Translam Subwoofers with 18" Passive Radiators - The Jedi Mind Tricks

[wogg]

Also then... question: Generally accepted practice is to route chamfers for air movement behind active speakers... should we do the same for passive radiators? Gluing the baffles on and THEN making the cuts complicates any machining on the back side of the baffle, but that could be roughly done with a dremel or sanding drum on a hand drill.

For small drivers, yes. For these I don't think you'll get a significant amount of restriction from the baffle thickness. The 18 won't be affected al all for sure. I hope to see these things!

[JavadS]

Agreed, doubtful a chamfer will change anything on a driver this large with so much flow area in the basket, take a look at the basket and you'll see your answer. Javad

[KEtheredge87]

Hey Guys,

Out of a 5 day weekend I had for the July 4th holiday, I got to spend a solid 3 1/2 days in my garage working on these subs and problem solving. Absolutely GREAT way to spend some R&R time . I hope you guys enjoyed some R&R over the weekend as well!

Back to the project though... I spent a good bit of time machining and veneering the MDF baffles with the walnut, and even more time starting my block sanding process. At the moment, I'm taking the flexible sanding block and 120 grit paper to the sides of the cabinets to make sure I get all of the little mini gouges that were left from the belt sander worked out. Its hard to see them unless I'm at the right level and lighting condition. Once that's done, The whole thing will get a sanding to 180 grit, then 220. I already hit the curved tops with the 180 grit and it feels INCREDIBLY Smooth. It's actually a bit ridiculous when I think about it. I've sanding things beyond 180 grit before, but this feels much smoother than the other times! Fingertips must be playing tricks on me...

On the baffles, I've got them veneered, and mostly trimmed. There's a few little bits of paper backing that I need to tend with a razor knife, but otherwise we're soon to be in business. I will route the rear baffles before installing them on the cabinet, but the front baffles will be glued in and then machined. Before any of that though, I'll want to stain the walnut so I don't get stain all over the plywood!

Last rambling thought of the night... I knew the baffles weren't going to sit 100% flush across the entire cabinet (because of stacked parts, careful-as-possible belt sanding, and general luck) so now that I have baffles with veneer on them... I need to figure out how to glue them in while they look their best. I have ordered that guitar purfling, but I am admittedly a bit scared to do any more routing on these cabinets since the baffles and cabinets aren't absolutely lined up. Probably better to skip the purfling and use timbermate to fill any small gaps between the baffles and the cabinets.

[tomzarbo]

That's pretty cool... the grain of the veneer does carry the 'look' of the ply's horizontally across the baffle really well, good choice!

How will you apply the purfling? Around the edges of the baffle, then glue to the cabinet? I think if you do that and just apply an extra generous amount of PL Premium to the mating surfaces and are careful to line the panel up flush in front, any small gaps inside will fill with the PL and you'll be fine. I imagine a few clamps top to bottom will keep the panel lined up and in place while the adhesive sets up. It's really made to fill smallish gaps and provide superior strength while doing so.

That thing looks great, you must be feeling pretty good!

TomZ

[KEtheredge87]

Hey Tom,

The purfling plan originally hatched to address cabinet walls leaning and any major gaps between the MDF baffles and the cabinet walls. My thought was to take a 1/4" router bit and cut a shallow groove where the baffle transitioned to the cabinet, so the purfling would cover the gap equally on both sides, and sit proud of the cabinet so it could be scraped/sanded back to the flat level afterward. This really only works if the baffles and the cabinet mate up and form a flat plane on the front of the subwoofer. As things sit now, this isn't the case, as there is some area near the corner where the sanding got a bit too aggressive. Since this flat plane condition does not exist all over, I can't make a single router pass and get a consistent depth to install the purfling. The picture I've attached kind of illustrates my dilemma. The lighting isn't great, but you can see the baffle sits a bit further in on the far edge, and there's some difference in the top of the baffle and the top of the cabinet. As I'm typing this, the picture has come through upside down... so maybe download and rotate for the right visual references... as the picture has uploaded, the top of the cabinet is in the bottom of the picture. The far side of the cabinet is still correct as-described.

One option would be to use a flush trim bit on the front facing surface of the cabinet's top (the ~3/4" of plywood directly above the MDF baffle). This would true up the major edge of concern, but would then make the front visibly "not flat"... which I think would be a poor trade.

The other option is to forget the purfling, as the amount of gap is really quite small. Easily covered by a line of wood filler, but I will have a bit of a lip on the front of the cabinet that hangs over the baffle like a baseball hat.

I hope I'm explaining this well. Very easy to understand in person... but typing things out sometimes results in communication failures!

Overall I am really happy to see where these are going. At this exact moment I am a bit frustrated, but mostly intrigued as I work through a solution for the slight inconsistency in my baffle to cabinet mate up on the cabinet in the pictures. I can't really be "mad" since I knew this was a possibility from the moment I chose to reduce cost and material scrap and design with separate walls, but I'm still hoping to arrive at a cosmetically invisible solution, or at least minimally offensive one!

[KEtheredge87]

Tonight's update will be brief. Spent another hour and a half block sanding the second cabinet down to 120 grit. Finally have all of that done! I'll start progressing up through 180 grit then to 220 grit by the end of the sanding. Hopefully that should go a lot easier since I spent lots of energy sanding out the little belt sander marks! The garage was hot and humid tonight. I felt like a swamp monster!

[Kevin K.]

No pics! I'm highly disappointed.

I feel your grief man, the humidity has been so bad here in Texas that the state is considering charging visitors a sauna fee. Be glad your not spraying primer or paint. What was suppose to be dry in an hour was taking a half day or longer.

[KEtheredge87]

No pics! I'm highly disappointed.

Back to our regularly scheduled programming!

Tonight I had enough time to route the 12" subwoofer clearance for one of the rear baffles. This was the first time I have ever routed my driver hole after veneering, and I suppose it went OK. There were a few small chippy places where I crossed the quarter-sawn grain pattern at 90 degrees. Given the nature of this project's assembly, I really can't router before veneering (at least on the big PR's baffle). Still, having tried both ways now, I think I still plan to route first, then veneer on future projects.

The baffle has a good fit to the mounting flange, and there isn't a large gap between the mounting flange and the cutout itself. All the same, I took the time to add a layer of flat black latex paint on the MDF just to make it blend in should someone get a look at the edge and see the MDF.

Tomorrow I'll route the other one and see where I end up. While it may extend the project, I think I may focus efforts on one cabinet to see what can be finished before MWAF. I still might be taking them raw, but I would really like to have some drivers mounted and have the completed look about them! We'll see what I can do. Busy week coming up!

[tomzarbo]

That's the same paint I use on non critical stuff. It covers mdf end grain in one coat and dries in like 20 minutes. Good stuff!
TomZ

[KEtheredge87]

That's the same paint I use on non critical stuff. It covers mdf end grain in one coat and dries in like 20 minutes. Good stuff!
TomZ

That's good to hear! I just grabbed it because it was small and cheap!

[Kevin K.]

Back to our regularly scheduled programming!

Tonight I had enough time to route the 12" subwoofer clearance for one of the rear baffles. This was the first time I have ever routed my driver hole after veneering, and I suppose it went OK. There were a few small chippy places where I crossed the quarter-sawn grain pattern at 90 degrees. Given the nature of this project's assembly, I really can't router before veneering (at least on the big PR's baffle). Still, having tried both ways now, I think I still plan to route first, then veneer on future projects.

Got a good laugh from your opening statement.

What kind of router bit did you use to cut the woofer opening? A spiral downcutter works really well for this and you usually don't have problems with chips.

[jhollander]

I tried spraying it, but it did not flatten out very well.

[KEtheredge87]

What kind of router bit did you use to cut the woofer opening? A spiral downcutter works really well for this and you usually don't have problems with chips.

Oh yeah... I forgot that detail. I was using a spiral UPCUT bit so that I would clear the sawdust rather than jamming the dust down into the cut. I have a spiral down cut flush trim bit that I used on the outside of the veneer panels, and it behaved very nicely. Seeing how this was my first "veneer then route holes" approach, I forgot to get an appropriate router bit for that order of operations.

Do you think plunge cutting with a spiral down cut bit would cause problems, or am I worrying about nothing?

Thanks for getting me to think!

[KEtheredge87]

I tried spraying it, but it did not flatten out very well.

Sorry John, I'm not following... what are you referring to here?

[jhollander]

I like cutting the hole then rabbeting the recess, but you got to like math.