Author Topic: Acoustic Geometry for 3D Printed cases  (Read 3420 times)

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Offline bishopj7

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Acoustic Geometry for 3D Printed cases
« on: Mon, 27 June 2022, 07:26:21 »
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!

Offline Leslieann

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Re: Acoustic Geometry for 3D Printed cases
« Reply #1 on: Mon, 27 June 2022, 09:37:53 »
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.
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Offline bishopj7

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Re: Acoustic Geometry for 3D Printed cases
« Reply #2 on: Mon, 27 June 2022, 12:11:20 »
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.

Offline vvp

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Re: Acoustic Geometry for 3D Printed cases
« Reply #3 on: Mon, 27 June 2022, 13:52:18 »
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.

Offline MajorKoos

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Re: Acoustic Geometry for 3D Printed cases
« Reply #4 on: Mon, 27 June 2022, 14:48:38 »
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. 
« Last Edit: Mon, 27 June 2022, 14:50:57 by MajorKoos »

Offline Findecanor

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Re: Acoustic Geometry for 3D Printed cases
« Reply #5 on: Mon, 27 June 2022, 16:56:22 »
People put damping material such as foam or silicone inside their cases. Perhaps you could 3D-print a mould for an insert in plastic and cast silicone inside that. Silicone does not stick to anything (but silicone), but I dunno about types of foam.

I have been toying with the idea of having the entire bottom of a keyboard be a single piece of silicone, thus being both sound-dampening inside the keyboard and the keyboard's feet. But I dunno if that is a good idea or not.

Offline Leslieann

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Re: Acoustic Geometry for 3D Printed cases
« Reply #6 on: Mon, 27 June 2022, 17:50:47 »
help fill the empty space in a more material-efficient manner.
Honestly, the plastic in 3d printing is about the cheapest, most efficient method of filling that empty space.*

Foam or cotton works but that takes human time to do, can also be messy and not as nice looking to someone buying. Casting a silicone block looks and works well but go look up how much just the silicone will cost compared to the plastic it replaces... TONS more money and you still need mold release, cups, stir sticks, scale, and if necessary a degassing chamber, and it will increase shipping costs due to weight.  In total it adds a LOT of cost. Worse still, none will likely have as much effect as different plastics, infill % and infill style. They would still help, but those really only help mitigate other bad choices, they shouldn't be the first choice.

Plastic is cheap, and yes, it will take a few more hours but they are machine hours and if you're talking an extra 3 hours on a 24-36 hour print, it's a negligible amount.


*Before you get too far down this hole,
Do some testing because this is one of the traps of 3d printing people often fall down. Draw up a simple cube, check how long that print time is now punch a hole through it and check print time again. We think of holes as reducing material because you're working from the perspective of it being solid, in a honeycomb object traditional "lightening" methods are out the window because every wall means extra plastic. I know it sounds counterintuitive but until that wall removes more than the infill, infill is faster and cheaper and you'd be surprised just how efficient that infill really is. Any time you try and reduce print time or plastic make two versions and run them through slicer, often the difference is negligible at best and sometimes it's better to give up a little plastic for a much faster print.
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Offline Leslieann

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Re: Acoustic Geometry for 3D Printed cases
« Reply #7 on: Mon, 27 June 2022, 18:06:42 »
People put damping material such as foam or silicone inside their cases. Perhaps you could 3D-print a mould for an insert in plastic and cast silicone inside that. Silicone does not stick to anything (but silicone), but I dunno about types of foam.

I have been toying with the idea of having the entire bottom of a keyboard be a single piece of silicone, thus being both sound-dampening inside the keyboard and the keyboard's feet. But I dunno if that is a good idea or not.

Silicone isn't really good for structure, nor is it very tough. It will chip/tear away little by little over time.
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Offline bishopj7

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Re: Acoustic Geometry for 3D Printed cases
« Reply #8 on: Tue, 28 June 2022, 08:04:21 »
People put damping material such as foam or silicone inside their cases. Perhaps you could 3D-print a mould for an insert in plastic and cast silicone inside that. Silicone does not stick to anything (but silicone), but I dunno about types of foam.

I have been toying with the idea of having the entire bottom of a keyboard be a single piece of silicone, thus being both sound-dampening inside the keyboard and the keyboard's feet. But I dunno if that is a good idea or not.

You know, I've considered seeing what would happen to the sound if I sprayed a coat of Plasti-Dip or something similar into the bottom... Might also give it a try to do some kinda janky silicone pour in one and test it out sometime.


Offline bishopj7

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Re: Acoustic Geometry for 3D Printed cases
« Reply #9 on: Tue, 28 June 2022, 08:11:08 »
help fill the empty space in a more material-efficient manner.
Honestly, the plastic in 3d printing is about the cheapest, most efficient method of filling that empty space.*

Foam or cotton works but that takes human time to do, can also be messy and not as nice looking to someone buying. Casting a silicone block looks and works well but go look up how much just the silicone will cost compared to the plastic it replaces... TONS more money and you still need mold release, cups, stir sticks, scale, and if necessary a degassing chamber, and it will increase shipping costs due to weight.  In total it adds a LOT of cost. Worse still, none will likely have as much effect as different plastics, infill % and infill style. They would still help, but those really only help mitigate other bad choices, they shouldn't be the first choice.

Plastic is cheap, and yes, it will take a few more hours but they are machine hours and if you're talking an extra 3 hours on a 24-36 hour print, it's a negligible amount.


*Before you get too far down this hole,
Do some testing because this is one of the traps of 3d printing people often fall down. Draw up a simple cube, check how long that print time is now punch a hole through it and check print time again. We think of holes as reducing material because you're working from the perspective of it being solid, in a honeycomb object traditional "lightening" methods are out the window because every wall means extra plastic. I know it sounds counterintuitive but until that wall removes more than the infill, infill is faster and cheaper and you'd be surprised just how efficient that infill really is. Any time you try and reduce print time or plastic make two versions and run them through slicer, often the difference is negligible at best and sometimes it's better to give up a little plastic for a much faster print.

The efficiency I'm most concerned with is the printing time - Turning up the fill density isn't off the table, but I'm hoping to keep myself under a 36-hour ceiling between the top and bottom prints to give me the best opportunity for print turnover as well.

Offline Leslieann

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Re: Acoustic Geometry for 3D Printed cases
« Reply #10 on: Tue, 28 June 2022, 12:17:21 »
The efficiency I'm most concerned with is the printing time - Turning up the fill density isn't off the table, but I'm hoping to keep myself under a 36-hour ceiling between the top and bottom prints to give me the best opportunity for print turnover as well.

What you want is precisely at odds with reduced print time.
Your options are either build a small print farm or look at other (also expensive), alternatives such as casting silicone.  There is no getting around the fact that low volume manufacturing is costly and the faster you want it the more expensive it will be.

If you're going to be doing manufacturing with 3d printing you need 3 things; speed, reliability and multiple printers.
Most printers are quite frankly, extremely slow and unreliable. If you can't go faster, get more, this is how most print farms operate. More printers mean more maintenance so you REALLY want something reliable with low maintenance. The fix for slow print times is more printers and bigger nozzles, a bigger nozzle will alter looks, sound, tolerances and strength, requiring a whole new round of testing but your cheapest option.



Tips for a mini print farm..
Many will say Prusa is a good choice, and while Prusa does operate a print farm, from experience, that is actually not the best option. It's a good printer but even it is high wear/high maintenance compared to some higher end (including open source) printers. Prusa has a lot of people running their farm but their farm is partly promotional, it helps drive printer sales, yours is not, you want as little effort as possible. Parts and design matter a ton when you have a massive duty cycle. Some printers run rings around Prusa in terms of speed and reliability however it does come at a cost but that gets reimbursed over time through less work, faster prints and parts lost. Basically look at potential wear points, sensors (and types), and top end parts designed for high wear, every wear point is a potential source of failure. Also, pro-tip, get rid of EVERY connector you can on the motion assembly, they are notorious for being a weak point.

Something like an Ender is going to run you ragged in volume with slow print times and high maintenance... An Ender will run half the speed of a Prusa, a Prusa will run half the speed of something like a high end coreXY. Maintenance is similar with a good corexy needing FAR less work. Other than cleaning my print bed my printers go thousands of hours @ 100-200mm/s between maintenance and usually wear a hole though the feed tubes or wear out a hobb before anything else has a problem.

Oh, and lastly, consider a dedicated print room (as in spare bedroom or garage), do some tests for various plastics to see your reaction and consider some sort of hepa filtration. Some plastics, including PLA give me headaches so I either need to run a filter or choose my plastics carefully. I do both in a separate room.

Expensive? Yep, welcome to manufacturing.
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Offline Findecanor

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Re: Acoustic Geometry for 3D Printed cases
« Reply #11 on: Tue, 28 June 2022, 15:55:52 »
People put damping material such as foam or silicone inside their cases. Perhaps you could 3D-print a mould for an insert in plastic and cast silicone inside that. Silicone does not stick to anything (but silicone), but I dunno about types of foam.

I have been toying with the idea of having the entire bottom of a keyboard be a single piece of silicone, thus being both sound-dampening inside the keyboard and the keyboard's feet. But I dunno if that is a good idea or not.

Silicone isn't really good for structure, nor is it very tough. It will chip/tear away little by little over time.
That depends on what type of silicone you'd get.
The silicone widely available for mould making is much too soft and brittle, yes.

Offline Leslieann

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Re: Acoustic Geometry for 3D Printed cases
« Reply #12 on: Tue, 28 June 2022, 16:35:51 »
People put damping material such as foam or silicone inside their cases. Perhaps you could 3D-print a mould for an insert in plastic and cast silicone inside that. Silicone does not stick to anything (but silicone), but I dunno about types of foam.

I have been toying with the idea of having the entire bottom of a keyboard be a single piece of silicone, thus being both sound-dampening inside the keyboard and the keyboard's feet. But I dunno if that is a good idea or not.

Silicone isn't really good for structure, nor is it very tough. It will chip/tear away little by little over time.
That depends on what type of silicone you'd get.
The silicone widely available for mould making is much too soft and brittle, yes.
It's still not cheap.
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| KBT Race S L.E.
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| Logitech Illumininated | IBM Model M (x2)
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Offline bishopj7

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Re: Acoustic Geometry for 3D Printed cases
« Reply #13 on: Wed, 29 June 2022, 07:18:32 »
Yep, welcome to manufacturing.


Super reduced but effective quote.

I've been cutting my teeth for a little bit on the mini print farm practice. When I can step up to higher-grade equipment, I absolutely will. I have a little bit of a road map of sorts for my plans, but that's beside the point. Getting a chance to hear feedback and learn through the discussion is super helpful.

Added to the pile though, I'm adapting a handwired design to use a PCB - which makes sound comparison between the two an apples/oranges deal since there's a fraction of the filler by comparison (to only name the starting point). Maybe it's time to gut open a pillow for the next test build lol