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The challenge rules:
Minor rules include:
The challenge I saw was finding a tweeter that can go low enough to mate with a large woofer. The GRS 3 1/2" open back tweeter will do that and I assume that it's closed back version won't go low enough because the rear chamber volume is too small. I'm going to experiment with my own larger rear chamber to see if that's the case. https://parts-express.com/GRS-PT2522-4-3-1-2-Planar-Tweeter-4-Ohm-272-122?quantity=1
My goal for the woofer was to find something that would go low and still be able to go high enough to mate with the GRS tweeter. It looks like the Dayton DCS205-4 subwoofer would do that. https://parts-express.com/Dayton-Audio-DCS205-4-8-Classic-Subwoofer-4-Ohm-295-200?quantity=1
Modeling the woofer in 1.2 cu. ft. gives an F3 of 31 and F10 of 26.
My first rub is that the faceplate for the tweeter is 4.25" by 3.5" so I have to cut the faceplate down or 3d print my own to get under the 4.125" limit.
I picked up the woofers with the 15% black Friday discount. I'd already picked up the tweeters and faceplates with an earlier 20% November discount. Time will tell if I can make this work.
Square 4x4 or 4.125 diameter tweeter.
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I haven't followed the rules, but if you rear mount the tweeter isn't the faceplate just the portion that protrudes through the opening?
From the rules on the PE forum: "No tweeter faceplate must exceed 4.125" diameter or edge to edge." Did I miss something in the PE forum thread? Can I mount the tweeter with out the optional factory face plate like Ed said?
Post #31 from PETT:
"I think there was some misunderstanding going on. This past SDC weekend told me that. if the tweeter has a waveguide and is as small as required, only then are waveguides permissible. You cannot add your own. Cutting down of faces to fit the rules is also prohibited."
PE Post #25 info by query;
I am fine with either 4-in square or 4 1/8 diameter that is fine.
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I'm not talking about a waveguide. The tweeter is a planar tweeter and you can get an optional flat faceplate for it. If you don't use the manufacturers faceplate you have to come up with your own mounting solution.
Hi Ron, I was looking for dome tweeters without a faceplate but never could find one that would work. But if I had, I wasn't sure what the rules would allow, so just wanted to point that post out if you hadn't seen it.
By the way, I used the GRS PT2522 in my speakers at SDC 2022. I built a 3/4" deep (but really not that deep) back cup (a rectangle made with MDF) filled with felt and a DIY waveguide. The GRS face plates literally came out the week before SDC so I had to do something. I changed to the PT2522C, with cup, and used the GRS faceplate when I brought them to Iowa.
I experimented with different DIY waveguides using different roundover bits but I did NOT experiment with different back cups. I actually thought the deeper backcup had a lot of potential but I ran into a lot of problems with my speaker so was trying to simplify as much as possible. I think with your 3D printer you have a lot of flexibility.
I couldn't ever get either version of the PT2522 to measure smoothly, but they still sounded good. If you don't already know, Charlie Laub used the open back in his OB SDC speaker that won first place in the Open/Unlimited category.
This is my first try with the GRS tweeters. I've used the BG tweeters and they didn't measure very well either but they sounded great too.
I had an old 1 cu. ft. test box laying around and used it to get an idea of how the woofer frequency response measures. The box is just some cheap 1/2" plywood and is unlined and unstuffed. I looks like it will work well up to 1K. I'm not sure why the data sheet only recommends a response from 30-200Hz.
1 cu. ft. sealed near field response
I also got the ports printed. I plan to use 2 per box.
I switched 3D CAD programs from Fusion 360 to FreeCAD. It took a while to get a handle using both but I managed to print a faceplate for the GRS tweeter last night using a file generated with FreeCAD. PLA plastic isn't very rigid for a part this thin so I have some PLA infused with carbon fiber on the way. The faceplate has a nice textured face that looks really bad when photographed. It fits like a glove.
Next up will be a back cup.
Looking great! It's been a while since I've used my printer, but I was also using FreeCAD. CAD commands just seem strange after working with Adobe products for a few decades!
Ron (or Tom), why did you switch from Fusion 360 to FreeCAD?
Years ago I worked with a simple 2D CAD programs (Autosketch V2). 3D is a whole new world. I was able to figure out how to do everything I wanted to do but put a chamfer on the back side of the tweeter cutout. I just made the cutout slightly bigger and it looks just fine. FreeCAD seemed to be a little more intuitive to me and didn't have the limitations that came with the free version of Fusion 360.
I had a hard time getting a handle on the user interface. I'd want to make a change and couldn't find a way to alter an existing dimension. I'd want to make something and I wouldn't be able to find the tool I wanted to use. You're limited to 10 files which are stored on the cloud. I didn't like having to renew my license after a year which they didn't make real easy.
I much prefer the FreeCAD system that has menus where I can see all the tools.
Can you do 2-D drawings in FreeCAD? I've been using NanoCAD but there's a dimensioning glitch in the free version.
FreeCAD starts with 2D sketches that get extruded to make 3D images. The 2D part is pretty easy. This is the 2D sketch I started the faceplate with.
Ditto! My son had been using Fusion in high school and showed me the basics. But I didn't want to go through the hassles Ron mentioned with the free version. FreeCAD's whole extrusion concept is similar to some of the 3D plugins I use in After Effects at work. I still think FreeCAD's interface could be better, but it's been a few years since I've used it. There may have been some refinement in the last 18 months.
I've got the back cup designed and printing. I ended up with a strange artifact left over from putting a counter bore for the head of the screw and then putting a chamfer on the block the screw goes through. It's highlighted in yellow. I appears to have no sidewall although the slicer is printing a support for it which is not a big deal.
The back cup turned out OK even though the supports fell over before they got to the counter bores for the screws.
I received the carbon fiber infused PLA and didn't have any problems printing with it. It has a matte finish and I bought a replacement magnetic bed so the face looks as good as the tweeter. The carbon fiber PLA is a little stiffer than the regular PLA but it still wasn't stiff enough to compress the gasket without warping the faceplate. I ended up leaving the gasket out and just snugging up the faceplate bolts and sealing the back side edges of the tweeter with silicone.
I mounted the tweeter on a 10 3/4" x 22" scrap of plywood and took response measurements with and without the rear chamber.
I filled the rear chamber with a 2 inches of cotton insulation.
Red is the response without the rear chamber and green is with the rear chamber.
I looks like it will go as low as I want to go.
The neo3's (and it's clone) are such a fantastic tweeter. Even with the weird 15K bump, sound so good.
But difficult to get the balance between sibilant and dead, at least in my experience.
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I took time out from all the other projects to cut some wood today.
That looks like good quality plywood. Did you get that from one of the big box stores?
It's Baltic birch from the Woodsmith Store in Des Moines which is about 45 minutes away. It's the good stuff and pretty much all I use.
I just looked at their website and the war in Ukraine is affecting their supply. It looks like they might have shipped it in the past but aren't right now.
Started gluing today and put the tops, bottoms and sides together wrong. Now I get to cut new fronts and backs because the speaker is wider and shorter than what I designed.
I've done that a few times myself.
Pretty sure I did that once too.
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