Hi Brandon,
Did you revisit the throat ring? Uploading the 6" and 6.5" somasonus Bliesma models to i.materialise.com still show a ring about 1 mm thick around the throat.
Ok, here are the results of distortion testing prompted by an issue a user had with the T25B waveguide where distortion was much higher when attached to the waveguide. IIRC the tweeter was replaced by Bliesma due to an off-center diaphragm. First is the distortion with the factory tweeter mounted to my baffle, followed by two of my own pair (serial # 293 & 294) just to check for any current issues before starting the tests.
Following is the T25B mounted to my current 5" waveguide:
Here are two 6" waveguides, one with current tweeter mounting interface, and another without this lip, just a smooth surface over the entire tweeter face:
Given the fundamental changes, you compare difference between F1 and the harmonics, not just harmonic level. THD % is also plotted so this does the work for you, but is heavily weighted by the 2nd harmonic, so that can skew perception a bit. Within the passband of the waveguide I just don't see much difference within the tolerances of the measurement setup. Below that there is a rise in distortion in the waveguides, though I wonder if this is mostly to do with the simple fact that F1 might radiate widely, but its harmonics are being focused by the waveguide and so have a higher SPL on the measurement axis. If that is the case, it is just the reality of horns, and not real relevant given you wouldn't be using the horn well below its cutoff anyway.
Also included are results of the SB26CDC, pretty much the same as above:
As always, use foam under the clamp and just snug it so the tweeter doesn't move, don't put a lot of force into it.
Following is the T25B mounted to my current 5" waveguide:
Here are two 6" waveguides, one with current tweeter mounting interface, and another without this lip, just a smooth surface over the entire tweeter face:
Given the fundamental changes, you compare difference between F1 and the harmonics, not just harmonic level. THD % is also plotted so this does the work for you, but is heavily weighted by the 2nd harmonic, so that can skew perception a bit. Within the passband of the waveguide I just don't see much difference within the tolerances of the measurement setup. Below that there is a rise in distortion in the waveguides, though I wonder if this is mostly to do with the simple fact that F1 might radiate widely, but its harmonics are being focused by the waveguide and so have a higher SPL on the measurement axis. If that is the case, it is just the reality of horns, and not real relevant given you wouldn't be using the horn well below its cutoff anyway.
Also included are results of the SB26CDC, pretty much the same as above:
As always, use foam under the clamp and just snug it so the tweeter doesn't move, don't put a lot of force into it.
Awesome, thanks a bunch!
What were the output levels / input voltages for the distortion measurements?
3.1V I think? The reason I for the exercise is to make sure attaching the waveguide is not doing anything to impact the diaphragm movement. I did not for me. I'm not sure what caused the issue with the one user, but it must be their tweeter had an existing issue (off center dome) that was made worse for some reason with he attached the waveguide. I've reattached mine probably a hundred times and it seems no worse for the wear. I'm still probably going to upload the new version because it doesn't use the alignment pins which require support material to be printed and removed. That always leaves a rough texture and I worry about sealing and wear on the dome surround where it is glued down. With no alignment pins the bottom is smooth and doesn't have a lip at the throat so it spreads the forces out. I did put a circle groove in so you can still align the tweeter when you attach the clamp.
Augerpro, sorry I insist, but do you know how much is the average cost to "print" one of the 6.5" waveguides in one of those "3d printing services" available in China and/or USA? Just a ballpark.
I tried Manufacturing on Demand | Instant Quotes, Custom Parts | Xometry but they say they can't print it.
Thank you again for these designs!
I tried Manufacturing on Demand | Instant Quotes, Custom Parts | Xometry but they say they can't print it.
Thank you again for these designs!
Brandon,
I'm the user you are talking about. The problem was not alignment pins but the throat little ring that was exercising pressure on the glued dome surround in the case of the T25B. It is so easy to get too much pressure on that very small surface nearby the dome when you attach the clamp. I strongly suggest to get rid of that ring in the case of that particular tweeter AND as you said to not exercise too much force when clamping the tweeter to waveguide. Use blue tack if you are afraid of air leak
I'm the user you are talking about. The problem was not alignment pins but the throat little ring that was exercising pressure on the glued dome surround in the case of the T25B. It is so easy to get too much pressure on that very small surface nearby the dome when you attach the clamp. I strongly suggest to get rid of that ring in the case of that particular tweeter AND as you said to not exercise too much force when clamping the tweeter to waveguide. Use blue tack if you are afraid of air leak
Prices are very fluid with the printers, so I can't really say. I would check with imaterialize, they have good prices and finish options.
I agreed that the lip could be an issue, which is why I did these tests. But I didn't replicate your results at all, so I don't believe we can say that anymore. I will still change the design just in case, and for the other reasons I listed, but at this point it looks like you had issue specific to your conditions. I don't know why that is, an off center dome is just my guess.
i.materialise quotes $108ish a crack for 6.5" T25 waveguides in natural white polyamide (nylon), around $112-$114 for dyed or painted, and a couple bucks more for polishing. You also get a tiny discount on two parts.
My take, to match textures I'd get the parts polished if the mid drivers were metal cone and keep them matte with paper cones. The change in surface roughness is less than a millimetre so acoustics would be identical.
I understand the waveguide should be "matched" to the CD or the dome for the best response, but I think I can still get a the benefits of a shallow WG If I could pair it with my compression driver, as most of the Horn/WG available are not precisely matched to my compression driver.
I am not keen enough in 3D modelling to mod the 6.5" WG from Brandon and add a 1-3/8"-18 TPI female thread, but If someone is willing, I will print it and test it with my Celestion 1746 and provide the proper measurements.
If only I could get my 3D printer setup to cooperate... I would love to print some oof these designs, but my setup just won't print cleanly, even after spending a bunch of time and money on a decent printer and throwing parts at it. I have over a grand in my printer setup and its still junk. Thats why its better to just pay a pro to print it for you.
