A gift for many? - The Mechano23

[technodanvan]

I've been thinking of making a set of gift speakers for a while now, something I could give to friends and family that wouldn't break the bank and was reasonably simple to manufacture quickly. In lieu of designing something for myself I think I have settled on the Mechano23, designed by Xmachinik. His website is linked below, as is the thread at ASR where it is well documented and discussed (and where I first discovered the design) and Amir's review of the design using his fancy gear.

Xmachinik Website
AudioScienceReview Post
AudioScienceReview Review by Amir

This speaker uses the affordably priced Scan Speak H2606/920000 tweeter ($47.80 at the time of this writing) and the even more affordably priced SB Acoustics SB13PFCR25-04 midwoofer ($36.80) in a roughly 8 liter box. Just under $170 USD (plus tax and such) is pretty darn solid for drivers these days, and with all the positive reviews from the various websites and users it was hard for me to ignore. I had originally pushed this project off with a reminder to look at it closer toward Christmas, but I came across a project on Makerworld that reminded me of it a bit sooner than expected.

Mechano-23-CS on Markerworld

This project was posted by user_1168315211 (no other identifier that I could find, but I wanted to be sure to call out their work) and appears to be intended for experienced builders and those new to DIY. The model is split into several parts: the woofer portion, tweeter portion, crossover boards, and port (which could be modified for various tuning). This was also seemingly intended for a variety of 3D printers with the woofer and tweeter portions split as they were. There was some effort to stiffen up the sides of the cabinet by adding some vertical ribs as well, though this is also a function of the infill density and wall loops, among other things that can be adjusted within the slicer software. I went ahead and printed one cabinet to see how it looked.






I noticed a few things about the build that I felt required a little attention, the most obvious one (to me) being the portions that would be adhered to each other could have a means of holding everything aligned during that process, but there were a few other small details I felt I could help with. I reached out to the original CAD / Slicer model but didn't receive a response, so I decided to recreate it myself. I'm not sure I'll share the files on Makerworld, but we'll see. I'm also not sure I'll 'only' make the Mechano23 with a printer but I figured I'd give it a go.

I had a few goals with this design.

1. First, the largest dimension is only 290mm, meaning it'll fit on my printer - I won't need to do a split cabinet design. However, there will still be a few separate pieces by necessity. The seams should be more natural though.
2. I want to minimize to the maximum extent possible the number of supports that need to be printed. I'm just not a fan of them and they can often be engineered out in designs such as this.
3. Glue should not be necessary.
4. Baffle and rear will be printed separately and bolted on.
5. The outer cabinet (sides and top) will be printed in one piece. The major downside here is the print time could be several days and use two or more rolls of filament per side. That's a long time for something to go wrong. Hard to avoid this.
6. Threaded heatset inserts will be used extensively.
7. Gaskets will also be printed from TPU (or, perhaps, cut from neoprene using the printer)
8. Braces will be integral to the design (and also printed).

Gotta run more to come...

[technodanvan]

Alright, back at it. My first intent is to create some 'shells' to prototype the models. This one I printed at 25% infill (i.e. not just a shell, which might just be 5%) with PETG-CF (carbon fiber) so it's really quite solid. I think in an ideal world I'd use CF for all parts but the available colors aren't going to work for every situation. I want to test this with regular PETG to see how much difference that might make. A couple key notes about the below baffle compared to the speaker design by Xmechanik and the original model on Makerworld:

1. The original baffle (in addition to all other sides) called for 18mm of Baltic birch. Obviously this is a great starting point for a small speaker! However, I'm working with plastic here and the interior will probably be ~75% air in the finished model. I felt I needed to go thicker to shore up the strength a bit, so I elected to go with 36mm. This will also increase the volume a little, which I'll need later.
2. I couldn't tell if the original design called for carving out the back of the baffle around the woofer. The 3D printed version did not. I have included this in my redesign.
3. The original design has no chamfer or roundover on the edges of the baffle. Given how well it measures and the reception it has received I guess this works just fine. However, that seems kinda boring to me, and it must have to the 3D printed modeler as well since they included a pretty good roundover on the vertical edges. Normally I would do that same, but a 3D printed roundover in which the baffle is constructed from back to front ends up looking a little rough. I think it looks really quite nice with a relatively steep chamfer instead, which I placed on all four edges.
4. This baffle is held on by eight 1/4-20 bolts. Six would have been fine, but I decided having 4x arranged around both the tweeter and the woofer would look nice. The current print uses the low profile 316 stainless hex top bolts I have set aside for another project, thinking they would be nice here too. These are expensive, something like $10+ apiece. There will also be eight on the back, so that would be $160+ per side, or in other words, WAY too much for ~$170 worth of drivers total, especially if I'm making multiples. Making the change to 82 degree countersunk hex bolts (still 316 stainless) runs about $1 each for the same size. Still pricey for what amounts to a pretty (but nice) bolt, but FAR more palatable to the wallet. I'll see if I can find a way to buy some in bulk.
5. The drivers will be attached with M3 bolts (for the tweeter) and M4 bolts (for the midwoofer). I haven't priced these yet, but I'm obviously hoping they'll be cheaper still.

The other side of the baffle is currently flat. I have thought about including guide pins, or a groove for the gasket, or even a groove that might fit a corresponding protrusion of sorts on the cabinet itself. I do not think these are necessary - the bolts will essentially be pins that will aid in alignment. I learned from the AliExpress 'sub' box that having a groove on both the cabinet and the baffle is kind of a pain to align and keep in place while clamping down, and I have a groove located on the cabinet already. The current baffle also does not require any supports when printed back to front.

[technodanvan]

So this is where things started to look a bit more complicated than the print I did from Makerworld. Here are the individual parts shown (or, at least, mostly shown) in the images below, along with a few features.

1. Cabinet (sides/top/bottom)
   1. Can be printed in one piece with supports only used for one of the grooves. All the angles shown are important in order to make this possible. It could be printed from back to front or front to back, but I'd probably go with the former.
   2. This would be a 3-day print at 25% infill. That's twice as long as anything I've done, but having minimal supports (and in this case, no supports after the first hour or two) really increases the likelihood of success.
   3. This would be a minimum of 2 kg of filament per cabinet.
2. Top brace/port
   1. 180 degree roundover on the inner port
   2. Slides into the cabinet from the back. Unknown how these tolerances are so that'll be something to watch for
   3. Printed with only a support for the groove in the back for the gasket.
3. Mid brace
   1. Not much to say here, other than I might make this go closer to the driver yet. Need to measure the tolerances for that.
   2. Slides into the cabinet from the back.
   3. Printed with only a support for the groove in the back. I opted to have the gasket 'seal' the braces so there would be contact with the rear. Might help a little with resonances.
4. Bottom brace/crossover bracket
   1. This is designed around a PCB someone made for the crossover, which I'll be using (and linking later). This should speed up assembly if I'm making multiples.
   2. Slides into the cabinet from the back.
   3. This might be the smallest piece in terms of filament usage (other than the gaskets) but it's the most complicated in that it'll currently need more supports. I am considering a way to print this such that it would need less. That would entail changing the way it attaches on the sides and I'm not sure I want to do that.
5. Baffle gasket
   1. Pretty straightforward, but one thing (that should have been obvious) I learned from the AliExpress subwoofer cabinet is you don't make the gasket the same size as the groove. It fit on one side with some effort, but there was no chance it would go into the corresponding slot on the baffle. This time, I made the gasket a little smaller than the groove so it'll easily fit. It's 3mm thick with a 2mm deep groove too, which is a bit thinner that I had used previously as I observed little compression. This'll be trial and error as well to get right.
6. Rear gasket
   1. No notes here, same thought process as stated in previous bullets.

So here's the question then: Is there anything obvious I'm missing from the design so far?

Other than the entirety of the back, of course!

[technodanvan]

It was pointed out to me that I could improve the port geometry by looking into the work augerpro has done, in addition to the effort STV has done at DIYAudio. This seems to be realized in a fantastic little website by Naturlyd (also at DIYAudio) that can output the port in a printable format.

Optimal Port Designer

Now, there are some potential issues here that I need to experiment with:

1. Should I keep the ~45Hz tuning that Xmechanik used?
2. What volume do I actually have when this is all said and done? (original spec was around 8L)
3. Do I want to use the port as a brace as originally intended?

[technodanvan]

Alright, so I have a little more time and a few things have finished printing. First up is the cabinet sides and top - this was a test run so I had it printing fast and basically hollow, but it works for what I need right now.



First impressions are pretty good. I'm continually impressed with what these machines can do even under stress. To go with the cabinet I also printed the original port and crossover platform so I could test fitment. Looks pretty good! It was a bit of a challenge to shove them in the last inch or so, but once they're in I really don't think they're coming loose. Could use epoxy to be sure but I'm near certain it isn't necessary.



Of course, there were problems too. Printing things this large tends to have the corners pull up off the plate. I'm not sure how to counter this, but I've seen it before. I can use better adhesive but sometimes that doesn't help, the plate just comes up with the corners.



Another potential issue are the mounting holes on the front (I printed face down, so they were supported). I think this is because they aren't considered one of the first few layers anymore, leading to the printer moving very fast through this section. I think I can counter this because I'll be having it print more layers on the faces themselves (at 100%) and I'll be slowing the printer down for the real print. Remember, this only took one night (~10 hours) to print where the real thing will take 3 days.



I also printed the new port. I like it!