DIY 3D printed 3 way speaker with concrete infill

[willi_vintage]

Derived from the thread: https://www.audiosciencereview.com/...are-to-conventional.56770/page-5#post-2339145
Focus of the latest iterations was:
-> reduce enclosure resonances
-> DSP/Amp design
-> Tweeter Waveguide
-> going now on a 3 way design

Enclosure resonances:
3D printing is great for rapid prototyping and applying shapes you are not able (or only with plenty of handcraft/tools) to do on your own. But standard polymers (PLA, ASA etc.) are not great to absorb resonances. So I run a DOE with high performance concrete and damping additives in order to understand how the wall can be filled and how a high level of damping and stiffness can be achieved. And: I am quiet happy now with the solution (no, I will not tell the recipe )

DSP/Amp:
Frontend is now standard amanero Module with XMOS 316 to feed via I2S a DSP (ADAU 1466), converted after DSP to analog and amplified with TPA3255 (would go for purify amp but costs and size....)

Tweeter Waveguide:
Goal is to achieve a constant directivity with opening of ~100 and 80 ° (hor, vert). I designed the waveguide with use of BEM/LEM simulation and figured out following design in latest sim as best case:

example: BEM @ 8 kHz, 3 mm mesh

3 way design:
had issues with lobing beginning at ~ 1,3 kHz. Lowest crossover cut off is somewhere @ 1,6 kHz. So I wanted to avoid lobing. Getting mid-woofers closer together? Impossible! Also driving a ported mid woofer up to ~1,8 kHz is not a great idea. So I replaced one woofer with a mid (same geometry/size, just more stiffness and lower mechanical loss). Also tried to get vented port on the side of the enclosure but that's very tricky with the design (issue to print).
Next step: enclosure is printed. Fill it up with concrete and start first measurements to design the filters etc.

 

[stuartkohl]

The mention of concrete reminded me of an article in an electronics magazine from the '50s (Wireless World maybe?) that showed how to make DIY concrete speaker enclosures. Yours are far more advanced.

This looks very interesting! I bet it's a lot of fun to design and build too.

 

[TheWoolyBully]

Very interesting. You mentioned you will keep the "recipe" to yourself, but will you at least show us the effect (as in measurements)?

 

[DVinylfan]

Very interesting project. The tweeter waveguide is giving Rocky Horror Show vibes

 

[DatSpeakerTho]

Very interesting. You mentioned you will keep the "recipe" to yourself, but will you at least show us the effect (as in measurements)?

Don't worry, secrets in the diy space are both dumb, but also they tend to not last very long. Someone else will be inspired, figure out how they did whatever they did, and do it better while documenting it all.

 

[stuartkohl]

Don't worry, secrets in the diy space are both dumb, but also they tend to not last very long. Someone else will be inspired, figure out how they did whatever they did, and do it better while documenting it all.

I agree. I missed the part where he's keeping "secrets" when I first read this. It makes his post rather a waste of time. A bit sophomoric as well.

 

[Redacted]

Does it sound 'gritty' ?

 

[willi_vintage]

Guys, please be respectful and understand that R&D—which requires a lot of calculations and time—isn’t shared in an open forum! The project aims to demonstrate what’s acoustically possible with 3D printing and concrete as infill. Feel free to copy with your own development! But also feel free to ask commercial manufacturers if they're willing to reveal their technology So please keep the discussion on a scientific level and refrain from making derogatory comments. That will only result in the thread being closed, and you'll end up with nothing at all!

Back to topic: Measurements are, of course, still being taken. At the moment, the hydrostatic pressure is still a bit too high, so the concrete isn't flowing 100% into the structure, which is why adjustments need to be made to the 3D print. If you're interested, I'd be happy to print specimens that uses measurement techniques to illustrate the differences between various infill levels (polymer infill such as PLA, ASA, etc.) all the way up to solid infill with concrete.

 

[Sokel]

Guys, please be respectful and understand that R&D—which requires a lot of calculations and time—isn’t shared in an open forum! The project aims to demonstrate what’s acoustically possible with 3D printing and concrete as infill. Feel free to copy with your own development! But also feel free to ask commercial manufacturers if they're willing to reveal their technology So please keep the discussion on a scientific level and refrain from making derogatory comments. That will only result in the thread being closed, and you'll end up with nothing at all!

Back to topic: Measurements are, of course, still being taken. At the moment, the hydrostatic pressure is still a bit too high, so the concrete isn't flowing 100% into the structure, which is why adjustments need to be made to the 3D print. If you're interested, I'd be happy to print specimens that uses measurement techniques to illustrate the differences between various infill levels (polymer infill such as PLA, ASA, etc.) all the way up to solid infill with concrete.

Just a question out of pure intuition (so probably wrong) :

Isn't the recipe requires some short of way to bond concrete with plastic? Like a resin of some shorts?
A good idea about it maybe, is the recipe they use for those super nice new floors which is in essence the old industrial shiny concrete plus resins and stuff.

Sticks like the devil everywhere, at any surface and bonds tight (I build a new house these days and I find all these new stuff fascinating)

An example:

(that's metallic epoxy)

 

[a4eaudio]

...But also feel free to ask commercial manufacturers if they're willing to reveal their technology...

Commercial manufacturers don't usually post in the DIY sub-forums.

 

[willi_vintage]

Yes, that’s a valid question! First, the good news: the wall features the classic infill structure you use in 3D printing. In my case, I had to resort to gyroid-structure. It’s very twisted, and its high surface roughness also provides “good” adhesion, but could be improved. What you describe seems to be a bit like mixture of epoxy resin + mineral fillers such as quartz sand, etc., as used in machine beds or, for example, sink basins (or in your example with polymer fillers) This property can be greatly improved with epoxy, but that comes at the cost of two drawbacks: poor damping of the epoxy and poorer flow properties, which make filling the mold more difficult. PU would be another option (good damping, good viscosity), but I haven't checked yet to see if it can be mixed in. A peel test would certainly be interesting in this regard!

 

[DatSpeakerTho]

Guys, please be respectful and understand that R&D—which requires a lot of calculations and time—isn’t shared in an open forum! The project aims to demonstrate what’s acoustically possible with 3D printing and concrete as infill. Feel free to copy with your own development! But also feel free to ask commercial manufacturers if they're willing to reveal their technology So please keep the discussion on a scientific level and refrain from making derogatory comments. That will only result in the thread being closed, and you'll end up with nothing at all!

Back to topic: Measurements are, of course, still being taken. At the moment, the hydrostatic pressure is still a bit too high, so the concrete isn't flowing 100% into the structure, which is why adjustments need to be made to the 3D print. If you're interested, I'd be happy to print specimens that uses measurement techniques to illustrate the differences between various infill levels (polymer infill such as PLA, ASA, etc.) all the way up to solid infill with concrete.

Are you a commercial speaker manufacturer?