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Small 2-way speakers with linear on-axis and power response characteristics (Scan Speak and SB Acoustics drivers). H&V off-axis measurements included

Very cool 3d printed baffle! Great work.

Another speaker that has a 3D printed baffle is the Audio First Fidelia, which is a commercial "kit" and has rave reviews both here and by Erin. The Fidelia is a similar size but costs a lot more. The Fidelia has a lot more curved front baffle and I wonder what the effect of something like that would be on the M23? Once you get into 3D printing the baffles, the limits on shape go away and creating curved surfaces is easy.

I wonder if anyone has actually compared the M23 to the Fidelia and what their thoughts are?
 
In addition to improved directivity, I would expect the distortion measurements on the Fidelia would be lower given they appear to use SB Acoustics ceramic line. That's just based on other DIY designs I've seen and/or heard using those drivers, I didn't look at any reviews to confirm. Lots of other DIY efforts out there using the same (or similar) models. I have the some parts sitting in storage somewhere myself awaiting construction that I need to get to sometime.

While we could potentially improve directivity of the Mechano23 by making some kind of optimized baffle for the tweeter I do not think it is something I could do myself. Or rather, I could add random large curves to the baffle but if they don't match the tweeter than it's not going to do much, and may be measurably worse than the the integrated waveguide ScanSpeak already uses. Also, while there could be further optimizations for distortion I do not think we can approach that of the SB ceramic line. A curved baffle would not really impact this greatly, IMO. It's a limitation of the selected drivers - but they are around half the combined price of those in the Fidelia, so that should be expected.
 
In the Fidelia's case the waveguide is part of the baffle, not part of the tweeter as in the M23. That's the major part of the Fidelia's use of curves. There's also the taper of the baffle sides to reduce the baffle diffraction effects, but that's a secondary issue with a waveguide like this on the tweeter, hence the lack of roundover on the sides and top.
 
XMechanik said:
The idea here was that if we added a new trap in a new location in the circuit, the old trap might no longer be needed at least in its current form, so we could remove one component. The increase in the number of components of the modification would be two instead of three (we add R, L, and C and remove one C).

No it doesn't.
Click to expand...
Forgive me if this is covered already. I see the 0.82 mfd cap is not needed with the new THD trap installed. However, there is no mention of if one is to just not install the capacitor or if that leg needs to be shorted on the PCB. If I'm reading the schematic correctly, shorting it would bypass C4 and L3, so we don't want to do that. Just confirming it can simply be omitted and no other action needs to be taken.
 
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technodanvan said:
Forgive me if this is covered already. I see the 0.82 mfd cap is not needed with the new THD trap installed. However, there is no mention of if one is to just not install the capacitor or if that leg needs to be shorted on the PCB. If I'm reading the schematic correctly, shorting it would bypass C4 and L3, so we don't want to do that. Just confirming it can simply be omitted and no other action needs to be taken.
Click to expand...
You're right, I didn't mean shorting 0,82uF cap, just not installing it.
 
Minor status update on my 3D printed model. The baffle is at the 95% mark and should be good to go. Only tweaks remaining would be those necessary to get a quality print, and perhaps tweaking the heatsert holes.

IMG_0871.jpg


Crossover and THD boards will be here in a couple of days so I'll fix those braces (if needed) once I have them in hand. Plan here is to make the lower brace and middle brace identical with mounting options for both boards on them. We'll see if I can make that work. Upper brace I'm working on this morning, current plan may include attaching it to the top of the speaker cabinet as well as the sides. In the meantime, I made several ports using the Optimized Port Designer. This is the one I'll try first - 8L/55Hz/90dB SPL. The flange being 110mm is somewhat important to ensure the through hole can be sufficiently large for a variety of port tunings. This one is set up for eight socket head bolts countersunk into the port flange - I elected to make the bolts in this design a feature throughout the project.

Port Designer (8L, 55Hz).png



Speaking of bolts, there are several more holding the binding post plate on the cabinet. I was going through my inventory of binding posts and realized most of them had different through diameters. I wanted to keep this box somewhat modular for other DIY efforts (both my own and others) and printing the rear is a timely affair. If I wanted to change the posts after it was made I'd need a whole new one...unless I just made a plate that was removable and could have the holes scaled as necessary. That little design is pending.
image3.png

I printed an example of the rear and port. The port is probably the 4th or 5th attempt on as I was having trouble with printing it face (outer flange) down. I seem to have mostly resolved this issue, but it could still use a bit of sanding - which I've never done before on plastic, so that should be interesting! I neglected to select 'avoid crossing wall' on this most recent print, hence some of the extra wispy material shown. The rear printed near flawlessly, I'm not sure I have much more to do there unless I need to tweak the heatsert holes for the binding post plate. I struggled a bit with determining if I should put a chamfer on the edges to match the baffle but elected not to do so on this version.

IMG_0877.JPG


IMG_0876.JPG


I will be sharing the files once done, of course, so others can tweak and/or use as they see fit. I'll probably just put it on Makerworld and link to it here, but we're a ways away from that right now.
 
technodanvan said:
Thank you! It really doesn't feel like work though, I'm having a fair amount of fun with this project.

As an aside, I'm guessing some folks might prefer a roundover on the baffle edges so I made an alt version, though I did not test print it.

View attachment 543429
Click to expand...

Do you mind posting the STL files? Not sure I'm going to build any of these soon, but maybe some day I make some for some family members.

I totally understand that "having fun" part, in my book that's what DIY is all about.
 
gabo4au said:
Do you mind posting the STL files? Not sure I'm going to build any of these soon, but maybe some day I make some for some family members.
Click to expand...

Not at all, I do intend on posting everything once done on Makerworld. I can try uploading here...do you know if ASR can handle those file types, or even a zip file? Did you want the files now or when I'm done with them?
 
Hmm....this post didn't post for some reason. Trying again?

A super minor update since this did not take long to print. I have several pairs of these binding posts for some reason. Must have been a sale a while back. I don’t care for them since the gold finish kind of looks bad for the price, but they are the largest post of any that I have (~3/8") so I sort of designed the plate around them. Conveniently, they are also designed for a metal plate that has all the dimensions shown that I needed.

I was set to use M3 screws to hold this on the rear but the holes printed a little on the small side so I need to widen them a hair. On the other hand, the plate itself is very tight to the rear so I think I might loosen that up a bit. It’s only barely removable at this point…unless I put it in backwards, which would then match the finish of the port. Might need to think about that.

IMG_0878


IMG_0880

Edit: I’m rethinking the lack of chamfer on the back. I think it kind of looks ‘off’ since the bolt holes are spaced so far in. This matches the front though, so adding a chamfer might make that look better. It’d need to be pretty steep though since the port is pretty high.
 
technodanvan said:
Hmm....this post didn't post for some reason. Trying again?

A super minor update since this did not take long to print. I have several pairs of these binding posts for some reason. Must have been a sale a while back. I don’t care for them since the gold finish kind of looks bad for the price, but they are the largest post of any that I have (~3/8") so I sort of designed the plate around them. Conveniently, they are also designed for a metal plate that has all the dimensions shown that I needed.

I was set to use M3 screws to hold this on the rear but the holes printed a little on the small side so I need to widen them a hair. On the other hand, the plate itself is very tight to the rear so I think I might loosen that up a bit. It’s only barely removable at this point…unless I put it in backwards, which would then match the finish of the port. Might need to think about that.





Edit: I’m rethinking the lack of chamfer on the back. I think it kind of looks ‘off’ since the bolt holes are spaced so far in. This matches the front though, so adding a chamfer might make that look better. It’d need to be pretty steep though since the port is pretty high.
Click to expand...
This is all really interesting to me as I'm kinda new to the 3D printing world and ever curious. Would you mind sharing what you use for design software? Also, filament type?
 
carbidetooth said:
This is all really interesting to me as I'm kinda new to the 3D printing world and ever curious. Would you mind sharing what you use for design software? Also, filament type?
Click to expand...
I'm using the hobbyist (free) version of Autodesk Fusion360 for the CAD work. It's missing some pro features but certainly does everything I need it to do.

I've been using PLA for most of these prototype prints as I have a lot of spare rolls of it. I just got in some PETG though; my understanding is it tends to work a little better than PLA for speaker cabinets but I have not seen (or looked for) actual data that support that assertion. It's something I want to look into sometime, and maybe investigate on my own. I think number of walls, number of top/bottom layers, infill type, and infill density would certainly play a role in all of that as well. Additionally, I suspect certain types of PLA may also be as good (or better) than some types of PETG. I've been sticking with Bambu filament for my printers and am interested in PLA Tough+ but have not gotten around to acquiring any.

On top of all this, I LOVE the finish of the carbon fiber variants of both PETG and PLA. However, I have read some convincing arguments against its use, at least in this application. If nothing else, it is notably more expensive and colors and availability are limited.

In the end, it is my intent is to use PETG wherever possible but I won't limit myself to it if a color I want is only available in PLA.

Since you're a bit new to 3D printing (I'm only intermediate at best) be aware there is a certain amount of shrinkage for each type of filament. I want to say PETG shrinks a little more than PLA. This is esepcially important once parts cool to room temperature. So, since we're making a number of holes large and small it's a little important to make test prints if you use a different filament type. I noted in an earlier post today that 3mm holes were a little on the small side so bolts wouldn't easily pass through them. Not a huge deal but something that is fixable, I'll probably set them at 3.5mm for the next print. Sometimes it's easiest (at least for small holes) to just put together a test panel of them, say, 2mm to 5mm if testing both 3 and 4mm bolts, and have them numbered so you know what actual size you need to model for your specific brand/model of printer. Some kind folks have done this already. Here's an example:


That said, I've generally had pretty good luck with my Bambu H2D in getting sizes very close to what I use in CAD.
 
technodanvan said:
Not at all, I do intend on posting everything once done on Makerworld. I can try uploading here...do you know if ASR can handle those file types, or even a zip file? Did you want the files now or when I'm done with them?
Click to expand...

Nah, just wait till you're done with them. I think you can upload here, seems like I've downloaded STL zipped files from here before, although I'm on so many forums maybe it was somewhere else. But I'm not on Makerworld, maybe I need to go find that and sign up.

Nice hole gauge!
 
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XMechanik said:
Before the audio show, I experimented a bit more with the THD trap. This time I used a 0.1mH inductor and a 5.1uF capacitor, without a resistor. I measured the impedance characteristics of the resonant circuit, disconnected the midwoofer from the crossover, and measured the near-field SPL, where the driver's breakup frequency was clearly visible. I noticed that the two frequencies didn't match very precisely. The impedance peak was at a slightly lower frequency than the breakup (around 7kHz vs. 7.15kHz). I unwinded the coil until the two frequencies matched. Below is a comparison with the measurement of the previous THD trap implementation.
Click to expand...

To be clear, is the recommendation to go with the 5.1 uf cap and 0.1mH inductor, with no resistor? I haven't seen many folks reference this post. I'm open to experimenting on my own of course but would like to make the recommended build first.
 
technodanvan said:
To be clear, is the recommendation to go with the 5.1 uf cap and 0.1mH inductor, with no resistor? I haven't seen many folks reference this post. I'm open to experimenting on my own of course but would like to make the recommended build first.
Click to expand...
This is what I currently have installed in my M23. The 0.82uF capacitor is removed, and the trap circuit is without a resistor but I'll try to confirm this with notes/photos.
As a result, there's only one more component comparing to the prototype - one removed and two added. However, don't take this as a definitive recommendation.
 
Excellent, thank you! PCBs came in yesterday, I sprung for ten of them in white. Unsure why the order quantity appears to jump from 5 to 10 but here we are. They aren't terribly expensive so no big deal. Guess I'll be making a few extras...eventually. Ordered the crossover parts necessary for a single set for now. I need to make one pair of boards so I can get height measurements before I can finalize the location of the THD filter. I'd like to place it vertically so the inductor faces a different direction than the four on the main crossover, but we'll have to see where that can happen in the current design with all the bracing.

Crossover parts were ordered from three vendors. I want to order some more inductors to see if non-Solen parts from another brand would fit okay. Nothing against Solen, but international shipping and tariffs make the hobby less fun (I'm in the US). To ensure I can get one set working I did end up ordering all inductors from Solen. I went with Bevenbi capacitors from Cinergy Audio (they are also reasonably compact, I'm hoping they work) and Mundorf resistors from Madisound (I wouldn't have done this but I already had a few other things in my cart from them and I wanted to see if the 'green' metal oxide film resistors everyone sells would also fit). I may try some of the inductors from Jule Fidelity as possible replacements; listed measurements make them seem 'thicker' than the Solen inductors, though not as large in diameter.

I thought the crossover brace was at the 95% mark but I'm rethinking a few things. Current one is shown below, the board fits a little tight but that could be due to installing the heatsert by hand (one or more could be a little crooked). Plus I installed the heatsert backwards for some reason. Anyway, these braces are a tight fit and really aren't removable once installed in the cabinet.

IMG_0894.jpg
 
Upper bracing is now a bit overengineered I think, and it may get even more so as I consider replacing portions of it with TPU. I'm making a long print of the first cabinet (sides and top) now; the first prototype used two exterior walls and 5% grid infill and printed in 12 hours with high flow nozzles, which was intentional as I just needed something to test tolerances and such. This one has six walls, 25% gyroid infill, and will take almost 3.5 days on a slower (i.e. higher quality) setting. Sometime after I started printing I did a little more research and determined we probably have enough rigidity but little damping, hence the possible use of TPU in the bracing. We shall see what we get, or even if it finishes without errors!

1783735583056.png


Top brace fits together with dovetails - they're pretty darn tight right now! I'm very glad I marked the pieces so it was simple to put together. Minimal support was needed.

IMG_0905.JPG


IMG_0906.JPG


IMG_0908.JPG
 
@XMechanik It just occurred to me that perhaps the development of the 3D printed cabinet might be derailing the thread a bit. Please let me know if you'd prefer not to have all these posts in here! I bring this up because I think I'll be attempting to quantitatively test a few cabinets and bracing methodologies. Tentative plan is below.

Static test materials:
  • PETG Baffle, Rear, Port, and Terminal Plate (6 wall loops, 25% gyroid infill each)
  • Same woofer and tweeter between tests (tweeter just being a seal for the hole in the baffle, intent is to test woofer only unless I hear I should do otherwise from members here and elsewhere)
  • TPU gasket for the tweeter (it otherwise has no gasket) and the stock 'foam' gasket for the woofer
    • As an aside, the stock foam gasket is, IMO, not very good. The frame is also not flat (there are cavities in it), which leads me to believe the stock gasket material may not make a great seal. I may test TPU and neoprene gaskets on the final cabinet design, but I think most builders (especially new builders) would probably just use the stock foam.
    • Ideally we'd use sorbothane, I think, but it's a little pricey.
  • Modern recommendations indicate using neoprene o-rings between the screw head and woofer frame may be of use as well, so my intent will be to do this. That said, if the woofer 'sides' are snug in the baffle I'm not sure there is a point to this. It should probably be 'loose' or 'floating'.
  • TPU Gaskets for Baffle, Rear, Port, and Terminal Plate
    • As with the woofer, I may try testing neoprene gaskets on the final cabinet design.
  • I'll experiment with stuffing, but I'm not sure I want any for this test. Whatever the result I'll use the same amount between tests. Open to thoughts here.
There are so many possible variable here that could (and maybe should) be tested, but I've narrowed it down to this for now. I have several other open speaker projects that this test will inform and I may evolve the testing for those based on these results.

Cabinets:
  • PETG Cabinet (18mm sides, bottom, and top), 6 wall loops, 25% gyroid infill
  • PETG Cabinet (18mm sides, bottom, and top), 6 wall loops, 10% gyroid infill
  • If a significant difference is seen between the above, then: PETG Cabinet (18mm sides, bottom, and top), 6 wall loops, 15-20% gyroid infill
Bracing:
  • No bracing (cabinet only, albeit with t-slots for bracing that may add rigidity compared to a cabinet without the t-slots)
  • Rigid bracing bars in the t-slots (PETG, 6 wall loops, 25% gyroid infill) with TPU beams connecting them (the 'X' shape in my previous post)
  • Rigid bracing bars in the t-slots with rigid beams connecting them (PETG, 6 wall loops, 25% gyroid infill)
I'm open to ideas on testing methodology, but I think this is the plan to keep things short and sweet:
  1. Woofer sweep, quasi-nearfield response and distortion measurement. Thought process here is that vibrating walls would influence woofer behavior. Ideally I could also do 1+ meter measurements but I'd either need a quiet place outdoors (I live by a reasonably busy street so...nope) or an anechoic chamber (definite nope).
  2. [Idea from augerpro's various threads around the web] Measurement sweep dead center on one side of the speaker, 1/2" distance from the side and gated to (hopefully) remove woofer response. I'll need to reread his threads to confirm methodology. Thought process here is that if a panel vibrates it probably makes some amount of sound. Curious to know the amount of it.
 
technodanvan said:
@XMechanik It just occurred to me that perhaps the development of the 3D printed cabinet might be derailing the thread a bit.
Click to expand...
There's absolutely no prblem with that. This thread is to present and discuss different aproaches to Mechano23 implementations. Thanks for shaing your work!
 
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