REPORT. Measurements and Judgments of Sound in relation to Human Sound Perception. Client: Nordtest. 23 August AV 1461/01 Page 1 of 7 + Appendix

Transcription

1 AV 1461/01 Page 1 of 7 + Appendix REPORT DELTA Danish Electronics, Light & Acoustics Building 356 Akademivej DK-2800 Kgs. Lyngby Denmark Measurements and Judgments of Sound in relation to Human Sound Perception Client: Nordtest 23 August 2001 Tel. (+45) Fax (+45) The report must not be reproduced, except in full, without the written approval of DELTA. 80rap-uk-a

2 AV 1461/01 Page 2 of 7 Title Measurements and Judgments of Sound in relation to Human Sound Perception Journal no. Project no. Our ref. AV 1461/ THP/CLF/lm Client NORDTEST Postbox 116 FIN Esbo Finland Summary It is recognised that A-weighted measurements of sound pressure levels and sound power levels alone are insufficient for measurements in relation to product sound quality and noise annoyance potential. This has led to an increasing interest in objective and subjective methods giving results in closer agreement with human sound perception. As a result of the work in this project a guideline consisting of two parts has been worked out. Part 1 gives instructions on how to supplement the A-weighted data from standardised measurements of sound pressure and sound power with meaningful results of measurements of loudness. Part 2 describes principles for making effective and reliable listening tests. For some topics the guideline gives specific recommendations, for other topics the text has the character of a list of items to remember or to consider. A number of definitions within the fields of product sound quality and listening tests are given. DELTA, 23 August 2001 Torben Holm Pedersen Acoustics & Vibration

3 AV 1461/01 Page 3 of 7 Contents 1. Background Aim Project Group Work in the Project Group The Result of the Project... 7 Appendix: Nordtest Guideline Draft Measurements and Judgments of Sound in relation to Human Sound Perception Common Introducion (AV 1458/01) Part 1: Measurement Positions for Measurement of Loudness (AV 1457/01) Part 2: Guidelines for Listening Tests (AV 1456/01)

4 AV 1461/01 Page 4 of 7 1. Background There is an increasing recognition that in a number of contexts A-weighted noise levels are insufficient for assessment of noise problems and sound from products. This has led to an increasing interest in measurement and evaluation methods which agree with human sound perception to a higher degree than earlier. Loudness is an obvious example of an objective goal which is closer to the sound perception than the A-weighted levels normally used. db Pink noise Bandpassfiltered noise Tone Air hammer Organ harmony Electronic warning signal Electric high speed tool Figure 1 Illustration of the relevance of supplementing A-weighted measurements with measurements of loudness. Upper curve: A-weighted sound pressure levels with time weighting F (uncalibrated) Lower curve: Loudness versus time of the same sounds

5 AV 1461/01 Page 5 of 7 Figure 1 illustrates the relevance of supplementing the A-weighted measurements with measurements of loudness. It is seen that for different noises with the same A-weighted level (upper curve) significant differences in the loudness (and the perception of the intensity) are found. Several instruments and analysers are now available which can measure loudness in a homogeneous and simple way, so the time is ripe for supplementing the (standardised) measuring methods with the possibility of supplementarily and comparably stating e.g. values of loudness. It might also be relevant with other psychoacoustically related measures as e.g. sharpness, roughness, etc. Measuring positions etc. are not defined in present standards with this end in view. This applies especially to standards for measurement of sound power. Therefore there is a need that standards etc. are supplemented with directions determining relevant measuring positions etc. for this purpose. Correspondingly the interest in using listening tests both as objective and subjective measuring tools is increasing. Unfortunately there are no commonly accepted guidelines in this field, so the results are seldom comparable. It has not been possible at present to determine detailed guidelines for performing listening tests. But within the scope of this project guidelines are given as to what should be taken into consideration and reported when carrying out listening tests. It is meant as a valuable contribution in the process of making listening tests an operational measuring tool. Many are of the opinion that the use of A-weighted levels in time should be replaced by other and more relevant measures, but as the major part of our empirical and legislative basis is founded on A-weighted values, changes have been avoided so far and for very good reasons. It is our hope that the Nordic countries could be the initiators of an appropriate development by creating the possibility of in a homogeneous way being able to supplement the traditional measures with measures, which conform better to the knowledge we now have of human sound perception. 2. Aim The aim of this project was to give a supplement to existing standards for measurement of sound power and sound pressure levels in the shape of: 1. Instructions/directions for measurement of loudness and other psychoacoustic parameters. 2. Guidelines for topics, which should be considered when making a listening test. The work is delimited to relevant ISO and NORDTEST standards and perhaps a few IEC standards.

6 AV 1461/01 Page 6 of 7 3. Project Group The project group consisted of: Torben Holm Pedersen, project leader DELTA Acoustics & Vibration Akademivej, Building 356 DK-2800 Kgs. Lyngby Denmark thp@delta.dk Torben Holm Pedersen prepared Part 2 Guidelines for listening tests of the method. Truls Gjestland SINTEF Telecom and Informatics N-7465 Trondheim Norway truls.gjestland@informatics.sintef.no Mendel Kleiner Chalmers University of Technology Room acoustics group S Göteborg Sweden mk@ta.chalmers.se Panu Maijala VTT Automation Safety Engineering Tekniikankatu 1 P.O.Box 1307 FIN TAMPERE Finland panu.maijala@iki.fi The group was supplemented with: Carsten L. Fog DELTA Acoustics & Vibration Akademivej, Building 356 DK-2800 Kgs. Lyngby clf@delta.dk Carsten L. Fog prepared Part 1 Measurement Positions for Measurement of Loudness of the method.

7 AV 1461/01 Page 7 of 7 4. Work in the Project Group The project group had two meetings at DELTA in Lyngby. Before the first meeting drafts of the two parts of the methods were sent to the participants. Principles and methods were discussed. On the basis of the discussions a revised draft was sent to the participants for further comments. These comments were taken into account, and in general the drafts were brought to a more complete stage before the second and final meeting. At the second meeting the drafts of the method were discussed, and after the meeting the report and final drafts were sent to the participants for approval. 5. The Result of the Project The result of the work is a draft for a NORDTEST guideline consisting of two parts (Part 1: AV 1457/01 and Part 2: AV 1456/01) with a common introduction (AV 1458/ 01). The guideline is enclosed.

8 Nordtest Guideline Draft AV 1458/01 Measurements and judgments of sound in relation to human sound perception Part 1: Measurement positions for measurement of loudness Part 2: Guidelines for listening tests Introduction This NORDTEST guideline consists of two independent parts: Part 1: Measurement positions for measurement of loudness It is recognised that A-weighted measurements of sound pressure levels and sound power levels alone are insufficient for measurements in relation to product sound quality and noise annoyance potential. This has led to increasing interest in measures in closer agreement with human sound perception as e.g. loudness, sharpness roughness.. Equipment, which gives easy and reliable measurements of loudness and other psychoacoustic parameters, is now available, and therefore there is a need to supplement existing measurement methods with procedures for measurement of loudness etc. In the existing ISO-standards for measurements of A-weighted sound pressure levels and sound power levels, measurement positions are not defined with the purpose of giving meaningful measurements of e.g. loudness. Part 1 of this NORDTEST guideline gives instructions on how to supplement the A-weighted data with meaningful results of measurements of loudness. Part 2: Guidelines for listening tests The interest in using listening tests as both an objective and a subjective measuring tool is increasing. There are no generally accepted guidelines for making listening tests so the results are seldom comparable, and there is a risk that newcomers in this field make fundamental methodological errors. Part 2 of this NORDTEST guideline is meant as a help to make effective and reliable listening tests. For some topics the guideline gives specific recommendations, for other topics the text has the character of a list of items to remember or to consider. As new concepts within acoustics are introduced, the section with definitions and terms is rather comprehensive.

9 (page 1) Nordtest Guideline Draft 8 th working draft AV 1457/01 Part 1 prepared by Carsten L. Fog Measurements and judgments of noise in relation to human sound perception Part 1: Measurement positions for measurement of loudness Contents 1. Scope Field of application Normative references Definitions Sound pressure level, in decibels, L p Energy-equivalent sound pressure level, in decibels, L eq,t Sound intensity level, in decibels, L I Sound power level, L w Loudness Loudness Loudness level Other metrics related to human hearing Related EN and ISO standards General overview Noise declaration measurements Determination of (stationary) loudness Determination of sound pressure level Determination of sound power levels Determination of sound power level based on sound pressure Determination of sound power level based on sound intensity Measurement guidelines Types of sound sources Instrumentation Test environment Specification of installation and operating conditions Specification of measurement positions At the operator s position Enclosed work station position At the bystander position Measurement positions in other cases Measurements Measurement time interval Steady noise Non-steady noise Measurements in frequency bands Repetition of measurements Impulsive sound Supplementary measurements Accuracy Information to be recorded and reported Information to be recorded... 11

10 (page 2) Product under test Test conditions Acoustic environment Instrumentation Location of specified positions Noise data Information to be reported Bibliography... 12

11 (Part 1, page 3) Part 1: Measurement positions for measurement of loudness 1. Scope The traditional physical descriptor, the A-weighted sound pressure level, L PA, is often not an adequate objective descriptor for perceived sound. The sounds of different products with the same L PA do not always sound equally intense to the user. So, objective descriptors are needed, which correlate better with subjective perception, as a supplement to the A-weighted based parameters sound pressure and sound power. The scope of this Nordtest Guideline is to supplement existing standards for measurements of sound pressure levels and sound power levels with guidelines for measurements (and calculations) of loudness and other psychoacoustic descriptors for product sound quality. 2. Field of application This guideline is related to the Machinery Directive (89/392/EU) and the new Outdoor Directive (2000/14/EU) and their requirements on low-noise design as an integral part of machinery safety and environmental protection - Machinery must be so designed that risks resulting from noise are reduced to the lowest level taking account of technical progress and the availability of means of reducing noise, in particular at the source. This guideline is a supplement to existing noise source measurement guidelines described especially in the EN ISO 3740 to 3747 and the EN ISO standards. Specific guidelines on how to perform such measurements in the field are found also in product-relevant standards (Noise Test Codes) for the specific product. 3. Normative references The following normative documents contain provisions, which constitute - through reference in this text - provisions of this Nordtest Guideline. Parties using this Nordtest Guideline are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to apply. Nordtest as well as members of ISO and IEC maintain registers of currently valid International Standards. 1. EN ISO 4871, Acoustics - Declaration and verification of noise emission values of machinery and equipment 2. EN ISO , Acoustics - Determination of sound power levels of noise sources guidelines and using 3. EN ISO 9614, Acoustics - Determination of sound power levels using intensity 4. EN ISO , Acoustics Noise emitted by machinery and equipment Guidelines for the use of basic standards for the determination of emission sound pressure levels at a work station and at other specified positions 5. EN ISO 12001, Acoustics - Noise emitted by machinery and equipment Rules for the drafting and presentation of a noise test code 6. Noise test codes 7. IEC Publication 61672, Electroacoustics - Sound level meters 1) 8. IEC Publications and 60804, Sound level meters 9. IEC Publication 60942, Acoustic calibrators 10. IEC Publication 61260, 1/3 and 1/1 octave filters 11. ISO (E), Acoustics Method for calculating loudness level, Section two 12. ISO 226, 1987 (E), Acoustics Normal equal-loudness level contours 1) To be published, replaces IEC and IEC

12 (Part 1, page 4) 4. Definitions 4.1 Sound pressure level, in decibels, L p The sound pressure level L p is given by L p = 10 lg p p 0 2 db p = Root mean square sound pressure, in pascals p 0 = Reference sound pressure, 20 µpa 4.2 Energy-equivalent sound pressure level, in decibels, L eq,t 2 ) The value of the A-weighted sound pressure level of a continuous steady sound that within a specified time period has the same mean square sound pressure as a sound whose level varies with time. It is defined as t2 2 1 p ( t) Leq, T = 10 lg dt t t db 2 p 2 1 t1 0 L eq,t = Energy-equivalent sound pressure level for the time interval T, starting at the time t 1 and ending at the time t 2, in decibels p 0 = Reference sound pressure, 20 µpa p(t) = Instantaneous value of the sound pressure of the noise signal, in pascals 4.3 Sound intensity level, in decibels, L I The sound intensity is defined as L I = 10 log I I 0 db I 0 = Reference sound intensity, 1 pw/m 2 I = Sound intensity, in watt/m Sound power level, L w The sound power is defined as L w = 10 log w w 0 db w = Sound power, in watt w 0 = Reference sound power, 1 pw L WA is the A-weighted sound power level. 2) The expression equivalent sound level may be used in order to simplify a text. If A-weighting is used, the term is L Aeq,T

13 (Part 1, page 5) 4.5 Loudness Loudness Loudness belongs to the category of intensity sensations for sound. The unit for loudness N is Sone. A 1 khz tone with a sound pressure level of 40 db re 20 µpa is defined as having a loudness of 1 sone. Signals perceived as being twice as loud have a loudness of 2 sone. In the mid-frequency range and above sound pressure levels of 40 db, an increase of the level of 10 db leads to a multiplication of loudness by a factor of two, see Normative references 11 of Part Loudness level The loudness level L N of a given sound, measured in phon, is the sound pressure level of a reference sound, consisting of a sinusoidal plane progressive wave of frequency 1000 Hz coming directly in front of the listener, which is judged by otologically normal persons to be equally loud as the given sound, see Normative references 11 and 12 of Part Other metrics related to human hearing Many specialised (product) sound quality metrics and combinations of metrics have been developed such as Sharpness, Fluctuation Strength, and Roughness. These are further described in the Appendix of Part 2 of this Nordtest Guideline. 5. Related EN and ISO standards The requirements of the Machinery Directive that the noise level shall be so low as can reasonably be expected have led to European and international standardisation organisations preparing several guidelines regarding noise attenuation. Manufacturers must now in many cases make available specified quantitative information on noise emitted under defined operation, e.g. noise declarations. Furthermore, in this way manufacturers are made active participants in low-noise design and noise and vibration control. 5.1 General overview In order to help manufacturers make the required specified quantitative information, the CEN (CENELEC) has prepared general harmonized standards and guidelines. These comprise the following issues: Noise declaration measurement guidelines - Sound pressure level at operator's position Sound power level for the product/equipment Guideline: Preparation of Noise Test Codes Declaration of noise-attenuating equipment. Measurement guidelines for: - Silencers - Enclosures - Screens Guideline - Design of low-noise work stations Guideline - Design of low-noise machinery Guideline - Systematic collection and comparison of noise data

14 (Part 1, page 6) Guideline - Preparation of the noise sections in specific machinery safety standards Noise declaration measurements Noise declaration can be defined as a specification of the sound radiation from a given source (indication of noise data of the source). This implies that noise declaration guidelines do not automatically also include specification of limit values for sound radiation. As previously mentioned this must be left to individual agreements between supplier and purchaser or to rules stipulated by national authorities. Noise declaration may serve a number of purposes: 1. Comparison of sound data for corresponding products of different makes 2. Calculation of the influence of a sound source on its surroundings 3. Control that a product is in accordance with given limit values as regards sound 4. Determination of noise-attenuating effort, if needed 5. Evaluation of the effect of noise-attenuating measures 5.2 Determination of (stationary) loudness The method for determination of stationary loudness is described in ISO 532 B it is, however, a little complicated and time-consuming to do it manually. It is easier to use a sound level meter which has this option or a postprocessing method using recordings. A standardised method for calculation of non-stationary loudness is on its way as an addendum to DIN Several measurement systems have the feature for calculating non-stationary loudness, but the results are very dependent on what system is used. 5.3 Determination of sound pressure level The EN ISO standards describe guidelines for the determination of the sound pressure level at operator's position or at another specified position. Determining which of the guidelines is relevant, depends on the measurement accuracy desired, the acoustic environment of the measurement site, and of course also on the product in question. EN ISO gives guidelines for the use of basic standards for determination of emission sound pressure levels at a workstation and at other specified positions. EN ISO describes the measurement of emission sound pressure levels at a workstation and at other specified positions engineering guideline in an essentially free field over a reflecting plane precision grade 2. EN ISO describes the measurement of emission sound pressure levels at a workstation and at other specified positions - survey guideline in situ - precision grade 3. EN ISO describes the determination of emission sound pressure levels at a workstation and at other specified positions based on the sound power level, grade 2 or 3. EN ISO describes the measurement of emission sound pressure levels at a workstation and at other specified position where environmental corrections are required - grade 2 or 3.

15 (Part 1, page 7) 5.4 Determination of sound power levels Determination of sound power level based on sound pressure The EN ISO describes methods for determination of the sound power level of noise sources. The methods of EN ISO are based on measurements of sound pressure level Determination of sound power level based on sound intensity EN ISO 9614 is based on the use of sound intensity measurements to determine the sound power. The standard consists of two parts: Part 1: Measurement at discrete points and Part 2: Measurement by scanning. These standards are more complicated to use, and advanced measurement equipment is necessary. 6. Measurement guidelines 6.1 Types of sound sources The methods specified in this guideline are applicable to all types of sound sources both moving and stationary for indoor and outdoor use. For different types of sound sources the following descriptors should be measured: Small units Loudness level at operator's position Sound pressure level at operator's position Sound power level (measured in laboratory) Single machines Loudness level at operator's position Sound pressure level at operator's position Sound power level (measured in industrial environment) Large/composite plants Loudness level measured in specified positions Sound pressure level measured in specified positions Sound power level for sub-components 6.2 Instrumentation Measurement equipment applied for this measurement guideline can be performed either using monaural or binaural techniques, i.e. using one microphone or a mannequin (artificial head / artificial head and torso). For comparison between measurements from different laboratories, measurements based on pressure microphones are normally preferred. Under certain conditions, particularly where the sound sources are close to the (operator s) head, there may be an essential difference between monaural and binaural measurements. If a mannequin is used, then the quality of the microphones should conform to the relevant standard for microphones and the mannequin. In diffuse field a correction for the influence of the head should be applied. The type of mannequin and correction should be specified in this case. In order to perform postanalysis (other sound quality metrics) it is recommended to carry out recordings.

16 (Part 1, page 8) A linear recording device should be used. If codecs are used, care should be taken by making comparative measurements with a linear device. Normally, an integrating-averaging sound level meter complying with IEC 804 shall be used to measure the loudness (and emission sound pressure level). If it can be shown that the sound pressure level fluctuations measured with the time-weighting characteristic S, are less than ± 1 db, a conventional sound level meter complying with IEC 651 may be used. In this case, the sound pressure level is taken to be the average of the maximum and minimum levels during the period of observation, measured with the time-weighting characteristic S. All the equipment shall be calibrated according to relevant regulations and guidelines before the actual measurement. Ambient condition may have an adverse effect on the system used for the measurements. Such conditions (e.g. strong electromagnetic fields, wind, temperature, etc.) shall be avoided by proper selection or positioning of the system. 6.3 Test environment The test environment should resemble the typical environment of a typical user situation as much as possible. At least the following information should be described: a) If indoors, description of physical treatment of walls, ceiling and floor; make a sketch showing the location of the product under test and room contents; acoustical qualification of room in accordance with 6.2 of EN ISO b) If outdoors, make a sketch showing the location of the product under test with respect to surrounding terrain, including 1) physical description of test environment 2) air temperature in degrees Celsius, barometric pressure in pascals, and relative humidity as a percentage 3) wind speed, in metres per second In both cases it is recommended to specify all other relevant details and if possible take a picture! It is recommended that the background noise of the loudness measurements should be more than 20 phons below the value of the total measured loudness level of the sound source under test. If it is less than 10 db, special care should be taken. Regarding background noise of other measurements it should be at least 6 db and preferably more than 15 db below the level due to the sound source under test. 6.4 Specification of installation and operating conditions The manner in which the sound source under test is installed and operated may have a significant influence on the loudness levels at the specified positions. Relevant instructions of a noise test code, if any exists for the family of sound source under test, should be followed. The operating conditions used during the measurements shall be representative of normal use of the product following a given noise test code. If there is no test code, the product under test shall, if possible, be operated in a manner which is typical of normal use. In such a case, one or more of the following operating conditions shall be selected: a) Sound source under specified load and operating conditions b) Sound source under full load (if different from the first condition above) c) Sound source under no load (idling)

17 (Part 1, page 9) d) Sound source under operating conditions corresponding to maximum sound generation representative of normal use e) Sound source with simulated load operating under carefully defined conditions f) Sound source under operating conditions with characteristic operational cycle Loudness levels at specified positions shall be determined for any desired set of operating conditions (i.e. temperature, humidity, device speed, etc.). These test conditions shall be selected beforehand and shall be held constant during the test. The product under test shall be in the desired operating condition before any noise measurements are made. Use of standardised operating conditions gives a possibility of a general, correct comparison of noise data of different makes. It is also important to note that the standardised operating conditions cannot be adequate for all relevant applications of the machine in question. If, when purchasing a machine, there is a need for noise data for specific applications, it is necessary to perform measurements under the operating conditions in question. 6.5 Specification of measurement positions At the operator s position One or more operator positions shall be specified for equipment which requires operator attention while in operating mode at a typical listening position Enclosed work station position When the operator is located in an enclosed cab or in an enclosure remote from the product under test, the cab or enclosure is regarded as an integral part of the machine under test and, consequently, sound reflections inside the cab or enclosure are considered contributions to the emission sound pressure level. No environmental corrections are permitted. During measurements, doors and windows of the cabin or enclosure shall be open or closed as defined in the noise test code for the machinery or equipment being measured. If the work station or bystander s position of the product is located inside a cab or a cabin, an additional conventional work station or bystander s position outside the cab or cabin (e.g. for maintenance) in the vicinity of product under test shall be specified At the bystander position For equipment which does not require operator attention while in operating mode, an operator position need not to be specified. But a conventional work station for services, maintenance, etc. or one ore more bystander positions shall be defined and stated in the noise test code Measurement positions in other cases In this case at least 4 bystander positions shall be defined. Typically one will place the measurement equipment 1 m away from a virtual reference box as defined in EN ISO 3744 or EN ISO 3745 at a height of 1.5 m above the ground. 6.6 Measurements Measurement time interval The measurement time interval shall be chosen in such a way that the loudness level and, as required, the time characteristics of sound emission at specified positions can be determined for the specified operating conditions.

18 (Part 1, page 10) For products with a specified operational cycle, it is usually necessary to extend the measurement time interval to an integral number of consecutive operational cycles. The measurement time interval shall correspond only to the operational periods for which the emission sound pressure level and, as required, the time characteristics of sound emission are desired. Values of the measurement time interval, possible sub-measurement time intervals and number of operational cycles contained in the measurement time interval are usually to be found in the noise test code specific to the family of machinery or equipment to which the product under test belongs, if any exists. In any case, these values shall be identical to those defined for determining the sound power level of the product under test Steady noise If the sound emission at a specified position is steady for the specified operating conditions, the measurement time interval shall be at least 15 seconds Non-steady noise If the sound emission at a specified position is not steady for the specified operating condition, the measurement time interval and operational periods of the product under test shall be carefully defined and reported in the test results. They are normally specified in the relevant noise test code, if any exist Measurements in frequency bands If supplementarily, measurements are to be made in octave or 1/3 octave bands, the minimum observation shall be 30 seconds for the frequency bands centred on or below 160 Hz, and 15 seconds for the frequency bands centred on or above 200 Hz Repetition of measurements In order to reduce the uncertainty of the determination of loudness, levels at the specified positions, it may be necessary, for a specific type of product, to repeat the measurement a number of times as specified in the noise test code for the family of products or equipment to which the product under test belongs. The value to be used after repeated measurements shall be that defined in the noise test code, if any exists. Repeating measurements involves the following procedure: a) The product under test is turned off and on again, if feasible b) The microphone or mannequin is moved away and set again at the specified position c) The measurement is carried out again in the same environment, with the same instrumentation over the same measurement time interval and for the same mounting and operating conditions Impulsive sound If the sound emission is impulsive, particular care shall be taken when measuring to ensure that the dynamic range of the instrumentation is sufficiently large, and the sound level meter / mannequin system is equipped with an overload indicator. For measurement of the time characteristics of impulsive sound emissions, additional to the repetition procedure described in section 6.6.5, the measurement time interval shall include at least 10 impulsive events, unless other is specified in the noise test code, if any. In order to determine whether or not the sound emission contains impulsive components, one of the procedures given in Bibliography [8] may be used Supplementary measurements If technically possible, it is recommended also to measure and include the A-weighted level and 1/3 octave bands as supplementary information.

19 (Part 1, page 11) 6.7 Accuracy Noise data should always also include information on measurement accuracy, as the measurement accuracy should be taken into consideration when indicating guarantee values and at control measurements. The uncertainty rises from several factors, some associated with the environmental conditions, some with the instrumentation, and some with performing the measurement. Different degrees of accuracy can be obtained - depending on what is asked for - engineering or survey precision, see EN ISO11201 or section 4. When using a measurement system with a mannequin bias from transmission, disturbance of the sound field, the diffuse field correction etc. should be taken into account. If digital equipment is used, the influence of resolution should be stated. 7. Information to be recorded and reported 7.1 Information to be recorded The following information, when applicable, shall be compiled and recorded for all measurements made in accordance with this guideline. Rounding of computed data values shall occur only after performing the final computational step before reporting Product under test Description of the product, including its - type - technical data - dimensions - manufacturer - product serial number - year of manufacture Test conditions a) Precise quantitative description of operating conditions and, if relevant, operational periods and cycle b) Mounting conditions c) Location of product in the test environment d) If the product under test has multiple noise sources, a description of the sources in operation during the measurements Acoustic environment Description of the test environment with relevant sketches and photos, see also section Instrumentation a) Equipment used for measurements, including name, type, serial number and manufacturer b) Method used for verifying the calibration of the measuring system; the date, place and result of calibration shall be recorded c) Characteristics of windscreen (if any)

20 (Part 1, page 12) Location of specified positions A precise quantitative description shall be recorded of all positions where the loudness levels have been measured Noise data All measured loudness level data Other supplementary sound pressure level data Background noise levels and possible correction at each specified position. If required, background noise levels and correction in frequency bands. 7.2 Information to be reported Results of the loudness measurements at the specified positions. The loudness N shall be reported with one decimal in sone and the loudness level L N with one decimal in phon. If a standardised noise test code exists for the product under test, the supplementary data to be reported are probably specified in this. Additionally, the following information shall be given: State that the measurement has been performed in accordance with the specifications in the present Nordtest Guideline Recording and analysis equipment, type, make and model including calibration Place and date when the measurements were performed, and person responsible for the test, date 8. Bibliography 1) Bernsen, J. et al., Sound in design, Danish Design Centre & DELTA Acoustics & Vibration, ) Blauert, J. & Jekosch, U., Sound Quality Evaluation a multilayered problem, EEA-Tutorium, Antwerp, ) Bodden, M., Importance of binaural hearing, Psych. Acoust., Editor A. Schick., Universität Oldenburg, ) Fog, C.L., Optimal Product Sound: Design and Construction Guidelines for Developing Products with Desirable Sound Characteristics and Minimal Noise, Report SPM 144 (in Danish), DELTA Acoustics & Vibration, Copenhagen, ) Järvinen, A. & Maijala, P., On the use of real head recordings in product sound design, Inter- Noise 1997 Proceedings, Vol. II, p ) Maijala, P., Better binaural recordings using the real human head, Inter-Noise 2001 Proceedings, Vol. II, p ) Pedersen, T. Holm & Fog, C.L., Optimisation of perceived product quality, Euronoise, ) Pedersen, T. Holm, Impulsive noise - Objective method for measuring the prominence of impulsive sounds and for adjustment of LAeq, Inter-Noise 2001 Proceedings, p. xx-xx. 9) Porter, N.D. & Berry, B.F., A study of standard methods for measuring the (product) sound quality of industrial products, MPL report CIRA(EXT)021, January ) Zwicker, E. & Fastl, H. Psychoacoustics, Fact and Models, Springer Verlag, 1999.

21 (Part 2, page 1) Nordtest Guideline Draft 5 th working draft, AV 1456/01 Part 2 prepared by Torben Holm Pedersen Measurements and judgments of sound in relation to human sound perception Part 2: Guidelines for listening tests Contents 1. Scope Field of application Normative references Definitions and terms Listening tests Product sound Psychoacoustic metrics Metrics related to sound pressure levels Instrumentation Recording and playback equipment Measuring equipment for physical measurements Types of listening tests Semantic differential test Paired comparison test Selection of words Selection and training of test persons Test jury Expert panel Planning and preparing the listening test Form of test Modes of listening Randomising Listening conditions Duration of tests Recording and reproduction The sound samples Announcements Running the test sessions Introduction to listening test Instruction of test persons Sample answering sheets and pretest Listening test Debriefing Physical measurements Statistical methods Accuracy and significance Information to be reported Bibliography Appendix Psychoacoustics Psychoacoustic metrics Psychoacoustics Psychometric methods...20

22 (Part 2, page 2) Part 2: Guidelines for listening tests 1. Scope It is the intention of these guidelines to provide a tool to increase effectiveness and reliability of listening tests. The guidelines are also meant as a help to perform comparable listening tests. One of the essential items when performing listening tests is to distinguish between objective and subjective tests. This matter is clarified in the guidelines. Since new concepts within acoustics are introduced, section 4 Definitions and terms is rather comprehensive. For some topics in this guideline specific recommendations are given. For other topics the text has the character of a list of items for consideration because the relevant choices depend on the specific test situation. 2. Field of application This guideline is related to listening tests in the field of product sound (e.g. for optimising product sound quality) and of psychoacoustic testing. The principles may also be utilised in measurements of the annoyance potential (see definitions) of environmental noise and noise at workplaces. In general annoyance of environmental noise should be performed as surveys according to ISO/DTS 15666, see section 3 Normative references. The results of listening tests according to these guidelines may be used for comparison of different products, situations and/or working conditions. The results may also be a supplement to physical measurements of the sound/noise or may be used for finding the relevant physical measure (metric) for a certain sound characteristic or situation by correlating the results from the listening tests with measurements using technical instrumentation (physical measurements). 3. Normative references The following normative documents contain provisions that constitute - through reference in this text - this Nordtest Guideline. Parties using this Nordtest Guideline are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to applies. Nordtest as well as members of ISO and IEC maintain registers of currently valid International Standards. 1. IEC Publication 61672, Electroacoustics - Sound level meters 1) 2. IEC Publications and 60804, Sound level meters 3. IEC Publication 60942, Acoustic calibrators 4. IEC Publication 61260, 1/3 and 1/1 octave filters 5. IEC Publication series, Sound system equipment 6. IEC Publication , Listening tests on loudspeakers 7. ISO 1996/1, Acoustics - Description, measurement, and assessment of environmental noise. Part 1: Basic quantities and assessment procedures 8. ISO/CD , Acoustics - Description, measurement, and assessment of environmental noise. Part 2: Determination of environmental noise levels, ISO/DTS Draft Technical specification, Acoustics - Assessment of noise annoyance by means of social and socio-acoustic surveys, ISO/TC 43/SC 1, N1313, ISO (E) Acoustics - Method for calculating loudness level, Section two 11. ISO 226, 1987 (E) Acoustics - Normal equal-loudness level contours 12. ISO 5492, Sensory analysis Vocabulary 1) To be published, replaces IEC and IEC

23 (Part 2, page 3) 13. ISO 4121, Sensory analysis - Methodology - Evaluation of food by methods using scales 14. ISO 4121, Sensory analysis Methodology Paired comparison test 15. ISO 6658, Sensory analysis Methodology General guidance 16. NORDTEST Method proposal , Impulsive noise, Objective method for the measurements of prominence of impulsive sounds and for the adjustment of L Aeq, Definitions and terms 4.1 Listening tests Listening test A listening test is a test where one or more persons in a systematic way are presented to samples of sound and requested to give their evaluations/response in a prescribed manner. Listening tests may be either objective (perceptive - what do the persons hear) or subjective (affective - what do the persons prefer or dislike) as illustrated in figure 1. It is essential for the results that a clear distinction between these two types of tests is made. Physical masurement Auditive measurement Affective test Filter 1 Filter 2 M1 M2 M3 Physical stimulus Perceived stimulus Preferences Sensory sensitivity and selectivity Mood Interest Emotion Background Expectation Objective Subjective Figure 1. Simplified illustration of human sound perception and affection. Filter 1 symbolises our senses (e.g. hearing). Filter 2 symbolises our mental processing of sensory perceptions. M1-M3 illustrates different measuring points. Measurements at each of these points may be made independently of each other, and for a certain purpose measurements in any point(s) without the others may be made. M1: physical measurements (sound pressure levels, loudness ), M2: perceptive measurements (psychoacoustics), and M3: affective tests Perceptive measurements Perceptive tests are objective tests (sensory evaluations, perceptive analysis) where humans are used as measuring instruments. The characteristics of the perceived stimulus are rated in objective terms without asking the test persons for any preferences. The tests are usually made with a panel of trained experts. The persons are trained to express their sensory perception in terms that have been well defined to the test persons in advance. The panel may be trained for a specific purpose. The tests may be discriminative (e.g. paired comparison) or descriptive (e.g. semantic differential test).

24 (Part 2, page 4) Auditive measurements - objective listening tests Auditive tests are perceptive measurements with sound as the stimulus. They are objective listening tests where the test persons express their perception of the sound characteristics in terms which describe the sound as e.g. loud, soft, audible tones, sharp, rough, pulsating, etc. The main purpose is to give information about the character of the sound as perceived by humans Affective tests subjective listening tests Affective tests are subjective listening tests normally performed with a group of naive (untrained and without experience in listening tests) test persons who are representative of the relevant user group a consumer jury. As they may use other words than acousticians for the attributes of the product they hear, the relevant words for expression of the heard sound often have to be found before the answering forms for the listening tests can be made. This can be done e.g. by interviews or focus group discussions. Answers as an immediate response of the persons judgments are preferred. Affective tests are used when the preferred characteristics or the dislikes of a product are sought (preference tests). The main purpose is to give information about humans in relation to the sound in a given context Assessor (sensory) / Test person / Subject Any person taking part in a sensory test. NOTE A naive assessor is a person who does not meet any particular criterion in relation to testing. An initiated assessor is a person who has previous knowledge relevant to the sensory test Selected assessor / Selected test person Assessor chosen for his/her ability to perform a sensory test Expert / Expert listener In the general sense, a person who, through knowledge or experience, has competence to give his/her opinion in the fields about which he/she is consulted. In sensory analysis there are two types of expert, i.e. the expert assessor and the specialised expert assessor Expert assessor Selected assessor with a high degree of sensory (listening) sensitivity and experience of sensory (listening) methodology, who is able to make consistent and repeatable sensory (listening) assessments of various products or sounds Specialised expert assessor Expert assessor who has additional experiences as a specialist in the product and/or process, acoustics and/or marketing, and who is able to perform sensory analysis of the product and to evaluate or predict effects of variations relating to design changes, sound propagation, influence of other (sound) characteristics, etc Panel / Jury Group of assessors chosen to participate in a sensory test Consumer Normally a person who uses a product (user). It may also be a person decisive for the purchase of products (manager, buyer) Neighbour For the purpose of this guideline a neighbour is defined as a person who is exposed to the sound/noise from a product without being a consumer of that particular product.

25 (Part 2, page 5) Expert panel A group of experts who participate in an objective (or perceptive) listening test Test jury A group of persons (users/ buyers/neighbours) who participate in affective (or preference) listening tests Acceptability State of a product or sound favourably received by a given individual or population, in terms of its attributes or its judged confirmation with standard(s) or stated requirement(s) Acceptance The act of a given individual or population of finding that a product or sound answers satisfactorily to his/her/its expectations Preference Expression of the emotional state or reaction of an assessor which leads him/her to prefer a specific product (or sound) to other products (or sounds) of the same type or function Noise annoyance Noise-induced annoyance is a person s adverse reaction to noise. The annoyance caused by noise is a complex relationship between the noise and other physical variables as well as personal, psychosocial, socio-economic and other non-physical variables. Noise annoyance may e.g. be measured by socio-acoustic surveys among people who have been exposed to the noise in a certain context (home environment or workplace) for a period of time (months) Annoyance potential Annoyance potential is the annoyance of sounds measured under laboratory conditions. The listeners may (recommended) or may not be presented to a scenario for the sound. NOTE - Reliable measurements of noise annoyance may not be obtained under laboratory conditions, and it is uncertain to which degree annoyance potential correlates with noise annoyance. If the test persons are presented to the context of the sound by instructions, by pictures, by simulated surroundings or similar, it is believed that the ranking of the annoyance potential of different sounds correlates with the annoyance Scenario A context for the perception of the sound that is simulated for the test person (by pictures, video ) or a context that the test person is asked to imagine (imagine that you hear this sound while sitting ) Auditory attributes Acoustic characteristics of a sound rendered by a perceptual analysis Antagonism Joint action of two or more stimuli, whose combination elicits a level of sensation lower than that expected from superimposing the effects of each stimulus taken separately Synergism Joint action of two or more stimuli, whose combination elicits a level of sensation in excess of that expected from a simple addition of the effects of each stimulus taken separately.

26 (Part 2, page 6) Masking Decrease in the intensity or change in the quality of the perception of one stimulus by the simultaneous exposure of other stimuli Contrast effect Increase in response to differences between two simultaneous or consecutive stimuli Convergence / Assimilation effect Decrease in response to differences between two simultaneous or consecutive stimuli. 4.2 Product sound Product For the purpose of this guideline a product is defined as the item under investigation. The term product is to be understood in a broad sense, the product might be a household article, a car, a train, a plane, a room, a factory... Even events (as e.g. traffic) may be defined as a product for the purpose of this guideline Perceived product quality Perceived product quality is a collection of features that confer the product s ability to satisfy stated or implied needs. This is evaluated on the basis of the totality of perceived features and characteristics of the product, with reference to the expectations and implied needs that are apparent in the users cognitive and emotional situations Product sound quality Product sound quality refers to the adequacy of the sound from a product. The adequacy is evaluated on the basis of the totality of the auditory characteristics of the sound, with reference to the set of desirable product features that are apparent in the user s cognitive and emotional situation. Product Sound Quality as defined above is a concept to emphasise that we are concerned with the characteristics of the product. Product Sound Quality is not an inherent quality of the sound or the product, but is a result of the perceptive and mental processes when a listener is exposed to the sound from a product. Product sound quality is not an absolute parameter, but oriented towards a certain product and customer. NOTE - Evaluation of product sound quality depends on three main areas of knowledge and experience: Acoustics, especially related to physical design and measurements Psychoacoustics: i.e. the relationship between the acoustic input and the perception of the sound Psychology, effects and rules, which govern the judgment process by which the product sound quality is assessed Meaningful and relevant listening tests shall take these three areas into account. The term Product Sound Quality indicates that we are concerned with the characteristics of the product Sound quality The sound quality is the quality (e.g. the fidelity of music, the intelligibility of speech) of reproduced sound or of generated signal sounds (e.g. warning signals). The term Sound Quality indicates that we are concerned with the characteristics of the sound Passive sounds Passive sounds are the sounds that are produced when the product is touched (knocked, pressed, etc.), switches are operated. Examples: the door slamming of cars, refrigerators, etc., the sounds when you operate a PC keyboard, the crunching sound of Cornflakes.