Buyout PR Subwoofer Project...

[tomzarbo]

A little while ago PE had some buyout Passive Radiators for sale, (I think they're sold out now though) I picked up a few and didn't do anything with them. Then Kenny K. whipped up a tasty cube of bass that closely mimics Wolf's "Triumph" subwoofer (which I also have). Here is the end of that thread which is actually Paul Carmody's "Voxel" thread: http://techtalk.parts-express.com/fo...mini-sub/page3

I ended up with a slightly different cabinet, a 10.5" cube, but the idea and inspiration was all Kenny K's... I never would have thought about pairing that PR with the 5.25 TB ferrite driver. (I was thinking PR's for a smallish tower speaker.) My box ends up being about an inch bigger than the "Triumph" sub, which was a 9.5" cube with .75" material.

Pieces for four of these cut out... hey, it's just as easy to cut out four than to cut pieces for one.





I recessed the PR's because they had a funky kind of rounded edge that would have looked goofy if I didn't recess them... kind of like a rounded edge, but with the biggest part at the edge. You can see it in the pic a few down...
I just flush mounted the TB sub.

See some glue discoloration on the cabinets near the roundovers? It's a 1.5" roundover I did in my router table... even though I had a board as a backing piece to minimize tear out on the edge of the cabinet, it still happened on a few of them. I tend to use a super-light touch when I'm using that router table with the big bit in there... as I've said before... that thing scares the carp out of me. I think I just wasn't pushing hard enough on the backer board. Anyway, I just lifted up the edge of the MDF that was lifted up and shot some glue in there and taped it down, problem solved.



It will use two of the buyout PR's and of course the 5.25" Ferrite TB sub along with a PE 25 watt plate amp. They just went on sale a few weeks ago luckily.



I used Walnut for the veneer. There are only two seams on the sides. I used 2' wide x 8' rolls and two sections meant that I had two seams to deal with. I ended up applying glue to the entire four sides of the box at once, and using the iron on method and cutting one layer over the other -- was able to glue up all four sides in one operation. I also veneered the top... the bottom I'm just putting some of the wipe-on poly on, and I'll call it done.







The F3 is about 34 Hz, and with 25 watts, it should hit 93 dB at that frequency.... F6: 31.5 Hz... F10: 29Hz. At 25 watts Xmax is never breached, so that's nice. The PR's are set up with the stock weight, there appears to be a mass of epoxy or something inside of where the voice coil is. There is no way to easily add mass, not that it's needed.

I know the 25 watt amp might be considered 'not enough' for a driver with a 40 watt power handling ability, but bumping the scenario up to 40 watts only yields 2 dB more of output at 30 Hz, so I think the cute little 25 watter' will work fine for this. I absolutely love my little "Triumph" subwoofer, which uses the PE 25 watt plate amp...and I'm hoping this one performs equally well.

This one will be for my father, to go with the "Encore's" I built him a few years back. He uses them with his computer setup in his mancave/bedroom. Another one will be for my niece's boyfriend, who has a set of Jeff Bagby's Quarks (which he loves) and I told him I'd get him some bass soon to go with them. I think these will be a good match for them, he uses them as a computer sound system as well, which works well for the PE 25 watt plate amp with it's on/off/volume knob.

Yeah, nothing too exciting here, but there doesn't seem to be a ton of construction pics floating around lately, so I'm posting what I've got.

TomZ

[Kevin K.]

Cool looking project Tom! It's to bad the PR's are sold out, could definitely see others replicating these. Your veneer work looks flawless as always and I especially like those roundovers. Just makes the cabs look more modern IMHO. Thanks for posting, the forum does seem a little void of new builds here lately. Maybe everyone is holding off posting anything because MWAF is coming up.

Take care,
Kevin

[donradick]

Beautiful work as usual!

Very sweet little subs. Lucky recepients!

[tomzarbo]

Thanks guys... but man, the flash sure makes everything look dusty as heck! It didn't look like that when I was seeing it.

TomZ

[mzisserson]

Looks beautiful man!

[philthien]

Did you use any software to model the enclosures w/ the passive radiators? Or did you model with a port and substitute the passive for the port?

I guess I'm wondering how you model a sub w/ passive radiator, especially one that seemingly cannot have any mass added or subtracted.

Nice cabinets, BTW. I've always enjoyed your cabinet work.

[dynamo]

Really nice Tom!

[careyink]

Great work again Tom!!! They look great!

[WernerM]

Very cool! Gives me an idea to go along with the B652's I just got for my daughter.

[kenny_k]

Bravo! Great looking subs, wonderful job. Now I got to get off my bottom and make some. 😁

[tomzarbo]

Did you use any software to model the enclosures w/ the passive radiators? Or did you model with a port and substitute the passive for the port?

I guess I'm wondering how you model a sub w/ passive radiator, especially one that seemingly cannot have any mass added or subtracted.

Nice cabinets, BTW. I've always enjoyed your cabinet work.

I used BassBox Pro to model this setup. Again, Kenny K basically did the design and thought the idea up, I just tweaked it a bit to fit a particular size. BassBox does a good job of modeling enclosures and it does PR's just fine.

There seems to be a "Sweet Spot" I've noticed with PR's. When I model them, it doesn't take much of a change in weight up or down to goof up the model a lot. It seems like driver/PR designers get the weight pretty good. There are many designs where no, or very little weight is added to the existing mass. This PR is heavier than most, but it seems to work well with this driver/box combo.

Thanks for the positive comments. I love smaller projects like these, they don't take up too much time, but the reward is still big. I expect this sub to sound pretty good; should be done in a few days, I'll report how it sounds then.

Kenny... build it! Yours will be a bit bigger but dig lower, right? BASS!!!!!!!! gotta love it.

TomZ

[kenny_k]

Thank you Tom, but this is YOUR build and YOUR interpretation of the design. So, give yourself a well deserved pat on the back. I like your plate amp choice. 👍

[scottvalentin]

Tom those look great and that Walnut really sings with the finish! Do you use Heat-lock glue for the iron on method or something else? I just picked up a roll of maple veneer and hope to improve from my first veneer job which was not that great. I used normal Titebond and the iron on method failed and the glue warped and bubbled the veneer. Oddly enough, I was successful using the 3M adhesive spray after the first 2 pieces failed.

[tomzarbo]

Scott,
Thanks for the kind words. Yes, I used heatlock and an iron for this. I almost always use that method, it's almost foolproof, which is good for me.
Couple of things to remember...
First the veneer needs to be "backed" veneer. The backing is usually paper, that works best with the iron-on method. Non-backed veneer will soak up the glue too much and get 'wavy', also the heat from the iron combined with pressure will cause the glue to 'bleed through' sometimes, happened to me once.
Second, although several others have used Titebond glue to do this with, I've only ever used the Heatlock glue, which is designed for exactly this procedure, and I've never had a failure in say, 7-8 yrs and probably 2-3 dozen cabinets over curves and bumps. It works 100% if done right.
Third, the glue roller makes it work. It allows for the glue to be distributed evenly with no 'dry' spots and no areas with too much glue which will not 'bond' with the heat.

After you roll out the glue on the box, do the veneer. By the time you're done that, you may notice that some areas of the box may look a little bit dryer, (this usually happens on end grain with MDF) you can re-roll those areas briefly with a slightly wet roller (don't have to fully dip in the glue, just redistributing the existing glue on the box) and let it sit until everything is dry to the touch. When I say dry, I mean when you touch with your finger, you don't bring back any glue. If it's a little bit 'sticky' that's okay but the glue should remain on the box or veneer and it shouldn't be soft to the touch. Then you're ready to go. I use a fair amount of the glue on the piece, but not too much, you want it to be able to dry in about 35-40 minutes or so. If you put too much, it won't dry even, then you'll have to reapply. I pour the glue into a plastic disposable plate for picnics. When the glue dries in the plate the next day, I peel it off in one sheet and reuse it.

My iron dial goes from 1-8, I use a setting of 5-6 usually with an all-cotton T-shirt scrap as a means of keeping the heat directly of the veneer so it won't scorch. Work center out and apply moderate pressure. After I think it's good, I "Pluck" the veneer with my fingernail to listen for any 'higher-pitched' noises that would indicate a non-adhered section. Also, I pay special attention to the edges and slightly press and roll the iron on the edges to make sure they are well adhered. And that's pretty much it. Like I said, I've had zero failures or lifting all these years so far, knock on veneer. The "Heatlock" glue is special stuff... it's very thick so it won't run down the side of an already veneered cabinet, and it isn't super-wet or moist, so it doesn't cause the material it's applied to to 'swell' with the moisture. They got the formula just right with it, and it's really not expensive for what it does. I know others have used Titebond with success, but I've found a method that works and I'm sticking with it.

I have a few videos in my sig at the bottom of this post, a few about veneering. They're boring, but there may be a few pointers that may help or just seeing it done helps me sometimes. It's easy once you get the feel for it.

TomZ

[Paul Carmody]

Great project!