Keyboards Are Percussion Instruments

As with stabilizers and switches, buying high-quality CNC milled aluminum or brass cases doesn’t get you off the hook. Keyboard cases are hollow for the most part, but combine that with the clacking of keycaps, and you have a percussive instrument on your hands. No wonder custom mechanical keyboard enthusiasts are quite particular about their sound. This is all the more important for expensive keyboards with CNC milled metal cases. These tend to have a higher pitch by the nature of the material, which makes them sound tinny and hollow without proper acoustic treatment. This guide intends to take care of that – that is, acoustically dampen the case as well as the plate to improve the way your keyboard sounds.

What You Need to Get Started

This keyboard modification guide is fairly uncomplicated. Taking apart and putting together custom mechanical keyboards is pretty straightforward. All you need for this mod is some good sound-absorbing material, sharp cutting tools, and accurate measurement instruments. The list of tools needed isn’t long, but I have included some optional tools that are more accurate and/or make the task easier.

  1. Sound-dampening material This comes in various forms. The one used in this guide is EVA foam, which is inexpensive and easily accessible in craft stores. Buy at least a couple of keyboard-sized sheets in 1mm and 2mm thicknesses. This will allow you to combine them to achieve the correct thickness. If you’re willing to spend more, you can get better results with rubber sheets. If your pockets run deep, you can try a made-in-USA alternative called Sorbothane. It’s used by NASA, so expect it to deliver the best results. However, it can get really expensive for what we intend to do in this guide.
  2. Sharp cutting tools The best tool for the job is a craft/hobby knife from a reputed brand such as Xacto. The sharper the blade, the quicker and cleaner your work will be. Box cutters work in a pinch, but they are relatively dull and unwieldy for the sort of fine cutting needed here.
  3. Measuring instruments While the humble ruler works for two-dimensional measurements, taking internal measurements of complicated 3D objects such as a keyboard case requires something more involved like digital or dial calipers. A tape measure also works in a pinch. Making measurement marks on a thin strip of paper is a handy way of gauging dimensions of complicated 3D objects. Just lay the paper strip out flat when you’re done marking, and measure the markings with a regular ruler.
  4. Screwdriver set5. Hole punch set (optional)6. Double-sided tape (thin) (optional)7. Pencil or other marking tool

Acoustically Dampening the Plate

A large part of a keyboard’s hollow, tinny note comes from the metal plate vibrating with the keystrokes. This is further amplified by the 3.5mm gap between the PCB and the plate acting as an acoustic chamber. We will fill this gap with dampening material to mitigate the hollow sound. The anti-vibration properties of material also prevent the plate from generating noise. This should allow the natural sound of the switch to stand out without being overshadowed by plate noise.

  1. This may sound counterintuitive, but we start off by measuring the case dimensions instead of the plate. This applies to all types of case mounting styles from tray mount to sandwich mount, as our goal is to have the acoustic dampening material (EVA foam in this case) to overshoot the plate in order to create an airtight seal with the case. This will greatly reduce internal noise from leaking outside the case. Foam is compliant, so you can either use exact dimensions if you’re using accurate measurement instruments, or you can add a millimeter to each dimension. It’s better to have more material and trim later than to fall short.
  2. Transfer the measurements to the EVA foam sheet. The gap between the plate and foam is 3.5mm across all keyboards. EVA foam is generally found in 1mm, 2mm, 3mm, and 5mm sizes. You’ll therefore have to use two 2mm sheets or a combination of 3mm and 1mm sheets. The extra 0.5mm thickness improves dampening. Use double-sided tape or foam-compatible glue to hold the sheets together. This is important to avoid headaches when cutting the sheet.
  3. Use the plate as a stencil to transfer the cut lines onto the EVA foam. Your cuts will be more precise if you use a fine marking tool and keep the cut lines closer to the plate edges.
  4. Use a sharp hobby/craft knife to make all cuts. Finer cuts, such as the holes for the switches, will come out clean and precise if you use a sharp blade. Using a dull blade will make your job longer, frustrating, and inaccurate. Tray-mount keyboards will need an appropriately-sized hole punch to create space for the tray-mount screw posts. You can carve out holes using a blade as well, but the result is neither as tidy nor as accurate as using a dedicated hole punch tool.
  5. Depending on the physical dimensions of your preferred stabilizer type, you may or may not have to trim some material off to accommodate them.
  6. Finalize the PCB/plate assembly by soldering switches to the PCB. Refer to our switch replacement guide to learn how to solder switches.

Don’t Forget the Case

Acoustically treating the case is much less complicated and tedious compared to the plate. Lining the inside of a box with foam isn’t complicated, but it is quite important. CNC-milled metal cases are highly dense mediums that transfer internal noise quite efficiently. Adding a sound-dampening layer prevents this from happening. The actual method will vary ever so slightly with the mounting style of your case. Be sure to read our keyboard basics guide if that sounded Greek and Latin to you. That article covers all the bases.

  1. The first step is figuring out the clearance between the floor of the case and the PCB to determine the thickness of the EVA foam sheet. For tray-mount cases, it’s down to measuring the height of the PCB mounting posts and deducting the height of the tallest component jutting out from the bottom of the PCB. In the example shown below, the PCB is mounted at a height of 3.2mm, and the tallest component at the underside of the PCB is a shade over 1mm, so we can use 2mm foam. Calculations are even easier for all other types of case mounting styles. All you have to do is measure the distance between the bottom of the plate and the case floor. Then subtract it with the mandatory 3.5mm gap between the plate and the PCB in addition to the thickness of the PCB and the tallest component jutting out from it. For example, if the distance between the plate bottom and the case floor is 10mm, PCB is 2mm thick, and the tallest component on the underside is 1.5mm high, then you can use 10 – (3.5 + 2 + 1.5) = 3mm thick EVA foam sheet.
  2. We have already measured the dimensions of the case, so all that’s left is cutting out EVA foam inserts to appropriate dimensions. Tray-mount cases require holes punched out for the mounting posts. Additional cut-outs for the USB port also need to be measured, marked, and cut as shown below.
  3. If your case has any hollow sections, measure the depth and fill with appropriately dimensioned EVA foam cut-out.
  4. With the floor of the case acoustically treated, we move onto the four vertical sides. Remember the distance between the plate bottom and the case floor you measured earlier? That’s the breadth of the strip of EVA foam you’ll need to cover the sides of the case. The thickness of this strip of foam should be at least 1mm for effective dampening and shouldn’t exceed 2mm, or the PCB will snag on it. Top/bottom-mount, gasket-mount, and sandwich-mount cases will require some gaps to be left in this strip as shown below. The gaps are needed to prevent clearance issues with mounting posts. That’s all there is to it. Assemble your keyboard and marvel at how radically improved it sounds.