A project funded by the Department of Trade and Industry to examine sound quality assessment for UK industries.
In the past, sound design has been about minimising the noise generated by a product. The assumption here is that the lower the noise the better. However, this design principle does not always work. In some cases, it may be impossible to lower the noise level below a certain value given the constraints of cost. Maybe the only way to lower the noise level is to make an ineffective product. In other cases, lowering the level of sound may actually result in customers being less satisfied, even if the product still functions. To take an example, we spoke to a manufacturer of outdoor products who designed a low noise leaf blower. However, when the leaf blower was sold, there were a number of returns from customers who assumed that low noise meant low power. In these kind of cases, there is a need to not only look at the total sound energy emitted, but also to look at the detailed quality of the sound. To take the example of the leaf blowers, maybe the solution would be to design one with a low noise level but one that still sounded powerful.
In this context, the process of sculpting of a sound is sometimes referred to as "sound quality", the term "product sound" is also used in this context. Essentially we are changing the sound of a product to increase customer satisfaction and thereby increase sales. A common example in this context is work by the automobile to optimise the sound of car door closures (this work has been made more widely known by the use of the research in car adverts). Car manufacturers realised that the door closure sound is an important first impression of a car, after all when you enter the show room, one of the first things you will do is open the door, sit in the car and close the door. Consequently, some automobile manufacturers have gone to great lengths to make the sound of the car door closing give the impression of a robust and well designed car.
Sound quality is also sometimes referred to as whether the quality of the sound befits the function of the product. But there is more to sound quality than simply making a kettle sound like a kettle. It is about what you want that product sound to portray: do you want it to give the impression of being powerful, robust, well made etc. Sound quality isn't always just about making the product acceptable (although that is an important part), it can also be about changing the impression of customers in a favourable way. Sound engineering isn't always about avoiding annoyance and bad impressions.
The project has been concerned with providing information and tools for the UK industry to promote the use of sound quality. Sound quality has proven to be a powerful tool in the automobile industry, but then that industry spends considerably more on product development. Nevertheless, sound quality has been used to improve customer satisfaction and sales. In crowded and mature markets, such as domestic appliances, sound quality testing is one way to differentiate a product from that competitors.
For more information about Sound Quality please email Trevor Cox at email@example.com.
Poggenburg and Genuit  give the example of a dishwasher. A clear aim was identified: Reduce the sound power level to as low as possible, which would also mean that overall a quieter machine would be made. This led to the assumption that the preferred machine would be the machine currently with the lowest sound power level. Dishwasher A had a sound power level of 44.6dB(A) whereas dishwasher B had a sound power level of 47 dB(A), a difference of 2.4dB which shows that B has close to double of the noise power of A.
However sound quality testing revealed that machine B was in fact the machine with the preferred sound. Further analysis revealed that this was because machine A produced a ‘splash’ sound which was more annoying than machine B. Machine A also had a much lower sound power level therefore the more annoying ‘splash’ sound was not masked by the general operational sound of the machine. This led to the preference for machine B, which had a higher sound power level, and was louder, but had a less annoying sound. Furthermore, a reduction of sound power level would have led to a worsening rather than an improvement of the sound of machine A, because there would be even less noise to mask the annoying sound.
In 1988 HS Sagoo’s PhD thesis  detailed a noise reduction project for vacuum cleaners, where the product sound was improved at a cost of 93.6p per vacuum cleaner. Prior to Sagoo’s work, noise consideration of the product had been given a low priority. It was discovered that vacuum cleaner design was not optimised from the point of view of noise emission. The designers' lack of experience in noise reduction was cited as a reason for this, and therefore Sagoo highlighted the necessity for education in noise reduction techniques and developed guidelines for good acoustical design. An investigation of the principles of noise generation for each major source in a vacuum cleaner revealed that the three major areas of interest in terms of noise and vibration were:
Sources from the electric motor included noise from bearings and/or from the rotor being ‘out of balance’. These sources were identified as being interrelated since any misbalance of the rotor will result in an additional load being placed on the bearings. Bearing noise was not identified as a major problem on a new product but could become a major problem later in the lifetime of a product. These noise sources could also result in additional structural vibration which in turn could lead to sound generated by the outer surface structure.
Vibrations caused by magnetic forces have been found to generate noise by transmitting vibrational energy to the outer casing of the motor. An effect which prompted Fujimoto (in 1983) to introduce a second motor which would counteract the vibrations of the first. The solution however is limited by cost.
The fan noise of the vacuum cleaner was found to generate both broad band noise as well as harmonic components. Harmonic noise relating to the frequency of the rotation of fan blades is what gives helicopters their distinctive sound. In the vacuum cleaner, it has been shown that this noise can be reduced by techniques such as the use of unevenly spaced blades to apply amplitude modulation to the tone and spread energy into the side bands. (It is also possible in some machines to change the frequency of the harmonics by changing the number of blades, blade size and speed of roatation, and therefore generate noise which is less audible). The main source of broad band noise is turbulence in the air flow. The interaction of turbulence with structures in the duct can also lead to the production of pure tones. Standing waves can be produced, or a sudden expansion or constriction within a duct can lead to oscillations which result in acoustic waves. Techniques such as using a sharp bend to change the attenuation at particular frequencies, adding an absorption treatment to the inside of the ducts or using circular ducts instead of rectangular ducts to change resonant frequencies, can all have important noise reduction effects if used appropriately. The addition of a silencer is another possible way to reduce unwanted sounds.
Noise source identification techniques such as the ‘sequential removal of components’ were applied. This is a technique where the noise levels and vibration of an appliance is recorded as it is systematically disassembled and then rebuilt removing constituent parts e.g the appliance housing or dust bag for a vacuum cleaner. This helped in the identification of the major sources of noise, thus allowing the application of noise reduction treatments in the most relevant areas. A resulting list of recommendations for good acoustical design practise included factors such as:
It was concluded that it is not only important to consider noise control at the early stages of design but to study the whole of the manufacturing process for a successful noise reduction. Variations of the motor and cleaner quality during manufacture on the production line had to be taken into account to maintain sound quality standards right through from the earliest conception of a new product to the final stages of manufacture.
The project began by defining the current state of the art and the stakeholder requirements for product sound quality. We carried out a survey of manufacturers, both SMEs and larger companies, within the UK. We also talked to consumer organisations, and those representing the elderly, hearing and visually impaired.
Initially a simple postal questionnaire was carried out in order to establish the perceived relevance of sound quality assessment in a variety of industries. Questionnaires were sent to one hundred UK based manufacturers of a wide variety of different types of products.
The types of product included in the survey, and the categories used to display the results are listed below:
|Outdoor Equipment||Domestic Appliances and White Goods||Heating and water||Home entertainment|
Mowers (domestic and commercial), and engines
DIY tools e.g. Electric screwdrivers, drills, multi-tools, circular saws, jigsaws, etc.
Vacuum cleaner and floor cleaning equipment (domestic and commercial), floor polisher (domestic and commercial), steam cleaner
Extractor hood for oven, small kitchen appliances e.g. juicer, ice-cream makers, steamer, slow cooker, fryer, can opener, bread maker, kettle, food processor, whisk, food mixer/blender, coffee maker, etc.
Fridge (domestic and commercial), freezer, cooker, washing machine, spin dryer, tumble dryer, dishwasher
BBQ, Hostess Trolley, Gas and Electric fire
Hair dryer, commercial hand dryer , electric toothbrush, electric shaver, trimmer and hair remover, massager
Heater (domestic and commercial)
Air conditioning equipment (domestic and commercial), ventilator (domestic and commercial), fan (domestic and commercial), dehumidifier (domestic and commercial)
Shower, water pump, catering and heating boiler
|Computer, projector, camera, camcorder, video recorder, DVD player, TV, mobile phone and associated equipment (e.g. hands free kit), photocopier, scanner, fax machines, printer|
(All products are for domestic use unless otherwise stated)
Forty seven questionnaires were received from companies, in all of the categories listed above, though not all of the specific types of product were covered by the replies. One of the questionnaires was incomplete and so the results from this have not been included. Two companies sent two completed questionnaires from different employees, and one manufacturer sent three completed questionnaires from different employees, since the replies in each case were slightly different, none of these questionnaires have been removed from the results.
The replies to each question received from all of the manufacturers is summarised below.
Respondents were asked to 'tick one box'. When asked is the loudness or quietness of your products important to customer satisfaction 50% of respondents answered 'always' and a further 37% answered 'often'. In reply to the question 'Do you think that the sound quality of your products is important to customer satisfaction?' 46% also answered 'always' and a further 24% answered 'often'. Only one manufacturer returned the answer 'never' in response to the question on sound quality.
This lends support to the idea that a significant proportion of manufacturing companies rate sound quality as an important factor when investigating the acoustic emissions of products. Interestingly one manufacturer said they considered sound quality as 'always' important to customer satisfaction whereas loudness was only 'sometimes' important.
These questions were designed to reveal when loudness and sound quality were considered in the design cycle of a product, and respondents were asked to tick 'as many boxes as apply'. From the replies 59% of the respondents said they considered sound quality at the 'early stages of design' (76% of respondents considered loudness at this stage), 48% 'once a prototype is produced' (54% said they considered loudness at this stage) and 37% at the 'end of product development' (more than the percentage that said they considered loudness at this stage which was 33%). Only three companies selected the options 'sound quality never considered' and one manufacturer selected 'sound quality not important'. None of the companies ticked the boxes 'loudness not important' or 'loudness is never considered'.
The majority of the respondents answers fitted into three categories. Those that considered sound quality: at the early stages of design (28%); once a prototype is produced (15%) or at all three stages of the design cycle (22%). Companies that returned the reply 'other' for consideration of sound quality were further investigated by including them in the list of manufacturers selected for telephone interview (see below).
The three answers to this question are shown in the diagram below along with the 'other' option; once again respondents were asked to tick 'as many boxes as apply'. Three companies had answered sound quality is 'never considered' to the previous question and therefore didn't reply to this question. The two most popular methods of sound quality assessment were found to be 'informal listening by the designers' (63%) and 'accessing acoustic signals on instrumentation' (72%).
48 % of respondents only used one method of sound quality testing. The two major categories being 17% of respondents who said that they used 'informal listening by the designers' alone (although two of these had also ticked the 'other' box), and 28% who said that they relied on 'accessing acoustic signals on instrumentation' alone (although one of these companies had also ticked the 'other' box).
46% relied on more than one type of testing for sound quality in two major groups: 28% said they used a combination of informal listening by designers and accessing acoustic signals on instrumentation and 15% said they used a combination of all three options.
Formal tests using independent juries was not used by any companies with less than 100 employees. Whereas 21% (five of the twenty four) companies with 100 to 1000 employees and 36% (four of the eleven) companies with more than 1000 employees used formal testing with independent juries.
The five companies that had selected the 'other' option for sound quality assessment were further investigated by including them in the list of manufacturers selected for telephone interview (see below).
The written questionnaire was followed up with telephone interviews of a selection of the companies. The time consuming nature of the telephone interview process placed limitations on the number of companies selected for telephone interview. Therefore this stage was not intended to give a representative cross-section of the role of sound quality throughout the whole of the UK's manufacturing industries. Instead the companies interviewed were chosen in order to investigate areas in which manufacturers appeared to demonstrate an enthusiasm about sound quality and its potential applications despite it not already being an established requirement of the product, or to investigate areas in which little sound quality research has been documented. Companies were also chosen to investigate opinions on sound quality in SMEs. The nature of the semi-structured interview strategy allowed this smaller sample to be examined in more depth.
Firstly heating and water is considered as a single category and secondly domestic products and white goods are considered together (several of the companies manufactured both types of product). The heating and water category contained manufacturers of all sizes, but the domestic products and white goods category mainly contained manufacturers with more than 100 employees.
The only manufacturer that returned the reply 'never', when asked whether sound quality was important to customer satisfaction was in the heating and water category.
One manufacturer in the heating and water category said that sound quality is 'not important' and one manufacturer said it is 'never considered'. The other two manufacturers that said sound quality is 'never considered' were in the mowers and outdoor equipment category. None of the manufacturers in the domestic appliances and white goods category said that sound quality was 'never considered' or 'not important'.
A high percentage of manufacturers in the domestic products and white goods category (27% compared to 20% for all of the manufacturers) said that they carried out formal tests using independent juries. This is possibly because these types of manufacturer were all medium or large companies (i.e. with more than 100 employees). Conversely the percentage of manufacturers of heating and water products doing formal tests using independent juries was very low (5% compared to 20% for all of the manufacturers). Most of the manufacturers which said they carried out formal jury testing were further investigated by telephone interview. Interestingly, the percentage of manufacturers using the sound quality method 'informal listening by the designer' was also very high (82% compared to 63% for all the manufacturers) in the domestic appliances and white goods category and low in the heating and water category (50% compared to 63% for all the manufacturers).
Twelve companies and other stakeholders such as consumer groups were selected for semi-structured interviews. The companies manufactured outdoor products, domestic appliances, air conditioning and heating systems, electric showers and audio-visual equipment. The written questionnaire replies of the selected companies are summarized below (click on image for larger version):
Fig 1. Summary of written questionnaire results for companies selected for telephone interviews
All except one of these companies considered that their products are important in terms of loudness and sound quality. Answers to the written questionnaire were used to generate subjects to be explored in the semi-structured interviews. Topics covered during each interview included:
In summary, small and large companies rely on a good work relationship between their marketing and consumers departments as the sound quality of their products is becoming increasingly important to their customers. Sound quality is mainly viewed in terms of noise level and annoyance. Perceptual testing is not usually rigorous instead it is carried out using informal listening by designers, or jury tests using staff and sound quality indices are not usually considered. The industry appears to welcome an approved standard method for sound quality testing. Consumers associations, consider criteria relevant to consumers which relate to the product as a whole; the ease of use, some key features and convenience, for example. Sound quality is mainly only considered for sound reproduction products.
Manufacturers were asked to differentiate loudness from sound quality. Loudness was mainly identified with the sound pressure level and sound quality was understood as an irritant noise, a rattle, a tone or an excessive whine. Manufacturers of air conditioning, some manufacturers of outdoor products and some of white goods mentioned sound that is pleasing to the ear, or sound that does not interrupt a normal conversation.
Manufacturers do not assess automatically the sound quality of their products. They only do it when they develop new products on a large scale or when a significant number of complaints from customers take place. Changes in legislation e.g. the Environmental Noise Directive for outdoor products may drive a manufacturer to take a greater consideration for sound quality assessment. It was also suggested by one manufacturer that sound quality could help Small Medium Enterprises (SMEs) to compete against bigger competitors.
When asked about considering sound quality at the early stage of product design interviewees replied that good sound quality begins with a good selection of components. However, all stressed that sound quality evaluation is an ongoing activity throughout product design, that it is impossible to say what sort of noise is going to be developed at the drawing board stage and that a prototype is necessary to carry out experiments. Sound quality assessment at the design, construction and testing stages is often carried out according to the manufacturers own experiences or standards.
Objective testing is usually crude. Testing is carried out by placing the product in a ‘sound’ room or in some other part of the factory with low background noise. The product is set to perform its normal functions as well as under extreme conditions. The sound level meter is used to obtain a range of figures in dB(A). Only a few companies mentioned using FFT analyzers to try to locate the cause of the annoying sound. One manufacturer mentioned using Cool Edit to hear how the sound would be after removing specific aspects of the noise spectrum.
Perceptual testing is used to pick up information that objective measurements would not. These tests tend to take place when the designers, engineers and quality technicians test prototypes of their product and an opinion of the sound is expressed. Identifying noises which create annoyance or have the potential to make customers believe the product is not working, for example. A shower manufacturer commented that it is also important to take account of the product’s connections with its surroundings as these could also potentially be another source of noise.
Jury testing is also carried out by manufacturers of outdoor products, white goods, air- conditioning and manufacturers of audio-visuals. Again tests often are carried out in rooms of low background noise or a ‘typical’ room such as a kitchen, an office, a domestic room or outside may be selected for tests of the product in situ. The testing panel usually consists of employees of the companies and sometimes of customers. The size of the panel appears to be less than 10 people and the jury is untrained.
It was found that different versions of the jury test are carried out:
Most of companies could not stipulate the exact amount of time taken up by sound quality, as the activity often is carried out during tests on the overall functionality of the product. Though all said only a small percentage of time is spent at present. Two manufacturers commented that subjective tests are faster than objective tests. The current process is reckoned to be reliable because of the low number of received complaints.
A product is considered aurally suitable when:
Manufacturers of appliances were asked to express opinions of their customers knowledge of sound quality.
58% of the companies thought that their customers know what they want from their products, while 42% thought they don’t. When asked about how customers would like their product to sound ideally, 83% said the customer would like their products to sound as quiet as possible. But 17% of the manufacturers acknowledged that quietness is not always that good, because the sound of the product is a source of information and part of the identity of the product. Furthermore when a product such as a hedge trimmer is quiet, it can become a dangerous tool. One manufacturer gave an example of a quiet vacuum cleaner for outdoor use. The vacuum was found not to be successful with the customers because they thought it was not working. They therefore preferred a product with a good sound rather than a quiet sound.
The manufacturers were also asked if they considered ageing and/or disabled populations when doing sound quality assessment. All disregard them with the exception of one manufacturer, who considers the possible interferences between the sound of their product and hearing aids. Such consideration was given because of the personal experience of the designer. Overall there is very limited consideration of the ageing population and people with audio or visual impairments.
None of the companies interviewed were required to comply with consumer sound labelling and regulations (except the regulations for outdoor products) manufacturers. However 60% had their own internal standards. In general the manufacturer’s opinion on sound labelling is relatively poor. They are fully aware of the energy label, however none mentioned:
Manufacturers of outdoor products have strongly expressed that the dB is poorly understood by consumers. The manufacturers therefore are in favour of a change from sound power label in dB(A) to a sound quality label.
Appliance manufacturers consider sound when identifying an annoying sound, but most of them do not look at the sound quality of their product, in a similar way to a car manufacturer. This means they are not after a sound that is, for example, sportive, robust or sharp. Measurements are already considered to be adequate; however, design teams often do not include an acoustics expert. This would explain why so few companies consider using FFT analysers. They also are unaware of the existence of software for sound quality. There appears to be a big gap between current practice in the UK and state-of-the-art sound quality assessment. However, state-of-the-art practices are relatively expensive. Attitudes towards sound quality assessment would also change if the product sound could be heard before purchase in the retail shop (as in the automobile/audio industry) or on internet.
Some companies would like to know how to use an FFT analyser to understand the noise of their product better and have access to rooms with defined acoustics. Others suggested access to some software for sound quality. With the exception of two companies, manufacturers seem to be unaware of psychoacoustics indices, but all agree that although sound quality is not directly measurable it can be described by adjectives and by answering carefully worded questions.
The Consumers Association usually looks at criteria relevant to consumers which relate to the performance of the product, ease of use, some key features and convenience. Sound quality is mainly considered for sound reproduction products because the sound is fundamental. When asked about sound quality of domestic appliances, they require them to be as quiet as possible with no annoying sound.
Associations representing people with hearing impairments consider the sound quality of some products without calling it ‘sound quality’. For example, they will create products which could be heard by people with hearing impairments such as alarm systems, ring tones on the phone or car indicators. Other products on the market can be modified in order to function better for deaf or hard of hearing (H-of-H) people, but this could involve a visual rather than aural modification. In the future, they would like to see products useable by everyone in society. In the case of the visual and hearing impaired, the product ergonomic is mainly considered rather than the sound quality. Some specific projects between the association and the manufacturer do take place where sound modifications can be done, but this is the exception rather than the rule.
A variety of routes were used to reach the industry. A few of these are given below.
Claire Chuchill was a research assistant employed on the project. Claire won the Perspectives poster competition for young researchers at the BA Festival of Science concerning the interaction of Science and Society. Scientists are increasingly being asked to communicate ethical and social issues that arise from their work. Perspectives encourages scientists, at the beginning of their career, to explore and discuss the social implications of their research with a general audience. There are two aspects considered: (i) what impact does the research have on society (direct and/or indirect) and (ii). to what extent can the research (or research area) has been shaped by society.
We held a one-day workshop on sound quality on 15th September 2004:
'Sound Quality Assessment: Will Improving Your Product’s Sound Increase Your Sales?'
After a study looking at the extent and the scope of sound quality testing in the UK industry, it was found that relatively little formal sound quality testing was being carried out in the UK, except in the automobile and in the audio-visual industries. Attempts were made to identify the reasons why so few UK manufacturers are aware of sound quality compared to some of their European compatriots. The two main reasons are the little knowledge manufacturers have of acoustics and the lack of standards and labelling, which would push the manufacturers to consider sound quality. Another reason which justifies the manufacturer’s choice not to consider sound quality in great detail, is the fact there are no facilities in shops allowing the customers to compare the product noise, as they would do for a TV or hi-fi. Interviews also highlighted that labelling is often misunderstood by customers, starting from a lack of understanding of the decibel scale used on some current labels. This has led the research to find out more about labelling across Europe and further afield, and to discuss future possibilities for practical sound labelling of domestic products useable by manufacturers and customers.
After a study looking at the extent and the scope of sound quality testing in the UK industry, it was found that relatively little formal sound quality testing was being carried out in the UK, except in the automobile and in the audio-visual industries. To encourage more testing, it was found necessary to define a cheap but effective method to encourage UK manufacturers of domestic appliances to assess product sound quality. This paper presents the application of this method to kettles of different water volumes, design and power. It is also known, that, among them, the 3kW kettle has given rise to complaints by some consumers as having a sound which is like "a plane taking off." Objective tests are used to estimate the psychoacoustic metrics, while a questionnaire designed for any products is also used for the laboratory-based subjective test. The results from these tests will be presented. In addition, it will be discussed how this has influenced the drawing up of a simple method for sound quality assessment.
This paper presents results from a study into the extent and scope of sound quality testing in the UK. While some European countries have been placing considerable effort to improve the sound quality of white goods, anecdotal evidence suggested that relatively little formal sound quality testing was being carried out in the UK except in the automobile industry. Manufacturers of domestic appliances, outdoor products, home entertainment, heating, air-conditioning and pumps were contacted using a questionnaire survey. A significant proportion of manufacturing companies rate sound quality as an important factor when investigating noise emission. Twelve companies and other stakeholders such as consumer groups have then been selected for semi-structured interviews. Small and large companies rely on a good work relationship between their marketing and consumers departments as the sound quality of their products is becoming increasingly important to their customers. Sound quality is mainly viewed in terms of noise level and annoyance: identify if the sound is quiet and if it is pleasant to the ear. Perceptual testing is not usually rigorous. It is mainly carried out using informal listening by designers, but some use their staff for jury testing. Sound quality indices are not usually used in objective tests. The industry appears to welcome an approved standard method for sound quality testing. Attitudes to labelling, national standards and approved test centres will be discussed.
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