C-Cake Design and build log

[skatz]

John

I don't know how you intend to use the spheres, but it occurred to me that maybe you could use world globes for fabricating what you want. I also recall seeing, I think on YouTube, a method of laying papier mache over balloons to make spheres. Are these to be reflectors that need to be hard? There are also glass globes that are used as lamp diffusers that might help you.

[dlneubec]

Wow, I had never thought about that. Dan how did you make the big deflector cones?

Currently I need something from 10K up for the AMT. The deflector is sized to reflect from 4K up. I just finish the proof of concept for mounting the tweeter. I'm pretty much committed to the current path

Looks like you are cruising right along!

Yeah, those diffuser cones were something else. I laminated pieces of mdf and purple heart together into a stepped cone (don't ask me why). My son-in-law was able to mess with them with a CNC he had access to at IU in the art department, and get them down to maybe 1/4" stair steps. Then, iirc, I figured out a way to spin them on my drill press and sand them down the rest of the way. Then I had to carve out the inside of the diffuser cones to accept a 6" dia waveguide with neo tweeter at the throat. It was a royal pain and not something I would ever do again!

[dlneubec]

I used to have a pair of Infinity speakers (back in about 1975) that had a walsh supertweeter on top that sent out a 360º spherical horizontal wave. It looked kinda like an ice cream cone. I think the supertweeter on those kicked in right around 10khz, so yours should have a similar effect.

[6thplanet]

Cool build Jonny! Nice to see outta the box thinking/design. I look forward to seeing them at the show!

[jhollander]

Eric, thanks your build was also motivation to get started.

Bottom box and box model. I've convinced myself that an internal offset port end will miss some of the resonance trash inside the speakers. There were more braces added than the few shown here.

[AEIOU]

What every speaker needs, a Mark and Daniel Omni Harmonizer. So add it all together this is the first design I came up with. It's based on using 12 inch and 8 inch round cylinders.

This is how Henry Wolcott did it, an omnidirectional horn (on the horizontal plane) using only a single dome tweeter. Initially the Dynaudio D28, later on the Morel MDT33.
Sorry for the poor picture, but if you squint you should be able to see the tweeter dome. LOL

[Wolf]

Couldn't you use a dimple dome and set the apex right in the dimple? Or set the tip of an XT25 right on it? It's been said more than once that ring radiators suit waveguides better. Just suggesting out loud, not telling you what to do.

Wolf

[jhollander]

Ben, feel free to suggest away. I've got a pair of the OT19s as back up https://www.parts-express.com/peerle...-ohm--264-1122

The ring radiator/ center "post" tweeters worked well in my wave guide tests as the post acted like a phase plug preventing a bigger on axis dip. I've discounted that benefit when using a reflector, everything is off axis. I still need to do a bit of testing but I'm not to concerned as I don't need much FR for the super tweeter.

I'm looking forward to your post for InDIYana 2020. I've already pulled down about 10 omni patents for ideas.

[Wolf]

I'm still mulling it over. Likely the week before Dayton as usual. Right now I'm in build mode.
Wolf

[jhollander]

A little more work. I got the top cabinets assembled. I used CA glue to reinforce the MDF for the super tweeter recess. Thanks to Mike C who CNCed my AMT3-4 recesses in small pieces of MDF. This saved me a ton of time compared to routeing and cutting down

Both the top cabinets and base cabinets were flattened with a combination of hand planes and sandpaper glued to MDF blocks. When I used my store bought sanding blocks and power sanders they tended to dish and roll over the edges, definitely not flat.

I'm working on the deflector and supper tweeter mounting next. I'll cut the woofer holes before I start the round over process. Probably not happening soon as this is going to be a long fishing weekend.

[jhollander]

Hear are some pictures of the deflectors from TN Allen and my tweeter mounting

[jhollander]

Here's my test setup. As dlneubec mentioned the reflector close to the dome gave the best measurement. That's about 1 mm in the last picture. What I found annoying is that my bracket causes a big dip on axis. I had planned a round over but that is not going to help much. I need another idea. I thought about two small posts but I don't like the look. I'm leaning toward similar bracket but on a 45 degree angle. Whatever I come up with has to be somewhat adjustable if I'm going to get 1 mm clearance from the dome.

[kenrhodes]

Linkawitz used a mirror to "aim" the baffles dipole notch so that he would have less reflective sound going to the listener.
Could you "aim" the notch to cancel of axis problems?

[dlneubec]

Here's my test setup. As dlneubec mentioned the reflector close to the dome gave the best measurement. That's about 1 mm in the last picture. What I found annoying is that my bracket causes a big dip on axis. I had planned a round over but that is not going to help much. I need another idea. I thought about two small posts but I don't like the look. I'm leaning toward similar bracket but on a 45 degree angle. Whatever I come up with has to be somewhat adjustable if I'm going to get 1 mm clearance from the dome.

John, I'm thinking you may be able to mitigate that by just routing 45's on the face of your bracket, so that it presents a pointed edge toward the done rather than a flat edge. Any dip should be substantially reduced and may only occur off axis, if at all. I assume you are getting an out of phase reflection back to the dome with that flat surface so close behind it.

Another option would be to create a bracket arm that runs up the back of the box and does not mount on top surface. This would push the arm out far enough that the reflection, would occur below the XO point. If it were me, I would probably to a combination of both were I presented 45's toward the dome and also moved the mount arm as far away as feasible.

[skatz]

If it was a permanent installation you could suspend the deflector from the ceiling, but I don't think you really want to do that. If you do it as Dan suggests and present 45 degree angles to the dome and mount it at the back, it would deflect those reflections to the sides, where listeners aren't (I presume).