**5. Product sound designer**

Sound design activities exemplified above are multi-disciplinary by nature and relate to three indispensable disciplines: *acoustics*, *engineering*, and *psychology.* Each of these disciplines contributes equally to the sound design process and a sound designer needs to have insights into each of them. Figure 4 demonstrates how knowledge from these disciplines feeds the sound design process. In the following paragraphs we will explain the individual contribution of these different fields of expertise and create the profile of a sound designer.

**Figure 4.** Main disciplines contributing to product sound design activity (adapted from: Özcan & van Egmond (2008)).

#### **5.1. Acoustics**

*4.3.2. Consequential sounds*

62 Advances in Industrial Design Engineering

**4.4. Stage 4: Detailing**

**5. Product sound designer**

For example, if a food chopper is producing an unwanted fluctuating sound and it has been found that the mill that turns the blade was found vertically tilted due to bad assembly; then, a better construction that stabilizes the mill could be proposed. In another example, the working principles of a coffee machine could be altered by… in order to create the feeling of efficiency and comfort. Furthermore, once the main assembly of the product is finished and a rough sound can be produced, it is possible that old-fashioned techniques of noise closures

The embodiment design phase is complete once the guidelines for the final prototype are achieved. It should be kept in mind that the product sound occurring at the prototyping stage may be different to the sound of the final product. Thus, the embodiment sound design phase consists of iterative stages of creating sounding models, (dis)assembling, and testing with the aim of achieving the desired experience with the final product. The tests involved here range from acoustical measurement and analysis of the sound via a computer to see whether the product sound fits the technical requirements, or cognitive evaluation of sound with potential users to ensure that the occurring sound semantically fits the desired experience. Moreover, with the sounding models, desired interaction with the product can be enabled and observed. This could be done with the help of potential users acting out towards the product and the

In the detailing phase, fine tuning of the product sound takes place. At this stage, the final prototype is built and the product to-be-produced takes its final shape. A more realistic sound is expected as an outcome. More extensive user research takes place with semantic differentials and observational studies. Collected data should yield more accurate results and conclusions regarding the desired experience and interaction. It is possible that the occurring sound still needs further adjustments. At the detailing stage, there will be room for further noise closure and dampening activities that roughly concern the outer shell of the product. At the end of

Sound design activities exemplified above are multi-disciplinary by nature and relate to three indispensable disciplines: *acoustics*, *engineering*, and *psychology.* Each of these disciplines contributes equally to the sound design process and a sound designer needs to have insights into each of them. Figure 4 demonstrates how knowledge from these disciplines feeds the sound design process. In the following paragraphs we will explain the individual contribution

of these different fields of expertise and create the profile of a sound designer.

and dampening could be employed before the casing is designed and assembled.

design team, enabling the interaction with the wizard-of-Oz techniques.

detailing, the product should be ready for manufacturing.

Acoustics is the science that tackles sound phenomena. The field of acoustics is concerned with basic physical principles related to sound propagation and mathematical and physical models of sound measurement. Therefore, the topics of interest for the field of acoustics are the medium in and through which sound travels, reflecting and vibrating surfaces, speed of sound, and other physical characteristics of sound such as sound pressure, wavelength and frequency.

Sound is a result of the energy release caused by objects in action. Although the physical quality of the sound is determined by the sound source and action, *acoustics* does not necessarily investigate the source per se. The physical properties of the source (e.g., the interacting materials, weight, size, and geometry of the objects) are of interest for acousticians. Further‐ more, sound propagates over time because it is the result of time-dependent dynamic events. That is, the physical character (i.e., spectral-temporal composition) of a sound changes over time depending on the type of actions and sound sources. For example, a piano produces a harmonically and temporally structured sound. A lady epilator produces a noisy sound because it contains multiple sound-producing events, each creating different harmonic partials and occurring at different time frames, causing temporal irregularity.

It is essential to understand the acoustic nature of the sound event when designing product sounds. Acoustic analysis of the sound can be first done during the problem analysis phase and can recursively occur until the problem has been defined. The field of acoustics provides tools and methods to analyse and simulate sound. Basic terms used for sound characteristics comprise of 'frequency' (variation rate in the air pressure), 'decibels' (sound intensity), and 'amplitude' (sound pressure). A spectrogram visualizes the frequency content of a sound and the intensity variations in time. Furthermore, a sound wave represents the temporal tendency of sound propagation and the sound pressure over time. It is possible to visually analyse the spectral-temporal composition of a sound event and precisely pinpoint the acoustical conse‐ quences of certain events. Moreover, various sound modelling techniques have been devel‐ oped in the field of acoustics. Simulating sounding objects that are perceptually convincing has been possible thanks to the available computer technology (Cook, 2002; Pedersini, Sarti, & Tubara, 2000; Petrausch, Escolano, & Rabenstein, 2005; Rocchesso, Bresin, & Fernstrom, 2003). Furthermore, sound simulation can also be necessary to test upfront the perceptual effects of the desired sound.

(for the sound of washing machine), wake-up call (for the sound of the alarm clock), and danger

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These conceptual associations of sound indicate that a fit of the sound to the product or with the environment in which the sound occurs is judged. Therefore, a design team cannot overlook the cognitive and emotional consequences of the sound. In various stages of design, user input needs to be carefully considered. Therefore, questionnaires that are aimed at

Above we discussed the major disciplines contributing to sound design. However, some hybrid disciplines also contribute such as psycho-acoustics and musicology. The field of psychoaoustics deals with the basic psychological reactions to the acoustic event. Sharpness (high frequency content), roughness (fluctuation speed of the frequency and amplitude modulation), loudness (sound intensity), and tonalness (amount of noise in a sound) are the main parameters used to observe the psycho-acoustical reaction of listeners. Although these parameters are supposed to be subjective, a general conclusion has been made in the past regarding the threshold and limits of human sensation to sounds. Therefore, psycho-acoustical algorithms have been presented to measure the above-mentioned perceived characters of sound (Zwicker & Fastl, 1990). These algorithms are used to measure the sounds perceptual quality and predict listeners tolerance to sounds. Thus, they are predictive of sensory pleas‐

Designers can design alarm-like synthesized sounds if they have knowledge and practical experience in the field of musicology, as composing music that requires knowledge on theories about musical structures and compositions and tools to create harmonic and rhythmic sounds.

A product sound designer should have knowledge and skills on three major disciplines (engineering, acoustics, and psycho-acoustics) and also on hybrid disciplines such as musi‐

A product sound designer is primarily an engineer that is able to manipulate the product layout and is skilful in applying physical and mathematical knowledge in order to analyse and

However, interpreting the physics of sound per se should also be one of the major roles of such an engineer. Skills in acoustic analyses and ability to simulate sound are necessary. Further‐ more, a sound designer should be able to link the structural properties of a sound to its acoustical composition. In addition, musical knowledge on how to compose synthesized

Furthermore, the psychological correlates of the product sound should also be considered when an engineer is tackling the physical aspects of sound and the product as a sound source. Ultimately, the product sound designer has the last word when judging whether the sound

to model the product lay-out while considering the consequences in terms of sound.

measuring the psychological and cognitive effect of sound could be used.

**5.4. Hybrid disciplines: Psycho-acoustics and musicology**

(for a warning buzzer).

antness or unpleasantness.

**5.5. Responsibilities of a product designer**

cology and psycho-acoustics (see Figure 5).

sounds is required in the case of the intentional sounds.

#### **5.2. Engineering**

Engineering is the discipline through which abstract scientific knowledge takes on an applied nature. For the design of product sounds, three main branches of engineering provide knowledge: mechanical engineering, electric-electronics engineering, and material engineer‐ ing. These relevant fields deal with sound indirectly and rather focus on manipulative (i.e., constructible) aspects of products. Various product parts, mechanisms, lay-out, materials, interactions, and working principles can all be engineered depending on the design require‐ ments of the product and its sound.

In product engineering, functionality of the product should be the main focus. Thus, suggested alterations for the improvement of the product sound can only be carried out if the function‐ ality of the product or product parts are kept intact. Engineers should have satisfactory knowledge on physics and mathematics, and they are able to calculate the energy release as sound or as vibration. Furthermore, the discipline of engineering provides various tools and methods to embody conceptual ideas and solutions to problems. Engineers and designers are well-supported on modelling, testing, and prototyping (Cross, 2000; Hubka & Eder, 1988; Roozenburg & Eekels, 1995). Similar tools and methods could be used for implementing product sounds as well.

#### **5.3. Psychology**

Sound design is not limited to finding technical solutions for a problem. The aforementioned disciplines deal with the physical aspect of sound and the object causing the sound (i.e., product). However, product sounds, just like other environmental sounds, have psychological correlates which may be on a semantic level or an emotional level (von Bismarck, 1974; Kendall & Carterette, 1995; van Egmond, 2004).

Listeners main reaction to any sound is to interpret it with their vocabulary of previous events. Such interpretations often refer to the source of the sound and the action causing the sound, such as a hairdryer blowing air Marcell, Borella, Greene, Kerr, & Rogers, 2000). Listeners are able to follow the changes in the spectral-temporal structure of the sound and perceive it as auditory events or sometimes as auditory objects (Kubovy & van Valkenburg, 2004; Yost, 1990). In the absence of image, just by hearing listeners can describe the material, size, and shape of the sound (Hermes, 1998; Lakatos, McAdams, & Causse, 1997).

For product sounds the conceptual network consists of associations on different levels (Özcan van Egmond, 2012). Source and action descriptions occur the most, followed by locations in which products are used the most (e.g., bathroom, kitchen), basic emotions (e.g., pleasantunpleasant), psychoacoustical judgments (e.g., sharp, loud, rough). In addition, source properties can also be identified (e.g., interacting materials or sizes of the products). Further‐ more, product sound descriptions could also refer to rather abstract concepts such as hygiene (for the sound of washing machine), wake-up call (for the sound of the alarm clock), and danger (for a warning buzzer).

These conceptual associations of sound indicate that a fit of the sound to the product or with the environment in which the sound occurs is judged. Therefore, a design team cannot overlook the cognitive and emotional consequences of the sound. In various stages of design, user input needs to be carefully considered. Therefore, questionnaires that are aimed at measuring the psychological and cognitive effect of sound could be used.

#### **5.4. Hybrid disciplines: Psycho-acoustics and musicology**

& Tubara, 2000; Petrausch, Escolano, & Rabenstein, 2005; Rocchesso, Bresin, & Fernstrom, 2003). Furthermore, sound simulation can also be necessary to test upfront the perceptual

Engineering is the discipline through which abstract scientific knowledge takes on an applied nature. For the design of product sounds, three main branches of engineering provide knowledge: mechanical engineering, electric-electronics engineering, and material engineer‐ ing. These relevant fields deal with sound indirectly and rather focus on manipulative (i.e., constructible) aspects of products. Various product parts, mechanisms, lay-out, materials, interactions, and working principles can all be engineered depending on the design require‐

In product engineering, functionality of the product should be the main focus. Thus, suggested alterations for the improvement of the product sound can only be carried out if the function‐ ality of the product or product parts are kept intact. Engineers should have satisfactory knowledge on physics and mathematics, and they are able to calculate the energy release as sound or as vibration. Furthermore, the discipline of engineering provides various tools and methods to embody conceptual ideas and solutions to problems. Engineers and designers are well-supported on modelling, testing, and prototyping (Cross, 2000; Hubka & Eder, 1988; Roozenburg & Eekels, 1995). Similar tools and methods could be used for implementing

Sound design is not limited to finding technical solutions for a problem. The aforementioned disciplines deal with the physical aspect of sound and the object causing the sound (i.e., product). However, product sounds, just like other environmental sounds, have psychological correlates which may be on a semantic level or an emotional level (von Bismarck, 1974; Kendall

Listeners main reaction to any sound is to interpret it with their vocabulary of previous events. Such interpretations often refer to the source of the sound and the action causing the sound, such as a hairdryer blowing air Marcell, Borella, Greene, Kerr, & Rogers, 2000). Listeners are able to follow the changes in the spectral-temporal structure of the sound and perceive it as auditory events or sometimes as auditory objects (Kubovy & van Valkenburg, 2004; Yost, 1990). In the absence of image, just by hearing listeners can describe the material, size, and shape of

For product sounds the conceptual network consists of associations on different levels (Özcan van Egmond, 2012). Source and action descriptions occur the most, followed by locations in which products are used the most (e.g., bathroom, kitchen), basic emotions (e.g., pleasantunpleasant), psychoacoustical judgments (e.g., sharp, loud, rough). In addition, source properties can also be identified (e.g., interacting materials or sizes of the products). Further‐ more, product sound descriptions could also refer to rather abstract concepts such as hygiene

effects of the desired sound.

64 Advances in Industrial Design Engineering

ments of the product and its sound.

& Carterette, 1995; van Egmond, 2004).

the sound (Hermes, 1998; Lakatos, McAdams, & Causse, 1997).

product sounds as well.

**5.3. Psychology**

**5.2. Engineering**

Above we discussed the major disciplines contributing to sound design. However, some hybrid disciplines also contribute such as psycho-acoustics and musicology. The field of psychoaoustics deals with the basic psychological reactions to the acoustic event. Sharpness (high frequency content), roughness (fluctuation speed of the frequency and amplitude modulation), loudness (sound intensity), and tonalness (amount of noise in a sound) are the main parameters used to observe the psycho-acoustical reaction of listeners. Although these parameters are supposed to be subjective, a general conclusion has been made in the past regarding the threshold and limits of human sensation to sounds. Therefore, psycho-acoustical algorithms have been presented to measure the above-mentioned perceived characters of sound (Zwicker & Fastl, 1990). These algorithms are used to measure the sounds perceptual quality and predict listeners tolerance to sounds. Thus, they are predictive of sensory pleas‐ antness or unpleasantness.

Designers can design alarm-like synthesized sounds if they have knowledge and practical experience in the field of musicology, as composing music that requires knowledge on theories about musical structures and compositions and tools to create harmonic and rhythmic sounds.

#### **5.5. Responsibilities of a product designer**

A product sound designer should have knowledge and skills on three major disciplines (engineering, acoustics, and psycho-acoustics) and also on hybrid disciplines such as musi‐ cology and psycho-acoustics (see Figure 5).

A product sound designer is primarily an engineer that is able to manipulate the product layout and is skilful in applying physical and mathematical knowledge in order to analyse and to model the product lay-out while considering the consequences in terms of sound.

However, interpreting the physics of sound per se should also be one of the major roles of such an engineer. Skills in acoustic analyses and ability to simulate sound are necessary. Further‐ more, a sound designer should be able to link the structural properties of a sound to its acoustical composition. In addition, musical knowledge on how to compose synthesized sounds is required in the case of the intentional sounds.

Furthermore, the psychological correlates of the product sound should also be considered when an engineer is tackling the physical aspects of sound and the product as a sound source. Ultimately, the product sound designer has the last word when judging whether the sound

**6.2 Consequential sound project**

**6.3 The study goals**

duction,

sound design. The goals are:

emotional domain into an adapted product design,

are presented in a colloquium and a written report.

**6.4. The case: Toothbrush**

**•** To learn basic principles of signal analysis (related to sound),

The consequential sound project focuses on the sounds radiated by domestic appliances, and are a consequence of their operating and construction. The students will analyse the sounds in the physical, perceptual, and emotional domain and try to relate these findings to the engineering parts of the product. A product should be disassembled and sound recordings will be made of different parts in order to obtain insight in the contribution of these different parts to the sound. The findings resulting from the analyses in the physical, perceptual, and

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The study goals provide a basis for the self-development of a designer in the field of product

**•** To be able to implement their findings from the analyses in the physical, perceptual, and

**•** To learn the effect of tolerances on the performance of the appliances and its sound pro‐

The students get 6 ects (European credit transfer system) for this elective course. This means that they have to invest 168 study hours to come to new ideas and realize them in an adapted or innovative product sound design. The valuable results of three years since the elective

First of all, because the education method of this elective was very successful it will be upheld. The students are working in project teams because of the complexity of the topic. The frontal lectures are limited to project planning and organization, and to an introduction into the basics of product sound design. Sound recording is explained as among which: use of software, lab set-up, and how to record. Most recordings will be carried out in the Audio Lab, but if the project requires recordings can be made at a specific location (e.g. public transport card project). The coaching of the teams is on the initiative of the students which stimulates them in their search for creative and innovative solutions. At specific moments during the project, teams have to explain the project progress. During these moments coaches discuss the progress and results and give advice to go into a certain direction when necessary The results of a project

We use a student project of a toothbrush as an example. The team measured the sound under load, shown in the lab setup in figure 6. This laboratory setup is easily adaptable to record the

emotional domain are used to redesign new parts or different working principles.

**•** To learn how sound is produced in products and experienced by people,

**•** To learn the relationship between product quality and sound quality.

started were used to develop further on the elective product sound design.

**Figure 5.** Professional domains of a sound designer (adapted from: Özcan & van Egmond (2008)).

fits the desired experience and the interaction within the context of use. Knowledge on psychoacoustical analyses is required to predict the first user reactions only to sound. Later, semantic analyses need to be conducted with potential users to make sure the sound design is complete and appropriate to the product.

### **6. Product sound design course**

Product Sound Design is an elective course of the Master of Industrial Design Engineering Education at Delft University of Technology. In product sound design we distinguish two main types of sounds: Intentional sounds and Consequential sounds. The two types of sounds are addressed to the second half year - in the first quarter intentional sound and in the second quarter consequential sound. The students involved are working in project teams of two or three students. The elective consists of a project with few lectures to support the project. The final results should be presented to all course members and stakeholders in a colloquium. The presentation takes approximately 25 minutes with 5 to 10 minutes for questions and discussion. The project is graded on the deliverables: presentation, and report. For the projects, domestic appliances are chosen such as: kids alarm, public public transport card check in and check out, electrical toothbrush, choppers in different versions, shavers, etc..

#### **6.1 Intentional sound project**

The intentional sound project approaches the design of these sounds from an interaction perspective. These sounds are synthesized or recorded and are often more musical or speechlike. Therefore, the sounds are created by use of music software. The function of sounds is often to alarm or to provide feedback to users. The project focuses on perception and re-design of these sounds from n interaction point of view . It is essential that these sounds are designed on the bases on the interactions, otherwise improper sounds will result.

#### **6.2 Consequential sound project**

The consequential sound project focuses on the sounds radiated by domestic appliances, and are a consequence of their operating and construction. The students will analyse the sounds in the physical, perceptual, and emotional domain and try to relate these findings to the engineering parts of the product. A product should be disassembled and sound recordings will be made of different parts in order to obtain insight in the contribution of these different parts to the sound. The findings resulting from the analyses in the physical, perceptual, and emotional domain are used to redesign new parts or different working principles.

#### **6.3 The study goals**

fits the desired experience and the interaction within the context of use. Knowledge on psychoacoustical analyses is required to predict the first user reactions only to sound. Later, semantic analyses need to be conducted with potential users to make sure the sound design is complete

**Figure 5.** Professional domains of a sound designer (adapted from: Özcan & van Egmond (2008)).

Product Sound Design is an elective course of the Master of Industrial Design Engineering Education at Delft University of Technology. In product sound design we distinguish two main types of sounds: Intentional sounds and Consequential sounds. The two types of sounds are addressed to the second half year - in the first quarter intentional sound and in the second quarter consequential sound. The students involved are working in project teams of two or three students. The elective consists of a project with few lectures to support the project. The final results should be presented to all course members and stakeholders in a colloquium. The presentation takes approximately 25 minutes with 5 to 10 minutes for questions and discussion. The project is graded on the deliverables: presentation, and report. For the projects, domestic appliances are chosen such as: kids alarm, public public transport card check in and check out,

The intentional sound project approaches the design of these sounds from an interaction perspective. These sounds are synthesized or recorded and are often more musical or speechlike. Therefore, the sounds are created by use of music software. The function of sounds is often to alarm or to provide feedback to users. The project focuses on perception and re-design of these sounds from n interaction point of view . It is essential that these sounds are designed

electrical toothbrush, choppers in different versions, shavers, etc..

on the bases on the interactions, otherwise improper sounds will result.

and appropriate to the product.

66 Advances in Industrial Design Engineering

**6.1 Intentional sound project**

**6. Product sound design course**

The study goals provide a basis for the self-development of a designer in the field of product sound design. The goals are:


The students get 6 ects (European credit transfer system) for this elective course. This means that they have to invest 168 study hours to come to new ideas and realize them in an adapted or innovative product sound design. The valuable results of three years since the elective started were used to develop further on the elective product sound design.

First of all, because the education method of this elective was very successful it will be upheld. The students are working in project teams because of the complexity of the topic. The frontal lectures are limited to project planning and organization, and to an introduction into the basics of product sound design. Sound recording is explained as among which: use of software, lab set-up, and how to record. Most recordings will be carried out in the Audio Lab, but if the project requires recordings can be made at a specific location (e.g. public transport card project). The coaching of the teams is on the initiative of the students which stimulates them in their search for creative and innovative solutions. At specific moments during the project, teams have to explain the project progress. During these moments coaches discuss the progress and results and give advice to go into a certain direction when necessary The results of a project are presented in a colloquium and a written report.

#### **6.4. The case: Toothbrush**

We use a student project of a toothbrush as an example. The team measured the sound under load, shown in the lab setup in figure 6. This laboratory setup is easily adaptable to record the

**Figure 6.** Laboratory setup and Barks analysis for the maximum and minimum load on the toothbrush. The load will be applied by hanging bolts on the toothbrush.

**Figure 7.** Inside image of the toothbrush.

**Figure 8.** Barks analysis on the complete disassembly of the toothbrush.

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**Figure 9.** Sketches of the redesign - in this case the working principle is changed.

sound of the toothbrush under different loads. A sound level meter is used to obtain the loudness level in decibels. The recordings will be analysed to get insight into the sound effects at different power loads. The brush force for brushing teeth effectively lies between a maxi‐ mum of 2N and minimum of 0.5 N in normal use.

The maximum load applied to the toothbrush is determined by the operation of the toothbrush at the boundary of the function in this case. The minimum load of the tooth‐ brush is determined by its own weight. Figure 6 shows the graph of 2N and 0.5N loads the influence of load on the toothbrush can be observed on the Bark scale. A peak is observed at 20 Barks for a load of 0.5N. It moves to a lower frequency domain of 15 Barks when the maximum load is reached.

The disassembly of the toothbrush is carried out in order to analyse the recordings of the parts contributing to the sound. In figure 7 the inside organization of the toothbrush is shown.

Disassembling of the toothbrush from complete product (situation black) to only the electro‐ motor (situation brown) the recordings in barks in figure 8. The different graphs of disassem‐ bling the product are given in different colours. With a decrease of number of parts (disassemble step after step), the sound will gradually cut down.

The main axel (situation blue) is the main cause in the irritating rattling noise. When removed (situation green), there is a big decrease in the peak around 20 barks and a lowering of 6dB in volume. In the last stage of disassembly (situation brown), only the motor is active, that results in a sound of 45 dB. Gearing parts are assembled on the motor; this will increase the resistance that contributes to a louder sound, especially in the lower-frequency domain.

**Figure 7.** Inside image of the toothbrush.

sound of the toothbrush under different loads. A sound level meter is used to obtain the loudness level in decibels. The recordings will be analysed to get insight into the sound effects at different power loads. The brush force for brushing teeth effectively lies between a maxi‐

**Figure 6.** Laboratory setup and Barks analysis for the maximum and minimum load on the toothbrush. The load will

The maximum load applied to the toothbrush is determined by the operation of the toothbrush at the boundary of the function in this case. The minimum load of the tooth‐ brush is determined by its own weight. Figure 6 shows the graph of 2N and 0.5N loads the influence of load on the toothbrush can be observed on the Bark scale. A peak is observed at 20 Barks for a load of 0.5N. It moves to a lower frequency domain of 15

The disassembly of the toothbrush is carried out in order to analyse the recordings of the parts contributing to the sound. In figure 7 the inside organization of the toothbrush is shown.

Disassembling of the toothbrush from complete product (situation black) to only the electro‐ motor (situation brown) the recordings in barks in figure 8. The different graphs of disassem‐ bling the product are given in different colours. With a decrease of number of parts

The main axel (situation blue) is the main cause in the irritating rattling noise. When removed (situation green), there is a big decrease in the peak around 20 barks and a lowering of 6dB in volume. In the last stage of disassembly (situation brown), only the motor is active, that results in a sound of 45 dB. Gearing parts are assembled on the motor; this will increase the resistance

mum of 2N and minimum of 0.5 N in normal use.

be applied by hanging bolts on the toothbrush.

68 Advances in Industrial Design Engineering

Barks when the maximum load is reached.

(disassemble step after step), the sound will gradually cut down.

that contributes to a louder sound, especially in the lower-frequency domain.

**Figure 8.** Barks analysis on the complete disassembly of the toothbrush.

**Figure 9.** Sketches of the redesign - in this case the working principle is changed.

In final stage, hand sketching is used to express the solution by means of the working principle. Sketching is a handy tool for the designer to visualize the working principle, product ideas, and parts quickly on paper. The sketches show how parts may be produced and assembled. However, implementing it in a product is often not feasible, therefore the intended sound cannot be measured. The toothbrush changes are based on sketching because making a prototype with rapid prototyping could bring you far away from the final solution because the replacement material has never the same sound property. In figure 9 sketches of a redesign are shown.

**Author details**

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Lau Langeveld, René van Egmond, Reinier Jansen and Elif Özcan

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