptionsgrades, des Reflexions-grades
und der Oberflächenimpedanz oder Oberflächenadmittanz von Werkstoffen oder Gegenständen
Inhalt
fest. Die Werte werden bei senkrechtem Schalleinfall durch Berechnung des Stehwellenfeldes einer
ebenen Welle in einem Rohr bestimmt, das durch Überlagerung einer einfallenden ebenen, sinusförmigen
Welle mit einer vom Prüfgegenstand reflektierten ebenen Welle erzeugt wird.
Dieses Verfahren kann zur Bestimmung des Schallabsorptionsgrades von Absorbern bei senkrechtem
Schalleinfall angewendet werden. Es kann außerdem zur Bestimmung der akustischen Oberflächen-impedanz
oder Oberflächenadmittanz von absorbierenden Werkstoffen angewendet werden. Es ist für die
Untersuchung von Parametern und die Auslegung von Absorbern gut geeignet, da nur kleine Proben des
absorbierenden Werkstoffes benötigt werden.
1.2 Im Vergleich zur Messung des Schallabsorptionsgrades in einem Hallraum (ISO 354) bestehen
einige charakteristische Unterschiede.
Die Impedanzrohrmethode kann zur Bestimmung des Reflexionsfaktors und auch der Impedanz oder
Admittanz angewendet werden. Der Schall trifft senkrecht auf die Oberfläche des Gegenstandes. Bei der
Hallraummethode wird (unter idealisierten Bedingungen) der Schallabsorptionsgrad bei diffusem Schall-einfall
bestimmt.
Die Impedanzrohrmethode beruht auf der Existenz einer ebenen einfallenden Welle und liefert unter dieser
Bedingung genaue Werte (Mess- und Montagefehler ausgenommen). Die Bewertung des Schallabsorp-tionsgrades
in einem Hallraum beruht auf einer Anzahl vereinfachender und ungefährer Annahmen, die
das Schallfeld und die Größe des Absorbers betreffen. Daher werden mitunter Schallabsorptionsgrade
mit Werten größer als Eins erhalten.

Acoustique - Détermination du facteur d'absorption acoustique et de l'impédance acoustique a l'aide du tube d'impédance - Partie 1: Méthode du taux d'ondes stationnaires (ISO 10534-1:1996)

La CEI/TR 60479-4:2011 résume les paramètres essentiels de la foudre et leur variabilité dans la mesure où ils s'appliquent aux corps humains et aux animaux domestiques. Les interactions directes et indirectes probables entre la foudre et le corps des êtres vivants sont indiquées. Les effets résultants dus au courant de foudre pour l'organisme sont décrits. L'objet de ce rapport est de montrer les différences existant entre les effets dus à la foudre sur le corps humain et sur celui des animaux domestiques en comparaison avec les effets des chocs électriques en provenance des installations électriques.

Akustika - Ugotavljanje koeficienta absorpcije in impedance zvoka v Kundtovi cevi – 1. del: Metoda razmerja v stoječem valovanju (ISO 10534-1:1996)

General Information

• Status: Published
• Publication Date: 30-Nov-2002
• ICS: 17.140.01 - Acoustic measurements and noise abatement in general
• Technical Committee: AKU - Acoustics
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 01-Dec-2002
• Due Date: 01-Dec-2002
• Completion Date: 01-Dec-2002
• Directive: 89/106/EEC - Construction products
• Ref Project: EN ISO 10534-1:2001 - Acoustics - Determination of sound absorption coefficient and impedance in impedances tubes - Part 1: Method using standing wave ratio (ISO 10534-1:1996)

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN ISO 10534-1:2002
01-december-2002
$NXVWLND8JRWDYOMDQMHNRHILFLHQWDDEVRUSFLMHLQLPSHGDQFH]YRNDY.XQGWRYLFHYL
±GHO0HWRGDUD]PHUMDYVWRMHþHPYDORYDQMX,62
Acoustics - Determination of sound absorption coefficient and impedance in impedances
tubes - Part 1: Method using standing wave ratio (ISO 10534-1:1996)
Akustik - Bestimmung des Schallabsorptionsgrades und der Impedanz in
Impedanzrohren - Teil 1: Verfahren mit Stehwellenverhältnis (ISO 10534-1:1996)
Acoustique - Détermination du facteur d'absorption acoustique et de l'impédance
acoustique a l'aide du tube d'impédance - Partie 1: Méthode du taux d'ondes
stationnaires (ISO 10534-1:1996)
Ta slovenski standard je istoveten z: EN ISO 10534-1:2001
ICS:
17.140.01 $NXVWLþQDPHUMHQMDLQ Acoustic measurements and
EODåHQMHKUXSDQDVSORãQR noise abatement in general
SIST EN ISO 10534-1:2002 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 10534-1:2002

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SIST EN ISO 10534-1:2002
EUROPEAN STANDARD
EN ISO 10534-1
NORME EUROPÉENNE
EUROPÄISCHE NORM
June 2001
ICS 17.140.01
English version
Acoustics - Determination of sound absorption coefficient and
impedance in impedances tubes - Part 1: Method using standing
wave ratio (ISO 10534-1:1996)
Acoustique - Détermination du facteur d'absorption Akustik - Bestimmung des Schallabsorptionsgrades und
acoustique et de l'impédance acoustique à l'aide du tube der Impedanz in Impedanzrohren - Teil 1: Verfahren mit
d'impédance - Partie 1: Méthode du taux d'ondes Stehwellenverhältnis (ISO 10534-1:1996)
stationnaires (ISO 10534-1:1996)
This European Standard was approved by CEN on 13 May 2001.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the Management Centre or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the Management Centre has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,
Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2001 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 10534-1:2001 E
worldwide for CEN national Members.

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SIST EN ISO 10534-1:2002
Page 2
EN ISO 10534-1:2001
Foreword
The text of the International Standard from Technical Committee ISO/TC 43 "Acoustics" of the
International Organization for Standardization (ISO) has been taken over as an European Standard
by Technical Committee CEN/TC 126 "Acoustic properties of building products and of buildings", the
secretariat of which is held by AFNOR.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by December 2001, and conflicting national standards
shall be withdrawn at the latest by December 2001.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Czech
Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg,
Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and the United Kingdom.
Endorsement notice
The text of the International Standard ISO 10534-1:1996 has been approved by CEN as a European
Standard without any modification.
NOTE: Normative references to International Standards are listed in annex ZA (normative).

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SIST EN ISO 10534-1:2002
Page 3
EN ISO 10534-1:2001
Annex ZA
(normative)
Normative references to international publications with their relevant European
publications
This European Standard incorporates by dated or undated reference, provisions from other
publications. These normative references are cited at the appropriate places in the text and the
publications are listed hereafter. For dated references, subsequent amendments to or revisions
of any of these publications apply to this European Standard only when incorporated in it by
amendment or revision. For undated references the latest edition of the publication referred to
applies (including amendments).
NOTE Where an International Publication has been modified by common modifications, indicated by
(mod.), the relevant EN/HD applies.
Publication Year Title EN/HD Year
ISO 266 1975 Acoustics - Preferred frequencies for EN ISO 266 1997
measurements
Acoustics - Measurement of sound insulation prEN ISO 354 2000
ISO 354 1985
in a reverbaration room

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SIST EN ISO 10534-1:2002

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SIST EN ISO 10534-1:2002
INTERNATIONAL
IS0
STANDARD
10534-l
First edition
1996-I 2-l 5
Acoustics - Determination of sound
absorption coefficient and impedance in
impedance tubes -
Part 1:
Method using standing wave ratio
Acoustique -
Dgtermination du facteur d’absorption acoustique et
de /‘imp&dance acoustique a I’aide du tube d/imp&dance -
Partie 1: M&hode du taux d’ondes stationnaires
Reference number
IS0 10534-I : 1996(E)

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SIST EN ISO 10534-1:2002
IS0 10534=1:1996(E)
Page
Contents
1
...........................................................................................
1 Scope
1
Normative references .
2
2
Definitions .
3
3
4 Principle .
3
..............................................................................
5 Fundamentals
5
...........................................................................
6 Test equipment
IO
..........................................
7 Preliminary tests and measurements
IO
.......................................................
8 Mounting of the test sample
IO
..............................................................................
9 Test methods
.................... 11
10 Transformation of reflection factor and impedance
12
...................................................................................
11 Test report
Annexes
14
A Preliminary measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6 Verification of the test equipment
19
C Pressure-release termination of test sample . . . . . . . . . . . . . . . . .I.
D Determination of diffuse sound absorption coefficient a,, of
20
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
locally reacting absorbers
0 IS0 1996
All rights reserved. Unless otherwise specified, no part of this publication may be
reproduced or utilized in any form or by any means, electronic or mechanical, including
photocopying and microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case Postale 56 l CH-1211 Geneve 20 l Switzerland
Printed in Switzerland
ii

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SIST EN ISO 10534-1:2002
IS0 10534=1:1996(E)
@ IS0
Foreword
IS0 (the International Organization for Standardization) is a worldwide fed-
eration of national standards bodies (IS0 member bodies). The work of
preparing International Standards is normally carried out through IS0
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. IS0
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 IS0 10534-I was prepared by Technical Committee
lSO/TC 43, Acoustics, Subcommittee SC 2, Building acoustics.
IS0 10534 consists of the following parts, under the general title Acous-
tics - Determination of sound absorption coefficient and impedance in
impedance tubes:
Part 1: Method using standing wave ratio
- Part 2: Method using two microphones
Annexes A, B and C form an integral part of this part of IS0 10534.
Annex D is for information only.

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SIST EN ISO 10534-1:2002
This page intentionally left blank

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SIST EN ISO 10534-1:2002
INTERNATIONAL STANDARD @ IS0 IS0 10534=1:1996(E)
Acoustics - Determination of sound absorption coefficient and
impedance in impedance tubes -
Part 1:
Method using standing wave ratio
Sound absorption coefficients exceeding the value 1
1 Scope
are therefore sometimes obtained.
1.1 This part of IS0 10534 specifies a method for
The impedance tube method requires samples of the
the determination of the sound absorption coefficient,
test object which are the size of the cross-sectional
reflection factor and surface impedance or surface
area of the impedance tube. The reverberation room
admittance of materials and objects. The values are
method requires test objects which are rather large
determined for normal sound incidence by evaluation
and can also be applied to test objects with pro-
of the standing wave pattern of a plane wave in a
nounced structures in the lateral and/or normal direc-
tube, which is generated by the superposition of an
tions. Measurements with such objects in the
incident sinusoidal plane wave with the plane wave
impedance tube must be interpreted with care
reflected from the test object.
(see 9.1).
This method can be used for the determination of the
For the computational transformation of the test re-
sound absorption coefficient of sound absorbers for
sults from the impedance tube method (normal inci-
normal sound incidence. It can further be used for the
dence) to the situation of diffuse sound incidence, see
determination of the acoustical surface impedance or
annex D.
surface admittance of sound-absorbing materials. It is
well suited for parameter studies and for the design of
I.3 This part of IS0 10534 gives preference to nu-
sound absorbers, because only small samples of the
merical methods of evaluation instead of graphical
absorber material are needed.
methods, because computers which can perform
these computations are assumed to be available.
Some of the quantities in the formulae are complex.
1.2 There are some characteristic differences be-
The arguments of trigonometric functions are in
tween this method and the measurement of sound
radians.
absorption in a reverberation room (see IS0 354).
The impedance tube method can be used for the de-
termination of the reflection factor and also the im-
2 Normative references
pedance or admittance. The sound is incident normally
on the object surface. The reverberation room method
will (under idealized conditions) determine the sound
The following standards contain provisions which,
absorption coefficient for random sound incidence.
through reference in this text, constitute provisions of
this part of IS0 10534. At the time of publication, the
The impedance tube method relies on the existence editions indicated were valid. All standards are subject
of a plane incident sound wave and gives exact values to revision, and parties to agreements based on this
under this condition (measuring and mounting errors
part of IS0 10534 are encouraged to investigate the
excluded). The evaluation of the sound absorption co- possibility of applying the most recent editions of the
efficient in a reverberation room is based on a number
standards indicated below. Members of IEC and IS0
of simplifying and approximate assumptions concern-
maintain registers of currently valid International Stan-
ing the sound field and the size of the absorber. dards.

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SIST EN ISO 10534-1:2002
@ IS0
IS0 10534=1:1996(E)
IS0 266:- 1), Acoustics - Preferred frequencies. 3.10 normalized impedance, Z: Ratio of the imped-
ance Z to the characteristic impedance ZO:
IS0 354:1985, Acoustics - Measurement of sound
absorption in a reverberation room. 2 = z/z,
3.11 normalized admittance, g: Product of the
admittance G and the characteristic impedance ZO:
3 Definitions
g = ZoG
For the purposes of this part of IS0 10534, the follow-
3.12 standing wave ratio, S: Ratio of the sound
ing definitions apply.
pressure amplitude at a pressure maximum, lpmax I,
3.1 sound absorption coefficient, a: Ratio of the
to that at an adjacent pressure minimum, lpmin 1 (if
sound power entering the surface of the test object
necessary after correction for varying values at the
(without return) to the incident sound power for a
minima due to sound attenuation in the impedance
plane wave at normal incidence.
tube):
3.2 sound pressure reflection factor at normal
incidence, r: Complex ratio of the pressure amplitude
of the reflected wave to the incident wave in the refer-
3.13 standing wave ratio with attenuation, s,:
ence plane for a plane wave at normal incidence.
Standing wave ratio of the nth maximum to the lath
minimum.
3.3 reference plane: Cross-section of the imped-
ance tube for which the reflection factor I- or the im-
3.14 free-field wave number, kO:
pedance 2 or the admittance G are determined and
which is usually the surface of flat test objects. It is
k. = m/c, = 2Tcflco
assumed to be at x = 0.
3.4 field impedance, Z(X): Ratio of the sound press-
w is the angular frequency;
ure p(x) to the particle velocity V(X) (directed into the
test object) at a point x in the sound field.
is the frequency;
f
is the speed of sound.
CO
35 . impedance in the reference plane, 2,: Ratio at
the reference plane of the sound pressure p to the
In general the wave number is complex, so
sound particle velocity v:
ko. = ko’ - jko”
zr = p/v
3.6 surface impedance, Z: Complex ratio of the
k,’ is the real component (ko’ = 27c/&);
sound pressure p(O) to the normal component of the
sound particle velocity v(O) at the reference plane.
k,” is the imaginary component which is the at-
tenuation constant in nepers per metre.
3.7 surface admittance, G: Complex ratio of the
normal component of the sound particle velocity
v(O)
3.15 phase of reflection (factor), @: Results from
to the sound pressure p(O) in the reference plane.
the representation of the complex reflection factor by
magnitude and phase:
3.8 surface admittance, G,: Admittance component
at, and normal to, the surface of the test object.
r’ + jr" = lri. ej@ =
r= Irl (cos @ + jsin @)
3.9 characteristic impedance, Zo: Field impedance
r = ,12 + y”2
(in the direction of propagation) in a single plane wave:
II J
20 = Poco
di=arctanc
r’
where
r’ =
is the density of the medium (air); r COS @
PO
I I
is the speed of sound in the medium.
CO
I/
r = r sin@
I I
1) To be published. (Revision of IS0 266:1975)
2

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SIST EN ISO 10534-1:2002
IS0 10534=1:1996(E)
@ IS0
3.16 working frequency range, f: Range within 5 Fundamentals
which measurements can be performed in a given
impedance tube:
5.1 General conditions
Ji The method of this part of IS0 10534 relies heavily on
the fact that there exist only plane incident and re-
where Ji and fU are the lower and upper frequency
flected waves propagating parallel to the tube axis in
limits, respectively.
the test section of the tube (the section where the
standing wave pattern is explored). The generation of
other wave forms (higher modes) shall be avoided
3.17 test section: Section of the impedance tube
(see annex B). It is further assumed that the sound
with no higher modes, in which the standing wave
wave propagates in the tube without attenuation. Cor-
can be explored.
rections can be applied for residual attenuations
due to friction and thermal losses at the tube walls.
Methods for the determination of these corrections
3.18 installation section: Section of the impedance
are given in annex A.
tube in which the test object is installed.
5.2 Formulae
NOTE 1 The time factor e-@t is omitted in the following
4 Principle
formulae.
The test object is mounted at one end of a straight,
The incident sound wave pi is assumed to be plane,
rigid, smooth impedance tube which is a tight fit (see
harmonic in time with frequency f and angular fre-
figure 1). The incident plane sinusoidal sound wave pi
quency w = 271~fi without attenuation (for a correction
is generated by a loudspeaker at the other end of the
of attenuation, see annex A), and directed along the
tube. The superposition p = pi + pr of the incident
axis of the impedance tube (in the negative
wave pi with the wave reflected from the test object,
x-direction)
pr, produces a standing wave pattern in the tube. The
evaluation proceeds from the measured quantities
pi(X) = poeikoX
. . .
(either in a linear or in a logarithmic scale) of the sound
pressure amplitudes (p(x,i”) 1 at pressure minima
w
2?f
(one or more), and Ip(x,,,) 1 at pressure maxima.
=- =-
. . .
(2)
k0
These data are sufficient to determine the sound ab-
co Co
sorption coefficient. In addition, the distance x,i” 1 of
the first sound pressure minimum from the reference where the amplitude p. is arbitrary.
plane at x = 0 (which is usually the plane where the
The wave which is reflected from the test object hav-
surface of the test object is placed), and the sound
ing a reflection factor Y is then
wavelength Lo must be determined to give the reflec-
tion factor Y and the impedance Z or the admittance
- jkox
G = l/Z.
. . .
(3)
P,(X) = r * PO *e
NOTE - The first pressure maximum to be measured shall normally be chosen to lie between the first two minima, as shown.
Figure 1 - Standing wave pattern in a test tube

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SIST EN ISO 10534-1:2002
@ IS0
IS0 10534=1:1996(E)
A pressure minimum occurs when they are in
The particle velocities of the waves (counted positive oppo-
site phases
in the negative x-direction, see figure 1) are, respec-
tively
1
I . .
(4)
=- PiCx)
vi
ZO
Using the standing wave ratio
=-Ipr(x) . . .
(5)
. . . (12)
q(x)
s = lpmax l/iPmin 1
ZO
The field impedance (in the negative x-direction) in the
standing wave is
I-
I+1 I
=-
S and . . .
(13)
PiCx> + P,Cx> = z PiCx> + P,Cx>
-r
Z(x) = 6) I II
y(x) + v,(x) O PiCx)- P,(x) * * ’
s- I
=-
r . . .
(14)
I I
s+l
5.3 Inter-relationships
At the reference plane x = 0, therefore
5.5 Sound absorption coefficient
%*a
. . .
z=z(o)=z, 1 (7)
-
The sound absorption coefficient then follows from
equations (9), (12) and (14) with the measured ampli-
tudes lpmax I and lpmin I at a given frequency.
from which follows
(Z/Zo)- 1 If the sound pressure in the impedance tube is meas-
. . .
(8)
ured in a logarithmic scale (in decibels), and the differ-
r= (Z/Z(J)+1
ence in level between the pressure maximum and the
pressure minimum is AL dB, then
The sound absorption coefficient cx for plane waves is
s = 1 ow20
. . . (15)
a=l-lr12 . . .
(9)
The sound absorption coefficient then follows from
where I . . . I indicates the magnitude of a complex
quantity.
4 x 1 oM'*O
. . .
a= (16)
(1 o”‘*O + I)2
Equations (7) to (9) are the inter-relationships between
the quantities which are determined according to this
part of IS0 10534. If the reference plane is in the sur-
face of a flat test object, these quantities are the sur-
5.6 Reflection factor
face impedance, the reflection factor (for normal
sound incidence) and the absorption coefficient (for
The phase angle CD of the complex reflection factor
normal sound incidence) of the test object, respec-
tively. If the reference plane is in front of the test ob-
r +.i@ . . .
r= (17)
I I
coefficient remains
ject (X > 0), the absorption
unchanged; the reflection factor r and the impedance
follows from the phase co ndition for a pressure mini-
Z will change to quantities which are said to be
mum in the stand ing wave
“transformed to a distance”, namely the distance
between the reference plane and the object surface.
0 + (2n - 1)7C = 2kOXmin n
This concept is used sometimes in connection with
,
structured test objects (see 9.1 and clause 10).
refer-
for the .th minimum (n = 1, 2,. .) in front of the
ence plane (towards the sound source).
5.4 Standing wave
From this it follows that
A pressure maximum in the standing wave occurs
when pi and pr are in phase, i.e.
4x ”
mln,n_2n+l
@=n: . . .
(19)
. . .
(10)
IPmaxI = IPol-(l+ lrl)
a0
t 1
4

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SIST EN ISO 10534-1:2002
0 IS0
IS0 10534=1:1996(E)
and for the first minimum (n = 1) The test equipment shall be checked before use by a
series of tests. These help to exclude error sources
and to secure the minimum requirements. Procedures
. . .
(20)
for these tests are given in annex B.
The complex reflection factor is then
6.1 Impedance tube
r= rp + jrfr 0 0 . PI)
6.1 .I Construction
r’ =
r -COS@ . . .
(22)
I I
The impedance tube shall be straight, with a constant
N cross-section (to within 0,2 %) and with rigid, smooth,
. . .
r = r l sin @ (23
I I
non-porous walls without holes or slits in the test
section. The walls shall be heavy and thick enough
(preferably made from metal or, for tubes of larger
cross-sections, from tight and smooth concrete) not
5.7 llmpedance
to be excited to vibration by the sound signal, and not
to show vibration resonances in the working fre-
From equation (7) one obtains the normalized imped-
quency range of the tube. For metal walls, a thickness
ance 2 = Z/Zo:
of about 5 % or about 10 % of the cross-dimension is
recommended for circular or rectangular tubes, re-
z=z'+ jz" . . .
(24)
spectively. Tube walls made out of concrete shall be
sealed by a smooth tight and highly adhesive finish.
I- r’2 - r”*
The same holds for tube walls made of wood. These
. . . (25)
” = (I _ r’)* + r”2
should be re-inforced and damped by an external
coating of steel or lead sheets.
2 rN
/I -
. . .
2 - (26)
The shape of the cross-section of the tube is arbitrary,
(I- ,‘>* + r”*
in principle. Circular or rectangular cross-sections are
recommended (if rectangular, then preferably square).
If rectangular tubes are composed from plates, care
5.8 Wavelength
shall be taken that there are no slits in the corners
(e.g. by sealing with adhesives or with a finish).
The wavelength il, at the frequency f of the sound
signal follows either from the equation
. . .
(27) 6.1.2 Working frequency range
a0 = co/f
The working frequency range 6 where co is the sound velocity (for the determination
ance tube is determined by its length and cross-
of co see annex A), or from the distance between two
dimension. In order to be able to explore two pressure
pressure minima of the standing wave (with a rigid
minima even for unfavourable reflection phases, the
termination of the impedance tube) which are num-
bered IZ and m, respectively [see equation (19)] length of the test section of the tube shall be
I 3 3&/4 at the lower frequency limit Ji.
2
. . .
(28)
a 0 = z Xmin,n - Xmin,m
( )
The loudspeaker will generally produce higher wave
modes besides the plane wave. They will die out
within a distance of about three tube diameters or
three times the maximum lateral dimension of rectan-
gular impedance tubes below the lower cut-off fre-
6 Test equipment
quency of the first higher mode. Test objects with
laterally varying acoustic qualities (e.g. resonators) will
The test eq uipment consists of an impedance tube, a
produce higher-mode contributions to the reflected
test-sample holder, a probe microphone, a device to
wave.
move and position the probe microphone, signal-
processing
equipment for the microphone signal, a
The test section of the impedance tube shall avoid
loudspeaker l , a signal generator, possibly an absorber
both ranges of possible higher modes. Thus the tube
termination of the impedance tube, and a thermome-
length I between the front surface of the test object
ter.
5

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SIST EN ISO 10534-1:2002
@ IS0
IS0 10534-1:1996(E)
and the loudspeaker is related to the lower frequency
d s 0,58;1, . . .
(32)
IimitJi of the working frequency range by the condition
. . .
f”d 6 200 (33)
1~250,‘f+3d . . .
cm
for circular tubes with the inside diameter &% in metres.
where
1 is the length, in metres;
6.2 Test-sample holder
is the frequency, in hertz;
f
The sample holder is either integrated into the im-
d is the inside diameter (or the maximum side
pedance tube or is a separate unit which, during the
length), in metres.
measurement, is tightly fixed to one end of the tube.
(For possible arrangements, see figure 2.)
The upper limit of the working frequency range, fU, is
given by the possible onset of propagating higher
The length of the sample holder shall be large enough
modes. The condition for& is
to install test objects leaving air spaces of a required
depth behind them.
d s o,5ao . . .
(301
If the sample holder is a separate unit, its interior
shape and dimensions shall conform to those of the
. . .
f”d s 170 (31)
impedance tube to within 0,2 %. The mounting of the
tube shall be tight, without insertion of elastic gaskets
for rectangular tubes with fU in hertz and the maxi-
(Vaseline is recommended for sealing).
mum side length d in metres; and
b
a) With removable cover
P b
4
b) With a separate unit
Figure 2 - Sample holder
6

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SIST EN ISO 10534-1:2002
@ IS0 IS0 10534=1:1996(E)
pressure minima and for the acquisition of sound
It is recommended to integrate the sample holder into
the impedance tube and to make the installation sec- pressure amplitudes (or levels) in the maxima and
minima of the standing wave.
tion of the tube accessible by a removable cover in
order to insert the test object. The contact surfaces of
Either the microphone moves outside the impedance
this removable cover with the tube shall be carefully
tube, in which case it is connected to a probe tube
finished and the use of a sealant (Vaseline) is rec-
with a sound pick-up opening in the impedance tube,
ommended to avoid small leaks. Generally, with rec-
or the microphone itself is placed (and is movable) in
tangular tubes it is recommended to install the test
the impedance tube. The blockage of the cross-
object from the side into the tube (instead of pushing
section of the impedance tube by the microphone
it axially into the tube); it is then possible to check the
and/or supports and/or other installations shall not be
fitting and the position of the test object in the tube,
larger than 5 % in any cross-section of the test section.
to check the position and the flatness of the front sur-
face, and to reposition the reference plane precisely in
relation to the front surface. A sideways insertion also
6.3.1 Microphone with probe tube
avoids the compression of soft materials.
The probe tube shall be of metal with sufficient wall
The back plate of the sample holder shall be rigid and
thickness to avoid cross-talk of the sound field into the
shall be fixed tightly to the tube since it serves as a
probe tube through the walls. The boring of the tube
rigid termination in many measurements. A metal
should be relative to its length; a long probe tube of
plate of thickness not less than 2 cm is recommended.
small diameter may have too high an internal attenua-
tion (for a check, see annex B). In a horizontal imped-
For some tests a volume of air behind the test object,
ance tube, a centrally mounted probe tube shall be
with a depth of Ao/4, acts as a pressure-release termin-
supported to avoid flexion of the probe tube, as this
ation. Movable plugs in the sample holder are used
might give rise to higher sound modes. The supports
sometimes as rigid terminations, which allow for a
shall not be close to the sound pick-up opening.
variable depth of this air gap. They should be used
with great care, because even tiny leaks between the
In a vertical impedance tube with the installation sec-
plug and the wall of the sample holder will lead to er-
tion at the lower end, the micropho
...