Acoustic Horn Design – The Easy Way (Ath4)

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#15,261
mabat said:
So far I'm still struggling a bit to get nice smooth absolute responses with these smaller, somewhat lower-DI waveguides. [...]
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One thing that comes to mind is a possible mismatch of the (overall) expansion within the phase plug and that of the exit section. I really don't know to what lengths they go when designing the drivers to make all of this a one system. It may be that by inserting a ring plug into the exit section (changing the expansion), this system is disrupted and additional resonances are induced (which leads to the wavy frequency responses).
 
#15,262
Segmented version of the A520G2 is now available as E520G2 ("EXAR 520G2", only shorter).

e520g2-8.jpg
 
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#15,268
If you skim through the measurements posted in a couple of pages back you'll see that the latest big horn(s) make virtually any 1" driver perform very well, either short or extended throats. The drivers will differ mostly in the top octave and probably in the maximum SPL available (which I won't test, as each of them for sure provides more output than I'm really interested in). I really have no particular favourite that would surpass the others in everything, and I think that all of the tested drivers will actually sound very similar in the end. I would pick the DF10.171K at the moment, if you asked me what I would use. Or the NDX595 🙂
 
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#15,271
@olegtern , @mabat and others who have recently printed these devices: any tips for printing, which filament and why? Are the prints resonant sounding when knocked or sufficiently damped so that there is no fear of the waveguide ringing? I guess PETG works fine? how about surface finishing? How to glue and with which glue that finishing doesn't get into a struggle?

If these are trade secrets then perhaps some gemeral tips for beginner? Thanks a bunch!
 
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#15,274
tmuikku said:
any tips for printing
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I don't have much experience with 3d printing even though he's already printed a lot of stuff. My thoughts:

  • If you're not sure about the stability of the z-axis, place the waveguide parts at a 90-degree angle when printing, or at multiple angles (in the slicer prepare several files with different arrangements of parts on the table). I printed all the parts in the same position, and as a result, the error accumulated and gave a large variation when putting everything together, which required more post-processing. If you change the position of the part when printing there is a chance to reduce the error. Even better is to use a printer with good stability in all axes 🙂
  • I used an infill 5% the first time, and 15% the second time. The second pair of horns turned out much stiffer, I think this is enough, although if you have the patience you can increase the fill.
  • If gyroid filling is used, channels are formed inside and communicate with each other (as opposed to a grid, where each channel is separate). This makes it possible to fill the inside of the hollow parts with epoxy resin, you need to drill a small hole and you can pour the resin into it with the syringe. Only it should be taken into account that when curing the resin heats up, it can spoil the print. You can fill in small portions, letting each one harden, or try to mix cold resin, and after filling seal the hole and immerse the part in water, which will give cooling. Or choose a resin that is slightly warm when cured.In case you need a rock solid horn, or if you want to save printing time and then seal the horn with resin on postprocessing.
  • A 3D printing pen can be useful to connect the pieces before the glue/epoxy cures. Costs a bit, can be useful.
  • I still like the matte look of chalk paint, I might settle on that. The spray paints that I tried, even the matte ones, gave a slight sheen that I don't like. But it has to be varnished on top, otherwise it's afraid of water. Also this paint is easy to work with, it sands well and adheres well to plastic.
  • It might be worth considering using fuzzy skin, but I haven't experimented with that.
  • I now bought a bigger printer (Ender 5 Plus) and installed a 1mm nozzle on it — and it's much faster than even the 0.6mm I was printing with previously. But accuracy suffers, may need more post-processing if it doesn't suit you. But I'm not patient and would choose to print faster, I hate to wait 🙂
  • I changed all the fans in the printer to quiet ones, and this has reduced the noise level considerably. My printer is in a common room, and given that I was printing almost around the clock, this was important.
 
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#15,276
tmuikku said:
@olegtern , @mabat and others who have recently printed these devices: any tips for printing, which filament and why?
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I still print mostly prototypes from PLA, the cheapest I can find... With an epoxy coating I would consider it usable, but likely far from the best.
Hard but still flexible sounds good to me, that's what I would try for a "final" print (there's also a Shore 58D TPU, or even Shore 83D). PCTG looks also interesting. No experience yet.

There's also a number of options how to print the parts - densities and types of the infill, wall thickness, etc. To me it's an adventure 🙂
 
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#15,277
Yeah no printer yet so trying to get something to start with. Checked out videos about filaments and PCTG seems good for hard parts. TPU seems the one that might have damping property, infill affects tremendously to stiffness for example. I didn't find any knock tests so far, but luckily on one video the tuber dropped one TPU part on the table and it had quite dead "klunk" kinda sound 😀 seems quite expensive, 30€ for 500g of I saw right so need to try smaller pieces first and finishing options.

How much PLA the big 520g2 takes? I'd assume fill kilo or more?
 
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