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

[KEtheredge87]

Hi Everyone,

When Dayton Audio released their new line of passive radiators styled like the RSS series of subwoofers, I wanted to give them a try. I decided I would build not one... but two subwoofers to use these new passives, and while I'm at it... I'll make them translam designs! I bought two RSS315HF 12" subwoofers and two RSS460PR 18" passive radiators to use in this build, and I intend to face the 18" PRs toward the listening space so it "looks" like I have two 18" subwoofers. The 12" active drivers will fire out the rear end of the cabinet. Because of this not-so-little trick I am playing, the working title for this project to call them the Jedi Mind Tricks. Just imagine Obi-Wan Kenobi waiving his hand mystically in front of your face while saying "you believe this is an 18" subwoofer"!

I picked the combination of 12" active and 18" PR after playing with the numbers in BassBox Pro. The cabinet occupies a 21.25" cube of airspace. The internal volume is 2.6 cuft (accounting for internal bracing volume and driver volume displacement) The design should have an F3 around 25 Hz, and be capable of 110 dB @ 25 Hz when fed with 350W.

I mentioned this was going to be a translam design. I fully admit I got inspired by Javad's Strafi build for the 2017 MWAF, so I took the extra challenge to make this translam instead of a basic MDF box. Since I was going this far... I also decided to try my first build with baltic birch plywood to take advantage of the translam process. I've been told that imitation is the most sincere form of flattery... with that in mind, I hope Javad doesn't mind how much I've learned from him and straight up copied some of his construction and assembly methods!

I keep mentioning challenges and things being more than just a basic box... well... I went all out here. Not only are the sides curved on these cabinets... but the top is too! I'm hoping the plywood layers make a really neat pattern when they are slowly exposed. I have an idea how I'm going to pull this off, but it hasn't happened yet. That'll be a good future post.

I'll try to keep up a solid build log here, but I tend to suck at updating those regularly. We'll see how it goes.

[KEtheredge87]

Here's some CAD giving a rough idea what this should look like when i'm done.

[tomzarbo]

Looking good so far.

You're wise curving the top also, that way nobody can put a drink on that thing and goof up the finish!
Looks mean already, man!

So that should be around 116 db at 25 Hz with two of these? Yikes.

I was around that output level with my "The Beast" subwoofer using a quad of 12" Titanic MK2's vented several years back. I could literally make the wall at the end of my house flex when I had it cranked.

"The bass is strong with this one."

I'm looking forward to seeing this come alive.

TomZ

[donradick]

Monster build, dude.

[KEtheredge87]

Thanks Tom and Don!

"The bass is strong with this one."

YES! I love that line!

For fun, I timed myself going through the process of making two of the curved wall pieces last night. My whole process is:

1) Drill #6 screw holes and attach templates
2) Trim excess on the bandsaw
3) Router table to get the final shape (few light passes to avoid burning)
4) Drill press for size F wooden dowel holes
5) Remove templates and lightly sand to remove fuzzies.

It took me 27 minutes to make one left and right side. The bandsaw trimming is the most time consuming part. I have 78 more wall pieces to go for two subwoofers... so 39 batches... at 27 minutes each... means I have 17.5 hours of wall-making ahead of me . I hope I get faster along the way!

[Kevin K.]

Thanks Tom and Don!

It took me 27 minutes to make one left and right side. The bandsaw trimming is the most time consuming part. I have 78 more wall pieces to go for two subwoofers... so 39 batches... at 27 minutes each... means I have 17.5 hours of wall-making ahead of me . I hope I get faster along the way!

Nice progress already Keith! I'm still jealous of that table router. What bandsaw are you using and what size blade? If you want to move through the wood in a hurry, use a 1/4" blade with 6 teeth per inch. If you cant find a blade like that for your saw, let me know, we have a company pretty close to us that makes custom blades and the price is not bad. You may also be trying to cut to close to your guide, 1/4"-3/8" away should be fine with that router bit we talked about.

[KEtheredge87]

Thanks Kevin,

I picked up a Wen 3962 10" bandsaw and promptly removed the stock blade. I replaced it with a Timberwolf 1/4" blade with 6 TPI like you suggested. I spent some time setting the blade and bearings up well, and changed the motor to high speed mode. It cuts very quickly and cleanly. As you've correctly guessed, I am trying to to get very close (1/16 - 1/8")with the bandsaw to reduce the amount of work the router bit is doing.

If you see the burn marks on the inside of some of the layers in the photos above, I'm suspecting that I'm not routing as efficiently as I think I am. That piece was cut with the router on full speed, pushing the material against the rotation of the bit (not climb cutting). If I get the material to move quickly I don't get burning. However if I move slower (where I feel much more in control) I get burn marks that I don't want. I backed the router speed off a bit which seemed to help, but this bit is not cutting through the plywood like a hot knife through butter. I can avoid burn marks if I cut small segments, essentially chipping away at excess material until I get to my template, but I don't want to spend hours doing that either.

Maybe I need to clean the bit already? Maybe there's a load of pitch that accumulated on the bit from the first few burns? Maybe there's just loads more glue in this plywood since it has more layers? I am certainly confused here, and wondering if I'm doing something stupid by accident.

I appreciate any thoughts or tips you can provide. That router bit was EXPENSIVE, so I'd rather not ruin it!

[Kevin K.]

Can you shoot a video when you cut your next set? I'm not understanding why it would be giving you so much trouble, that cutter should be flying through the birch with ease if you are cutting that close to the templates.

[donradick]

Ketheredge87 -

Following this thread closely!

Usually when I try to make a baltic birch ply baffle with a clear finish, I will burn it somewhere, and have to paint it.
I'd be real interested to learn how not to burn the wood.

[KEtheredge87]

Can you shoot a video when you cut your next set? I'm not understanding why it would be giving you so much trouble, that cutter should be flying through the birch with ease if you are cutting that close to the templates.

Hey Kevin, the wife was nice enough to hold my phone for me and shoot a quick video to show the way the router bit is behaving. I have been using a medium to low speed with the bit to avoid burning, but I also cranked it to full speed for demonstration's sake. The bit I volunteered to burn a little will be facing inside, so that wasn't a big deal. Have a look and see if I'm doing something obviously stupid. Any reason why this bit isn't eating through this wood like a starving gorilla in a banana warehouse? https://youtu.be/djOYbhMqvx8

Usually when I try to make a baltic birch ply baffle with a clear finish, I will burn it somewhere, and have to paint it.
I'd be real interested to learn how not to burn the wood.

Don... I'm hoping I don't burn too many pieces either. I have enough material left over that I can make some replacement pieces if certain parts get too gnarly, but here and there I think it may add a bit of character. At the very least it will reflect the my skill level in much the same way a preschool kid makes macaroni art and sticks it on the fridge at home!

[KEtheredge87]

Daily update time! I made a bit of progress today. Shot the youtube video linked above to help explain my router situation. Cleaned the bit before I started work today with a brass brush and some CMT bit cleaner since it was gummed up with God knows what...wood pitch and plywood glue I suppose. When I'm stacking each wall piece up just for grins at the moment I feel kinda like I'm playing Jenga with myself. 70 more layer pieces to go!

[Kevin K.]

Man, something just doesn't look right about how that cutter is behaving, it acts like its worn out already and you haven't done near enough cuts for that. You may have told me before but remind me again, what is the router, what horsepower and what RPM is it capable of?

[KEtheredge87]

Hey Kevin, I suppose I'm glad that you agree something isn't right. I'm using a Bosch 1617 EVS router. 2.25HP, capable of 8,000 - 25,000 RPM under no load. Should I contact Whiteside maybe?

[Gordy]

When I have had issues like that with spiral bits it is dull around the top of the bit near the bearing. I use cheap ones for MDF and have some good ones for hardwoods. I have used these bits before with varring success with hardwoods. I try to use templates that are at least 1/2" so the bearing can ride higher and the spiral bit can get more bite. Baltic birch is near hardwood-esq. I solved my issues with a 1/2" shank 2" cutting length flush trim bit from whiteside. Whiteside also makes an ultimate trim bit but it is pricy. You may end up going through a few bits on this project. That's my $.02.

[KEtheredge87]

Thanks Gordy, the bit I'm using actually is Whiteside's RFT5200 flush trim spiral bit. My template is 1/4 inch aluminum since I wanted it to last for the whole project. I'd feel a pretty jipped if Whiteside actually sold me a bit that came dull from the factory. You thinking that's a possibility here?