The filling layer is the critical variable that transforms a keyboard from merely « making noise » to « sounding great. » Its fundamental purpose is not simply « noise cancellation, » but rather reshaping vibration transmission paths and sound wave reflection patterns through the density and damping characteristics of various materials. Current mainstream filling configurations consist of four layers—plate foam, switch pads, switch socket foam, and case foam—each corresponding to specific acoustic frequency ranges and physical locations. However, more filling is not necessarily better; excessive filling compromises the flex and « bounce » space inherent to Gasket-mounted structures, turning a keyboard’s feel from « bouncy and responsive » to « stiff and dead. »
I. Quels sont les problèmes que les couches de remplissage résolvent-elles ?
The « hollow sound » (or cavity resonance) in mechanical keyboards stems from two physical mechanisms. First is the rigid contact between the internal assembly and the outer case; typing vibrations travel through the mounting plate and PCB to the case, creating resonance within the internal cavity. Second is the gap between the switches and the PCB, as well as the air layer between the PCB and the bottom case; sound waves bounce back and forth within these spaces, creating a dull, low-frequency « humming » or « buzzing » sound.
The role of the filling layer is to occupy these spaces with materials of varying densities, absorbing and scattering sound wave energy to reduce resonance and echoes. However, the effect is not merely « silencing »; effective filling results in a more focused, textured sound rather than simply a quieter one.
II. Rôles et matériaux des quatre couches de remplissage
Les configurations de remplissage de clavier courantes comprennent généralement quatre couches, disposées de l'interrupteur jusqu'au boîtier : mousse de plaque, coussinets d'interrupteur, mousse de prise d'interrupteur et mousse de boîtier.
Sa fonction principale est de minimiser le contact direct entre la plaque et le circuit imprimé et de réduire la résonance de la cavité. Les matériaux courants comprennent le PORON, le silicone, l'EVA et le feutre. Le PORON est le plus performant dans les structures montées sur joint, offrant un profil sonore solide et une sensation de frappe douce; le silicone offre une transmission de la lumière supérieure, ce qui le rend idéal pour les claviers avec éclairage latéral; le feutre est l'option la plus rentable mais offre une absorption acoustique limitée.
The switch pad adheres to the PCB surface directly beneath the switch and is the key layer for producing the popular « Mahjong sound » (a deep, clacky acoustic signature). What it alters is the impact sound produced when the switch bottoms out: as the stem strikes the PCB, the switch pad acts as a buffer, transforming the sharp « plastic-on-plastic » clack into a deeper, fuller « thock » or « dack » sound. Among common materials, IXPE (cross-linked polyethylene foam) produces a crisper sound that preserves the switch’s inherent tonal characteristics; PORON yields the deepest, most muted sound—often the source of the sought-after « Mahjong tile » sound profile; EPE (pearl cotton) is the most cost-effective option with a distinct sound signature, making it suitable for mass-produced switches with average acoustic qualities.
Sa fonction est de supprimer davantage la résonance creuse (son son de cavité) qui se produit entre le circuit imprimé et le boîtier inférieur. Certains produits utilisent des tampons acoustiques en PET au lieu ou en plus de la mousse de PCB.
La mousse du boîtier inférieur est posée tout en bas du boîtier du clavier, remplissant le vide entre le circuit imprimé et le boîtier. Cela sert de dernière ligne de défense contre la résonance métallique creuse souvent associée aux boîtiers vides. En ce qui concerne les matériaux, le silicone est le plus performant dans les claviers en plastique produits en série, tandis que le PORON est plus courant dans les kits de montage sur joint personnalisés.
III. The « Degree » of Filling: Why More Isn’t Always Better
Il existe un compromis facilement négligé concernant les couches de remplissage : elles peuvent entrer en conflit avec la sensation de frappe douce et flexible caractéristique des structures à montage sur joint.
The core of a Gasket-mount design is the suspension of the internal assembly (plate and PCB) via gaskets, allowing for slight deformation when keys are pressed. However, if the bottom case foam is too thick or dense, leaving no room for the assembly to flex downward, the Gasket mount effectively reverts to a rigid « Tray-mount » structure. Case studies have shown that if the space allocated for the switches is too tight, adding bottom foam and PET layers can eliminate any remaining room for downward flex.
Une autre considération est l'équilibre entre l'acoustique et l'éclairage. Pour obtenir des effets lumineux latéraux, les claviers transparents omettent souvent la mousse PCB, en utilisant un coussin acoustique en acrylique transparent pour sceller le son tout en laissant passer la lumière à travers les panneaux latéraux.
Furthermore, there is a limit to how much filling material can « improve » the sound. Discussions on Zhihu suggest that the primary factors influencing keyboard sound rank as follows: structure > kit (plate, dampening materials) ≥ switches > keycaps; dampening materials represent just one variable within the kit itself. If a keyboard kit inherently lacks acoustic consistency, simply adding foam cannot fundamentally alter its sound quality.
IV. The Engineering Logic: From « Noise Dampening » to « Acoustic Tuning »
The approach to dampening layers is evolving from a simple question of « presence or absence » to a refined process of selecting specific materials and determining precise quantities.
The Dareu A98 Pro employs a six-layer dampening configuration—latex foam, IXPE switch pads, PET acoustic pads, latex bottom foam, and EVA bottom pads—paired with a polymer plate, aiming for a « more focused sound and a softer typing feel. » During the development of the NuPhy Gem80, engineers discovered that the holes drilled into the PCB for RGB LEDs altered sound propagation, resulting in a « plasticky » sound; they addressed this by specifically adjusting the dimensions of the PCB foam to compensate.
These examples demonstrate that designing a dampening scheme is no longer a matter of simply « stuffing the case »; rather, it is a systems engineering task that requires coordinated tuning alongside the plate material, structural type, switch characteristics, and even the layout of the RGB LEDs.
