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Guidelines for Jury Evaluations of ... - Sound and Vibration

1 Sound AND Vibration /APRIL 2001 This article provides a set of Guidelines intended to be usedas a reference for the practicing automotive Sound quality (SQ)engineer with the potential for application to the field of gen-eral consumer product Sound quality. Practicing automotivesound quality engineers are those individuals responsible forunderstanding and/or conducting the physical and perceptualmeasurement of automotive Sound . This material draws uponthe experience of the four authors and thus contains a num-ber of rules-of-thumb which the authors have found workedwell in their many automotive related Sound quality projectsover past years. When necessary, more detailed publicationsare referenced. The intent here is to provide a reference toassist in automotive Sound quality work efforts and to solicitfeedback from the general Sound quality community as to thecompleteness of the material is there subjective testing and analysis in automotivesound quality investigations?

2 SOUND AND VIBRATION/APRIL 2001 • Analysis Methods • Subjective to Objective Correlation. Before any type of jury evaluation can be conducted an ad-equate listening space is …

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Transcription of Guidelines for Jury Evaluations of ... - Sound and Vibration

1 1 Sound AND Vibration /APRIL 2001 This article provides a set of Guidelines intended to be usedas a reference for the practicing automotive Sound quality (SQ)engineer with the potential for application to the field of gen-eral consumer product Sound quality. Practicing automotivesound quality engineers are those individuals responsible forunderstanding and/or conducting the physical and perceptualmeasurement of automotive Sound . This material draws uponthe experience of the four authors and thus contains a num-ber of rules-of-thumb which the authors have found workedwell in their many automotive related Sound quality projectsover past years. When necessary, more detailed publicationsare referenced. The intent here is to provide a reference toassist in automotive Sound quality work efforts and to solicitfeedback from the general Sound quality community as to thecompleteness of the material is there subjective testing and analysis in automotivesound quality investigations?

2 One might ask why bother withthe trouble of conducting subjective testing in the first place?In the authors experience, conducting subjective jury evalua-tions of automotive sounds has led to a deeper understandingof those sounds and the way potential customers react to andsometimes appreciate automotive sounds. The following is anattempt to describe subjective testing and analysis as appliedto Sound quality and its relevance to gaining this deeper un-derstanding. The remainder of this article draws upon the ex-perience of the four authors and as a result, may be biased to-ward the techniques they have commonly used or have foundto work well in their automotive Sound quality studies. How-ever, an attempt has been made to address other techniquescommonly used by other researchers in the general field ofproduct Sound quality. Although not a comprehensive docu-ment, it is hoped that this article will provide a set of guide-lines which addresses a majority of the issues and techniquesused in the field of automotive and general product soundquality.

3 It is hoped that this guide will act as a springboard: alaunching point for your own individual investigation into sub-jective testing and analysis for automotive Sound is appropriate to begin with a few fundamental definitionsof terms used throughout this document:Subjective. In Webster s Dictionary, subjective is defined by thefollowing: .. peculiar to a particular individual, .. modi-fied or affected by personal views, experience, or back-ground, .. arising from conditions within the brain or senseorgans and not directly caused by external stimuli, etc. Incertain situations, the word subjective conjures up negativeconnotations, as though subjective results are less valuablepieces of information than objective results. We do not holdthat opinion in our treatment of this topic but consider sub-jective evaluation to be a vital, information-rich portion ofautomotive Sound quality Again Webster helps to clarify what we are investigat-ing. According to Webster quality is.

4 A distinguishingattribute, .. the attribute of an elementary sensation thatmakes it fundamentally unlike any other sensation. Noticethat goodness or badness does not enter into the Testing and Analysis. Subjective testing and analy-sis involves presentation of sounds to listeners, then request-ing judgment of those sounds from the listeners and finallyperforming statistical analysis on the Testing. Jury testing is simply subjective testing done witha group of persons, rather than one person at a time. Subjec-tive testing can be done with a single person or many peopleat a time; both cases have their own set of benefits and cave-ats (see Figure 1).The Task of Sound Quality. In automotive Sound qualitywork, one tries to identify what aspects of a Sound define itsquality. It has been the experience of most persons involvedin noise and Vibration testing, that analysis of acoustic signalsalone does not identify the quality (as defined by Webster) ofthose signals.

5 Individuals will use words like buzzy, cheap, luxurious, weak, etc., to describe the defining attributes insounds. Knowing how to design the correct attributes into avehicle- Sound directly impacts the appeal of the vehicle andultimately impacts the profitability of a vehicle line. No instru-ments or analysis techniques have to date been able to quan-tify the descriptive terms mentioned above without the aid ofsubjective testing of some kind, hence, the need for subjectivetesting and remainder of this guide will take you through most ofthe salient issues involved in subjective testing for automotivesound quality work. This article is not intended to cover psy-choacoustic testing but rather to provide guidance for the prac-ticing Sound quality engineer. Specific topics to be coveredinclude: Listening Environment Subjects Sample ( Sound ) Preparation Test Preparation and Delivery Jury Evaluation MethodsGuidelines for Jury Evaluations ofAutomotive SoundsNorm Otto and Scott Amman, Ford Motor Company, Dearborn, MichiganChris Eaton, Ericsson, Inc.

6 , Research Triangle Park, North CarolinaScott Lake, General Motors Corporation, Milford, MichiganBased on paper number 1999-01-1822 1999 Society of AutomotiveEngineers, Inc. presented at the SAE 1999 Noise & Vibration Confer-ence & Exposition, Traverse City, MI, May 1999. The work on this pa-per was performed while coauthor Chris Eaton was employed by HEADA coustics, Inc., Brighton, MIFigure 1. Typical jury testing room setup (Ford Motor Company).2 Sound AND Vibration /APRIL 2001 Analysis Methods Subjective to Objective any type of jury evaluation can be conducted an ad-equate listening space is required. This is the topic of the EnvironmentRoom Acoustics. If the sounds are presented over loudspeak-ers in any room other than an anechoic chamber, the frequencycharacteristics of the room will be superimposed on the fre-quency characteristics of the loudspeaker and the resonances will then have an effect on the perceivedsound. Additionally, if a jury evaluation is being conducted inwhich the subjects are physically located in different positionswithin the room, the room acoustics will affect the Sound dif-ferently for each subject.

7 No longer will all the subjects expe-rience the exact same Sound , thus, introducing a bias into theresults. If it is necessary to conduct listening Evaluations us-ing loudspeakers, adherence to Sections (Room size andshape), (Reflections and reverberation), and (Roommodes) of the AES standard1 is recommended. It is recom-mended that loudspeaker arrangement conform to AES20-1996 Section (Loudspeaker locations) and location of listenersconform to AES20-1996 Section (Listening locations).Ambient Noise. Control of ambient noise is essential for theproper administration of a subjective listening sources within the listening room can be due to: com-puter fans, fluorescent lighting, HVAC, etc. The influence ofthese sources can be minimized through the remote locationor containment of computers in acoustic enclosures, incandes-cent lighting and HVAC baffles/ Sound treatment. High trans-mission loss into the room is desirable to minimize the influ-ences of outside value dB or dBA levels are generally inadequate indescribing the ambient noise levels of indoor defines octave and one-third octave band noise lev-els for audiometric test However, bands below 125 Hzare undefined and everyday sounds with energy below 125 Hzare commonly encountered.

8 As a result, it is recommended thatambient noise levels should conform to NCB (noise criteria) 20or better3 which specifies allowable levels in the 16 to 8000Hz octave jury Evaluations , the station at which the subject islocated should be free from influences from the other times partitions are placed between subjects to minimizeinteraction between subjects. When listening to low levelsounds, subjects with colds or respiratory ailments can makeit difficult for not only themselves but also adjacent subjectsto hear the The listening room should be a comfortable and in-viting environment for the subject. The room should look natu-ral as opposed to high tech. The more clinical the room looks,the more apprehension and anxiety the subjects will experi-ence. Neutral colors should be used for the walls and chairs and headphones (if used) are essential toreducing distractions and keeping the subject focused on thetask at hand. Moderate lighting should be used.

9 Lighting whichis too dim may reduce a subject s attention to the desired task,especially, during lengthy or monotonous listening Circulation, Temperature and Humidity. The listeningarea should be air conditioned at 72 to 75 F and 45 to 55%relative humidity. Air circulation and filtration should be ad-equate to prevent distractions due to lingering odors. Construc-tion materials used in the facility should be this article, the term subject is used to refer to any per-son who takes part in the evaluation of sounds in a listeningstudy. This section discusses the selection and training of Selection. Some of the factors that should be con-sidered when selecting subjects include subject type, the num-ber of subjects required and how these subjects are Type. Subject type is defined based on listening ex-perience, product experience and Experience: As a general rule, it is desired that thelistening experience level of subjects be appropriate to the taskat hand as well as representative of the target customer.

10 Anexperienced listener may be more capable of judging certainsound attributes than an inexperienced subject. An exampleis the evaluation of loudspeaker timbre for high end For this task, audiophiles familiar with the conceptof timbre are the subjects of choice. An inexperienced listenerwould no doubt have difficulty in discerning the nuances im-portant to the expert. However, most Sound quality evaluationsdo not require such a high level of expertise. Most automotivesound quality work falls into this category and, generally, sub-jects are not required to have previous listening fact, in these cases, using only experts may not be a desir-able thing. Experts often pick up little things that are not par-ticularly important to the customer. Generally, screening sub-jects for hearing loss is not done. To be done properly, hearingtests require skills and equipment usually not at one s addition, such testing may violate subject privacy. Presentedin the Test Preparation and Delivery section are methods ofdetecting poor subject performance and these methods willhelp to identify any hearing related performance Experience: Listener s judgments of sounds are al-ways influenced by their expectations.


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