GM's MLTL with 416-8B

GM · March 25th, 2011, 06:03 PM

OK found the sim and since no one has built one yet I've changed its name to 'Westend'.

Yes, though I use scrap Neoprene.

Yes triangulating panel areas really stiffen them up, just try to bend a triangle, but not a good plan for stiffening up TLs as we don't want the turbulence they would create.

GM

**westend9** · March 25th, 2011, 10:01 PM

Lol, I like the name! I feel like I'm in the ranks of H. Ford, A. Bose or the much more revered T Crapper.

I am about to cut braces and two panels for the top and bottom. That will pretty well chew through the last of five sheets of plywood for those that are keeping count. At 65lbs/sheet, the weight of each cabinet, just the plywood, is 162.5 lbs.. I have an appliance dolly.

BTW, GM, no traingles will be forthcoming, I want this to be like the leading edge of the Darpa.

**westend9** · March 26th, 2011, 04:41 PM

OK, we now have all of the panels ready for routing a dado to accept braces. Rather than chronicle in this Forum, the techniques used, I've posted a parallel thread at Audiokarma that shows some detailed processes of the cabinet build. I'm not going to leave the experienced Altec guys in this forum without build specifics but thought the Audiokarma crowd would benefit more from the tool usage and such.

Last night, after sweeping up, I decided to investigate further the Golden Ratio and how I could use it for the bracing. I actually went through the proof of the theorem to better understand how Phi is calculated. Since digesting the mathematics, I've come up with some numbers for brace lengths and placement.

My initial thoughts on bracing were to build "X'd" window pane braces, one to run vertically that would tie the front and back panel together and also support the driver motor. The other window pane brace would be halved to join the first brace and also run vertically, to join the side panels to the center brace. This would, in effect, tie all of the six sides of the cabinet together.

After reading GM's advice on keeping the disruption of sound waves to a minimum and the fact that I have burned through most of the BB plywood at hand, I've decided to keep the first driver supporting brace and to use a smaller vertical brace inset into each side panel. I will use three cross braces that will tie the vertical side panel braces into the central window pane brace from each side. This will also bring all six sides together and allow for the least turbulence inside the cabinet. All of the bracing will be inset into dados because it is easy to do and allows for the most effective joint.

The attached picture shows some detail of the dado and the insetting of a brace piece.

**Vint_age** · March 27th, 2011, 09:34 AM

Originally Posted by westend9

OK, we now have all of the panels ready for routing a dado to accept braces.

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.

GM · March 27th, 2011, 10:47 AM

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** · March 27th, 2011, 11:27 AM

Originally Posted by Vint_age

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.

Originally Posted by 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

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** · March 27th, 2011, 04:25 PM

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?