**4. Product sound design process**

Aforementioned intentional and consequential sounds can be designed in order to facilitate a certain product experience. The main aim of the sound design process is to facilitate an auditory experience by using product sounds that are complimentary or supportive to the main product experience. For example, the warning signal of a microwave oven could be designed to be 'inviting' or a shaver could be designed to sound 'sporty'. In both examples, the desired auditory experience can only be achieved by forcing changes into the constructive elements of the main product, as sound is a natural consequence of objects/materials in action.

The design of the consequential and intentional sounds undergoes an iterative process (similar to the method suggested by Roozenburg and Eekels, 2003) that runs parallel to the main design process so that communication between different design teams is kept at its highest level of knowledge-exchange. Thus, a product sound design process incorporates four stages (see Figure 3):


In light of the four-stage sound design process, it is often the case that sound design process starts with the main design brief, in which special attention may have been paid specifically to sound. However, usually the main design concept suggested in the brief can be taken as the basis for sound design.

**Figure 3.** Methods for product sound design -related activities (adapted from: Özcan & van Egmond (2008))

#### **4.1. Stage 1: Sound analysis**

sound models, in terms of specific perceptual effects." Parametric synthesis offers great flexibility, but at the cost of an increased effort to generate realistic, appropriate sounds.

The product sound designer should decide whether the sound will be presented static or dynamic. In the case of static sounds, one may choose to save them as samples to a dedicated piece of memory. The samples can then be played back on-demand. This is often the case with auditory icons and earcons. However, for sonification and continuous sonic interaction, both dynamic by definition, the synthesis model itself will have to be implemented in the chipset of the product. The sound will then be generated and manipulated in real-time, depending on the input of sensors. Note: the implementation of a synthesis model is not always feasible for

Finally, a sound that has been created digitally requires at least a digital-to-analogue convertor, and a loudspeaker or piezo element to be heard. For optimal acoustic efficiency, the resonance frequency of the cavity in which the loudspeaker or piezo element is mounted may require

Aforementioned intentional and consequential sounds can be designed in order to facilitate a certain product experience. The main aim of the sound design process is to facilitate an auditory experience by using product sounds that are complimentary or supportive to the main product experience. For example, the warning signal of a microwave oven could be designed to be 'inviting' or a shaver could be designed to sound 'sporty'. In both examples, the desired auditory experience can only be achieved by forcing changes into the constructive elements of the main product, as sound is a natural consequence of objects/materials in action.

The design of the consequential and intentional sounds undergoes an iterative process (similar to the method suggested by Roozenburg and Eekels, 2003) that runs parallel to the main design process so that communication between different design teams is kept at its highest level of knowledge-exchange. Thus, a product sound design process incorporates four stages (see

**4.** *detailing* of the product for manufacturing with sounds fine-tuned to their purpose.

In light of the four-stage sound design process, it is often the case that sound design process starts with the main design brief, in which special attention may have been paid specifically to sound. However, usually the main design concept suggested in the brief can be taken as the

complex sounds that require CPU processor-intensive models.

tuning to the frequency content of the envisioned sound.

**4. Product sound design process**

58 Advances in Industrial Design Engineering

**1.** *sound analysis* within product usage context;

**2.** *conceptualization* of ideas with sounding sketches;

**3.** *embodiment* of the concept with working and sounding prototypes;

Figure 3):

basis for sound design.

The sound analyses stage starts by first determining when and how the product emits sound and how the sound is incorporated into the human-product interaction. Therefore, observa‐ tional research with high-definition audio-visual recordings is necessary to place the sound in context with the user in an environment natural to human-product interactions. In such observations, the following issues should be considered or paid attention to:


After tackling these issues and making a map of auditory experience within context, dry recordings of the product sound in a studio environment can be taken. Both dry and environ‐ mental sound recordings can be further analysed in terms of acoustic content of the sounds (e.g., Spectrograms, Bark scales) and their basic relevance to psychoacoustics. Subsequently, a comparison can be graphically made between a product sound occurring in a natural environment and the actual sound of the product without any environmental effects.

The acoustical analysis of sounds is also used to pinpoint acoustic regions that can cause sensory discomfort and locate the region or part where the problems with sound occur. Thus, the sound analyses stage continues by analysing the effect of the assembly parts of the product on the product sound. This is carried out by disassembly of the product in a by step-by-step fashion and recording at each stage of disassembly until the last sound-producing component is left. Again, acoustical and psychoacoustic analyses are required for each recorded sound. This is a crucial stage in product sound design that aims at determining which existing component of the product is problematic and can be replaced.

(and the desired experience, directly or indirectly). Sound sketching can be done via tinkering with objects, vocalizations of sounds, and/or using a sound sketching tool (e.g., PSST! Product Sound Sketching Tool). With tinkering, designers are encouraged to find objects that can express the desired auditory expression when in interaction with other objects. It is important here how designers tackle the objects, with what actions and movements. Tinkering is all about creating sounds with ordinary daily objects. With vocalization, designers can vocally imitate the sound with auditory expressions of the desired experience. For example, having learnt during the prior bodily/physical explorations that a *sporty* sound should be *energetic*, *dynam‐ ic*, *determined*, etc., designers can vocalize an engine sound with such auditory expressions. Finally, if designers have access, they can sketch sounds with a specially designed interactive tool such as PSST! (Jansen, Özcan, & van Egmond, 2011). PSST! allows designers to create digital sounds with previously recorded samples by manipulating the timbre, sound intensity,

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The conceptualization phase is complete once the desired auditory expression has been determined. The sound sketches can be further used as a guide for the prototyping of the

In the design and construction of the products, the embodiment phase is the first moment when designers encounter sounds emitting from the newly designed product. The embodi‐ ment phase for sound design concerns the physical product parts that need to be altered/ replaced in order to create the desired auditory experience. Therefore, the problematic parts encountered in the analysis stage will be tackled at the embodiment stage. One activity that is essential to this stage is the prototyping. Designers need to partially prototype the product in order to observe the occurring sound and verify its fit with the desired auditory features and

Similar to the sound analyses stage, each occurring sound needs to be acoustically analysed. The same methods of sound recording and analysis such as used in the analyse phase can be adopted here. However, the observations and conclusions should be tackled around the

Tools and methods used for the embodiment design of sounds depend on the type of sound. Intentional sound design and application require more digital techniques to construct the sound and consequential sound design and application would require more analogue

Intentional sounds are by nature music-like sounds, thus they can be created from scratch with the help of a musical instrument or a computer with proper sound editing tools (e.g., Garage band, Audacity). Timbre, temporal structure, and length are some factors that need to be considered when designing intentional sounds. The intentional sounds are already described

and pitch. PSST! is more suitable for consequential sounds.

product with the desired auditory expression.

**4.3. Stage 3: Embodiment**

desired auditory experience.

*4.3.1. Intentional sounds*

in chapter 3.

techniques to construct the product, hence the sound.

experience.

As exemplified above, the sound analysis stage is based on many iterative processes that involve observations and analyses into human-product interaction within context, the acoustical content of the sound, and physical construction of the product. Such analyses lead to understanding the conceptual and functional role of sound in human-product interaction.

#### **4.2. Stage 2: Conceptualization**

Once the conceptual and functional problems with product sounds are identified during the sound analysis phase, designers can proceed with conceptualizing the to-be-designed new product sounds. The conceptualizing should incorporate the desired product experience (as defined in the product brief) as a reference but focus on the sound-specific relevance to the desired experience. For example, if a shaver is being designed to be *sporty*, the sound does not necessarily have to refer to this concept directly. Semantic associations (i.e., sub-concepts) of *sporty* (e.g., *powerful, dynamic, energetic*) applied on the shaver sound would be also satisfactory as a contribution to the overall product experience.

Therefore, at this stage, it is important first to define the semantic associations of the desired product experience in order to determine what underlying concept could be taken further for sound design. Such conceptual analysis can be made with the help of a couple of methods (Özcan & Sonneveld, 2010). Mindmapping, bodily explorations, and acting out are compli‐ mentary methods that help to deconstruct the meaning of a desired experience. With bodily explorations, designers try to put themselves in a, e.g., *sporty* mood and determine situations when one feels sporty (e.g., jogging, playing tennis). They internally observe what happens in their body if they are sporty and further check their emotional state to determine how pleasant, aroused, or powerful they feel. With acting out, designers physically act out, e.g., *sporty* by moving their bodily parts, vocalizing sounds accordingly, and interacting with other objects. This method is important to determine the physical and temporal properties of the desired experience. Once such explorations into meaning deconstruction are complete, designers can summarize their experiences with the help of a mind map (a.k.a. knowledge map). The purpose of the mindmap is to systematically unravel the meaning of a desired experience, which is an abstract term, and relate it to physical properties of objects/interactions/sounds, which are concrete entities. Furthermore, mindmaps often help designers to determine metaphors which may be useful for the application of the concept. As a result, a concept supporting the desired product experience can be taken further for sound sketching.

Once a concept is selected, a next step is to audiolize this concept with sound sketching. The ultimate goal of sound sketching is to find auditory links that may underlie the selected concept (and the desired experience, directly or indirectly). Sound sketching can be done via tinkering with objects, vocalizations of sounds, and/or using a sound sketching tool (e.g., PSST! Product Sound Sketching Tool). With tinkering, designers are encouraged to find objects that can express the desired auditory expression when in interaction with other objects. It is important here how designers tackle the objects, with what actions and movements. Tinkering is all about creating sounds with ordinary daily objects. With vocalization, designers can vocally imitate the sound with auditory expressions of the desired experience. For example, having learnt during the prior bodily/physical explorations that a *sporty* sound should be *energetic*, *dynam‐ ic*, *determined*, etc., designers can vocalize an engine sound with such auditory expressions. Finally, if designers have access, they can sketch sounds with a specially designed interactive tool such as PSST! (Jansen, Özcan, & van Egmond, 2011). PSST! allows designers to create digital sounds with previously recorded samples by manipulating the timbre, sound intensity, and pitch. PSST! is more suitable for consequential sounds.

The conceptualization phase is complete once the desired auditory expression has been determined. The sound sketches can be further used as a guide for the prototyping of the product with the desired auditory expression.

#### **4.3. Stage 3: Embodiment**

The acoustical analysis of sounds is also used to pinpoint acoustic regions that can cause sensory discomfort and locate the region or part where the problems with sound occur. Thus, the sound analyses stage continues by analysing the effect of the assembly parts of the product on the product sound. This is carried out by disassembly of the product in a by step-by-step fashion and recording at each stage of disassembly until the last sound-producing component is left. Again, acoustical and psychoacoustic analyses are required for each recorded sound. This is a crucial stage in product sound design that aims at determining which existing

As exemplified above, the sound analysis stage is based on many iterative processes that involve observations and analyses into human-product interaction within context, the acoustical content of the sound, and physical construction of the product. Such analyses lead to understanding the conceptual and functional role of sound in human-product interaction.

Once the conceptual and functional problems with product sounds are identified during the sound analysis phase, designers can proceed with conceptualizing the to-be-designed new product sounds. The conceptualizing should incorporate the desired product experience (as defined in the product brief) as a reference but focus on the sound-specific relevance to the desired experience. For example, if a shaver is being designed to be *sporty*, the sound does not necessarily have to refer to this concept directly. Semantic associations (i.e., sub-concepts) of *sporty* (e.g., *powerful, dynamic, energetic*) applied on the shaver sound would be also satisfactory

Therefore, at this stage, it is important first to define the semantic associations of the desired product experience in order to determine what underlying concept could be taken further for sound design. Such conceptual analysis can be made with the help of a couple of methods (Özcan & Sonneveld, 2010). Mindmapping, bodily explorations, and acting out are compli‐ mentary methods that help to deconstruct the meaning of a desired experience. With bodily explorations, designers try to put themselves in a, e.g., *sporty* mood and determine situations when one feels sporty (e.g., jogging, playing tennis). They internally observe what happens in their body if they are sporty and further check their emotional state to determine how pleasant, aroused, or powerful they feel. With acting out, designers physically act out, e.g., *sporty* by moving their bodily parts, vocalizing sounds accordingly, and interacting with other objects. This method is important to determine the physical and temporal properties of the desired experience. Once such explorations into meaning deconstruction are complete, designers can summarize their experiences with the help of a mind map (a.k.a. knowledge map). The purpose of the mindmap is to systematically unravel the meaning of a desired experience, which is an abstract term, and relate it to physical properties of objects/interactions/sounds, which are concrete entities. Furthermore, mindmaps often help designers to determine metaphors which may be useful for the application of the concept. As a result, a concept supporting the desired

Once a concept is selected, a next step is to audiolize this concept with sound sketching. The ultimate goal of sound sketching is to find auditory links that may underlie the selected concept

component of the product is problematic and can be replaced.

as a contribution to the overall product experience.

product experience can be taken further for sound sketching.

**4.2. Stage 2: Conceptualization**

60 Advances in Industrial Design Engineering

In the design and construction of the products, the embodiment phase is the first moment when designers encounter sounds emitting from the newly designed product. The embodi‐ ment phase for sound design concerns the physical product parts that need to be altered/ replaced in order to create the desired auditory experience. Therefore, the problematic parts encountered in the analysis stage will be tackled at the embodiment stage. One activity that is essential to this stage is the prototyping. Designers need to partially prototype the product in order to observe the occurring sound and verify its fit with the desired auditory features and experience.

Similar to the sound analyses stage, each occurring sound needs to be acoustically analysed. The same methods of sound recording and analysis such as used in the analyse phase can be adopted here. However, the observations and conclusions should be tackled around the desired auditory experience.

Tools and methods used for the embodiment design of sounds depend on the type of sound. Intentional sound design and application require more digital techniques to construct the sound and consequential sound design and application would require more analogue techniques to construct the product, hence the sound.

#### *4.3.1. Intentional sounds*

Intentional sounds are by nature music-like sounds, thus they can be created from scratch with the help of a musical instrument or a computer with proper sound editing tools (e.g., Garage band, Audacity). Timbre, temporal structure, and length are some factors that need to be considered when designing intentional sounds. The intentional sounds are already described in chapter 3.

#### *4.3.2. Consequential sounds*

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

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

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

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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

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,

and occurring at different time frames, causing temporal irregularity.

**5.1. Acoustics**

#### **4.4. Stage 4: Detailing**

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 detailing, the product should be ready for manufacturing.
