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issue: November 2004 APPLIANCE European Edition

Engineer Sound Quality
Sound Quality Assessment and Labeling

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by Sophie Maluski, Claire Churchill, and Trevor Cox , University of Salford, Salford, UK

The sound that a product makes can tell the user a lot about its quality and functionality. This information may be combined with other non-aural information, such as the product’s performance, design, color, or feel, to give some overall impression. Products that make annoying sounds are unlikely to be well-received, yet proper product sound assessment does not appear to be widely considered throughout the UK.

Sound quality is about measuring and assessing the sound produced by a product. While some countries, such as Germany, Sweden, and France, have made considerable effort to improve the sound quality of white goods, anecdotal evidence suggests that relatively little formal sound quality testing is being performed in the UK. The principle exceptions are the audio-visual and automotive industries, which use product sound as part of television advertising. To properly assess the use of sound quality testing in UK industries, manufacturers of domestic appliances, outdoor power equipment, home entertainment products, heating and air-conditioning equipment, and pumps were surveyed via questionnaire and telephone interviews. This article provides a snapshot of how these industries view product sound.

In a study sponsored by the UK Department of Trade and Industry (DTI), 100 questionnaires were distributed to appliance companies to determine how sound quality is tested across the UK and to generate subjects for more detailed follow-up interviews. Of the 100 questionnaires, 50 were completed and returned. These questionnaires give some insight into sound quality testing in the UK.

A large majority (87 percent) of respondents thought that the loudness or quietness of their products was always or often important to customer satisfaction. But sound quality is not just about whether a product is noisy. It is also about the quality of the noise that is being produced. A product that produces a whine can still be problematic, even if the whine is relatively quiet. When asked if the quality of the sound, rather than its loudness, was important to customer satisfaction, 70 percent answered “always” or “often.” Only one manufacturer responded “never.”

Acoustic engineers often complain that their advice is sought too late in the product design cycle, making it difficult to correct or “design out” problematic sounds in the early stages of product development. However, when UK manufacturers were queried on this point, the situation appeared less problematic. Sixty-percent of respondents said they considered loudness in the early stages of design. About half considered sound quality and loudness after a product prototype was produced, and one-third considered sound quality and loudness in the final stages of product development. All of the respondents felt that loudness was important and considered it at some point during product development.

A dozen companies were selected from the completed questionnaires for more detailed phone interviews, which included manufacturers of outdoor power equipment, domestic appliances, air-conditioning and heating systems, electric shower heaters, and audio-visual equipment. These companies considered their products to be important in terms of loudness and sound quality.

Sound Quality

One method used in sound quality assessment is measuring product sound by using microphones linked to sophisticated sound analysis software. The system samples the sound produced by the product using a model of the human head to make binaural recordings. The software produces a set of acoustic indices that are designed to relate how humans respond to sounds such as loudness, roughness, and sharpness, which are used in product development.

One advantage of this test protocol is that it can eliminate the need for lengthy testing using customer focus groups, but only after considerable research has been conducted to determine which indices are appropriate for each product type. Apart from the automotive and audio-visual industries, the UK respondents do not currently use this protocol and are unaware of sound quality indices. For instance, when asked about loudness, it was mainly identified as the sound pressure level measured in decibels of working products, while loudness better relates to how consumers respond to various frequency sound levels.

The survey revealed that UK industries do conduct sound quality tests without actually calling it sound quality testing. Appliance producers know there are specific sounds that are bad selling points and, therefore, need to be avoided. Those surveyed only do so when new products are developed on a large scale or after a significant number of consumer complaints. Only those that produced outdoor power equipment, as well as some white goods and air-conditioning manufacturers, consider product noise level mainly to comply with the EU Noise Directive and room acoustics standards.

Respondents were asked when a product is considered aurally suitable. Typical answers included the product’s sound level (loudness, quietness); absence of adverse sounds; a pleasant or good sound; sounds better than a competitor’s products; and positive responses to testing by customer focus groups.

Most of the respondents could not tell how much time was devoted to sound quality since most only perform sound assessments while reviewing a product’s complete functionality. Many felt the assessment methods they used were reliable because of the low number of consumer complaints they received about their products’ sound quality.

Sound Quality and Consumers

Small and large companies rely on a good working relationship between their marketing and consumer departments to identify what consumers want from various types of appliances. This can include sound quality issues.

When asked how their customers would like their products to sound ideally, a large majority of companies said customers wanted their products to sound as quiet as possible. One-fifth of the respondents thought that quiet-sounding products were not always ideal because the sounds produced by a product can be a source of information. For example, whether a product is turned on can be important for power tools.

Sound Labeling and The Impact of Sound Labeling Standards

Interviewees were also asked about sound labeling. The best-known sound labeling in the UK include the EU Energy Performance label, the EU Noise Directive’s sound power level, and the European Ecolabel.

The EU Energy Performance Energy label is compulsory for white goods, such as refrigerators, washing machines, dryers, freezers, and dishwashers. The label mainly prioritizes water and energy consumption and enables consumers to make important energy comparisons between products. Also included on the label are requirements for noise levels. The noise level is measured according to the EN 60704 requirements of the Energy Performance Directive 86/594/EEC.

The requirements implemented by the EU Noise Directive in 2000 harmonizes member states’ national laws for noise emission limits and labeling requirements at the manufacturing stage. The label is compulsory for 57 types of outdoor power equipment such as construction machinery, lawnmowers, edge trimmers, and leaf blowers. Sound power is measured in accordance with EN ISO 3744 and EN ISO 3746.

The EU Ecolabel, also known as “the Flower,” was established in 1992 but was later re-lunched in 2000. It is used by goods and services as a voluntary scheme that drives consumer market demand by actively encouraging manufacturers to design products with reduced environmental impacts.

Outdoor power equipment manufacturers that were interviewed all felt that sound quality labeling is the future. Some even expressed a preference for a sound quality label, rather than the EU Noise Directive label, perhaps influenced by their own difficulties in reducing product noise levels. Many were concerned about how sound levels can be translated in a way consumers can understand. If consumers struggle to understand a sound-quality label, introducing more parameters is unlikely to be useful.

White goods manufacturers also expressed some dissatisfaction with the EU Energy Performance label. The fact that that noise requirements are voluntary means that some companies will perform sound testing, while others will not. Some would prefer that the sound label be either compulsory or non-existent. Manufacturers that are not currently required to comply with sound labeling, but provide product noise levels on a voluntary basis made similar comments. These manufacturers found too many noise variants between their own and their competitors’ products and would welcome standardization of noise measurements.


There is relatively little formal sound quality testing being conducted by the UK appliance industry, with the exception of the automotive and audio-visual equipment industries. This may be attributed to manufacturers’ limited acoustic expertise and a lack of sound labeling guidelines and standards. The absence of consumer demand for better sound quality may also be attributed to a lack of awareness of what modern acoustic engineering can achieve.

Presently, only a few products must comply with European sound labeling requirements. Manufacturers are also discouraged from joining a sound-labeling scheme because of vague requirements, a lack of information on the character of sound, and the cost constraints of sound quality research.

About the Authors

Dr. Sophie Maluski coordinated the DTI sound quality project while at the University of Salford, Salford, UK. Currently, she is an acoustic engineering consultant for Hoare Lea in Manchester, UK.

Claire Churchill joined the University of Salford as a research assistant for the DTI’s Sound Quality Project. This is her first acoustics project.

Professor Trevor Cox carries out research, teaching, and commercial activities in acoustics for the University of Salford.


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