The sound of science

Today, manufacturers and to some extent, end-users are requiring that switches produce specific sound effects in order to match the final application. C&K Components product manager, Eric Grange, looks at the reasons why. Everyone who drives an automobile is familiar with the sound that automatic door locks make. People are so accustomed to that sound that if it werent audible and consistent in tone, how would you know that it really locked? By the same token, the switch controls throughout an automobile, from cruise control buttons to window controls to changing channels on the radio, all feature recognizable sounds consistent to the car manufacturer.

Indoor acoustics with respect to switches produce the same kind of expectations from both the brand manufacturer and the consumer. There are an increasing number of applications where the manufacturer is branding its product by the feel and sound of the switch controls. Companies would also like to further brand their product by being able to establish a specific switch sound and feel. The demand for specific sound and continuity of sound is becoming a significant trend, particularly in the automotive industry. This trend is growing within the industrial and medical markets as well, with respect to control panels and monitoring systems.

The familiarity of the sound, the click and the feel of the switch are now characteristics that can be associated with a specific action. Some products that exhibit a hard actuation and a loud click may be associated with a less insulated, lower cost device, whereas a softer, more cushioned sounding device might reflect a higher end quality product. The sound distinction between the door of a truck closing and that of a luxury vehicle door is becoming as important for some product applications involving switch controls.

Sound requirements
Switch controls can be associated with a brand and/or a particular level of performance. Yet the sound emitted by a switch is determined by the switch design itself and cannot be controlled by the end-user. As a result, manufacturers are requesting that sound requirements be met at the outset of the design. In many cases, sound tunable switches and the subsequent technology are derived from existing switch designs. This automatically speaks to the reliability of the sound tunable device. Because of the extended life cycle of many tactile switches, some in the range of one million cycles, developing the sound tunable aspect of the switch from an already existing tactile device allows manufacturers to confirm the reliability of the device rather than have to predict what it could potentially do. Because the design relies on a proven switch contact and mechanism, the sound tunable switches are derived from proven technology and materials and provide the necessary reliability for todays high volume/high operation applications. In addition to reliability, utilizing parts from an existing design greatly reduces the overall cost of the switch for the manufacturer and in turn, the customer.
Since manufacturers are not altering parts that affect overall switch performance, life cycle or reliability, the actual tuning of switches involves physics and the materials used to attain certain consistent sound emitting switch designs. As such, switch manufacturers are studying the affects of different materials used, to the point where manufacturers have succeeded in getting the device to function as a predictable sound filter. This sound intensity is defined by the correlation between force and travel and is controlled by the attenuation of the switch. Sound intensity can be described as low (<30dBa) and high (>60dBa). In manufacturing, sound intensity is directly linked to the energy created.

In one instance, C&K Components received a request from a customer for a switch that matched indoor acoustics in terms of feel and sound. The switch needed to have a tactile effect yet the car manufacturer did not want it to make any sound. In this case, the switch was constructed in order to match the very low sound intensity that was required.

Sound response, measured in intensity and frequency, is defined by the sound emitted during the actuation of the switch. Sound emission is the combination of sound intensity and sound response. The chart below depicts the resonance of C&Ks KSC ST Series sound tunable switches by the correlation between intensity and frequency.
If customers were only requiring one switch to emit a certain sound, the process of adding or removing filters to meet sound intensity levels would be fairly simple. But the trend towards utilizing switch sound to aid branding is growing, and customers are demanding that all switches within the application produce the same exact sound and feel in order to complement the rest of the car design.

Whether an array consists of two or 20 switches, the demand is requiring homogeneity across the printed circuit board. Regardless of PC board size or overall product size, there is no limit to the number of switches on the board that must sound identical. As the size of the switch array increases, it can become increasingly difficult for manufacturers to produce a homogenous sound from switch to switch.

There are several variables that effect the creation of a homogenous sound, including the material of the actuator and its function as a filter. The PC board material that the switches are mounted on will typically be the same thickness throughout, so the variables become the switch materials and the construction of the switch. By equating sound to force and travel, it is possible to measure whether a switch is actually producing the sound through mechanical measures. As such, each switch on the board can be measured through force and travel for the precise sound.

20 years ago, PBX phone systems, along with other devices, featured a number of key switches that all felt differently because tactile feel was determined by the spring underneath the switch. Today, through the management of materials and the measurement of force and travel, homogeneity can be achieved.

While meeting all of the demands of sound in terms of intensity and response, switch manufacturers are still required to maintain the integrity and reliability of the switch. To achieve a specified sound response without affecting the mechanical characteristics of the switch is paramount.

In addition, cost is always a concern to the end-user, so the initial challenge was taken one step further, requiring switch manufacturers to provide a technical solution that offers different sound intensity responses for the same initial product. This allows the switch manufacturer to avoid rebuilding a brand new product, along with the associated risks and necessary investments. Not only is the inherent reliability of the original switch present in the sound tunable design, manufacturers are then able to offer the same version of a switch with varying sound intensity levels.

Matching switch style to the application is more than just the tactile feel. Its matching the sound intensity, response and emission to not only the application, but to the end-users corporate branding strategy as well. While many switch manufacturers are designing sound tunable switches to meet these demands in the automotive, medical, and industrial industries, there are still challenges in which a solution has not been found, particularly for those customers who require a specific sound response in terms of intensity and frequency. While switch manufacturers are working diligently and making significant progress to find a resolution for this design challenge, a definitive solution has yet to be reached.