The Besta Subwoofer

[wogg]

This project has been in planning for years.... Here's my living room HT setup.


That's an IKEA Besta cabinet for the equipment, modified slightly to not overheat stuff by leaving the back open with a cross beam for stability, and using a hole cutter under the AR on the left and the PC on the right to allow air in from the bottom. Nice little setup for what I've got.

That sub cabinet on the right is an Eminence Lab 12 driven with a 200W plate amp, the box is about 30 years old. It's survived my teenage years, moved around with me in college and beyond, and has landed here. It's been peed on by many pets, soaked up spilled drinks, been re-built a few times, sanded, refinished, and that grill has been busted off and repaired countless times.

It's also not super optimal. It's big, ~4 cu ft, but constructed from 5/8" particle board with a 3/4" baffle and no cross bracing, just a couple 1x1's glued at an angle to add some rigidity to the sides. The port is a little small at 3.5", but surprisingly chuffing is a rare problem. It also works really well for my use, response into low 20's and loud enough to feel the floorboards shake for movie effects, also accompanied by shaking whatever we have on top of it to the floor. It's just showing some major aging, like this:



That's many, many years of moisture damage.

So after trying to come up with cabinets to match the rest of the aesthetics, I thought... I have another Besta frame and feet sitting in the garage with a glass top panel and everything. Why not use that and build it into a sub to perfectly match the entertainment center?

The Besta frame is not what I would call robust enough for a decent sub. The sides are 3/4" particle board, and the top and bottom are about 1 1/8" thick but hollow, made from what seems to be 1/8" HDF with a cardboard lattice between them for rigidity. The idea is to use 1/2" MDF cut and glued around the frame for the cabinet walls, with a 3/4" MDF rear panel and a doubled 3/4" MDF baffle. The port will be a 4" precision port firing down to the floor. Looking like this:



Calculating that up comes up with 3.63 cu ft of volume without driver, bracing, or port. Modeling the Lab 12 in that sucker works fine, ~3.25 cubes net tuned to 21Hz with an F3 around 25Hz. I cab pull this off with a couple project panels from the hardware store.

For aesthetics I'm going for roll on Duratex on the back, and wet sanded gloss black on the front to match up with the glass doors a bit on the entertainment center. For the woofer, I really liked how the recessed metal grill ended up looking on my little Indy 8 sub, so I want to do that here. I found a JL Audio SGRU-13 grill for their 13" woofers that will give plenty of clearance around the Lab 12 frame and room for full exertion. The outer baffle board will be cut to fit that grill in place, press fit with some weather stripping to keep it in place and kill rattles.

The trickiest construction bit will be getting the precision port through the bottom. My thought is to seal the inner board right against the 4" tube. The cut out of the IKEA bottom panel will be ugly, so the flare will be needed to hide that, and I'm hoping the flare is done by the time the 1/2" MDF board is reached. We'll see how that works out, some improvising may be in order.

Ordering parts today.. I should be able to pull this off for around $100!

[wogg]

Parts in hand, just got to wait on life to be able to cut wood and start assembly.

Here's the JL Audio grille. Nice and understated, exactly what I was looking for and with plenty of clearance for some woofer excursion.

The outside dimension is 12 11/16", I'll do the recess cut about 1/4" bigger than that to allow some weather stripping thickness to hold it in place.

The profile of the grille kicks in right at about 3/4", which is perfect to sit down in the outer baffle layer.

[wogg]

For the 4" Precision port kit, I haven't broken out the wood yet but based on measurements I'll cut the 6.25" hole on the bottom of the Besta panel, and a bit less to fit on the inside. It looks like the flare profile ends at about 1.25" which is right at the thickness of the Desta bottom panel, so the important part will be accurately hitting the outside diameter of the tube with the inner MDF wall to seal the cabinet.


There may be a little fun sanding and sealing involved to get it tight, but with some careful work and epoxy it will work fine. There's enough slop around the outer lip to be able to cover the ugly guts of the Besta panel. Without a press or a drill guide I'll hit these dimensions by carefully measuring the MDF inner panel, and the top / bottom of the Besta panel to find center. There's some tolerance allowance for sure so I'm confident I can pull that off.

[wogg]

I made all saw cuts yesterday, hotter than Hades out there. I was trying not to sweat too much on the MDF to avoid swelling

No picture updates yet, next step is cutting the circles. I need 3 circle cuts for the port: Outside bottom panel, inside bottom panel, and then the 1/2" MDF layer which will be the internal seal tight against the port. Then it's just the two baffle cuts for the woofer and grille and it's assembly time.

[wogg]

The circles have been jigged and it's glue up time. For the precision port I cut 3 circles, one through the 1/2" MDF and 1 on each side of the thick Besta cabinet bottom. Here's the internals to that panel.

With a larger circle on the outside surface for the flare of the precision port and a little scissor action to cut the internal mesh, the port drops right in.

This comes together with the 1/2" MDF internal board to make a clean exit. The center pin in the Jasper jig fell out while cutting that one, nothing some extra glue won't fix.

[wogg]

I cut the woofer and grill holes on my double baffle boards and did a test fit of the grille. This will look pretty tight on a gloss back baffle.

I twist locked the sides of the cabinet up and applied some Gorilla heavy duty construction adhesive to hold the 1/2" internal board in place. The port is in there to ensure alignment, and now we wait for the glue to set before working our way around the sides lining the whole thing with that MDF.

The double baffle had a think layer of Titebond II spread about and with some alignment for my 1/2" rabbet around the outside is now sitting with some weight to dry as well.

[wogg]

Since I had the woofer out to validate the cutout dimension, I ran DATS to check the actual parameters of the LAB 12 after a good 12 years of service. I ran 2 measurements with DATS and averaged them, the numbers aren't as repeatable as you'd think, but should be good enough to validate the target. The Vas is definitely larger than the spec sheet, and the Q slightly lower over time, but the modeled response is hardly any different. The red line is the OEM spec sheet, the red is the actual measured values. The actual values work best by taking a couple inches off the port length, raising tuning a bit from 21 to 23Hz.

I'm showing -3dB at 26Hz with about -8dB at 20Hz, should still be awesome for movies and what not.



Power capability dips just under 200W at 30Hz, cutting the power handling under the thermal limit but right in line with the 200W plate amp I'm using. This isn't going to impress the multiple UM18 crowd here, but over the last decade I've been really happy with the output.

[tomzarbo]

Sounds like you've got some love for that driver. I had a Cadence Solobaric 12 that I really loved the sound of. Wouldn't even register today, but did everything I asked of it. That one lived 2 or 3 lives as well.

Nice project so far. Ikea makes some pretty decent speaker enclosures apparently.

TomZ

[wogg]

Sounds like you've got some love for that driver. I had a Cadence Solobaric 12 that I really loved the sound of. Wouldn't even register today, but did everything I asked of it. That one lived 2 or 3 lives as well. Nice project so far. Ikea makes some pretty decent speaker enclosures apparently. TomZ

Well you know, if it ain't broke... There are several 12" woofers that will drop into this cabinet if anyone wants to do something else. That new GRS high excursion woofer would be perfect, a UM12 perhaps with some creative plumbing to tune even deeper. This box is going to be setup with an 11.125" cutout and a 8 bolt pattern with 8-32 machine screws and inserts, I should be able to update if the box outlasts the woofer and amp.

[wogg]

The outer frame is coming together. Squish top in with glue, lay in side and plop in 4 wood screws to add tension against the glue.



Flip it over and repeat, then put it top side down to weight the top panel against the glue. There's nothing for screws to grab on the top and bottom, so the side panels and the glue will hold them up. I plan on a vertical and horizontal 1x2 brace as well, so that will keep it all tight. The back panel is just shoved in there for a bit to keep the box square while everything cures.

[wogg]

The 1x2 poplar lip is going in around the back side to support the hardware for the removable rear panel. No screws, so this is an exercise in glue, clamp, let sit 1hour +, flip, repeat.



The front panel is pressed in, not glued. I'll be doing the finish on that out of the box.

[wogg]

For fun... here's a few things I've f%^ed up in this build already

• Didn't measure the front / back spacing around the perimeter when I glued in the 1/2" MDF. I had a little slop around the port to get closer to center, but I didn't even check. The front will be recessed slightly while the back sits proud. I'll bevel the back to make it look like it was on purpose.
• Mis-assembled the top panel of the Besta by putting it on backwards. There is a very slight difference in the faux finish on the front vs. back edges of the Ikea cabinet, it will likely only bother me.
• I meant the port to be firing out of the rear left of the cabinet, but wasn't paying attention to front / back there either so now it's firing out of the front right. Due to the baffle coming in 3/4" I'll have to shave a flat spot in the internal port flare. Will have no effect on the result, but will annoy me slightly.

[wogg]

It's been a minute, lost some weekends due to travel and what not. Work has progressed a bit, and I'm into the finishing mode for the baffle. First, here's the prep of the back for mounting.



The back was chamfered, then the pilot holes drilled for the hardware.



10-24 insert nuts added to my polar glued in supports, supporting the large head furniture screws I'm using to mount the panel.



Ta Da!

This panel will be simple rolled on duratex, so it's set aside while I do the baffle.

[wogg]

And the baffle, here's what the fit looks like unfinished.



Good fit. little tight so I suspect I'll have to plane or sand a bit more once I get some paint on there.

For the gloss finish, I've opted to skip an additional seal process and go straight to rattle can primer, using a 2 in 1 filling sandable stuff from Krylon. This worked well for my mini speakers, but this has a lot more surface. The consequence of that decision is that I've used a full can and a half of the primer to get good coverage, the sealer likely would have cut that down. It looks spotty when sprayed on, but is turning out good when sanded at 220 grit. I've done a few rounds of spray / sand repeat at this point.



At this point, I'm ready for the gloss black enamel. My mistake when doing my mini speakers was laying it on way too thick so it took weeks to cure enough to complete the finish and would still dent or take on patterns for weeks after that as it continued to cure. This round, I'll be doing this over the whole next week doing thin coats daily with a full 24 hours of cure between before the next coat.

[wogg]

The auto gloss black enamel I choose has a couple issues. First, the nozzle is terrible and throws drips when released. Second, it's a 48 hour cure between coats. I'm rolling with it, and will be wet sanding at 500 between coats until I'm happy with the thickness to up the grit and polish.

Meanwhile, I stuck in 4 cross braces glued in with Tightbond under tension against the surfaces. The knock test is now acceptably solid even without the baffle.