Everyone who drives or has ridden in an automobile is familiar with the sound that automatic door locks make. People are so accustomed to that sound that if it weren't audible and consistent in tone, how would you know that it really locked? In the same way, the switch controls throughout an automobile—from cruise-control buttons to window controls to changing channels on the radio—all feature recognizable sounds which are consistent to that car manufacturer. With respect to these switches, indoor acoustics 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 just as important for some product applications involving switch controls.
Before discussing the mechanics of controlling switch intensity and sound response, it is important to understand why it is important. Today, for a number of reasons, manufacturers (and to some extent, end-users) require that switches produce specific sound effects, in order to match the final application design. Quality of sound and the switch feel are being used to help brand products and help control indoor acoustics. Branding also translates into the reliability of the device, which is becoming a more popular requirement for higher-end products.
One illustration of this is an application where a manufacturer implements a two-switch system to control one circuit. The second switch provides a backup function in the event of a failure in the first switch. In a gearbox application, for example, having two switches controlling one circuit provides the backup and reliability necessary for continuous operation. In the original design, the manufacturer had a difficult time getting the two switches to actuate simultaneously in order to feel like one.
Not only was the tactile feel of the two switches different, but it sounded like the two switches were actuating at different times. To solve this problem, two sound-tunable switches were selected and designed into the application to deaden the sound of the second switch. Thus, the operator would only hear and feel one of the switches, even though two were being actuated. The uniform feel and sound of this two-switch design translated into the desired reliability of the end product and reinforced the manufacturer's initial branding efforts.
As noted above, 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 adds 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 existing tactile device allows manufacturers to confirm the reliability of the device, rather than have to predict what it, Figure 1.
Figure 1: C&K Components' KSC ST Series of sound-tunable switches feature life cycles to 1 million rotations
Since the design relies on a proven switch-contact and mechanism, the sound-tunable switches are derived from proven technology and materials, and so provide the necessary reliability for today's high-volume/high-operation applications. In addition to reliability, using parts from an existing design greatly reduces the overall cost of the switch for the manufacturer and, therefore, for 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 effects of using different materials, to 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 (<30 dba)="" and="" high="" (="">60 dBa). 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 to match the very low sound intensity that was required, Figure 2.
Figure 2: C&K's KSC4D switch is offered with both high and low sound-intensity levels
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. Figure 3 shows the resonance of C&K's KSC ST Series sound-tunable switches by the correlation between intensity and frequency.
Figure 3: The resonance of a sound-tunable switches shown by the correlation between intensity and frequency (here, the C&K's KSC ST Series)
(Click on image to enlarge)
If OEM customers only had a single switch which they required to emit a certain, specific sound, then the process of adding or removing filters to meet sound-intensity levels would be fairly simple. But the trend towards using switch sound to aid branding is growing, and customers are demanding that all switches within the application produce the same sound and feel, in order to complement the rest of the car design.
Whether an array consists of two or twenty switches, this demand is requiring homogeneity across the printed circuit board (PCB). Regardless of PCB or overall product size, there is no limit to the number of switches on the board that must have identical sound. 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 affect the creation of a homogenous sound, including the material of the actuator and its function as a filter. The PCB material on which the switches are mounted 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 through mechanical measures whether a switch is actually producing the sound.
Each switch on the board can be measured through its force and travel for the precise sound. In comparison, PBX phone systems of twenty years ago, along with other devices, featured a number of key switches which 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 is 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 building a completely 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. It's matching the sound intensity, response, and emission not only to the application, but also to the end user's 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 for which a good 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 and making significant progress to find a resolution for this design challenge, a definitive solution has yet to be reached.
About the author
Eric Grange has been a Product Manager with C&K Components Corp. for three years, and is based in Dole, France. He was previously employed at Amphenol Corp., where he was a product manager for high-frequency connectors, mobile-phone connectors and antennas for five years. Eric has a MsC inf mechanical engineering and materials.