this post was submitted on 12 Dec 2024
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Playing with some ugly old TPU (lemmy.world)
submitted 5 days ago by j4k3 to c/3dprinting
20 comments fedilink hide all child comments
 

Compliant tube based headphone pad idea I had while riding a bicycle two days ago. I got the thickness and dimensions dialed for printing and bending, but I either need to setup my old KP3 kingroon with a longer 2040 Z extrusion or print this in 2 pieces. Either way, the joint connection needs more than just the overlap and glue. TPE would probably be better too, although I have no idea what shore hardness this $10 clearance spool of TPU has. The sound quality seems a little tinny and I have no way to tell how loud it is externally, but it is just my first iteration that I can put around my ear and test. TPU is so slow to print and the moisture levels impact the qualities drastically. I actually like the texture and properties of wet TPU more than dry, but it is hard to get it just right. With the design's compliant bend, consistency is kinda important. Anyways, just another boring project. On the bright side, this seems cooler temperature wise when the TPU pad is against my ear.

I spent all day chasing custom logarithmic infill patterns that might incorporate a compliant bend but only learned about how not to do a thing like that in CAD.

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[–] LouNeko 10 points 5 days ago (1 children)

Is it safe to have dyed soft plastic have skin contact for prolonged periods of time? I'd check the rating of the plastic, wouldn't want chemical dye or softener to leach into my skin.

[–] j4k3 13 points 5 days ago (2 children)

The vinyl of all headphones is plastic. I'm not concerned at all. The fear of plastic is mostly paranoia. The vast majority of micro plastics are from car tires yet that is not what people freak out about.

I painted cars for a long time and worked in heavy industry for awhile. I've been exposed to truly nasty stuff. Other than my horns, and third arm, I'm mostly fine so long as a full moon doesn't happen on a Thursday.

Plastics like this are generally stable. TPU is used in the interior of your car and the grips on power tools. There may be some in your sports clothing. You are likely eating food that is packaged in PLA and PET. There is ABS is everything. These are all around you and come in printable forms. The colors made in the modern world are not arsenic, mercury, chromium, and lead based, like was common 200 years ago.

[–] [email protected] 12 points 5 days ago

The vast majority of micro plastics are from car tires yet that is not what people freak out about.

The majority of microplastics are from synthetic fibers in clothing, actually. Your point is valid though.

[–] IMALlama 4 points 5 days ago* (last edited 5 days ago)

You are likely eating food that is packaged in PLA and PET

"But I only eat canned food!" Canned food containers are plastic lined, but don't worry - we've moved from BPA linings to less studied linings that are totally safer in the long run

"Paper cups and containers!" If it's touching something wet, odds are they have a plastic lining

"But I drink soda/beers out of metal cans!" Oh, hum

"Glass containers!!" Many have plastic on the metal lids

Etc etc. If you eat out you're eating tons of food that was heated and/or kept warm in some kind of plastic liner.

[–] [email protected] 9 points 5 days ago (1 children)

Silly suggestion for testing how loud it is externally; put the headphones on your leg/thigh and test them, it should be a reasonable approximation of your head.

Also forgive my ignorance, but why are you printing this as straight pieces that require gluing as opposed to printing it as a solid circle?

[–] j4k3 6 points 5 days ago (1 children)

Mostly, the design is motivated by the aesthetics, but also TPU sucks at bridging and supports.

Testing the loudness really needs two sides and a later stage prototype. It is also very subjective without a repeatable testing technique. I personally loath the subjective nature of opinions people have about anything audio related and avoid saying anything about such myself to the best of my ability.

The overlapping joint insert was just a first idea for a design. There is a section at the top of this joint that I didn't bother to optimise for vase mode but the rest of the print is possible. It would take some tuning to get vase mode fully dialed. I would probably need to use some helix trickery to get the exact stiffness where I need it. Vase mode was and is still likely in the cards.

I also have a design in CAD that I made today. It has an exposed infill pattern and solid shell in places. I used the pictured design to conceptualize how the infill would behave and how much movement to expect. I may never print that one. I still don't have a way to connect it that I like.

I'm also playing with the idea of covering a print in textile materials and or altering pockets and chambers.

You don't find many printed headphone pads and the ones that do exist are very ugly IMO. Prototyping in yellow is only just that. I have other colors of TPU on hand.

Overall, this has the potential to dial in many properties from fit to audio properties. The orientation is ideal for the properties of TPU. The abstract concept is broadly universal where this will technically work for the majority of headphones. As is, it doesn't look terrible in person and I can make this much prettier if I choose.

The pictured setup is an early alpha phase prototype and it is not glued while it is close to the right size so just the friction is holding it together in the pic. I could glue this and it would likely work fine.

[–] [email protected] 2 points 5 days ago (1 children)

Mostly, the design is motivated by the aesthetics, but also TPU sucks at bridging and supports.

Have you ever tried Creality's HP-TPU? It only comes in transparent and white unfortunately, but I've printed it at 150mm/s and had no issues with bridging at all. I don't have much experience with other TPU, but I've liked using that one. The base price isn't very good, but sometimes they have really nice discounts on it.

[–] j4k3 1 points 5 days ago* (last edited 5 days ago)

I haven't tried a lot of flex materials. I've only used them for things like a few seals. Compliant mechanisms have been a curiosity of mine for a long time, but I haven't had the intuition to establish an entry point project worth trying on my own.

Like as a totally random aside, if this TPU is super dry like how the one test print that looks super crisp with sharp edges, it appears to be air tight. I see a lot of potential for building cheap pneumatic, cable, or passive force driven actuators while playing around with my thumbs sealing each end.

I intuit that this level of usefulness in mechanisms would be hampered by the low quality of the first bridging layers. Absolutely any moisture in the TPU causes random gaps to form as the steam escapes at the nozzle tip in small bursts. Any larger bridging is going to have some amount of dropped passes as a result. I don't think this is a real issue if the TPU is very dry on a totally enclosed dry feed path to the extruder, but I don't like the properties of this material when it is super dry. Overall, my design method in this case is likely oriented in the best way for the properties of TPU and the mechanical best case for compliant design. The layer deposition steps and top/bottom layer properties of FDM are not optimal for compliance in most cases. This particular design is capable of compliance both for the bending form to create the headphones pad, and as a pad against the ear after it is installed.

It is also ~$10-$15 for replacement headphone pads, so making and sharing such a design should be limited to materials most people already have on hand. I'm very tempted to try this with a 98A TPE, but it is just too expensive of a material to justify for this project when I've had 3 rolls of TPU banging around for years unused and only got them because they were dirt cheap clearance sale materials. I would do a lot more if I had an IDEX, but I don't need that rabbit hole money bonfire.

If anything, a dirt cheap foaming TPU could be interesting if such a thing existed. It might be possible to create something functionally similar if TPU could somehow be exposed to a humidity controlled environment at a specific percentage, but I have no idea how moisture saturation works on a deep level, like if the saturation would remain regulated by the humidity percentage or if the exposure would allow the filament to always wick all available moisture where a much more complicated setup would be required to ensure consistent properties. Anyways, my point here is that the best properties for me are not from the super dried TPU needed for bridging and bridging is itself a poor mechanism with FDM. It is best if it can be avoided at the design level like I have done here.

[–] IMALlama 4 points 5 days ago (1 children)

This is very cool! Wear glasses and have been tempted to make my own TPU ear pads with some notches to better accommodate my glasses frames. That will obviously nerf the seal some, but it sound be a low cost reversible thing I can try and revert if I don't like it.

I was considering printing them with no walls and varying amounts of gyroid infill to get the right amount of squish.

Be sure to post a follow up and impressions once you've used them for a little while.

[–] j4k3 2 points 5 days ago (1 children)

Unless you've got a way to mathematically generate the change in infill, don't bother. Lining up infill patterns and logarithmic strategies are hard. The solid parts are just as important as the flex. Keeping things straight is a challenge.

[–] IMALlama 2 points 5 days ago (1 children)

I was thinking about doing this purely with a slicer and infill density. If it needs a solid layer or two for some reason you could leave top/bottom layers as non-zero.

[–] j4k3 2 points 5 days ago* (last edited 5 days ago) (1 children)

The problem is that the infill layers are not well fused and the lack of alignment means they will only cross at angles. This post design can be made solid and turned into cubic with no anchor. That might work with a softer material, but there are still overhangs and the infill pattern is likely to create non linear twist to the bending. At least on my headphones, the tightest part of the bend needs to obfuscate around 60% of the vertical distance on the other side. In other (poor) words, for ever 10mm of vertical height, 6mm is folded out of the way. That is a lot of bulk to push out of the way. Even in this instance I posted, the back side has sections with thinner walls in some areas to make the flex work in such a tight bend without buckling.

[–] IMALlama 2 points 4 days ago (1 children)

Oh, I see where you're coming from - you want to print a straight line than you can bend. I was thinking to completely 3D print the pad and remove/replace the stock units. This would let me print them as an oval.

[–] j4k3 2 points 4 days ago (1 children)

I thought about doing it like this for a long time but never tried it because I think it has several issues. The horizontal layer deposition lines are aesthetically ugly IMO.

Then there is the issue of how you are going to create compliance. If you are going to rely on some super soft filament, I think it kinda defeats the point. Replacement pads are much cheaper than buying some specialty filament.

By printing and bending a tube, it becomes possible to design for both bending into a loop and for the properties of a soft pad.

Lastly, the majority of pads require a sleeve like retention ring that barely slips into a groove around the plastic enclosure body of each side of the headphones. There is a open pocket sewn into the back side of each headphone pad that is a stretchy layer of vinyl used to slip into the groove. It is possible to replace the plate that is used to form this slip ring retainer groove, but then you'll have exposed screws.

I'm not looking to replace any parts of the headphones, so I need a way to retain the pad using this existing groove. In the pic for the post, one of the test prints is oriented to show the way I incorporated the retaining groove into the design.

Of course, not all headphones are designed like this with the same pads. However, these style pads are used on most low and mid tier headphones because they are all contract manufactured in the same place with only minor variations and where these semi universal type pads are a major cost cutting factor. So designing for this type of pad is designing for the most common style of headphones. One might argue that these are the cheapest pads to replace, and they are. But, knowledge about how modern contract manufacturing works is rather rare, and no one is advertising that their products are the same as everyone else with just a different sticker and color applied or a single variation of molding dies added to create a slight variation in appearance. These pads can be found for $10-$15, but you have to know they are universal and be willing to gamble a bit by buying from whatever middleman has too much stock of these or dies not see them as a profitable thing to market at a markup.

[–] IMALlama 2 points 3 days ago (1 children)

I appreciate the detailed reply! You've certainly spent more time thinking about this than me.

My train of thought so far has been, "I wonder if I could partially notch my ear pads to fit my glasses better" -> "I could probably print something out of TPU" -> "I've seen gyroid only prints with no walls, varying the infill density could be a halfway decent method for messing with how squishy the print will be and without walls air shouldn't be trapped"

On my headphones, the pads snap into the headphones:

My stock pads are starting to fall apart and I have a pair of replacements on the way, so I am considering disassembling them for their rings and clips and gluing the print to that.

And you're right! While I was looking for replacements, I discovered that the stock units are functionally compatible with a bunch of other units although the finish materials are different.

[–] j4k3 2 points 3 days ago* (last edited 3 days ago) (1 children)

Cool! I love that you are engaged on my level. Today I had a new idea. I thought of the pop-tube kid's toys randomly.

I was combining that with an idea I had yesterday. Yesterday, I properly measured my ear after I glued up a print and actually tested it by listening to music for a few hours.

So first off, my empirical hypothesis is that the sealing properties and the air volume are the primary factors that determine the perception of frequency response. The design pictured in this post adds a little bit of volume overall compared to the original. It doesn't have quite the same bass response but it adds a lot of crisp clarity in the ~200Hz+ range. I think this is just due to the spacial volume.

After measuring my ear and looking at the CAD and print, my first prototype adds enough fore to aft clearance around my ear. It added around 3mm of extra depth. This clears my ear depth by about 1.7mm too far and is primarily from designing in a stiffer material than the original pad. The original pad touches my ear in several places which gets hot and annoying, especially in the summer.

So I started thinking about how I can alter the print to shape it and completely clear all of my ear. The printed pad is already cooler, but adding full clearance could make it even more comfortable. I was perplexed about how to accomplish this though because it would likely require me to replace the base plate if I am going to shape the print further. My present design is just a 9mm single instance of the tube shape with the pattern repeated and a little underlap sleeve added at the end. What I really need is to vary the spacing of each conforming section to control where and how each bend happens. This would likely make the unsolved clasping connector issue worse.

The pop-tube idea might solve my problem though. I don't need to think about the bend joint like a spring. I need to think of it like a bistable switch and design the bends to snap into shape. I'm still mentally sorting out the idea before trying to design it. I'm essentially decoupling the bending from the shape itself. The challenge is how to do this in a continuous print without gaps in a vase-mode like mindset. I'm adamant on the vase-mode approach because I think I can better tune the pad conforming behavior based solely on single wall extrusion properties. Also, TPU is always more ugly for me if I allow z-hops and travel.

Anyways, if I introduce this disconnected level of complexity to my next iteration, I can likely also add something like a recess for glasses too. I have the same issue with my reading glasses and just use ear buds instead when I need them.

I also want to thin all of the walls of the tube and use a mathematical spreadsheet based pattern to stiffen some sections, but that is a secondary objective. My next step is to make a bistable bending action. I'll see if I can make it tunable for a 4 corner topology so that it can work for oval and rectangular designs – not that you should wait or anything like that. I'm fundamentally unstable and unreliable due to my physical disability. Like yesterday was my big cooking day for 2 weeks of food and I'm mostly recovering so far today. I don't know if my back will settle down enough for me to spend competent time designing today, but maybe after lunch and Adderall I'll get an hour or two to mess around if I lay on a heating pad.

[–] IMALlama 2 points 1 day ago

I share your curiosity, but I don't have a ton of time to dig into this right now beyond the thought experiment. That's the reason for my slower responses :( Work is busy and the kids eat up most of free time.

You're right - the seal will directly impact bass. This is why the sound on some headphones will change fairly dramatically as you move your head around - you're breaking the seal. For me, the head position most likely to break the seal is turning my neck fully in one direction and looking up, but it can also happen with less extreme head motions depending on the cans. I could see volume also playing a role, since the air volume inside the pad is effectively a resonator and changes in air volume will impact how it resonates. I suspect the material of the cup itself will also play a role. Something dense/reflective, like leather, will likely sound somewhat different than say a suede or a microfiber. That was one reason why I was considering gyroid - it would be reasonably non-reflective.

After measuring my ear and looking at the CAD and print, my first prototype adds enough fore to aft clearance around my ear. It added around 3mm of extra depth. This clears my ear depth by about 1.7mm too far and is primarily from designing in a stiffer material than the original pad. The original pad touches my ear in several places which gets hot and annoying, especially in the summer.

Sounds like a similar motivator to my "I wish these didn't press on my glasses frames so hard" ;)

A pop-tube seems like it would be hard to print vertically oriented. I suspect it would move around some as you're printing thanks to not being very rigid. It wouldn't hurt to try it. Printing it sliced down the center and laying across the bed horizontally seems like it would be easier. I certainly hear you on the joys of TPU stringing, but if it's limited to the far ends of the print it shouldn't be too horrible to clean up. You could even design it a touch too long and cut the ends off.

Anyways, if I introduce this disconnected level of complexity to my next iteration, I can likely also add something like a recess for glasses too. I have the same issue with my reading glasses and just use ear buds instead when I need them.

Depending on the spacing of the tube crinkles, you might be able to line them up so your frames fit between them. You could also probably make one crinkle stick out a little less and line that up with your frames.

not that you should wait or anything like that.

At this point, I have nothing but time. I'm also trying out a pair of 'real' ANC headphones, vs my office drone headset that happens to have defeatable ANC. They have ridiculously sized pads and they're actually pretty comfortable with glasses. I am somewhat tempted to type out a mini-review somewhere here, but have no idea where I would post it.

[–] [email protected] 4 points 5 days ago (1 children)

Like the idea, be great if you had something like miniDSP ears to test with. Would denser infill help the sound? Pads are massive in terms of sound, I put the wrong pads on my dt880s in the past and they sounded like straight garbage, be worth trying to replicate the same sort of density/sealing of your existing pads.

[–] j4k3 4 points 5 days ago

This is a major curiosity of mine too. Just the shell seems to be pushing the amount of flexibility of this material in my present design. I'm not using any infill. I can alter the shape a lot. I have a cheap pair of thermal cycling bib shorts that were way too small and I never sent back. Those may become a covered print experiment. That material is thick, dense, and still conforms a lot.

I'm most interested in exploring wave shaping. It would be trivial to add more complex shaping in the center cavity. I can imagine making a print support that sits inside the tube and enables me to create some more complex voids in places.

My main goal right now is to com up with an integrated clip that allows one end to open and close easily while looking pretty. Then I can move on to more audio quality tuning.

[–] MacedWindow 3 points 5 days ago

Cool project