Acoustics research centre
Definition of sound quality and products manufactured by the company
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.
Methods of testing and the design and manufacturing process
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:
- In the case of outdoor products, the manufacturer will consider the noise at ear position of both a user and an observer;
- Some manufacturers don’t ask specified questions but instead gauge people’s reactions when the product is switched on specific settings;
- Some manufacturers invite customers to use the products in their houses and complete a questionnaire;
- One company made the comment that to access customer’s opinion, they ask questions at retail outlets;
- There are other manufacturers who consult tests made by consumer associations rather than conduct their own jury test, because they provide a comparison with the competitor’s products.
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.
What is the target sound?
A product is considered aurally suitable when:
- It has a low sound level or the product noise is quiet;
- Adverse noises are non-existent;
- It is a good sound;
- It sounds better than the competitors’ products;
- Subjects give positive comments.