The Besta Subwoofer

[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.

[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]

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.

[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]

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 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]

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]

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]

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!