Tuba-18 subwoofer build completed

setzer808

Heya gang, just thought I'd do a little post since I've finished my first BFM cab, a Tuba 18. This is a repost of my thread on the BFM forum if anyone reads both and has deja-vu.

I used the MCM driver and pine plywood from lowes/home depot (I'll be going to a lumberyard next time...).

This is my second project ever building a speaker cabinet out of wood, I built a small 2 way bookshelf using drivers I had lying around as a warm up for this one. I'm very pleased with the build results, considering I made it in my 10x12ish dining room using tools that would make a carpenter cringe



The finish looks a lot more even in person than in the photos. I did a few coats of primer after sanding and using wood filler for the more offensive cracks/screwholes. Then I used some textured spray paint to cover up some of the woods imperfections...I really didn't realize how bad the plywood was until I tried to get an even coat of primer on it...

As for the sound, its well beyond what I thought I could be achieved with a sheet of plywood and a $30 8" driver. The bass is very clean, and the output is shocking. I've ran it some at home, and at the office and its had quite a few dropped jaws. My building at work is about 60ft wide and probably about 150 ft long. I had people from the other side of the building (through at least 4 walls) asking me if I had heard the car out in the parking lot that was making their lights rattle....and that was maybe 30-40% on the volume knob.

I'm powering it with one of the Foster WF-100k plate amps I'll try to post some detail/build photos throughout the day.

edoggrc51

Nice build!! Gotta love DIY!

Storminone

Looks good. I'm interested in the build photos since I'm trying a table tuba after I finish a pair of tritrix speakers for my daughter.

setzer808

Here are some more pics, including some build pics.









I don't have a router, and didn't think I would have enough room to remove the driver from the access panel if I installed the recommended 1" anchors to attach a flush driver access panel to, so I used an oversized cover as you see in the above photo. I used lots of screws, compression weatherstripping, and rope caulk to make sure its very tight and well sealed.

zingo

Great work! I'm been eyeing Tuba designs as the bass for a DIY 3-way horn project. How's the sensitivity with that smaller driver?

Storminone

Nice
The whole angle cutting thing frightens me a little which is probably why I haven't started it yet.

Did you try it with the home theater yet? Put in War of the Worlds and crank it up

Jstas

Dude, nice work!

Some advice on materials next time though, use a cabinet grade plywood. The stuff you used looks like sheathing or a construction grade. The problem with that is that grade of plywood often has voids where knots popped out or where the glue didn't fully cover the sheet of wood used to make one of the layers. This creates airspace and week spots that can eventually start vibrating and causing coloration of the sound. It can also cause excessive flexing which can color sound as well.

If you use a cabinet grade, it will have even gluing of the layers as well as no or minimal voids. This makes for a much more dense and sonically dead cabinet. Personally, I prefer using a wood core plywood. It's more expensive but considerably lighter than the cheaper MDF core plywood. It's also stronger than the MDF core plywood. Although, the MDF core has a slight edge in density and sonic deadness so for a subwoofer enclosure, that would probably be a better option.

And all those sharp, interior corners? Yeah, what I usually do is a two-fer deal. I will run a bead of silicone caulking along each corner and smooth it out with my finger. This does two things for you. One, it takes those sharp edges away. By doing that, it helps greatly reduce standing waves and high pressure spots caused by reflections and cancellations of backwaves. That's especially important in a folded horn or bass reflex enclosure. Number two, it seals every joint so you don't get leaks which can interrupt airflow and cause coloration from turbulence caused by the hole. The whistling is very apparent, especially in a sub enclosure.

But that's some real nice work you've done there. Especially for a second go around.


Oh, if that plywood does end up vibrating on you, what you can do is quite simple. You find the piece that is vibrating and using your fingers, push hard on the piece until you find the spot that flexes. Mark it so you don't lose it. Then get yourself a fairly large syringe. One that will have a needle large enough to push diluted wood glue through. Then take some carpenter's glue and dilute it at least 30% with water. It's gotta flow easier than normal. Fill the syringe with the glue. Then take an iron or a clothes/upholstery steamer and steam the spot where the loose void is. The steamer is easy but the iron, you might need to wet a wash cloth and press the iron on to that over the loose spot to get the steam you need. That will soften that top layer of wood a bit so you can get that syringe in. When it's softer, stick the syringe in slowly until you feel the tension ease up a bit. You found the void. Now squeeze the syringe and fill the void with the glue. Pull the syringe, wipe away any excess glue and let it dry. The glue will brace the void and hopefully keep it from vibrating anymore.

setzer808

@Storminone: Don't fret the angles, they took a lil more time of course than the straight cuts, (I made this entire thing with a $30 circular saw) but precision on these isn't as bad as you might expect...for example....a if your 3 degree angle ends up being 5 degrees or your 13 degree ends up being 9 or 10...don't sweat it too much. Just follow the lines on your side as close as you can, and clamp in place with PLENTY of PL Premium on the joint...the PL will more than take care of a couple degree difference...its easy to see why Bill recommends the stuff so much after you start using it.

Also, as for sensitivity...it really doesn't take much at all to drive this thing to great levels...I plan on doing some tests at different frequency ranges / distances over the long weekend with my SPL meter, so hopefully I can give you some numbers. Running some bass tracks off my MP3 player on an un-modded WF-100k plate amp...which given the T18's impedance should be giving it about 80ish watts I don't need to go above 55-60% amp volume to reach the highest output I feel to be needed from one box.


@jstats: Thanks, nice tip on the wood-glue / syringe method, so far no issues but I'll keep it in mind. Its pretty sound structurally, the main flaws are mostly cosmetic pitting/scratches...but I certainly wouldn't classify it as quality wood. I've been scouting out local lumber yards for next time.

Jstas

setzer808 wrote: »

@jstats: Thanks, nice tip on the wood-glue / syringe method, so far no issues but I'll keep it in mind. Its pretty sound structurally, the main flaws are mostly cosmetic pitting/scratches...but I certainly wouldn't classify it as quality wood. I've been scouting out local lumber yards for next time.

yeah, I also forgot to mention that if you get a cabinet grade, at least one side will be a finished veneer. It'll still be slightly grainy but nothing a little 400 grit and a palm sander couldn't smooth out. Makes the finish real smooth and worthy of furniture.

Face

Void free 13 ply(3/4")Baltic Birch also works very well for speakers/subs, but isn't as nice looking as finished cabinet grade plywood.

Jstas

Face wrote: »

Void free 13 ply(3/4")Baltic Birch also works very well for speakers/subs, but isn't as nice looking as finished cabinet grade plywood.

It can be a pain to cut though with all that glue. Might destroy his $30 saw.

That's a good point though. The more layers, the more rigid and stronger the plywood is. But it can also be heavier and not as easy to work with. It's also more expensive. Most of the 3/4" stuff has at least 6 layers counting the veneer layer. Decent 1/2" will have 5 layers counting the veneer. I've seen more and less layers too.

You can get the stuff without the veneer though and it'll be cheaper but you'll have to do more with finishing it. You can sand it down smooth and finish it that way but you'll get the odd looking grain pattern that shows up from the shaving of the log. But, you can use body filler too and smooth the whole surface and primer and paint or even lacquer for that "piano black" finish. Lotsa options for the non-veneer stuff as well.

But yeah, most of the cabinet grade stuff you can get cheap is Baltic Birch as well unless you go with something really fancy like a mahogany or oak or walnut veneer.

If you're painting and want a smooth finish, MDF is an option that while not as strong as plywood is still pretty strong and rigid but much heavier. It's softer too so it can get banged up easily.

setzer808

Yeah, this sub is kinda just a jack-of-all trades design...play with it in the home theater...take it to some parties, show it off at work etc, so I didn't have a firm finished appearance in mind. If I was to make one soley for HT/Stereo use I'd consider at least making the outer panels out of MDF or as someone suggested covering the outer panels with 1/4 MDF. I wouldn't want to use MDF on any design I plan to move a lot though, MDF worries me with its tendency to absorb moisture and swell or to crush/wear into dust.

I can't imagine how much these BFM design subs start to weigh if you make them completely out of MDF...even this little 8" sub and its 18"-ish square design weighs quite an impressive amount with cheapo plywood.

Jstas

Dude, MDF sucks as a finish material. I wouldn't use it as a veneer at all. I'd sooner cover plywood in body filler, sand and paint that way. MDF is far too soft to maintain a finish. If you wanted to do a veneer to paint, I'd do a poplar veneer. Poplar has a wide, smooth grain like maple but about half the price. It's fairly dense too which means it holds a good edge and you can make precision cuts with it easily. It also would need very little doctoring to make a smooth paintable finish.

And yeah, part of the fun with DIY is there are so many options and things to try. All kinds of ideas and suggestions too. Some good, some bad but it's all part of the creative process. If you're really careful and take your time, you can end up with a very functional work of art!

setzer808

Good info, I've only tinkered with MDF in the past.

Face

Since you plan on moving it around a lot, how about coating it with Plasti-Dip or bed liner instead?

Jstas

Face wrote: »

Since you plan on moving it around a lot, how about coating it with Plasti-Dip or bed liner instead?

Bed liner! Yes! Good idea!

Bed liner actually adds structural rigidity to the box and helps with vibration dampening. Just don't put it on the horn surfaces. Outside only.

setzer808

Bed liner-like material is what I plan to finish this sub, and any future subs in. This one is just a learning sub really, so there's still many changes I'm sure i'll make...like handles for instance.