GM's MLTL with 416-8B

[GM]

Yeah, for pipe designs there ideally should be no horizontal cuts or wide joints since the majority of the pressure waves are vertical and no sense in adding any more HF 'hot spots' than necessary, so as I previously noted, vertical boards boned on edge and maybe a screw or two (or air staple if one has the luxury) to hold it in place while it sets with tie boards to bind them together horizontally and one running the full vertical length to tie together all of them plus provide some driver support/mass loading. That, or use a vertical 'X' frame to 'kill all the birds with one stone'. One example: http://homepage.mac.com/tlinespeaker...aps-211010.pdf

I always did the former to use up scrap or used stock found at work sites or at the curb. I built a lot of cabs that had braces made from scrapped concrete former boards.

At one point I wound up with many hardwood closet rod, so made 'X' braces by tying them together with safety nut wiring with some PL400 as a bit of extra security because I had the appropriate tool. Today, I wonder if inexpensive tie wraps/PL400 or similar might not work just as well.

Anyway, I didn't own a router until some years after my peak building 'career' and frankly have only played a bit with the two given me, so while I can marvel at what some folks can do with them, it's just too much extra time for too little real benefit at the casual DIY level for me to bother if I ever get the chance to resume speaker building when butt joints and the occasional glue/screw block clamped with two or four picture framing clamps suffice. I shake my head in wonder when I see a complicated superstructure of varying size clamps to hold a simple rectangular cab together. I am big on diying jigs from scrap to streamline construction though, so I guess to each his own.

GM

[westend9]

If you cut a dado in the middle of the panel, you have just reduced the stiffness of that panel. A better way to attach the brace is to use pocket screws and glue. Also, much easier than cutting a dado.

There are adherents to different methods, and lacking the testing required to assess the merits of different joinery, I'm going with what I know works best for me. The underlying question of the structural integrity of these two methods would be: Does using fasteners and not creating a 1/8" dado have more structural integrity than cutting the dado and insetting the brace into the panel? I'm thinking there isn't much difference.

Yeah, for pipe designs there ideally should be no horizontal cuts or wide joints since the majority of the pressure waves are vertical and no sense in adding any more HF 'hot spots' than necessary, so as I previously noted, vertical boards boned on edge and maybe a screw or two (or air staple if one has the luxury) to hold it in place while it sets with tie boards to bind them together horizontally and one running the full vertical length to tie together all of them plus provide some driver support/mass loading. That, or use a vertical 'X' frame to 'kill all the birds with one stone'. One example: http://homepage.mac.com/tlinespeaker...aps-211010.pdf

I always did the former to use up scrap or used stock found at work sites or at the curb. I built a lot of cabs that had braces made from scrapped concrete former boards.

At one point I wound up with many hardwood closet rod, so made 'X' braces by tying them together with safety nut wiring with some PL400 as a bit of extra security because I had the appropriate tool. Today, I wonder if inexpensive tie wraps/PL400 or similar might not work just as well.

Anyway, I didn't own a router until some years after my peak building 'career' and frankly have only played a bit with the two given me, so while I can marvel at what some folks can do with them, it's just too much extra time for too little real benefit at the casual DIY level for me to bother if I ever get the chance to resume speaker building when butt joints and the occasional glue/screw block clamped with two or four picture framing clamps suffice. I shake my head in wonder when I see a complicated superstructure of varying size clamps to hold a simple rectangular cab together. I am big on diying jigs from scrap to streamline construction though, so I guess to each his own.

GM

Thanks for your reply about the bracing, GM. I believe we are on the same page as to the bracing and general construction techniques. Initially, I was going to build the bracing very close to the linked Pensil 12 cabinet. I changed my thoughts about that when considering the benefit and material use of the side to center brace window pane, combined with the obstruction they would cause to the pipe effect.
Instead, I am using two horizontal members joined to each side brace to tie to the center brace. It is, in some ways, more work, but I'm only doing this build once so I can rationalize the extra joinery required.

I'm fairly new to using a router but the ease of some operations make it a have-to-have tool for me now. It is like the advent of the battery powered screw guns, the epiphany being, "how did I get along without this sucker?"
I am just about done with the bracing, only needing to machine the center brace and ease some edges. Standby for pictures of a myriad of clamps.

[westend9]

I've done just about all of the router work, cutting the dados that accept the bracing and cutting out the hole for the woofer. Next will be tackling the center brace so I will tempoarily mount a woofer to get clearances around the woofer and establish good measurements for the magnet cradle. I still have to cut the vent openings, also. Should I position the vent in about the same relationship as the woofer, i.e. about 3" from the bottom of the front panel?

[westend9]

I was able to put off making the central brace for just a bit by getting into fashioning an access hatch in the bottom of the cabinet. I cut an inner panel out and am saving the cutout. It will be edged with felt and bolted to the exterior bottom panel. The bottom panel will bolt into T-nuts that are inserted into the inner panel. To insure that the bottom is sealed, I routed a channel into the bottom of the inner panel and have an EPDM "D" shaped gasket that will afford a good seal between the two panels. The gasket should compress just enough to fill the channel when the two panels are bolted together.









Bottom surface of inner panel:



The doubled bottom panels together:

[westend9]

I eased all of the edges of the braces on the router table, finished up on the SAH (subsurface access hatch) and cut the vents, today. This alignment called for the stock vent size of the Model 19, 11" x 2 1/2". I hemmed and hawed about where to position the vent, having read in another thread GM remarking that "near or at the bottom" is a good location. I left myself some wiggle room and cut the vent in at 2" above the front panel bottom edge. This is 1 5/16" above the cabinet inner bottom panel. That should leave me enough room to lengthen the vent, should it be necesary.

[westend9]

I am templating the center brace, any caveats......? I plan to leave a little over 1/4" of space between the driver cradle and the back of the woofer. I will shim this space to load the driver into the cradle.

[westend9]

OK, I believe I have a workable template for the center brace. I marked out the area where I thought the brace should not be cut to insure the most structural integrity. Using the information from GM's linked cabinet drawings, the Pensil 12, that "30-50% should be removed", I marked out the cut outs. I chose to use a diamond rather than circles since circles would be way to much time and expense in router bits. That, and I can't cut a circle worth a d*&^ with a jig saw.

The area directly behind the woofer could possibly have a bit more cut out. I will take a look at that area when I have wood cut and not working off cardboard. When I have all the cut outs made, I'll ease all of the opening edges with a roundover bit.

Am I forgetting anything?

[GM]

How do you plan to support the driver vertically?

GM

[westend9]

How do you plan to support the driver vertically?

GM

Hey, GM, I don't think it shows up that well in the pictures of the cardboard template but I cut an opening (a cradle) that will be 1/4" larger than the magnet. There are two small corners that will support the magnet and the back of the magnet will be loaded against the center brace with a shim. Attached is a picture of the cradle cutout transcribed onto the yet-to-be-cut center brace. Do you think it needs more support that this? I could make two half "rings" to attach to the brace, holding the magnet very securely.

I am trying to keep everything non-essential out of the inside of the cabinet. Last night, I did some calculating using numbers for the area displaced by the center brace that were a bit optimistic. My new calculations give an internal box volume, calculating for everything in the cabinet, including the 416, to be between: 16.323 -> 16.466 cu. ft.. I believe this is very close to the original design criteria of 16.4 cu. ft.. I did not calculate the roundovers on bracing nor the air spaces in the frame of the woofer into the calculations, extracting the volume by a solid cone of it's measurements.

Anything I am missing in the build, so far? Do you think the vent placement wil be allright? I know it might need to be adjusted as to the room or the performance of the woofer. One last question, please, about stuffing the line. I've read some folks have used sheet fiberglass (OC 703 or similar) with good results but are there any other materials I might use for the stuffing?

Thanks for all your help so far. I would be lost on most of this without guidance.

[GM]

Greets!

You're welcome!

No, I missed the 'step' in the cutout.

Not really, just stick some thick enough felt or similar pads on the 'steps' to snug it up.

At 16+ ft^3, a couple of 10ths off either way isn't audible.

I guess not other than I don't see any provision for easy vent tuning. It's location is fine.

Yes, this is my insulation of choice same as Altec after the asbestos laced Celotex was outlawed. Many manufacturers, DIYers use polyfil and the material properties MJK uses in his software with lamb's wool being considered the Rolls Royce of speaker damping.

Then there's open cell foam now that they've learned how to keep it from dissolving over time. I've experimented with open cell sleeping pad since it's so cheap at the local Wal-Mart, K-Mart, Cloth World or similar 'big box' discount stores. No doubt there's other materials out there and seems to me I read something awhile back about 'green' ground up T-shirts or jeans or some-such, so with each of these having radically different damping coefficients, you would have to experiment to find the optimum amount.

Just don't use closed cell foam..........

GM