Foam mods and what they do to the sound
Updated
Foam fills the empty space inside a keyboard so less of it rings: more foam sounds deeper, drier and quieter, less sounds louder and more resonant. Case foam, plate foam, PE foam on the circuit board and painter's tape on its back are all versions of the same idea.
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Pick a pack, then press any key or tap the keys below. These are the same samples the app plays.
The layers, from the top down
| Layer | Where it goes | Example |
|---|---|---|
| Switch pads or switch foam | Under each switch | Epomaker lists “switch foam” as the third foam layer |
| Plate foam | Between the plate and the circuit board | Keychron Q1 kit: 3.5 mm Poron “sound absorbing foam” |
| PE foam | On the circuit board, under the switches | Keychron Q1 kit: 0.5 mm XPE “PE foam” |
| Tape mod | On the back of the circuit board | Blue painter’s tape, “Typically 3 total layers” (Switch and Click) |
| Case foam | In the bottom of the case | Keychron Q1 kit: 2.5 mm Poron “bottom frame acoustic foam”; Epomaker suggests 3 mm EVA |
Keychron says its kit “can further eliminate the hollowness of the keyboard and reduces the resonance on each keystroke.” Epomaker’s glossary names hollowness as a defect: “Cheap, echoey character from an empty case interior with no foam on a non-tuned build.”
What each does to the sound
Epomaker frames foam as a dial rather than a fix: “More foam = deeper, drier, quieter. Less = louder, more resonant.” Its recipes use it both ways. For thock, “Add case foam”, “3mm EVA foam between PCB and case bottom”. For silence: “Add full foam stack”, plus “Silicone case bottom mod” and “Tape or band-aid mod”. For a marbly or poppy sound it does the opposite and removes the case foam, because “The air gap is key.”
PE foam and tape do not only deaden. Switch and Click, which publishes a step-by-step tape mod guide, says the tape mod can sound “very similar to PE Foam Mod, giving your keyboard a ‘poppy’, ‘marbled’ sound signature”, and that the tape “accentuates certain frequencies while muting others.” It is the cheapest of these mods and the easiest to undo. Its warnings: “Make sure to use non-conductive tape for this mod, or you may damage your PCB”, and “do NOT do this mod with a battery inside your keyboard.”
Hear the ring go
Teclo models a keyboard’s plate and case as one ringing body. Foam shortens that ring, and the three packs in the demo span the range:
| Pack | What it imitates | Body ring in the model (ms) | 90% of energy in, measured (ms) | Press length (ms) |
|---|---|---|---|---|
| Muffle | Silent switches on foam | 14 | 8.3 | 55 |
| Butter | Linear, lubed, on gaskets and foam | 60 | 13.1 | 80 |
| Boulder | Linear in a heavy aluminium case | 200 | 18.1 | 90 |
Body ring is how long the lowest resonance of the body takes to fall to about a third, a setting in Teclo’s source code. Muffle also has the fewest resonances of any keyboard pack, 8, stopping at 3,800 Hz, and a filter over the top. Muffle is the deadest pack and Boulder the most resonant. They imitate the effect of foam and a heavy case; they are synthesized, not recordings of a modded board.
Foam and the mount work together; see gasket mount. For the whole list of mods toward a deeper sound, see how to make a keyboard thocky.
Questions
Does foam make a keyboard quieter?
Yes, and deeper. Epomaker: "More foam = deeper, drier, quieter. Less = louder, more resonant." Its recipe for a silent board adds "Case + plate + switch foam for maximum quieting."
What is the PE foam mod?
A thin sheet of polyethylene foam laid on the circuit board, under the switches. Keychron's acoustic kit includes one, 0.5 mm of XPE for the Q1.
What is the tape mod?
Layers of painter's tape on the back of the circuit board. Epomaker lists "Tape or band-aid mod" in its silent recipe as "Cheap, fast, dampens PCB resonance." Switch and Click says to use non-conductive tape and not to do it "with a battery inside your keyboard".
Can you add too much foam?
Yes, in the sense that the sound goes dull. Epomaker calls foam "The dial that decides 'muddy thock' vs 'clean thock'", and its recipe for a marbly sound removes the case foam on purpose.
Sources
Other facts on this page come from these pages, read on or before the date above.