ISO Muffler Stdl

© ISO 2011– All rights reserved

ISO/TC 70/WG13

Date: 2011-11-17

ISO/CD 15619

ISO/TC 70/WG13

Secretariat: SAC

Reciprocating internal combustion engines —Measurement methodology for exhaust silencers —Sound power level of exhaust noise and insertion loss using sound pressure and power loss ratio

Warning

This document is not an ISO International Standard. It is distributed for review and comment. It is subject to change without notice and may not be referred to as an International Standard.

Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are aware and to provide supporting documentation.

Document type: International standard Document subtype: Document stage: (20) Preparation Document language: E

ISO/CD 15619

© ISO 2010 – All rights reserved iii

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ISO/CD 15619

iv © ISO 2011 – All rights reserved

Contents Page

Foreword ............................................................................................................................................................ v

Introduction ........................................................................................................................................................ vi

1 Scope ...................................................................................................................................................... 1 1.1 General ................................................................................................................................................... 1 1.2 Limits of applicability ............................................................................................................................ 1 1.3 Measurement uncertainty ..................................................................................................................... 1

2 Normative references ............................................................................................................................ 2

3 Terms and definitions ........................................................................................................................... 3

4 Symbols .................................................................................................................................................. 4

5 Acoustic environment ........................................................................................................................... 4 5.1 Test environment ................................................................................................................................... 4 5.2 Criterion for adequacy of the test environment ................................................................................. 5 5.3 Criterion for background noise ............................................................................................................ 5

6 Installation and operation of source under test ................................................................................. 5 6.1 General ................................................................................................................................................... 5 6.2 Source location ...................................................................................................................................... 5 6.3 Source mounting ................................................................................................................................... 6 6.4 Operation condition .............................................................................................................................. 7

7 Instrumentation ..................................................................................................................................... 7 7.1 General ................................................................................................................................................... 7 7.2 Calibration .............................................................................................................................................. 7 7.3 Microphone windbreak ........................................................................................................................ 8 7.4 The facilities used in ICE dynamometer tests shall meet the specifications of ISO 3046-3. ......... 8

8 Measurement.......................................................................................................................................... 8 8.1 General ................................................................................................................................................... 8 8.2 Laboratory measurement ..................................................................................................................... 8 8.3 Site measurement ............................................................................................................................... 11

9 Calculation ........................................................................................................................................... 12 9.1 Calculation of insertion loss .............................................................................................................. 12 9.2 Calculation of power loss ratio .......................................................................................................... 14

10 Information to be recorded ................................................................................................................. 14 10.1 Description of the engine to which the exhaust silencer under test is fitted ............................... 14 10.2 Description of the exhaust silencer under test ................................................................................ 15 10.3 Description of equipments ................................................................................................................. 15 10.4 Acoustic environment ......................................................................................................................... 16 10.5 Test results and computational results ............................................................................................ 16

11 Information to be reported .................................................................................................................. 16

Annex A (normative) Qualification procedures for the acoustic environment ......................................... 17

Annex B (informative) The Measurement procedure for pressure loss ................................................... 22

Bibliography ...................................................................................................................................................... 23

ISO/CD 15619

© ISO 2010 – All rights reserved v

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.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of technical committees is to prepare International Standards. 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.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights.

ISO/WD 15619 was prepared by Technical Committee ISO/TC 70, Internal combustion engines.

ISO/CD 15619

vi © ISO 2011 – All rights reserved

Introduction

This International Standard specifies a method for measuring the sound power level of exhaust noise and the insertion loss of exhaust silencers which are equipped on reciprocating internal combustion engine and a method for measuring the power loss ratio of reciprocating internal combustion engine.

Sound power level of exhaust noise, transmission loss and insertion loss are parameters to characterize the acoustic performance of exhaust silencers. Transmission loss is the difference between the levels of the sound powers incident on and transmitted through the exhaust silencer which is the parameter to characterize the performance of exhaust silencer itself and is irrelevant with the reciprocating internal combustion engine while sound power level of exhaust noise and insertion loss are parameters to characterize the matching performance of exhaust silencer and reciprocating internal combustion engine. Power loss ratio and pressure loss are parameters to characterize the aerodynamic performance of exhaust silencers. Power loss ratio is an important parameter to characterize the matching performance of reciprocating internal combustion engine and exhaust silencer, whereas resistance coefficient which is closely related to pressure loss is to characterize the performance of the exhaust silencer itself and is irrelevant with the matching performance. Therefore, this International Standard utilizes the matching parameters of sound power level of exhaust noise, the insertion loss and the power loss ratio as the measurement parameters.

For sound power level of exhaust noise, the measurement results at 90° direction and 45° direction cannot be exactly the same. The measurement results at 45° direction is slightly greater than the actual value, the measurement results at 90° direction is much close to the actual results, so the measurement at 90°direction is adopted for measuring sound power level of exhaust noise. For insertion loss, the measurement results at 90° direction and 45° direction cannot be exactly the same. As the uncertainly value of measurement results at 90° direction is smaller than that of the measurement results at 45°direction, measurement results at 90° direction can be used in laboratory measurement. In site measurement, it can be difficult to meet the requirements of measurement at 90° direction, so measurement at 45° direction is adopted for the

convenience.

COMMITTEE DRAFT ISO/CD 15619

© ISO 2010 – All rights reserved 1

Reciprocating internal combustion engines —Measurement methodology for exhaust silencers —Sound power level of exhaust noise and insertion loss using sound pressure and power loss ratio

1 Scope

1.1 General

This International Standard specifies the measurement method and requirements for exhaust silencers used in reciprocating internal combustion engines, including laboratory measurement and site measurement. The following parameters are measured.

– The insertion loss of exhaust silencers,

– The power loss ratio of reciprocating internal combustion engine,

– The sound power level of exhaust noise at the exhaust outlets.

The laboratory measurement of this International Standard can be used to perform acceptance test. The site measurement of this International Standard can be used to perform comparative test.

The aim of laboratory measurements to measure sound power level of exhaust noise in this International Standard is a grade 2 (engineering) result (see table 1). When the correction for background noise exceeds the limit of 1.3dB but is less than or equal to 3 dB, and/or the environment conditions cannot meet the requirements of engineering method, then a grade 3 (survey) result is obtained (see table 2). The aim of site measurements to measure sound power level of exhaust noise in this International Standard is a grade 3 (survey) result. When the correction for background noise exceeds the limit of 3 dB, and/or the environment conditions cannot meet the requirements of survey method, then it cannot meet the requirements of this International Standard.

NOTE The grade 2(engineering method) and grade 3 (survey method) are specified in ISO 3744.

1.2 Limits of applicability

This International Standard applies to all exhaust silencers equipped on reciprocating internal combustion engines falling within the field of application of ISO 3046-1 and for other applications, if no suitable international standards exist (including the intake silencer).

The exhaust silencer refers to silencer; reciprocating internal combustion engine refers to engine in the following text.

1.3 Measurement uncertainty

Measurements made in accordance with this International Standard should result in standard deviation which are equal to or less than those given in table 3. The Uncertainties in table 3 depend not only on the accuracies with which sound pressure levels and measurement surface areas are determined, but also on the "near-field error" which increases for smaller measurement distances and lower frequencies (i.e. those below 250Hz). The near-field error always leads to sound power levels which are higher than the real sound power levels.

ISO/CD 15619

2 © ISO 2010 – All rights reserved

Table 1— International Standards used as a basis for determining the sound power level of a reciprocating internal combustion engine

International

Standards

Classification

of method1)

Test

environment

Volume of

source

Character of

noise

Sound power

levels obtainable

Optional information

available

ISO 3744

Engineering

(grade 2)

Outdoors or in

large room

Greatest

dimension less

than 15m

Any

A-weighted

and in one-

third octave

or octave

bands

Directivity information;

sound pressure levels

as a function of time;

other weighted sound

power levels

ISO 3746

Survey

(grade 3)

No special test

environment

No restrictions:

limited only by

available test

environment

Any A-weighted

Sound pressure levels

as a function of time;

other weighted sound

power levels

1)See ISO 2204

Table 2 — Limits for correction

Values in decibels

Grade of accuracy Background noise

correction Environment

correction

Grade 2 ≤1.3 ≤2

Grade 3 ＞1.3 but ≤3 ＞2 but ≤7

Special case1）

＞3 ＞7

1 ） For higher values of background noise and/or environment

correction, the real sound power level cannot be determined with acceptable uncertainty, but the result can be useful to estimate an upper limit of the exhaust noise radiated of the silencer to be tested.

Table 3 — Uncertainty in determining sound power levels, expressed as the largest value of the standard deviation

Values in decibels

Grade of accuracy

Octave centre frequency，HZ A-weighted

31.5-631）

125 250-500 1000-4000 8000

Grade 2 5 3 2 1.5 2.5 2

Grade 3

For s source which produces sounds that contain prominent tones.

5

For s source which produces sounds that are uniformly distributed in frequency over the frequency range of interest.

4

1）If measurement is outdoors.

2 Normative references

The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

ISO/CD 15619


ISO 3046-1, Reciprocating internal combustion engines — Performance —Part 1: Declarations of power, fuel and lubricating oil consumptions, and test methods — Additional requirements for engines for general use

ISO 3046-3, Reciprocating internal combustion engines — Performance —Part 3: Test measurements

IEC 60942, Electroacoustic — Sound calibrators

IEC 61260, Electroacoustic — Octave-band and fractional-octave-band filters

IEC 61672 (all parts), Electroacoustic — Sound level meters

3 Terms and definitions

For the purposes of this document, the following terms and definitions apply. 3.1 exhaust silencer

chamber with acoustic lining or special structure which effectively reduce the noise

NOTE The ICE exhaust silencer generally comprises the entire part from its inlet, but does not include the exhaust

manifold and pipe.

3.2 substitution pipe rigid non-absorbent pipe of the same length and cross-section with the tested silencer

NOTE The substitution pipe is used to keep the relative coordinates between source and measurement points

unchanged after the insertion in order to indirectly keep the sound field distribution at measurement points unchanged.

3.3 straight transition pipe straight pipe used to connect two pipes with different cross-section

3.4 bent transition pipe bend pipe used to change the airflow direction, connecting the two pipes with the same cross-section

3.5 insertion loss Di loss of sound radiation power due to the insertion of a component or device at some point in an exhaust system which is expressed as the reduction in sound power level (decibels). Specifically, it is the difference between the sound power level (in decibels) of exhaust outlet when the substitution pipe is fitted to the engine and when the exhaust silencer is fitted to the engine

WWi LLD （1）

where：

WL is the sound power level of exhaust outlet when the substitution pipe is installed in the system,

WL is the sound power level of exhaust outlet when the silencer is installed in the system

ISO/CD 15619


3.6 power loss ratio rp engine power ratio of differences between before and after installing silencer on the engine and installing substitution pipe on the engine

3.7 measurement surface S

hypothetical spherical surface of area S , enveloping the noise source, on which the measurement points are

located

3.8 measurement radius r distance from the centre of the exhaust outlet to the hypothetical spherical measurement surface, expressed in meters (m)

3.9 the centre distance of several exhaust outlets b double average distance from one exhaust outlet to the geometric center of all exhaust outlets

4 Symbols

Table 4 — Symbols

Symbol Definition Unit Reference

Di insertion loss d

dB 3.5, 9.1.2

r Measurement radius m

m 3.8, 6.2

K1 Background noise

correction

d

dB 9.1.1.3

K2 Environment noise

correction

d

dB 9.1.1.3

LP Sound pressure level d

dB 9.1

LW Sound power level d

dB 9.1.1.4

N The number of

microphone positions 1 9.1.1.2

P Power of engine k

kW 9.2

S Measurement surface m

m2

3.7, 9.1.1.4

rP Power loss ratio 1 3.6, 9.2

5 Acoustic environment

5.1 Test environment

5.1.1 Test environment of engineering method

（a）A laboratory room which provides a free field over a reflecting plane.

ISO/CD 15619


（b）A flat outdoor area that meets the requirements of 5.2 and Annex A of this International Standard.

（c）A room in which the contributions of the reverberant field to the sound pressure on the measurement

surface are small compared with those of the direct field of the source.

NOTE Conditions described under c) above are usually met in very large room as well as in smaller rooms with

sufficient sound-absorptive materials on their walls and ceilings.

5.1.2 Test environment of survey method

The test environment of survey method in this International Standard is a room or flat outdoor area that meets the requirements of 5.2.2 of this International Standard.

5.2 Criterion for adequacy of the test environment

5.2.1 Engineering method

As far as is practicable, the test environment shall be free from reflecting objects other than a reflecting plane so that the source radiates into a free field over a reflecting plane.

Annex A describes procedures for determining the magnitude of the environment correction. Normally this is less than or equal to 2dB. For spectral quantities levels according to this International Standard, environment correction for each frequency band of interest shall not exceed 2 dB.

5.2.2 Survey method

For the survey method of this International Standard, the environment correction shall be numerically less or equal to 7dB.

5.3 Criterion for background noise

5.3.1 Engineering method

Background noise is the noise from all sources except the source under test, including the noise radiated from other parts of the engine during operation. According to specifications of engineering method, the average sound pressure level of background noise shall be at least 6 dB and preferably 15 dB below the sound pressure level at a microphone position.

5.3.2 Survey method

According to specifications of survey method, the sound pressure level of background noise shall be at least 3 dB below the sound pressure level at each microphone position.

6 Installation and operation of source under test

6.1 General

The manner in which the source under test is installed and operated may have a significant influence on the sound power emitted from the source. This clause specifies conditions that minimize variation in the sound power output due to the installation and operation conditions of the source under test.

6.2 Source location

The dimensions (including shape, structure, length, and diameter etc.) of exhaust system under test shall be representative of normal use.

ISO/CD 15619


For the engineering method, exhaust outlets installed outdoors as much as possible or not in the same room with engine which meets the requirements of engineering method. The exhaust outlet at non-flow direction shall be equal to or more than 3 times the measurement radius from any reflecting plane, there shall be no reflecting objects at the direction of the exhaust outlet, or exhaust outlet shall be more than 5 times the measurement radius from reflecting planes, see Table 5. The requirements of measurement radius r see 8.2.2.2.

If the exhaust outlet and the engine are in the same room, installation of source under test shall meet the requirements of 6.3.2. Criterion for adequacy of the acoustic environment under test shall be evaluated according to Chapter 5, and the corresponding uncertainty of measurement results see 1.1.

Table 5 — Requirements for source location

Dimensions in meters

Parameter: symbol Requirements of engineering method

The minimum distances between exhaust outlet at non-flow direction and reflecting planes: d d/r≥3

The minimum distances between exhaust outlet at flow direction and reflecting planes: c c/r≥5

6.3 Source mounting

6.3.1 Straight transition pipe and bent transition pipe

If the diameter of exhaust pipe and the inlet of silencer are inconsistent, use straight transition pipe to connect, shall meet the following:

84.221

aa

l （2）

1a is the diameter of inlet of exhaust silencer;

2a is the diameter of outlet of exhaust silencer; is equivalent diameter for several exhaust outlets (area

calculated using the equivalent diameter are the sum of all areas of exhaust outlets);

l ： is the length of straight transition pipe.

See Fig.1,θ ≤10°

Fig. 1 — Straight transition pipe (schematic)

Change the direction of airflow if it is necessary can use the bent transition pipe, see Fig.2, shall meet the following:

ISO/CD 15619


2d

R （3）

R ：is the radius;

d ：is the diameter of steel pipe.

Fig. 2 — Bent transition pipe (schematic)

NOTE Minimize the number of bent transition pipe which affect the result of measurement parameters.

Noise and vibration isolation should be taken between the exhaust pipe and walls if the exhaust outlet outside.

6.3.2 Exhaust outlet and engine in the same room

If the exhaust outlet and the engine are in the same room then the following action shall be taken to reduce extraneous noise influencing the noise radiated from the outlet. The engine and dynamometer shall be shielded or wrapped with heavy material that has low noise transmission for the frequency of the additional noise sources.

6.4 Operation condition

The engine shall run under standard reference conditions of ISO 3046-3. Measurement shall begin only when power, speed of rotation, oil temperature and coolant temperature of the engine are stable. If ambient conditions cannot be controlled by the operator that shall be stated in the test report.

7 Instrumentation

7.1 General

The instrumentation system for measuring Sound Pressure Levels, including microphones and cables etc., shall meet the requirements of IEC 61672. Obtain grade 2 results shall meet the requirements of Type 1 instrument specified in IEC61672. Obtain grade 3 results shall meet the requirements of Type 2 instrument specified in IEC61672. Octave-band and one-third-octave-band filters used for frequency analysis shall meet the requirements of IEC61260.

7.2 Calibration

Before and after each series of measurements, the instruments shall be calibrated by the same sound calibrator. The sound calibrator shall meet the requirements of IEC60942.

The difference between two numerical values coming from calibrations before and after each series of measurements shall be no more than 0.3 dB in engineering method or 0.5 dB in survey method.

ISO/CD 15619


7.3 Microphone windbreak

If measurements are to be made outdoors, a windbreak is recommended. When the wind velocity at the measuring points exceeds 1 m/s, windscreens shall be used, but when the wind velocity at the measuring points exceeds 5 m/s, measurement shall be cancelled.

7.4 The facilities used in ICE dynamometer tests shall meet the specifications of ISO 3046-3.

8 Measurement

8.1 General

This International Standard specifies two testing methods that are laboratory measurement and site measurement. Laboratory measurement can provide relatively complete evaluation about an exhaust silencer. The main parameters to be evaluated are sound power level of exhaust noise, insertion loss and power loss ratio. Site measurement can provide comparative evaluation about different exhaust silencers equipped on the same engine. The main parameters to be evaluated are sound power level of exhaust noise and insertion loss.

The sound pressure level of exhaust noise and engine power shall be measured during the same testing period in the measurement.

To minimize the influence of observers on measurements, the microphone shall preferably be mounted on a rigid frame or stand and be connected to the sound level meter by a cable at least 2 m in length. It is essential to ensure that the rigid frame or stand is not connected to a vibrating surface.

The time weighting characteristic ―S‖ on the sound level meter shall be used to obtain the A-weighted sound pressure level. Subsequently, respectively take the readings of the time-averaged sound pressure level at each microphone position when the substitution pipe is fitted to the engine and when the exhaust silencer is fitted to the engine.

For spectral analysis, there still needs an octave-band filter or one-third octave-band filter which has frequency bands centred from 31.5 to 8000 Hz, and then take the readings of the period when observing the time-averaged sound pressure level. For the frequency bands centred on or above 200 Hz, the period of observation shall be at least 10s. For the frequency bands centred on or below 160 Hz, the period of observation shall be at least 30s.

Two series of measurements shall be carried out in the test conditions which are as similar as possible. The difference between the numerical results in two series of measurements shall be less than 2 dB. The engine shall not stop for over 30 minutes.

Keep the sound field distribution unchanged to reduce the measurement uncertainty when measuring insertion loss in two series of measurements. The relative coordinates between microphone positions and the reflecting planes shall remain same during testing for single exhaust outlet.

NOTE Two series of measurements includes the one-time measurements at all measurement points when the

substitution pipe is fitted to the engine and the subsequent one-time measurements at all measurement points when the

exhaust silencer is fitted to the engine.

8.2 Laboratory measurement

8.2.1 Measuring procedure for sound pressure level

Laboratory measurement is the measurement when the engine is in a test room, and the test environments of the test room and other test conditions shall be in accordance with the details as given in clause 5 and clause 6.

ISO/CD 15619


The measurement radius r shall be equal to or more than 5 times the diameter of pipe and not less than 0.25m. For two outlets, measurement radius r shall be equal to or more than 5 times the distance between the centres of two exhaust outlets and not less than 0.25m.

For this measurement direction, four measurement points are adequate. The four measurement points are arranged on the spherical measurement surface, which is a section through the centre of the outlet and at

90° from the flow direction.

The four measurement points are arranged at 45 ° with the level of the 90°section centre for horizontal

airflow, the key microphone positions on measurement surface are shown in Fig.3. The four measurement

points are evenly arranged on the 90° section for vertical airflow, the key microphone positions on

measurement surface are shown in Fig.4.

The measurement radius r shall be determined according to the following series: 0.25m, 0.315m, 0.4m, 0.5m, 0.63m, 0.8m, 1m, 1.25m, 1.6m, 2.0m and the priority series is 0.5m, 1m, 2 m. Also, the measurement radius r shall meet the requirements of Table 5.

a) front view b) right view

Key

1 microphone position




5 silencer

6 background

7 reflecting plane

8 hypothetical spherical measurement surface

Fig. 3 — Arrangement of the key measurement points and measurement surface for the exhaust

silencer (direction: 90°) (horizontal airflow) (schematic)

ISO/CD 15619


a) front view b) top view Key





5 silencer

6 background

7 reflecting plane


Fig. 4 — Arrangement of the key measurement points and measurement surface for the exhaust

silencer (direction: 90°) (vertical airflow) (schematic)

8.2.2 Determination of engine power

All measurements of the engine power shall be made in accordance with ISO 3046-1 and ISO 3046-3 and all measurements shall be recorded.

The engine shall run at the standard reference conditions when the substitution pipe is fitted to the exhaust system, record the power of engine at the rated speed in a steady state.

The engine shall run at the standard reference conditions when the exhaust silencer is fitted to the exhaust system, record the power of engine at the rated speed in a steady state.

If the engine operates under ambient conditions different from standard reference conditions, correct the power to the standard reference conditions according to ISO 3046-1. Then record the adjusted power at the rated speed.

Also, the measurement results of pressure loss of engine measured according to Annex B is only for reference.

ISO/CD 15619


8.3 Site measurement

Site measurement is the measurement during engine is in normal working condition and the test environments of the test room and other test conditions shall be in accordance with the details as given in clause 5 and clause 6.

For the measurement at this direction, one measurement point is adequate, the microphone positions on measurement surface are shown in Fig.5 (horizontal airflow) and Fig.6 (vertical airflow). Take any position of eight as far from the silencer body as possible as the measurement point. Two series of measurements shall keep the relative location between measurement points and exhaust outlet unchanged.

The measurement radius r shall be determined according to the following series: 0.5m，1m，2 m.

a) front view b) right view Key


2 silencer

3 reflecting planes

Figure 5 — Arrangement of the key measurement point and measurement surface for the exhaust

silencer(direction: 45°) (horizontal airflow) (schematic)

ISO/CD 15619


a) front view b) top view Key


2 silencer


4 background

5 reflecting plane

6 section of 45°

Figure 6 — Arrangement of the key measurement point and measurement surface for the exhaust

silencer(direction: 45°) (vertical airflow) (schematic)

All site measurements for comparison shall be carried out in the test conditions which are as similar as possible. The site ambient and the working conditions of the engine shall be stated in the test report.

Refer to 8.2.2 for the measuring procedure of sound pressure level of exhaust silencers.

9 Calculation

9.1 Calculation of insertion loss

9.1.1 Calculation of power level of sound radiated from exhaust outlet

9.1.1.1 General

Choose the results from measurement of 90°direction (see Fig.3 and Fig.4) to calculate sound pressure level

and sound power level of measurement surface.

ISO/CD 15619


9.1.1.2 Calculation of sound pressure level of measurement surface

Calculate the sound pressure level and sound pressure level of background noise averaged over the measurement surface, expressed in decibels (dB), using the following equation:

N

i

L

ppi

NL

1

1.010

1lg10

（4）

N

i

L

ppi

NL

1

1.010

1lg10

（5）

where

pL is the sound pressure level (A-weighted or in frequency bands) averaged over the measurement

surface, in decibels, with the source under test in operation

pL is the sound pressure level (A-weighted or in frequency bands) of the background noise averaged

over the measurement surface, in decibels

piL is the sound pressure level (A-weighted or in frequency bands) measured at the ith

microphone

position, in decibels

piL is the sound pressure level (A-weighted or in frequency bands) of the background noise measured

at the ith

microphone position, in decibels

N is the number of microphone positions

9.1.1.3 Corrections for background noise and test environment

Calculate the correction 1K by using the following equation:

pp LLK

1.0

1 101lg10 (6)

where

1K

is background noise correction(A-weighted or in frequency bands), expressed in decibels

Determine the environment correction 2K according to Annex A of this International Standard.

9.1.1.4 Calculation of surface sound pressure level

Determine the surface sound pressure level by using the following equation, in decibels:

21 KKLL pp （7）

9.1.1.5 Calculation of sound power level

Calculate sound power level WL , expressed in decibels (dB), by using the following equation:

ISO/CD 15619


0lg10 SSLL pW (8)

Where

S is the area of the measurement surface, expressed in square metres(24 rS )

2

0 1mS

9.1.2 Calculation of insertion loss

The calculation formula of insertion loss is given in 3.5 of this International Standard. If the substitution pipe and the exhaust silencer have the same positions, dimension, and sound field distribution, then calculate the insertion loss Di , expressed in decibels (dB), by using the following equation:

ppi LLD （9）

Where

pL is the average sound pressure level (A-weighted, or in frequency bands) after the correction of

background noise when the substitution pipe is fitted to the engine, in decibels

pL is the average sound pressure level (A-weighted, or in frequency bands) after the correction of

background noise when the exhaust silencer is fitted to the engine, in decibels

9.2 Calculation of power loss ratio

Calculate the power loss ratio Pr , by using the following equation:

%100

P

PPrP

(10)

where

P is the engine power when the substitution pipe is fitted to the engine, expressed in kW

P is the engine power when the exhaust silencer is fitted to the engine, expressed in kW

10 Information to be recorded

If applicable, data in 10.1 through 10.5 shall be recorded for all measurements made according to this International Standard.

10.1 Description of the engine to which the exhaust silencer under test is fitted

a) Description that identifies the engine including its

type,

engine number,

ISO/CD 15619


rated power,

rated speed of rotation,

displacement

manufacturer.

b) Ambient conditions, classified into standard reference conditions, test ambient conditions different from standard reference conditions and site ambient conditions, including

barometric pressure,

air temperature,

relative humidity, and

wind speed

c) Operating state during test described by the following:

engine power，

engine speed of rotation，

specific fuel consumption.

10.2 Description of the exhaust silencer under test

Description that identifies the exhaust silencer under test including its

type,

part number,

volume,

mass, and

manufacturer.

10.3 Description of equipments

Description of the equipments used for the measurements, including their respective

name,

type,

machine serial number,

manufacturer, and

result of calibration.

ISO/CD 15619


10.4 Acoustic environment

Description of acoustic environment including

literal description of relative location between the exhaust silencer under test and the engine to which the exhaust silencer is fitted to,

literal description of relative location between the exhaust silencer under test and ambient reflecting objects,

literal description of physical treatment of the engine (e.g. shielding and wrapping the engine and its driven machines),

literal description of physical treatment of the ambient reflecting objects to make the sound field at the measurement points as free as possible,

and/or sketch or picture showing the above relative locations and physical treatments,

description of arrangement of the measurement points, and

description of background noise and environmental noise after above physical treatments.

10.5 Test results and computational results

a) Accuracy grade,

b) Method of measurement (e.g. experimental measurement or site measurement),

if laboratory measurement, record sound pressure level at each measurement points, in 10.1.

if site measurement, record sound pressure level at each measurement points,

c) The area S of the measurement surface or the measurement radius r,

d) Back ground noise correction and environmental noise correction,

e) Computational results, like sound pressure level, sound power level, insertion loss, and power loss ratio,

f) Statement that whether the sound level is A-weighted or octave band, or one-third octave band,

g) Place, date when the measurements were carried out and the name of person responsible for the test.

h) The pressure loss of silencer ( Measurement procedure refer to Annex B if needed)

11 Information to be reported

The data specified in Clause 10 and required by the ultimate user shall be included in the test report. And the report shall state that the sound pressure level, the sound power level and the engine power were obtained in full conformity with the requirements of this International Standard and the report provides sound power level of exhaust noise, insertion loss of the exhaust silencer and engine power loss ratio.

Sound power level of exhaust noise, insertion loss, power loss ratio measured at standard power of ISO3046-1under standard reference conditions specifies in ISO3046-1 according to the measurement procedure of this International Standard may be referred to as the ISO15619 sound power level of exhaust noise, insertion loss and power loss ratio.

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Annex A (normative)

Qualification procedures for the acoustic environment

A.1 General

An environment providing an approximately free field over a reflecting plane shall be used for measurements made in accordance with this International Standard. It is permissible to use a semi-anechoic room, an outdoor space or an ordinary room if the requirements given below are satisfied.

The test room shall be large enough and, as far as is practicable, free from reflecting objects with the exception of the reflecting plane(s).

The test room shall provide a measurement surface that lies

a) inside a sound field that is essentially free of undesired sound reflections from the room boundaries or nearby objects, and

b) outside the near field of the sound source under test.

For open test sites which consists of a hard, flat ground surface, such as asphalt or concrete, and with no sound-reflecting objects within a distance from the source equal to three times the greatest distance from the source centre to the lower measurement points, It is assumed that the environmental correction K2 is less than or equal to 0.5 dB and is, therefore, negligible.

The environmental correction K2 is also assumed to be negligible for measurements made in semi-anechoic rooms which meet the requirements of IS0 3745, annex A.

NOTE An object in the proximity of the source may be considered to be sound reflecting if its width (for example, diameter of

a pole or supporting member) exceeds one-tenth of its distance from the reference box.

Evaluate environmental influences by selecting one of two alternative procedures (Refer to A.2) used to determine the magnitude of the environmental correction K2. Use these procedures to determine if any undesired environmental influences are present and to qualify a given measurement surface for an actual source under test in accordance with this International Standard.

The first qualification test (absolute comparison test) is carried out with a reference sound source (RSS) and can be used outdoors and indoors. It is the preferred procedure, particularly if data in frequency bands are required.

The second qualification test (method based on room absorption) requires the determination of the equivalent absorption area, A, of the test room with the aid of reverberation time measurements, or by estimating the mean absorption coefficient. This test procedure is based on the assumption that the room has approximately a cubic shape and is substantially empty and that there are absorption effects on the room boundaries. Under these conditions, if the source under test cannot be moved and if its dimensions are large, this is the preferred method.

The measurement surface in a given test environment is satisfactory for measurements complying with this International Standard only if the environmental correction K2 is numerically Less than or equal to 2 dB. If the environmental correction K2 exceeds 2 dB, repeat the procedure using either a smaller measurement surface or a better test environment.

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A.2 Environmental conditions

A.2.1 Properties of reflecting plane

Measurements are permissible in the following environments:

- over a reflecting plane outdoors;

- in a test room with sound absorptive walls ceiling, a sound reflecting floor and up to two further perpendicular reflecting surfaces.

When a reflecting surface is not a ground plane or is not an integral part of a test room surface, particular care should be exercised to ensure that the plane does not radiate any appreciable sound vibrations.

A.2.1.1 Shape and size

The reflecting planet(s) shall extend at least 2/ beyond the projection of the measurement surface on the

planet(s) for the lowest frequency of the frequency range of interest.

A.2.1.2 Sound absorption coefficient

The sound absorption coefficient of the reflecting plane(s) should preferably be less than 0.06 over the frequency range of interest. Concrete or smooth sealed asphalt surface(s) should be satisfactory.

A.2.2 Precautions for outdoor measurements

Take care to minimize the effects of adverse meteorological conditions (for example, temperature; humidity, wind, precipitation) on the sound propagation over the frequency range of interest or on the background noise during the course of the measurements.

If a device is used to shield the microphone from the effects of wind, proper corrections of the measured sound pressure levels shall be made.

A.3 Absolute comparison test

This procedure should preferably be used if the source under test can be removed from the test site.

A.3.1 Procedure

Mount a reference sound source (RSS) with characteristics that meet the requirements of ISO 6926 in the test environment, in essentially the same position as that of the source under test. Determine the sound power level of the reference sound source in accordance with the procedures of clauses 8 without the environmental correction K2 (i.e. K2 is initially assumed equal to zero).Use same measurement surface as that used for the measurements of the source under test.

The environmental correction K2 (A-weighted or in frequency bands) is given by

WrW LLK 2 (A.l)

Where

WL is the environmentally uncorrected sound power level of the reference sound source, determined

in accordance with clauses 7 and 8 when using the value 0 for K2;

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WrL is the calibrated sound power level of the reference sound source [reference 1pW (= W1210)], in

decibels.

NOTE This method is applicable to both directly measured A-weighted levels and frequency band levels. If the spectrum of

the source under test is very different from that of the RSS, it is recommended that K2A be determined from frequency band

levels.

A.3.2 Locations of reference sound source in test environment

Keep the geometric centre of reference sound source and the source under test the same.

With regard to a sufficient number of microphone positions, care shall be taken to fulfil the requirements of 8.2 and 8.3 respectively.

A.4 Determination of the environmental correction based on room absorption

Calculate the environmental correction K2 (A-weighted or in frequency bands) from

A

SK 41lg102 (A.2)

Where

A is the equivalent sound absorption area of the room, in square meters;

S is the area of the measurement surface, in square meters.

Environment corrections as a function of A/S calculated using equation (A.2) are illustrated in figure A.1.

A.4.1 Approximate method

In order to ascertain the acoustic characteristics of the test environment, determine AK 2 from equation (A.3)

using a value of A given in square metres by the formula

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VSA （A.3）

where

is the mean sound absorption coefficient, given for A-weighted quantities in table A.1；

VS is the total area of the boundary surfaces of the test room (walls, ceiling and floor),2m

Table A.1-Approximate values of the mean sound absorption coefficient

Mean sound absorption coefficient Description of room

0.05 Nearly empty room with smooth hard walls made of concrete, brick, plaster or

tile

0.1 Partly empty room; room with smooth walls

0.15 Room with furniture; rectangular machinery room; rectangular industrial room

0.2 Irregularly shaped room with furniture, irregularly shaped machinery room or

industrial room

0.25

Room with upholstered furniture; machinery or industrial room with a small amount of sound absorbing material on ceiling or walls (for example, partially

absorptive ceiling)

0.35 Room with sound absorbing material on both ceiling and walls

0.5 Room with large amounts of sound-absorbing materials on ceiling and walls

A.4.2 Reverberation method

Calculate the equivalent sound absorption area of the room from the measured reverberation time by the

Sabine reverberation time equation. At room temperature between 15℃ and 30℃

TVA 16.0 （A.4）

where

V is the volume of the test room,3m ；

T is the reverberation time, in seconds, for A-weighting or in frequency bands.

For the purpose of determination AK 2 directly from A-weighted measured values, it is recommended to use

the reverberation time measured in the frequency band with centre frequency of 1 kHz.

This method is not suitable for use in a laboratory quality semi-anechoic room or for outdoor measurements.

A.4.3 Two-surface method

Use this test method only in a room whose length and width are each less than three times the ceiling height. Select two surfaces that surround the sound source. The first surface shall be the measurement surface, for determination of sound power level. The area of the first surface shall be designated S. The second surface with

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area S2 shall be geometrically similar to the first surface and located further away and symmetrical with respect to the machine under test.

The microphone locations on the second surface shall correspond to those on the first surface. The ratio S2/S shall not be less than 2 and preferably should be greater than 4. The quantity M is calculated from

211.010 pp LL

M

(A.5)

where:

1pL Is the average sound pressure level on S, in decibels.

2pL Is the average sound pressure level on S2, in decibels.

For both average sound pressure levels, corrections for background noise shall be applied.

The ratio A/S is calculated from

2/1

)1(4/

SMS

MSA

(A.6)

The environmental correction K2 for A-weighting or in frequency bands is obtained from equation (A.2) for the A/S ratio calculated from equation A.6.

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Annex B (informative)

The Measurement procedure for pressure loss

B.1 General

Determine the back pressure and uncertainty of exhaust system according to ISO 3046-3.

B.2 Calculation of back pressure difference

Calculate the exhaust back pressure difference,exP , expressed in kPa, using the following formula:

21 exexex PPP (B.1)

Where

1exP is the back pressure when the exhaust silencer is fitted to the engine, expressed in kPa;

2exP is the back pressure when the substitution pipe is fitted to the engine, expressed in kPa.

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Bibliography

[1] ISO 2204:1979 Acoustics-Guide to International Standard on the measurement of airborne acoustical noise and evaluation of its effects of human beings.

[2] ISO 6926:1999 Acoustics-Requirement for the performance and calibration of reference sound sources used for the determination of sound power levels.

[3] ISO 3745 Acoustics-Determination of sound power levels of noise sources using sound pressure-Precision methods for anechoic and semi-anechoic rooms.

[4] ISO 3744 Acoustics-Determination of sound pressure levels of noise sources using sound pressure -Engineering method in an essentially free field over a reflecting plane.

[5] ISO 3746 Acoustic-Determination of sound power levels of noise sources using sound pressure-Survey method using an enveloping measurement surface over a reflecting plane.

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