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Acoustic Geometry for 3D Printed cases

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bishopj7:
Hello all.

As you may or may not be able to tell by a couple of my earlier threads, I have a bit of a focus on 3D-printed keyboards and designs.

I'm getting things together to offer a new throughole kit design, but I'm still experimenting with some design elements inside of the case. After opening up the lower case cavity to accommodate the PCB (and not having a handwired matrix to dampen the sound), I'm experimenting with the lower case model for different ways of diffusing the sound as it bounces back.

Has anyone else played around with this sort of thing? I'm wanting to find a way to take the edge off of the sound without the level of efficiency/print time sacrifice of just adding a bigger block of plastic to the bottom of the case. My initial thought is to add slopes/wedges to the lower case, but I've also considered smoother shapes like waves/curves, and even blocks of varying height. I'm looking to acoustic panels and padding to inspire these ides, but with the different materials, I think that's something that should be practiced with some reservations (at least for the results expected).


Thanks in advance for the discussion!

Leslieann:
It's too many variables.
You're dealing with several dozen of points of sound origin, not even accounting for how the switch body itself  and the pcb and plate will effect it. Worse, 3d printing isn't creating flat surfaces, the movements are digital, not analog and then you have a pulsing effect from the extruder, that would be a good thing were it not for the fact that it's all rounded off rather than squared off. Don't forget you have to account for how you print it as well, any changes to the bottom can effect the angle of the inner surface print and then you get into free space, infill, plastic type, etc... It's too many variables, all of which could be thrown off just by using the wrong slicing software.

In my experience, you're better of focusing on eliminating free space, plastic and infill type and amount to alter the sound, it's much simpler and won't compromise the external look.

bishopj7:
Absolutely fair, and exactly why I posed this question.

There are going to be millions of 'surfaces' due to the nature of FDM printing - though I'm curious to experiment with different shapes to help fill the empty space in a more material-efficient manner. A thicker bottom inside of the lower case can easily fill that gap, but I'm wanting to test to see what kind of results can be derived from different methods.

vvp:
I doubt rough surface of a 3D printed object makes much difference. 16 kHz tone has wavelength of about 2 cm. Much bigger than the irregularities of a 3D printed surface. Focus on resonance frequencies in the air cavities and in the plastic itself. You possibly can get some useful simulations of the air cavities. It will be harder with the plastics since it is 3D printed (complicated internal structure). Maybe only focus on not having any big areas of the case which are not fastened together. That will stiffen the case more and moves resonant frequencies up. Maybe fasten together using some rubber dampeners to dissipate sound energy in them.

If you only want to dampen the sound then just try fill in the keyboard with cotton wool. Maybe It will be enough for your needs.

MajorKoos:
Have you seen the Head(amame) headphones?

They opted for 11% gyroid infill and 2mm thick walls, plus a trick to not connect the infill to the vertical walls so it forms an open-celled structure. 

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