Or, What's REALLY The Deciding Factor In Silencing Topre Switches
by sth
To date, the common understanding of Topre silenced sliders has been that slider length is the primary factor in determining overall keyswitch travel distance. The reduction in travel when performing silencing modifications to stock/standard Topre stems is often referenced as evidence of this (such as with O-Rings or Hypersphere rings).
While the slider length and silencing ring thickness combined are certainly related to the total travel length, those factors alone would not account for the differences in travel when applying silencing modifications to other slider types. There are actually two additional very important aspects of slider design that determine the overall travel distance, and they are somewhat less apparent than slider length alone.
It is important to understand the whole picture when planning a Topre silencing mod or stem-swap -- and arguably interesting to those wanting to obtain a deeper understanding of the design details of their Topre keyboards. Thesefactors are what provide factory-silenced Topre boards with a comparable travel distance to non-silenced boards, without extensive and expensive factory production modification to the PCB position, rubber dome design, case design and/or barrel mounts of non-silenced keyboards.
Please note that the scope of this research does not currently account for Topre Hi-Pro design switches.
Illustration of additional differences
Fig 1 - Stock Topre left, silenced Realforce right - photo dgneo
On the left is a stock HHKB/Realforce slider. Note the effectively flat bottom surface - this is where the slider comes into contact with the rubber dome. On the right is a silent Realforce slider, which has approximately 1mm of relief molded into the bottom. We can observe a similar molding detail in the HHKB Type-S slider below:
Fig 2 - Stock Topre left, Type-S right - photo
The second factor, which has somewhat more to do with accommodating the slider position in conjunction with the relief design, is illustrated here:
Fig 3 - silenced Realforce left, stock Topre right - photo Bro Caps
The purple slider's base appears to be nominally thinner than on non-silenced sliders.When combined with the height of the O-ring, this would account for a similar overall base height. Because of the nature of the foam O-ring, an exact measurement cannot be obtained (and therefore neither can a precise and predictable "resting" position) - but the difference here is in the sub-sub-millimeter range and is likely undetectable by humans.
Initial Conclusions
Without the relief present in a silenced slider, the effective bottom of the slider is approximately 1mm lower, thereby pressing the rubber dome down more than is expected. This provides a solid explanation of why aftermarket silencing techniques, regardless of manufacture or material, will always reduce travel once installed, and theoretically could cause actuation issues on those Topre boards where actuation is higher than normal (as is possible with actuation-point-adjustable boards). It certainly affects the tactility of the rubber dome, something the relief-design sliders were engineered to circumvent.
From these observations, we can conclude that, when combined with the difference in slider position due to silencing ring installation (whether stock or aftermarket), the bottom-side relief (currently present only in factory-silenced sliders) is a deciding factor in the "resting" position of the the slider itself (this aspect is determined by the silencing ring) as well as compression on the rubber dome (which is affected by the relief).
Modification notes
We can conclude that adding silencing rings to a standard slider will unavoidably affect the travel. I was also curious to know if this was the case with the newly-released JTK MX sliders. Unfortunately at the time of this writing, the JTK sliders do not appear to have the same relief design as factory-silenced sliders.
Fig 4 - JTK sliders installed on Realforce - photo xondat
The same is true of Novatouch sliders:
Fig 5 - Novatouch slider bottoms - photo dorkvader
I am currently planning on investigating the differences between other available Topre-compatible sliders. I hope to include the following, pending determination that they are non-trivially different from existing designs that have been considered in this research:
- eBay-sourced "clear"/offwite sliders - these include preinstalled O-rings, and I am curious to know whether the manufacturer took into account the bottom-relief design of Type-S and silenced Realforce sliders
- Legacy Topre designs including Sony NEWS/BKE keyboards - my prediction is that these are roughly equivalent to non-silenced stock Topre sliders
- Leopold FC660C sliders
- TypeHeaven sliders
Next Steps
Obtaining accurate measurements of the various Topre slider types is going to help us in quantifying these results. Additionally, I am working on acquiring as many variants of available Topre stems as possible in order to provide my own photographs in a standard setting.
There is also a question of the difference between silent RF sliders and Type-S sliders. As shown in figs. 1 and 2, while the overall design is nearly identical, there are slight differences in some of the molding details that may affect user perception. Further study is needed into not only the design differences but also other factors including the type of plastic and O-ring material characteristics.
I would really like to start looking into alternative silencing methods in combination with existing O-ring-ready sliders- namely, how would alternative materials affect the sound and feel, given the same nominal thickness of the silencing material as stock O-rings.Possible avenues of inquiry include:
- Hypersphere rings
- Dental bands
- High-durometer O-rings
- Ironed landing pads
Concluding notes
If you have any information related to this that might shed more light on silencing options, please let me know. I can be reached on GH, DT and keyboardcommunity.slack.com via the username "sth" as well as on reddit as "guinanseyebrows".
Thanks to the following Topre freaks:
- nsmechkb (for kickstarting my research)
- Bro, xondat and dgneo (for providing research-specific photographic documentation)
- Dorkvader and Hordak (for their existing photographs used while researching and for illustrative purposes)
- Otesanek, fendent, rm-rf, firebort and anyone else involved in the discussion on #keyboards
