Keyboard Cases: Stuffed or Hollow?

[Hypersphere]

Do you prefer to keep your keyboard cases hollow or to stuff them with foam or other sound-deadening material? I suppose it depends on many variables, including case design, case material, switches, and a preference for a hollow reverberation vs a deadened sound.

If you do use foam or other sound absorbers, what particular material do you use and how do you use it? For example, do you fill the case so that it is under noticeable tension when putting it back together?

Sometimes I have put a layer of art foam between the PCB and a metal case to serve the dual purpose of electrical insulation and sound absorption. Usually I have found little apparent difference in the typing sounds, but I have not yet done objective tests with audio recordings.     

Some case(s) in point:

1. At the moment, I am completing a refurbishing job on a Leading Edge DC-3014 with SKCM blue Alps. I've replaced the keycaps -- dye-sub PBT from an SGI Granite for alphas and black ABS from Matias for mods and the spacebar.

I quieted the spacebar by replacing the blue slider and click leaf with a slider and tactile leaf from a Matias Quiet switch. I also put thin urethane foam under the spacebar where the stabilizer inserts hit the plate. These modifications make a very pronounced difference in the sound of the spacebar -- it now has a low-pitched thud with no rattle.

As for the DC-3014 case, for the time being, I have kept it hollow and not added any foam. I rather like the echoic thock of some of the keys -- especially the Return and Backspace (I have remapped Backslash as Backspace). The Right Shift is a bit too noisy, though (not rattly, just a very pronounced bottoming-out and return-stroke clack noise).

2. I also have two Northgate Omnikey 101 boards with SKCM white Alps. I put a sheet of art foam in the case on one of them, but it seems to make little difference in the typing sound. This keyboard has a most agreeable solid sound and feel in its native state.

[fohat.digs]

I love solid tactile and clicky feel, but noise is not desirable to me in any way, so I stuff.

Occasionally I cut a layer of my EPDM to fit the bottom pan, it is heavy enough to just lay there.

Many keyboards, especially the ones with curved back plates (I'm looking about you, IBM) have little or no clearance at the front (space bar) side but quite a bit at the back. Model Ms even have little dimples in the case back where the rivets (or nuts) go, and there is virtually no clearance for the first row or 2.

Otherwise, my 2 preferred materials are felt fabric and the "waffle" rubber sold as drawer liner.

For wide thin flat areas, I cut layers to fit from edge to edge. As the void gets thicker (usually going from front to back) I cut strips and fold them as many times as needed to get the thickness I desire.

Once that becomes too clunky, I evaluate each cavity individually. The easy and elegant way to fill a cavity is with fabric rolled into a cylinder. The width is easy - just cut a long strip at the width you desire. How long? Long enough so that it is tall enough to do the job when rolled up. Nearly any set of spaces can be filled cleanly with a succession of rolled cylinders.

But the easy way is to go to the fabric store and buy a bag of the kind of batting that is used to stuff pillows. Then just poke it in with a chop stick until it won't take any more.

[Hypersphere]

@fohat: Wow! You really do stuff 'em! These would qualify as WTP (Winnie the Pooh) cases -- "... all stuffed with fluff" as the song goes.

Have you made any before and after audio recordings? It would be interesting to sample the difference all this stuffing makes in the sound(s) of the keyboards.

Have you considered using some sort of "foam in place" process?

[Geroximo]

Stuffed of course.

[Giorgio]

With a pok3r, you need to stuff that noisy aluminium original case. But if you have replaced it with a cheap plastic one, I think that it's quiet enough. And nicer too.

[E3E]

Well, I'm most experienced with Alps here, but to make it quick and succinct:

I prefer dampening in every case I use aside from those used for clicky switches.

Using any form of dampening on my Orion with Alps SKCM Blue switches absolutely sucked the soul out of the switches. Similarly, in my 60% Eagle PCB builds (one in a Hammer 60% case and one in a FMJ design #1 case), dampening made Alps SKCM Amber and Alps SKCM Blue sound a bit anemic as well, but it might just be to my ears. 
 
Overall though, I prefer dampening and use sorbothane sheets to dampen my boards (isolate-it).  I dislike the resonance in my FMJ case, and I'm hoping a sorbothane sheet lets me enjoy that case more. Right now, it's only using strips of sorbothane I had left over from when I used some for my Hammer, but that isn't enough.

The sorbothane I use in them is thick to the point of the hot swap sockets I use leaving impressions in the material when I remove the PCB. It was about 1.5mm thick, I believe.

 
The only vintage I've deadened is my Tai Hao TH-5539 FAME keyboard, which has a metal back. I used memory foam inside the case, enough so it does put quite a bit of tension against the PCB.

Here is a video of how it sounds

[fohat.digs]

Have you made any before and after audio recordings?

Have you considered using some sort of "foam in place" process?

I try to ignore sound and have never made recordings.

My understanding is that foams made for insulation always expand as they dry and cure (to tighten the seal) but that would tend to "puff out" a plastic case.

[Hypersphere]

@E3E: Thanks for the details and for posting a video. Do the Sorbothane sheets exude plasticizer? I had some Sorbothane hemispherical feet that I was going to use for a keyboard, but they contained so much liquid plasticizer that it was literally oozing out of the material. I replaced them with non-sweating feet from 3M.

[Leslieann]

My Almost-A-Filco has foam in it to dampen noise.
I used motherboard foam (the foam it sits on in the packaging), it doesn't do as much as some others, but I knew it would be fine electrically as I knew it would be touching the pcb.

I think it helps with noise, but it's so overbuilt at this point, I couldn't tell you how much. Since I put it in, I added the stainless plate plus adapter, which also dampen the noise.

[E3E]

@E3E: Thanks for the details and for posting a video. Do the Sorbothane sheets exude plasticizer? I had some Sorbothane hemispherical feet that I was going to use for a keyboard, but they contained so much liquid plasticizer that it was literally oozing out of the material. I replaced them with non-sweating feet from 3M.

I believe the stuff I got was 50 durometer. In my experience, it hasn't ever gotten greasy, though it is a dust magnet. I used Isolate-It sheets that I bought from Amazon. Maybe the softer stuff is more prone to leaking plasticizers? I don't think anything softer is really necessary as this stuff is already pretty malleable. I'd never want to use this softness for keyboard feet.

[Hypersphere]

Some time ago, I put a KBP V60MTS-C into a TEK CNC aluminum case, which is merely a metal tray with virtually no potential for reverberation. It looked nice, but the aluminum case made the Matias Click switches sound higher-pitched and dead at the same time. I ended up going back to the stock plastic case, which has more hollow spaces and thin walls capable of some vibration. The keyboard sounded much better in the cheap plastic case, which also doesn't look all that bad.

Imagine the sound of your keyboard in this room:

One of the ultimate sounding boards -- the inside of a violin.

It is easy to imagine that paying more attention to the design of keyboard cases could have a major impact on the sound of the keyboard. Perhaps rather than trying to dampen the sound, we should work on tweaking the case to get the desired acoustic effect. However, acoustics is still a complex mixture of art and science. We still don't exactly know what makes a Stradivarius sound like a Stradivarius (in the hands of an expert violinist).

As far as I know, not too many violinists elect to stuff their violins with foam.

[SKD]

I did a build with neoprene http://imgur.com/a/vil6l between the plate and pcb. I didn't fill the space under the PCB as there's LED's for the underglow.

I don't have a comparison of the build without but in this video https://www.youtube.com/watch?v=FKCOsGrjg18 you can hear the sound does sound a bit dampened.