**2. Products**

is in fact creating a small musical composition (i.e., musical motives). Therefore, these sounds

Consequential product sounds are experienced as "noisy". It is very difficult for users, for designers, and for acoustical engineers to verbally express how they experience a sound. Several problems exist. In general, users lack the vocabulary to express themselves to explain what is wrong or right with a sound. They normally will say the product makes a unpleasant sound or noise. Designers also lack the vocabulary to express design concepts that may also be used in the design of a sound. The acoustical engineers have a very technical vocabulary from the disciplines of physics and sometimes psychoacoustics, which does not communicate very well to designers and to users. In addition, to understand the aesthetic and emotional experience of product sounds knowledge from the field of psychology (auditory perception, cognition, and emotion theories) is needed. As stated before, product sounds are loud and noisy. This inherent property makes it difficult to describe the sound in a structural manner. The reason for this is, of course, that noise by itself is random and lacks structure. However, product sounds do not produce completely random noise due to the resonance and engine/ boiler properties of products (of course, there are many sources that are responsible for the generation of sound in domestic appliances). It is the aim of this product sound course of Industrial design Engineering(IDE), Delft University of Technology (DUT) to try to relate descriptive aspects from the physical, perceptual, and experiential domain to each other in

The top-down processing (involving knowledge stored in memory or mental representations) will result in the attribution of meaning (e.g., recognition, identification), relating sound to certain events, evoking (cognitive) emotions. It is important to note that the sensorial experi‐ ence of a sound can be — often — directly related to the spectral and temporal features of a sound, whereas this is more difficult for top-down aspects (except for very well-structured sounds like speech and music). As described above, one of the aspects that is well known is the irritation that sounds evoke. The irritation can often be contributed to the sensorial processing of the sounds. It can be argued that top-down aspects, like the attribution of

meaning, can positively influence the experience whether a sound is irritating or not.

In courses, students hear the sound of an epilator. This sound evokes a rattling and rough experience. If the students are asked to tell the source of the sound most students say this sound stems from a hedge-trimmer or some other power tool. If they are told that it is an epilator and they listen to the sound for a second time, the look on their face is complete‐ ly different and reveals a sense of unpleasantness. Thus, the experience of a sound changes if the meaning is known. One of the perceptual aspects that cause this is the rattling of the product caused by the construction, the gears, and the engine. This aspect can be cap‐ tured by the measure of roughness. This attribute can be related to the structural proper‐ ties of the sound in spectral and temporal domains and is one of the determinants in the

can also be used to convey brand values of companies.

48 Advances in Industrial Design Engineering

order to improve the sound of domestic appliances.

**1.1. The perception of sound**

perception of sensory pleasantness.

A product is the result of a design process that starts with a design problem, involves ideation phases, and ultimately leads to a market introduction. In the context of product sound design, mainly domestic appliances are considered. The appliances have moving parts that can move linear or radial and are joined together in such a way to fulfills its functional aspect. and in particular the sound of the product. The product sound is influenced by many physical parameters such as: material, size, form, stiffness, load, energy etc.

#### **2.1. Technology**

Energy facilities are dependent on the place of use. For instance a product with a combustion engine is not used in houses or factory halls, because the pollution of the environment and sound intensity. Electricity is the most convenient energy type which is available in the form of batteries and power outlet. All other types of energy such as, hydro-electric power, fuel cells, human power, solar energy and atomic energy are not considered because the main power source is electricity. Electricity is easy to convert into another type of energy such as: thermo energy, mechanical energy, chemical energy, etc., but every conversion means an energy loss.

Product sounds manifest themselves in mainly three sources airborne sound, liquid sound and structure-borne sound. In a product we are dealing mainly with structure-borne sound sources that find their way to the outside environment by radiation. Transfer paths take care of the propagation of the sound from the source to the environment of the product. Structure-borne sound demonstrates itself in solids, in constructions that are built up from plates, beams, shells and shafts. The material properties determine the propagation speed, which is constant for certain waves and forms. The propagation speed depends on elasticity, specific gravity and contraction, which is different for solid materials. However, steel and aluminium have the same propagation speed because the division of the elasticity by the density is the same (E/ρ).


**Table 1.** Propagation speed for a number of materials, liquid, and air (Verheij, 1992).

The size of a product is determined by the required function and power needed to fulfil the function. For instance, a toaster: the electricity is converted into heating power for toasting the bread. The size of a toaster depends on the efficiency of the reflection and isolation of the power. The heating element is a sound source. An additional sound source is the relief mechanism.

designer, and manufacture. The relationship between the domains are the activities:

Product Sound Design: Intentional and Consequential Sounds

http://dx.doi.org/10.5772/55274

51

**Figure 1.** Figure 1: Product relationship with the domains production, embodiment, and design.

**Design Product Embodiment Production**

Observer level Sensory experience Aesthetically Availability Owner level Social experience Status symbol Benefit

User level Physical experience Practical Parts making & Assembly

Each domain is associated with different levels see table 2. The domain design associates the user, observer and owner level. The domain product points out the physical, sensory and social experiences (after derivation of design from the consumer's point of view (Heufler, 2004). The two other domains have also pointed out the levels, the levels are for embodiment: practical, aesthetically, and status symbol. The levels are for production: parts making and assembly, availability, and benefit. The eye catcher is 'benefit' at the domain production, because without any profit, no other activity shall be undertaken which results in the production of products. Investments are made in production and design. Finally the activities should be profitable in

Creating, Designing and Making.

a given period.

**Table 2.** Domains with their levels.

The bending stiffness is the elasticity (E) multiplied by the moment of inertia (I) which is dependent on the cross-section type and the dimensions. For instance an electric milk shaker has a bar with a certain mass on the end. If the bar turns around then it is bending under the gyroscopic force. Better bending stiffness could be achieved if a hollow profile is used. This is because the mass is further away from the centre of gravity. The bending energy is dependent on the stiffness but has a lower bending stiffness means a higher bending energy. This bending energy is transformed into sound.

A load is needed to fulfil the required mechanical function for a right performance of the appliance at a certain speed. The power required for the function fulfilling is the load a torque (T), that is necessary for processing times the speed (ω). The needed power out, Pout= ω x T. The power input multiplied by the efficiency of energy transforming ηet and mechanical transmission ηmt is, Pout = Pin x ηet x ηmt.. The choice of type of power and mechanical drive is really important for the overall efficiency ηeff. If the efficiency of the permanent magnetic motor is 50% and the mechanical drive 80% for each transmission in a three-step drive, then the efficiency is only 25.6%. The conclusion could be that the best drive is the one without the mechanical transmission, so the energy transforming is only responsible for the efficiency. The biggest advantage of a direct drive is less parts, which reduce enormously an amount of sound sources. The efficiency of a product depends on the energy losses which are transformed through friction into heat, and the movements of masses in sound or noise.

Moving product parts are necessary to fulfil the function of domestic appliances which have six degrees of freedom in a three dimensional space, three degrees are transversal and the other three are rotational. The complete drive of a domestic appliance consists of an electric motor with a mechanical transmission that will be built up with machined parts to adjust the revolutions per minute that is needed with a certain torque. The best drive is without any moving parts, the direct drive. For example, a gear shaft has only one degree of freedom, namely rotation around its own axis. All the other degrees of freedom will be restricted to zero by the construction. For this purpose, fixed, detachable, and combination joints are available. A certain clearance is needed to realize their relative movements. A minimum and a maximum clearance can be determined depending on the tolerances of two parts, as well as small expansions due to temperature increases. Tolerances are the result of the chosen manufactur‐ ing process, which is determined by material, shape, size and volume of production. The clearance in the joints of the parts has a certain freedom of movement of the masses. This costs an amount of moving energy which will be transformed in a product sound.

#### **2.2. Product domains**

The product has relationships with three domains: Design, Embodiment and Production (see figure 1). The domains have a relationship which three conditions: environment, designer, and manufacture. The relationship between the domains are the activities: Creating, Designing and Making.

**Figure 1.** Figure 1: Product relationship with the domains production, embodiment, and design.

Each domain is associated with different levels see table 2. The domain design associates the user, observer and owner level. The domain product points out the physical, sensory and social experiences (after derivation of design from the consumer's point of view (Heufler, 2004). The two other domains have also pointed out the levels, the levels are for embodiment: practical, aesthetically, and status symbol. The levels are for production: parts making and assembly, availability, and benefit. The eye catcher is 'benefit' at the domain production, because without any profit, no other activity shall be undertaken which results in the production of products. Investments are made in production and design. Finally the activities should be profitable in a given period.


**Table 2.** Domains with their levels.

The size of a product is determined by the required function and power needed to fulfil the function. For instance, a toaster: the electricity is converted into heating power for toasting the bread. The size of a toaster depends on the efficiency of the reflection and isolation of the power. The heating element is a sound source. An additional sound source is the relief mechanism.

The bending stiffness is the elasticity (E) multiplied by the moment of inertia (I) which is dependent on the cross-section type and the dimensions. For instance an electric milk shaker has a bar with a certain mass on the end. If the bar turns around then it is bending under the gyroscopic force. Better bending stiffness could be achieved if a hollow profile is used. This is because the mass is further away from the centre of gravity. The bending energy is dependent on the stiffness but has a lower bending stiffness means a higher bending energy. This bending

A load is needed to fulfil the required mechanical function for a right performance of the appliance at a certain speed. The power required for the function fulfilling is the load a torque (T), that is necessary for processing times the speed (ω). The needed power out, Pout= ω x T. The power input multiplied by the efficiency of energy transforming ηet and mechanical transmission ηmt is, Pout = Pin x ηet x ηmt.. The choice of type of power and mechanical drive is really important for the overall efficiency ηeff. If the efficiency of the permanent magnetic motor is 50% and the mechanical drive 80% for each transmission in a three-step drive, then the efficiency is only 25.6%. The conclusion could be that the best drive is the one without the mechanical transmission, so the energy transforming is only responsible for the efficiency. The biggest advantage of a direct drive is less parts, which reduce enormously an amount of sound sources. The efficiency of a product depends on the energy losses which are transformed

Moving product parts are necessary to fulfil the function of domestic appliances which have six degrees of freedom in a three dimensional space, three degrees are transversal and the other three are rotational. The complete drive of a domestic appliance consists of an electric motor with a mechanical transmission that will be built up with machined parts to adjust the revolutions per minute that is needed with a certain torque. The best drive is without any moving parts, the direct drive. For example, a gear shaft has only one degree of freedom, namely rotation around its own axis. All the other degrees of freedom will be restricted to zero by the construction. For this purpose, fixed, detachable, and combination joints are available. A certain clearance is needed to realize their relative movements. A minimum and a maximum clearance can be determined depending on the tolerances of two parts, as well as small expansions due to temperature increases. Tolerances are the result of the chosen manufactur‐ ing process, which is determined by material, shape, size and volume of production. The clearance in the joints of the parts has a certain freedom of movement of the masses. This costs

The product has relationships with three domains: Design, Embodiment and Production (see figure 1). The domains have a relationship which three conditions: environment,

through friction into heat, and the movements of masses in sound or noise.

an amount of moving energy which will be transformed in a product sound.

energy is transformed into sound.

50 Advances in Industrial Design Engineering

**2.2. Product domains**

The relationship between design and production is the activity creating, or availability of production facilities. The availability is necessary to create the production under the con‐ straints of the part design, manufacturing process and material. The designer must have good knowledge of: manufacturing and assembly, material, and aesthetics to create a successful product sound design.

always has limitations resulting from the starting material, for example wood is limited by the age of the tree. The volume of production can range from single pieces to mass; this requires constantly changing of the manufacturing processes and thus different clearance requirements are possible. At mass production, the tolerances are under control; otherwise the failure rate is too high. Zero defects is possible with mass production. However, before this is achieved,

Product Sound Design: Intentional and Consequential Sounds

http://dx.doi.org/10.5772/55274

53

The manufacture makes the parts between the upper and lower limits of the tolerance. The clearance between two assembled parts will be between maximum and minimum size of the individual components. A minimum clearance is preferred because the excitation has than the smallest movement, and the smallest influence on the components, resulting in a lower sound pressure. Of course it is unique to reach this situation by means of a manufacturing system. Most clearances are reached between averages of the tolerances. Every domestic appliances produce sound. The production of these sounds is a consequence of their operating and construction. Therefore, these sounds are called consequential sounds. These sounds should be analysed in the physical, perceptual, and emotional domain to relate subjective findings to

If a domestic appliance is switched on then the power will conduct through the construction of parts to fulfil the working principle. Efficiency of the function is never hundred percent the losses are raised by friction of moving parts and vibration of parts, by mechanical excitation

The consequential product sound model are shown in figure 2, with four main aspects: sources,

transmission of sound in the product, radiation, and transmission to receiver.

the entire production system must be calibrated.

the engineered parts of the product.

**2.3. Consequential product sound model**

of the construction.

**Figure 2.** Model for product sound.

The relationship between design and embodiment is the activity of designing, which is mostly carried out by a designer. Note that, designing is not engineering but creative problem solving, which always results in an embodiment. Engineering is a structured way of solving problems which lead to technical solutions that result in, objects, or systems.

The relationship between embodiment and production is the activity of making, the realization of a product with machinery or manually with a set of tools. Making gives satisfaction to a designer that a product can be realized. This experience is increasing the personality and identity of designer. The conditions form the relationship of the product with the domains of design, production and embodiment. Manufacturers make it possible to realize products by means of production This condition is an important connection in the product realization process. The designer is the condition to realize the product from a design. However, there are differences in the quality of the product design. This is caused by the personality and identity of a designer. The environment is the condition that an embodiment can be manifested as a product. The product should be manufactured from raw material to parts which will be assembled as a whole. This may be a component, a sub-assembly or a product. Two kinds of tolerances occurred, which are known as dimensional tolerances and geometric tolerances, in manufacturing of parts and in the assembly of parts into a whole. Every manufacturing process has its own tolerances that depends on material, type of process, stiffness, geometry etc. For steel and aluminium the ratio E/ρ is almost equal, so also sound prolongation speed. Elastic modulus is always influencing the stiffness coefficient EI with I as moment of inertia, which results in dimensional tolerances and geometric tolerances. However, the manufacturing process speed and force have influence on the size of tolerance, but not on geometric (form). The power of the manufacturing process is transformed is force and speed, which the tem‐ perature of the work will rise higher. The height of temperature is dependent on the power needed for the process and processed material. It results in temperature elongation, which influenced the tolerances after cooling of the work to the temperature of the environment.

The designers make the manufacturing process choices which depends on material, shape, size and volume of production, which results in certain dimensional and geometric accuracy. After assembling two parts, the clearance will manifest as a result of the separate accuracy of these parts. For instance for plastics it is harder to reach the accuracy, because the temperature elongation is much higher than that of steel. For instance a folding plastic garden chair should be able to fold up, which is made possible by hinge points which are required if the parts have to move freely. The chair does not have a power source to conduct, but has a force to hold. Here, large tolerances are acceptable while the comfort is not being affected. With plastic, these tolerances are achievable despite the poor accuracy of the manufacturing processes. Shape of a part is to be achieved by cutting, extrusion, forging, moulding, casting, stamping, forming etc. However, not every material is applicable for every manufacturing process. But the size always has limitations resulting from the starting material, for example wood is limited by the age of the tree. The volume of production can range from single pieces to mass; this requires constantly changing of the manufacturing processes and thus different clearance requirements are possible. At mass production, the tolerances are under control; otherwise the failure rate is too high. Zero defects is possible with mass production. However, before this is achieved, the entire production system must be calibrated.

The manufacture makes the parts between the upper and lower limits of the tolerance. The clearance between two assembled parts will be between maximum and minimum size of the individual components. A minimum clearance is preferred because the excitation has than the smallest movement, and the smallest influence on the components, resulting in a lower sound pressure. Of course it is unique to reach this situation by means of a manufacturing system. Most clearances are reached between averages of the tolerances. Every domestic appliances produce sound. The production of these sounds is a consequence of their operating and construction. Therefore, these sounds are called consequential sounds. These sounds should be analysed in the physical, perceptual, and emotional domain to relate subjective findings to the engineered parts of the product.

If a domestic appliance is switched on then the power will conduct through the construction of parts to fulfil the working principle. Efficiency of the function is never hundred percent the losses are raised by friction of moving parts and vibration of parts, by mechanical excitation of the construction.

#### **2.3. Consequential product sound model**

The relationship between design and production is the activity creating, or availability of production facilities. The availability is necessary to create the production under the con‐ straints of the part design, manufacturing process and material. The designer must have good knowledge of: manufacturing and assembly, material, and aesthetics to create a successful

The relationship between design and embodiment is the activity of designing, which is mostly carried out by a designer. Note that, designing is not engineering but creative problem solving, which always results in an embodiment. Engineering is a structured way of solving problems

The relationship between embodiment and production is the activity of making, the realization of a product with machinery or manually with a set of tools. Making gives satisfaction to a designer that a product can be realized. This experience is increasing the personality and identity of designer. The conditions form the relationship of the product with the domains of design, production and embodiment. Manufacturers make it possible to realize products by means of production This condition is an important connection in the product realization process. The designer is the condition to realize the product from a design. However, there are differences in the quality of the product design. This is caused by the personality and identity of a designer. The environment is the condition that an embodiment can be manifested as a product. The product should be manufactured from raw material to parts which will be assembled as a whole. This may be a component, a sub-assembly or a product. Two kinds of tolerances occurred, which are known as dimensional tolerances and geometric tolerances, in manufacturing of parts and in the assembly of parts into a whole. Every manufacturing process has its own tolerances that depends on material, type of process, stiffness, geometry etc. For steel and aluminium the ratio E/ρ is almost equal, so also sound prolongation speed. Elastic modulus is always influencing the stiffness coefficient EI with I as moment of inertia, which results in dimensional tolerances and geometric tolerances. However, the manufacturing process speed and force have influence on the size of tolerance, but not on geometric (form). The power of the manufacturing process is transformed is force and speed, which the tem‐ perature of the work will rise higher. The height of temperature is dependent on the power needed for the process and processed material. It results in temperature elongation, which influenced the tolerances after cooling of the work to the temperature of the environment.

The designers make the manufacturing process choices which depends on material, shape, size and volume of production, which results in certain dimensional and geometric accuracy. After assembling two parts, the clearance will manifest as a result of the separate accuracy of these parts. For instance for plastics it is harder to reach the accuracy, because the temperature elongation is much higher than that of steel. For instance a folding plastic garden chair should be able to fold up, which is made possible by hinge points which are required if the parts have to move freely. The chair does not have a power source to conduct, but has a force to hold. Here, large tolerances are acceptable while the comfort is not being affected. With plastic, these tolerances are achievable despite the poor accuracy of the manufacturing processes. Shape of a part is to be achieved by cutting, extrusion, forging, moulding, casting, stamping, forming etc. However, not every material is applicable for every manufacturing process. But the size

which lead to technical solutions that result in, objects, or systems.

product sound design.

52 Advances in Industrial Design Engineering

The consequential product sound model are shown in figure 2, with four main aspects: sources, transmission of sound in the product, radiation, and transmission to receiver.

**Figure 2.** Model for product sound.

The sources of sound are defined as: airborne sound, liquid borne sound and structure borne sound. Gaver (1993) mentioned the events as sound sources, the interaction of material at a location in an environment with a certain impact caused by the power. The power sources could be from outside the product as electricity, water, gas and air. For example electricity is mostly used in domestic appliances or consumer goods such as: coffee maker, dish washer, extractor fan, convection oven, electric drill, shaver, grinder, hairdryer etc. Examples for water could be the tap in the kitchen, water sprinkler for the garden, sprinkler installation as fire protection etc. Gas and air also have good examples in the home such as: stove in the kitchen, airbrushes for decoration etc.

**Sources Primary excited**

Air or

another gas

Construction

**Table 3.** Defining the sound sources.

**3. Intentional product sounds**

sounds is often to alarm or to provide feedback to users.

Air borne sound

Liquid borne

Structure borne sound

sound Liquid

**medium Type of excitation Examples**

Aero dynamical

Combustion

Hydro dynamical

Aero dynamical

Hydro dynamical

Electro mechanical

Intentional sounds are 'intentionally' implemented and are typically produced by means of a loudspeaker or piezo element. They are mostly digital and somewhat musical sounds often used in user interfaces. Intentional sounds can be found in, e.g., domestic appliances (e.g., alarm clocks, mobile phone button beeps, microwave oven finish bells, operating system welcome tunes), automotive (e.g., low fuel warning, unfastened seatbelt alert), public transport (e.g., beeps at check-in points), and healthcare (e.g., heart-rate monitoring). These synthesized or recorded sounds are typically created using music software. The function of intentional

Mechanical Compressor

Mechanical Plunger pump

Mechanical Inertia: unbalanced

Refrigerator

Turbulent flow

Gas burner

Gear pump

sawing

Air spray

Turbulence in flow Cavitation

Turbulence gas flow

Releasing of whirls Air jet on surface Water heating

Pole attraction

Magnetostriction in transformer

Autogenous welding

Exhaust gasses in the exhaust pipe

Product Sound Design: Intentional and Consequential Sounds

http://dx.doi.org/10.5772/55274

55

Collide: hammering, rolling, stamping,

Fan

The energy can also be stored in a battery, gas bottle, container or human. This energy can be delivered to the product at the desired moment for a limited time. For example, the water tank (container) of a toilet is used for flushing the toilet bowl after use of the toilet and it is then filled again. The water contains the amount of potential energy that is needed to flush the toilet.

In table 3 (next page) the sound sources with primary excited medium are defined. Type of excitation should be always an activity such as: mechanical, aero dynamical, hydro dynamical etc. The examples are experienced in daily life in a household and a manufacturing plant. Özcan has six product sound categories defined; these are not based on sources but on the experience of the sources. There is always energy stored in the sources or fed from outside the product by the power outlet.

Radiation is the excitation of airborne sound by surfaces and other parts of a product. In water such as: mobility for boats, water bikes, wind surfboard, etc. the radiation of sound is also important. Transmission of sound takes place by means of the transfer of the primary excited medium such as construction, air and liquid. In a product multiple propagation paths may occur depending on the product layout. Construction sound transmission are carried out by the components of the product, but air and liquid sound transmission is carried out by air and liquid -filled cavities or by the mediums air and liquid.

The receiver always experiences the product sound in an environment, but the sound propa‐ gates from the product by air. However, the sources are experienced after the transmission in the product and the radiation to the environment. Cooking on a gas stove is nice example because you experience the amount of gas flows that simultaneous burns. Besides you also experience the gas flow as high or low at a certain distance. The gas supply with small pressure and combustion have an interaction with the environment.

Two approaches are possible to create the desired product sound. The first approach may reduce noise, e.g., projector, air conditioning, air hammer etc. The second approach is a product sound design (powerful experience, intensive experience) to be designed; e.g., electric shaver, toothbrush, electric power tool.

Before the desired product sound can be designed, the product must be measured against the sound of an existing product. From a product design, a prototype can be built which can also be measured. Measuring the individual contributions of the parts and components are notified through disassembling (deconstruction) a product, removing part after part.


**Table 3.** Defining the sound sources.

The sources of sound are defined as: airborne sound, liquid borne sound and structure borne sound. Gaver (1993) mentioned the events as sound sources, the interaction of material at a location in an environment with a certain impact caused by the power. The power sources could be from outside the product as electricity, water, gas and air. For example electricity is mostly used in domestic appliances or consumer goods such as: coffee maker, dish washer, extractor fan, convection oven, electric drill, shaver, grinder, hairdryer etc. Examples for water could be the tap in the kitchen, water sprinkler for the garden, sprinkler installation as fire protection etc. Gas and air also have good examples in the home such as: stove in the kitchen,

The energy can also be stored in a battery, gas bottle, container or human. This energy can be delivered to the product at the desired moment for a limited time. For example, the water tank (container) of a toilet is used for flushing the toilet bowl after use of the toilet and it is then filled again. The water contains the amount of potential energy that is needed to flush the toilet.

In table 3 (next page) the sound sources with primary excited medium are defined. Type of excitation should be always an activity such as: mechanical, aero dynamical, hydro dynamical etc. The examples are experienced in daily life in a household and a manufacturing plant. Özcan has six product sound categories defined; these are not based on sources but on the experience of the sources. There is always energy stored in the sources or fed from outside the

Radiation is the excitation of airborne sound by surfaces and other parts of a product. In water such as: mobility for boats, water bikes, wind surfboard, etc. the radiation of sound is also important. Transmission of sound takes place by means of the transfer of the primary excited medium such as construction, air and liquid. In a product multiple propagation paths may occur depending on the product layout. Construction sound transmission are carried out by the components of the product, but air and liquid sound transmission is carried out by air and

The receiver always experiences the product sound in an environment, but the sound propa‐ gates from the product by air. However, the sources are experienced after the transmission in the product and the radiation to the environment. Cooking on a gas stove is nice example because you experience the amount of gas flows that simultaneous burns. Besides you also experience the gas flow as high or low at a certain distance. The gas supply with small pressure

Two approaches are possible to create the desired product sound. The first approach may reduce noise, e.g., projector, air conditioning, air hammer etc. The second approach is a product sound design (powerful experience, intensive experience) to be designed; e.g., electric shaver,

Before the desired product sound can be designed, the product must be measured against the sound of an existing product. From a product design, a prototype can be built which can also be measured. Measuring the individual contributions of the parts and components are notified

through disassembling (deconstruction) a product, removing part after part.

airbrushes for decoration etc.

54 Advances in Industrial Design Engineering

product by the power outlet.

toothbrush, electric power tool.

liquid -filled cavities or by the mediums air and liquid.

and combustion have an interaction with the environment.

### **3. Intentional product sounds**

Intentional sounds are 'intentionally' implemented and are typically produced by means of a loudspeaker or piezo element. They are mostly digital and somewhat musical sounds often used in user interfaces. Intentional sounds can be found in, e.g., domestic appliances (e.g., alarm clocks, mobile phone button beeps, microwave oven finish bells, operating system welcome tunes), automotive (e.g., low fuel warning, unfastened seatbelt alert), public transport (e.g., beeps at check-in points), and healthcare (e.g., heart-rate monitoring). These synthesized or recorded sounds are typically created using music software. The function of intentional sounds is often to alarm or to provide feedback to users.

This section first provides an elaboration on different functions and types of intentional sounds. Then, an overview will be given on commonly used techniques for implementation. A suggested design process for these sounds can be found later in this chapter.

semantic link between the sounds and the data they represent. Differentiation is commonly found in terms of pitch, rhythm, timbre, spatial location, duration, and tempo (Hoggan *et al.* 2009). A second class of intentional sounds are *auditory icons*. Contrary to earcons, these are natural, everyday sounds, which are described in terms of their sources (e.g., the air flow sound of a fan to represent the state of a steam vent). Due to their semantic link to the things they represent, auditory icons are supposedly easier to learn and remember than earcons (Hearst *et al.* 1997). A third class of intentional sound is *sonification*, which concerns continuous data display. An ongoing awareness of a total system can be created, by including both alarming sounds and reassuring sounds for 'normal' states. Barrass argues that sonification can be used for monitoring an entire system, whereas earcons and auditory icons are better suited for diagnosis of subsystems (Hearst *et al.* 1997). Finally, a fourth class of intentional sounds has emerged. Rather than focusing on system states, *continuous sonic interaction* aims at sonifying expressiveness in human-product-interaction. A study by Rocchesso *et al.* (2009) illustrates how dynamic, continuous sound can influence the way we interact with a range of experi‐

Product Sound Design: Intentional and Consequential Sounds

http://dx.doi.org/10.5772/55274

57

Intentional product sounds are typically generated with music software. The type of imple‐ mentation depends on the classes of intentional sounds. Two main approaches can be dis‐ cerned: recording and parametric synthesis. In the recording approach, (parts of a) product or environment are recorded, which can be done outdoors with a field recorder, or in an acous‐ tically-treated recording room. The absence of room reverb in the latter condition facilitates editing at a later time. Recordings can be manipulated (e.g., equalization, compression), sliced, and layered to create a more complex sound. The main advantage of using recordings is the ease with which a realistic sound can be obtained. This approach lends itself well to creating auditory icons. However, recordings are not as flexibly manipulated as sounds created with

Parametric sound synthesis concerns the creation of sound starting from nothing. This implies that every sound feature deemed important should be included in a model. With such a model, the sound can then be manipulated according to its corresponding parameters. Typical techniques include additive, subtractive, wavetable, amplitude modulation, frequency modulation, and granular synthesis (examples on these techniques can be found in Farnell, 2010). Here, the use of elementary waveforms (i.e., sine, saw tooth, triangle) and/or noise is the common starting point. Parameters usually relate to an acoustical description of the sound (e.g., saw tooth wave and filter cutoff frequencies). Another technique that has gained increased attention over the years is physical modelling. This technique commonly employs mass-spring, dampener, and resonator models that mimic the working principles and construction of, e.g., musical instruments. Consequentially, parameters relate to 'natural' features, such as plucking force, string length, and material thickness. Rocchesso *et al.* (2009) argue that for continuous sonic interaction "the main sound design problem is not that of finding which sound is appropriate for a given gesture. Instead, the main problem is that of finding a sensible fitting of the interaction primitives with the dynamical properties of some

mental kitchen appliances.

parametric synthesis.

**3.3. Implementation of intentional sounds**

#### **3.1. Functions of intentional sound**

Added sounds are regularly used to communicate abstract meanings or to provide information about the result of a process or activity (feedback). For example, when pressing membrane buttons on a microwave oven, the buttons themselves do not make sound. However, a 'beep' sound produced by a built-in piezo element will confirm the user's choice, after which the microwave's platform starts to rotate and produce its typical cyclic sound. This illustrates how as augmentation, intentional sounds are not inherently coupled to either a user's action or a product's functionality (see: consequential sounds). Yet, listeners learn to attribute meaning to added sounds, as they are generally designed to convey certain messages. For example, Edworthy *et al.* (1995) investigated the potential effects of changes in acoustic parameters (e.g., pitch, rhythm) on associated meanings (e.g., controlled, dangerous, steady). This attribution process is highly context-dependent. Consider how the perceived urgency of identical warning sounds may be different depending on whether it indicates a low battery warning of a mobile phone, or a problem with a heart rate monitoring system. See Hoggan *et al.* (2009) for an example on contextual differences in mapping audio parameters to informing signals by user interfaces (i.e., confirmations, errors, progress updates, warnings). Furthermore, product sounds are always part of a larger auditory environment. For example, an intensive care unit consists of a wide range of monitoring equipment. Lacking a standard for their alarm sounds, nurses potentially mistake a 'code red' alarm of one machine for a 'mild' alarm of another machine (Freudenthal *et al.*, 2005, Sanderson *et al.* 2009). Therefore, it is essential to design intentional sounds based on the interactions users (should) have with the product in a given context, and based on how people perceive these sounds.

One can differentiate between discrete and continuous feedback. The button tones of a microwave oven serve as confirmation of a completed action. They give discrete feedback, as they only sound once after a key has been pressed. This is different from continuous monitoring of a process, such as the series of beeps emitted by parking assistants in modern cars. Here, the time between consecutive beeps is inversely related to the distance to the car behind. Therefore, this is also an example of dynamic feedback. On the other hand, the microwave button tones always sound the same, regardless of how the user pushes them. Thus, this type of feedback can be called static. The decisions between discrete vs. continuous and dynamic vs. static feedback have consequences on the implementation of the corresponding sounds, as will be shown later.

#### **3.2. Classes of intentional sound**

One can discern between four main classes of intentional sounds: earcons, auditory icons, sonification, and continuous sonic interaction. The examples given so far mainly consisted of beep-like sounds. They are part of a larger class of discrete musical sounds which are called *earcons*. As discussed before, the abstract mapping of earcons must be learned, as there is no semantic link between the sounds and the data they represent. Differentiation is commonly found in terms of pitch, rhythm, timbre, spatial location, duration, and tempo (Hoggan *et al.* 2009). A second class of intentional sounds are *auditory icons*. Contrary to earcons, these are natural, everyday sounds, which are described in terms of their sources (e.g., the air flow sound of a fan to represent the state of a steam vent). Due to their semantic link to the things they represent, auditory icons are supposedly easier to learn and remember than earcons (Hearst *et al.* 1997). A third class of intentional sound is *sonification*, which concerns continuous data display. An ongoing awareness of a total system can be created, by including both alarming sounds and reassuring sounds for 'normal' states. Barrass argues that sonification can be used for monitoring an entire system, whereas earcons and auditory icons are better suited for diagnosis of subsystems (Hearst *et al.* 1997). Finally, a fourth class of intentional sounds has emerged. Rather than focusing on system states, *continuous sonic interaction* aims at sonifying expressiveness in human-product-interaction. A study by Rocchesso *et al.* (2009) illustrates how dynamic, continuous sound can influence the way we interact with a range of experi‐ mental kitchen appliances.

#### **3.3. Implementation of intentional sounds**

This section first provides an elaboration on different functions and types of intentional sounds. Then, an overview will be given on commonly used techniques for implementation.

Added sounds are regularly used to communicate abstract meanings or to provide information about the result of a process or activity (feedback). For example, when pressing membrane buttons on a microwave oven, the buttons themselves do not make sound. However, a 'beep' sound produced by a built-in piezo element will confirm the user's choice, after which the microwave's platform starts to rotate and produce its typical cyclic sound. This illustrates how as augmentation, intentional sounds are not inherently coupled to either a user's action or a product's functionality (see: consequential sounds). Yet, listeners learn to attribute meaning to added sounds, as they are generally designed to convey certain messages. For example, Edworthy *et al.* (1995) investigated the potential effects of changes in acoustic parameters (e.g., pitch, rhythm) on associated meanings (e.g., controlled, dangerous, steady). This attribution process is highly context-dependent. Consider how the perceived urgency of identical warning sounds may be different depending on whether it indicates a low battery warning of a mobile phone, or a problem with a heart rate monitoring system. See Hoggan *et al.* (2009) for an example on contextual differences in mapping audio parameters to informing signals by user interfaces (i.e., confirmations, errors, progress updates, warnings). Furthermore, product sounds are always part of a larger auditory environment. For example, an intensive care unit consists of a wide range of monitoring equipment. Lacking a standard for their alarm sounds, nurses potentially mistake a 'code red' alarm of one machine for a 'mild' alarm of another machine (Freudenthal *et al.*, 2005, Sanderson *et al.* 2009). Therefore, it is essential to design intentional sounds based on the interactions users (should) have with the product in a given

One can differentiate between discrete and continuous feedback. The button tones of a microwave oven serve as confirmation of a completed action. They give discrete feedback, as they only sound once after a key has been pressed. This is different from continuous monitoring of a process, such as the series of beeps emitted by parking assistants in modern cars. Here, the time between consecutive beeps is inversely related to the distance to the car behind. Therefore, this is also an example of dynamic feedback. On the other hand, the microwave button tones always sound the same, regardless of how the user pushes them. Thus, this type of feedback can be called static. The decisions between discrete vs. continuous and dynamic vs. static feedback have consequences on the implementation of the corresponding sounds, as

One can discern between four main classes of intentional sounds: earcons, auditory icons, sonification, and continuous sonic interaction. The examples given so far mainly consisted of beep-like sounds. They are part of a larger class of discrete musical sounds which are called *earcons*. As discussed before, the abstract mapping of earcons must be learned, as there is no

A suggested design process for these sounds can be found later in this chapter.

**3.1. Functions of intentional sound**

56 Advances in Industrial Design Engineering

context, and based on how people perceive these sounds.

will be shown later.

**3.2. Classes of intentional sound**

Intentional product sounds are typically generated with music software. The type of imple‐ mentation depends on the classes of intentional sounds. Two main approaches can be dis‐ cerned: recording and parametric synthesis. In the recording approach, (parts of a) product or environment are recorded, which can be done outdoors with a field recorder, or in an acous‐ tically-treated recording room. The absence of room reverb in the latter condition facilitates editing at a later time. Recordings can be manipulated (e.g., equalization, compression), sliced, and layered to create a more complex sound. The main advantage of using recordings is the ease with which a realistic sound can be obtained. This approach lends itself well to creating auditory icons. However, recordings are not as flexibly manipulated as sounds created with parametric synthesis.

Parametric sound synthesis concerns the creation of sound starting from nothing. This implies that every sound feature deemed important should be included in a model. With such a model, the sound can then be manipulated according to its corresponding parameters. Typical techniques include additive, subtractive, wavetable, amplitude modulation, frequency modulation, and granular synthesis (examples on these techniques can be found in Farnell, 2010). Here, the use of elementary waveforms (i.e., sine, saw tooth, triangle) and/or noise is the common starting point. Parameters usually relate to an acoustical description of the sound (e.g., saw tooth wave and filter cutoff frequencies). Another technique that has gained increased attention over the years is physical modelling. This technique commonly employs mass-spring, dampener, and resonator models that mimic the working principles and construction of, e.g., musical instruments. Consequentially, parameters relate to 'natural' features, such as plucking force, string length, and material thickness. Rocchesso *et al.* (2009) argue that for continuous sonic interaction "the main sound design problem is not that of finding which sound is appropriate for a given gesture. Instead, the main problem is that of finding a sensible fitting of the interaction primitives with the dynamical properties of some 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 complex sounds that require CPU processor-intensive models.

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 tuning to the frequency content of the envisioned sound.

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

observations, the following issues should be considered or paid attention to:

**•** facial expressions of users for detecting unpleasant or unwanted sounds,

**•** stages of product use and occurrence of sound in any given stage,

**•** other environmental/product-related sounds that could mask the sound in question,

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 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

Product Sound Design: Intentional and Consequential Sounds

http://dx.doi.org/10.5772/55274

59

**4.1. Stage 1: Sound analysis**

**•** acoustic effect of environment on the sound,

**•** interaction of the product with the user and environment,

**•** duration of the product use and exposure to sound,

**•** impact of sound on product usability.
