[Clarence]

This is a spin-off from the Most BASS for the $$$ thread.

Since finishing my HT earlier this year, I've been cruising a lot of the DIY subwoofer threads here. I bought 2 of the JBL GTO1514D subwoofer drivers... seemed like an affordable way to get started.

Last year I bought the plans for the THTLP (Tuba Home Theater Low Profile) and was originally going to build that, but it looks like the F-20 might be a little simpler to build. Plus I already had a couple of sheets of 3/4" ply in the garage that I needed to use. The THTLP insists on 1/2" ply, which I didn't already have, so I'd have to buy 3 sheets.

There are already a couple of good F-20 build threads. And since this is my first build, I'm sure they're probably better than I'll do. But the main F-20 thread is a little overwhelming, so this thread is mainly just notes to myself where I can consolidate my thoughts as I step through the build this week.




I'm currently using two 15" subs behind my AT screen, leftovers from the HT I built 10 years ago in our previous house:

• Definitive Technologies Powerfield 15
  Dimensions 17 1\\2H by 17W by 17D
  Freq. response 18-125hz
  Driver complement One 15" woofer with polymer laminated cone
  Amplifier 200 wattsRMS
  High pass filter 12db/octave selectable (50 or 100 cycles)
  Low pass filter 24 db/octave continuously variable (50 or 100 cycles)

• Cerwin Vega LW15
  Woofer size 15"
  Nominal (RMS) output power 200 Watt
  Response bandwidth 27 - 150 Hz
  Crossover frequency 40 - 120Hz
  Enclosure material MDF
  Weight 72.3 lbs

They're nothing special. Adequate. But I'm hoping for a little more oomph.


My inuke 3000DSP from ebay arrived today.

I drew a cut list to see if I could use the large scrap piece of ply I already had.

Only needed to buy one sheet.
So I got started.

I'd borrowed my friend's table saw. But I've borrowed it before and struggle with cutting large panels, especially since I'm usually working by myself. I could never cut a straight line with a circular saw... seems like the harder I try, the worse it gets.

So I did some googling on "building a jig to make cuts with a circular saw" and came across this thread. Too long... didn't read. So I just skimmed down to the picture at the bottom captioned "Make your cut" and thought "I can do that!"

I went to Home Depot, got a 16' long piece of 1"x2" finger-jointed pine ($6.44, only used half of it) and a 4x8 sheet of Tempered Hardboard ($13.44, only used 12" of it)... used my air stapler to staple the hardboard to the 1x2. Then ran my circular saw down each side, using the 1x2 as an edge guide. Voila... the blade just made its own cutting guide. I clamped it (using 2 of these $2.99 clamps from HF) to a 4x8 sheet and made my first cut.

OMG. I wish I would've learned this 40 years ago. I've never seen such a straight cut. Since the edge of the jig was cut with the blade of my own circular saw, it cuts exactly where it's clamped... no messing with drawing a line, no worrying about the thickness of the pencil line or the angle that you hold the pencil, no slipping straightedge as you try to draw a long line, no need to guess the width of the blade's cut width (kerf), no need to blow sawdust out of the way so you can see your pencil line as you cut.

Clamp the edge of your jig on your measured marks, place the saw on the jig, slide the saw along the edge of the 1x2. Perfect cut.

You can easily see exactly where the cut line will be by looking at the edge of the jig, so I used 2 folding tables to hold each side of the panel I was cutting. I just needed a gap as little as 1" between the tables. And I could push the saw from anywhere I could reach... no need to see the line, just push along the edge of the 1x2. Oh well... too much rambling over something so simple. Probably obvious to most of you, but maybe there's someone else out there that can't do straight cuts with a circular saw.

I cut 11 panels in about 30 minutes. Used a pencil to check off my cut list and labeled each board as panel 1-11.

Halfway though the cuts, UPS dropped off this box... contents: 15" JBLs, qty: 2.
You can see my fancy "sawdust management system"... a quick blast from the leaf blower after each panel.

Now to go read the next step on how to draw the points on the side panels to play connect-the-dots tomorrow with a jumbo tube of PL.

Gasket tape, speaker terminals, and duratex on the way from PE.

 

[Samps]

Are you building two? That's quite a bit more than "a little more oomph"

That's a lot more oomph!

 

[Clarence]

Yeah, one will probably be enough. I'm having a hard time imagining how much oomph one of these subs will give. If one is enough, then I won't need a second one. And if one isn't enough, then I'm not sure I'd want a second one. But the trend around here seems to be: if one is enough, then two is better, and more is more better. I still might try the THTLP with the second JBL.

Here are some other illustrations that I made from the instructions. I'm a visual thinker so labeling the panel names and sketching the measurement points helps me plot tomorrow's steps.

If anyone notices any incorrect interpretation, please speak up before I start gluing.

Point 1 is the top of the mouth opening, and is on the left side, 14-15/16” from the lower corner.

Point 2 is the corner of the chamber and the mouth flare, and is 12-11/16” up and 12-3/16” in from the lower right corner.

Point 3 is the corner of the flare near the top right of the cabinet. This point is located 9-1/16” in and 8-13/16” down from the top.

Point 4 is the end of the baffle at the top left of the cabinet, 5-5/8” down from the top and 5-¼” in from the front.

Now, connect point 1 to point 2 to point 3.

Next, we want to draw where the wood panels will be on the side panel. I’ll freely admit it - I cheat. I use a ¾” wide strip of 1/8” thick aluminum. This allows me to lay out both sides of the panel without moving the straightedge. Yes – the plywood is thinner, but the 1/32” is not that big of a deal.

OK, so two panels are in place. Measure in ¾“ from the front, draw in the front panel, then measure in 1-7/8” from the inside of the front panel to locate the horn side of the baffle. Connect this point to point 4, then draw the back side of the baffle. Four down.

Now – measure 19-¼” from the top of the baffle on the inside, then measure 18-½” down from point 3, but on the inside of the panel. Connect these marks, draw in the other side, and the chamber is complete. That’s five, four more to go, and three are super easy.

Using your straightedge, draw in the top, back, and bottom panels, three more down.

The final panel is located 11-¼” in from the top front corner, the panel end is 19-½” from the top edge, and is perpendicular to that edge.

 

[asarose247]

Sealing that chamber is, as you well know, of utmost importance
I can't pinpoint exactly where in the SUBMAXIMUS thread I posted pictures of my 1 x 3 oak inset set up for the access panel attachment but you might want to take a look,
it is probably overkill but it seems to be absolute
maybe inspire you to come up with something "simpler"


nice pics and layout thinking and visualizing . .

 

[LTD02]

bracing.

 

[michaelddd]

What driver does the F20 use? Very nice thread, BTW. I am a visual person too.

 

[LTD02]

I'm pretty sure it was designed for the mfw15, which was a buyout woofer at the time (a sub company went out of business so a whole bunch on the drivers were picked up cheap). several drivers work in the f20, but not all. check the thread. i think there was a post where lilmike was updating drivers that people were using and were proving to work.

 

[wormraper]

I'm pretty sure it was designed for the mfw15, which was a buyout woofer at the time (a sub company went out of business so a whole bunch on the drivers were picked up cheap). several drivers work in the f20, but not all. check the thread. i think there was a post where lilmike was updating drivers that people were using and were proving to work.

it was designed around the MFW-15 but the Dayton DVC-15 is a near perfect drop in, people have been using it for years

 

[Clarence]

Sealing that chamber is, as you well know, of utmost importance
I can't pinpoint exactly where in the SUBMAXIMUS thread I posted pictures of my 1 x 3 oak inset set up for the access panel attachment but you might want to take a look,
it is probably overkill but it seems to be absolute
maybe inspire you to come up with something "simpler"

Found your maximus access panel:
http://www.avsforum.com/forum/155-d...stereo-integrity-ht-18-a-10.html#post24625403

Love that thread.

I was planning something similar... a 3" picture frame mounted on the inside with gaskets.

Now I'm pondering something even simpler... what if I just mark (pre-drill 1/8" holes only 1/8" deep) the four corners on the exterior of the chamber. Under what circumstances will I need future access to the chamber? Only if I blow the subwoofer driver and need to inspect/replace it, right? When/if that happens, then I drill out the 4 corners, crank out the jigsaw, connect the dots, cut out the panel and mess with resealing it after the repair.

So I just "permanently" install and wire the subwoofer driver in the chamber before I seal on the lid. No access panel. Airtight. Clean.

Stupid plan? (or lazy or short-sighted?)

I love my kreg jig and thought I was going to get laughed at here in my next batch of pictures because I like spacing pocket holes every 6" or so, but it looks like you had 4" spacing. Most threads say the fasteners are just there to hold the panels in place until the PL adhesive expands and dries. I like screwed and glued.

And yes, lots of bracing. Might as well use as many of those panel scraps as possible.

 

[asarose247]

QED!

 

[michaelddd]

Thanks for driver info.
@Clarence: I think your idea is a good one. Being that the only time you'd have to access the driver chamber is if the driver dies, it wouldn't matter that you'd make a mess cutting out the access panel. Not having to deal with creating an access panel now simplifies construction/speeds things up.

However, I'll quantify my answer by asking "What is the plan for the finish on the F20s? If you are planning on a nice veneer or even a nice Duratex paint job, then I think you should build the access panel now and finish accordingly. Cutting out the access panel would make a mess of the finish. But if the plan for the finish is "Exquisite Flat-Black Rattle Can" then skip the access panel.

 

[Clarence]

What is the plan for the finish on the F20s? If you are planning on a nice veneer or even a nice Duratex paint job, then I think you should build the access panel now and finish accordingly. Cutting out the access panel would make a mess of the finish.

I've got a gallon of Duratex on the way from PE. Everything's behind an AT screen, so I don't need them to be beautiful, just black. But the OCD in me wants them to look good.

My main concern with the panel is potential for air leaks, even with double gaskets and 24 screws.

BTW, is there any advantage to putting polyfil in the chamber?

Today's status update: I cut the 3 bevels with the table saw. And I stacked up all of the 18.5" panels next to each other and shaved off maybe 1/16" from a few of the taller ones. They're all within about 1/32" now.

Next I've got to practice cutting circles with my router. I also have a rotozip, but I've snapped bits in drywall just cutting recessed lights, so I doubt it's going to work on 3/4" ply.

 

[VRausch]

Subbed! I have plans for the exact same build once I'm moved! (New house closes in a month).

Very much looking forward to following your process and findings with the JBL.

 

[Clarence]

32 degrees in the garage today.

Measured and marked the panel placement guides:

And I unboxed one of the JBLs:

 

[superedge88]

You'll most likely need to open the access panel after some of the first spirited bass movies to snug down the driver again. I had to do this with my THT.

 

[Clarence]

Yeah, I'm going to include the access panel. My first build is not the time to start tweaking and straying from a proven design.

I just found my router bits. We moved into a new house last year and a few boxes of tools were still unpacked. Unfortunately, I'm not sure if any of the bits will work. None of them say "speaker driver cutout" though. Is there a thread with tips on how to cut out the circle with a plunge router? I'll do a search.

FWIW, my router is a Ryobi RE180PL1 2HP variable speed 1/2" collet. I bought it years ago, used it once, can't even remember on what.

 

[Samps]

Without an access panel you would need to mount the driver before attaching the last panel. There is the potential for some glue squeeze out to drip onto the driver.

 

[asarose247]

Milescraft Router Guide Kit
$40 at Lowes


use a mortising bit,
adjust set-up get to proper/needed mounting diameter on a scrap piece first
feed downward slowly after each circular pass after set-up complete, 3/4 ply maybe 6-9 passes, YMMV
lay the center out
the kit uses a plastic pivot held at the center with a supplied "nail',
I always start the hole first with a punch, then the nail gets started and centers the pivot exactly,
bulls eye
the trick is removing the nail, for re-use
as it is flush to the top of the plastic pivot, you can't just yank on it or do anything to deform/bend the nail or pivot
I use a pair of electricians ***** on a 3/4 ply scrap block to come at it on the same horizontal plane to just get under the head of the nail
and then gently pry straight ,mol, up, maybe from several directions around the pivot
or once its started, a pair of vise grips pulling straight up
nail stays straight-primary/necessary objective


hope that helps

 

[asarose247]

great looking set of bits,
nice to have when you're inspired . . .

 

[michaelddd]

I'm not the expert by any means but the "Polyfil in driver chamber for horns?" question gets asked often over at the BFM forums and Bill's answer is always "NO." Something about that it's a horn, and the horn path affects the speaker, which affects the chamber and it's all related, etc. Polyfil changes the response of the driver in the chamber, which changes the overall response of the horn. So, no polyfil in driver chamber.

I forgot about having to tighten the driver down again after a few spirited playback sessions. Good catch, superedge 88. So yeah, access panel for you, Sir.