Congrats on the build, Rifleman! Looks awesome! I am mucking about with the GR Neo 3 waveguide and back cup as well. Did you have any concern about getting sealant from the back cup into the holes on the back of the driver? I was looking at sealing it today and my first thought was, damn, there's really not a ton of room for error here between the lip of the back cup coated in sealant and the acoustic vents on the back of the tweeter... Kinda worried about sealant getting down through the holes when I go to bind them together!
Yes, there is little room for mistakes. I tried to be sure that the back cup was flat to the tweeter before sealing it on, and then did my very best to apply a thin layer of sealant to the edge of the back cup. It shouldn't matter if there is no sealant at the inside edge of the cup if there is a consistent bead on the outside edge. I squeezed a little sealant onto my index finger and then raked my finger along the outside edge of the back cup to transfer a small amount of sealant to the edge. I kept doing that until I had a continuous bead around the cup. Looking at my figure 38, the bead doesn't look any too consistent, either. I also let the sealant dry a few minutes so it had more body and wouldn't squeeze out as much.
The joint doesn't have to be clamped tightly like a wood joint: all we have to do is get the sealant to touch all the way around, and then let it cure. I lightly twisted the back cup around just a teeny bit to try to ensure that I had contact all around, and then laid the tweeter on its face and let it cure for 24 hours.
If we're just looking for an air seal, we might be able to put small dabs of sealant in the four corners, apply the cup and let it cure, then go back and add sealant to the outside edge between the cup and the tweeter to seal the gap. Now it occurs to me that perhaps the cup can be held in place and then a CA glue like Superglue can be added around the seam between the cup and the tweeter: that should prevent any excess from migrating to the tweeter slots inside the cup. We do not care what it looks like outside the cup, just that the air is trapped, and trapping the low-pressure air should be easy.
Maybe a combination of these adhesives can be used: a couple drops of CA glue to hold the cup in place followed by a bead of sealant on the outside? Because the upper and lower edges are thinner, maybe we should not apply sealant to the edge, instead waiting until the cup is securely attached before applying the sealer to the outside edge of these gaps so we do not risk getting any goo in the tweeter slots? That may be the safest approach.
You're right that there isn't much room for error when attaching the back cup. Maybe some of these ideas will help. Please let us know what works best for you!
