GM's MLTL with 416-8B

[westend9]

Nice looking ply. Bet is was $$$
The results will be worth it, tho.

Not that bad with a Contractor's discount MDF would have been my other choice but I hate the dust and it's lack of structual strength. FWIW, my lumber salesman was out a couple of weeks ago after I had the BB in the shop and told me they have a void free veneered plywood that is less expensive.

Yes, this is my preference too. With this stuff I don't bother with any corner reinforcement even with butt joints. All it really does is create HF 'hot spots' that can't be easily damped except externally.

High aspect ratio cabs have the majority of its acoustic pressure along its length, so boards ~70% of its axial length long glued on edge down its length is desirable and offset by acoustic or golden ratio so that they average out any resonances rather than sum. Tops and bottoms would be done the same and for large width x depth such as these, some more boards randomly scattered down its length with one vertical one to tie all six sides together to ensure it can't 'breathe'. Done right, one can use it to brace/support the woofer too. If you're set up to drill myriad random size holes to minimize weight/internal net Vb losses, one can just make an offset 'X' frame with a driver notch out.

From this we see that typical window braces aren't all that great for pipe designs from a technical POV, but if you use them at least embed them well into the sides to minimize pipe action losses along its axial length as well as space with using an acoustic or golden ratio.

GM

Very interesting. I will try to adhere to the Golden Ratio, then. Even though I had been thinking about corner gussets running the full vertical length and possible exterior trim embellishments on the corners, I guess I'll forgo those and use the adhesive only.

When you advise to use boards of "70% of axial length" is this in the vertical axis? IOW, if the interior vertical dimension was 52", I would place a small cleat (board) that is 36" or so, vertically, onto the interior side panel? Is it a good idea to stagger these from the bottom and top?

If material allows, I may use an x window brace as I believe it is the most ridgid way to tie all the panels together. Your advice about keeping the edge of the pane cutouts toward the side to minimize pipe action is noted (if I'm understanding you correctly). Lacking the material, I'll certainly install cross bracing to the single plywood center brace.

I plan to double the bottom and top panels. I have added to the all of the panels vertical dimensions so that volume isn't decreased. One panel of the doubled panels will fit inside the four vertical panels. This should also offer to square up the carcass. I will add a few small cleats if necesary, to tie the top and bottoms to the other braces and panels.

One thing I have been thinking about and I should know this is: where do I position the woofer? Is there any special or advantageous height that I should adhere to? My initial thinking is to get it as high as possible to mate well with the top-riding horn and increase the length of the TL. Advice, please?

This is all very cool, I'm quite excited to get it all together and take the Altecs for a run. I'm glad I have this board and GM to navigate.:thankU:

Figured out how to export the Sketchup file but it is not scaled, I'm learning.

[GM]

Well, a thick bead of PL400 is a pretty decent gusset all by its lonesome. I lay it in with a caulking squeegee..............

Correct, you want stiffeners running along the longest axis, same as a horn.

I use 1x3 boards on edge or similar size scrap plywood.

There's no real advantage to vertically staggering them and if you get them too close to one end you create a 'hot spot'.

Well, you're creating offset 'X' frame braces with the lumber , but if you prefer to make all those extra cutouts that's fine too. Me, I was always in a time crunch and never had any effective dust control system, so tried to minimize cutting as much as practical.

If used, minimizing how much they protrude in the airstream along the walls is to *maximize* pipe action.

Unless the bottom is raised up off the floor, doubling up the bottom is a waste of time/materials and even then, bracing is sufficient since all the pipe's pressure is concentrated at the closed end (top) and why the panel bracing is along its axis.

Except for the full length vertical brace to tie the top, bottom and all four sides together there's no need for any more tie bracing, i.e. the object is to not have any bracing near any corners as these areas are already self braced by having glued joints as well as unbraced areas too small to resonate with any consequence.

There is a mathematically 'perfect' position along a pipe's length to place the woofer for smoothest response, though while a good point, I disagree with MJK's axial length 'L' x 0.349; instead using a different formula that includes the pipe's cross sectional area (CSA), but never having compared the two, I don't know if the differences seen in sims using his software are audible except possibly with the most minimal of internal damping.

Regardless, since your HF horn is on top, unless you sit really far away, like > 25 ft, then placing the woofer right up at the top of the cab is best overall and it also maximizes pipe action, ergo max vent damping.

Yeah, believe it or not, I get excited every time someone builds cabs like I learned to do so long ago. By age 22 when I did my first pipe horn designs, I was already pretty jaded WRT to high performance/SQ sound, but these took them to another level of BLH-like without all the extra bulk/woodworking, yet with the smoothness of low Qt sealed with none of 'boom'/'flabbiness' of the BR cabs of the day.

Of more interest to me though was that such alignments caused much greater improvements with 'el cheapo' drivers and I'm glad that now with MJK's software, the various TLs and their mass loaded (vented) variants are the de facto alignments for so-called 'full-range' drivers and their woofer + super-tweeter variants.

For this we have RCA's Harry Olson's circa 1949 MLTL design for his LC-1 'full-range' driver to thank, though he just called it a reflex, and the college student working at Altec that mentioned it to me when I toured the plant that year.

GM

[westend9]

Thanks, GM, for iterating what must seem to you, like school yard stuff. I've never built an enclosure of this size so construction techniques need to be learned. Thank God, I have enough of my faculties still in place to absorb most of it. And, thankfully, there are still a few souls left on the Planet that are helpful.

I'm beginning to understand that anything that will not diminish the pipe action, WRT braces should be part of my focus. If I think of this as an aerodynamic exercise, removing as many surfaces that would cause an eddy or disturbance to the "airstream" would be good. Do I have a handle on this?

I do have adequate dust collection systems and cutting or machining lumber (and thereby creating sawdust) is also part of my everyday life. I tell customers, when creating sawdust, that it is not dirt and happens to be the main constituent of floor cleaning products. This is not always received as good information.

I will do some calculations WRT as-built volume with braces added. I did size the first panels with a doubled top and bottom panel in mind but could easily forgo the doubled bottom. Removing the inset bottom panel will add about a .25 ft.^3 to the volume so it does have merit in that regard.

Thanks, also, for sharing your experiences at the advent of TL speaker design, priceless information, IMO. I have a pair of single driver BLH's and the designer reached the conclusion that much of horn's reinforcement was due to TL action and not from the horn, itself.

FWIW, I could not have picked a better time to launch on this project since we are caught up in a late winter storm that is making travel a struggle. It has been raining and snowing since last night and the roads are miserable. Staying in the shop and keeping the wood stove fired is a good priority, today.

Picture of woofer cutout marked---44" center from bottom of baffle.

Well, a thick bead of PL400 is a pretty decent gusset all by its lonesome. I lay it in with a caulking squeegee..............

Correct, you want stiffeners running along the longest axis, same as a horn.

I use 1x3 boards on edge or similar size scrap plywood.

There's no real advantage to vertically staggering them and if you get them too close to one end you create a 'hot spot'.

Well, you're creating offset 'X' frame braces with the lumber , but if you prefer to make all those extra cutouts that's fine too. Me, I was always in a time crunch and never had any effective dust control system, so tried to minimize cutting as much as practical.

If used, minimizing how much they protrude in the airstream along the walls is to *maximize* pipe action.

Unless the bottom is raised up off the floor, doubling up the bottom is a waste of time/materials and even then, bracing is sufficient since all the pipe's pressure is concentrated at the closed end (top) and why the panel bracing is along its axis.

Except for the full length vertical brace to tie the top, bottom and all four sides together there's no need for any more tie bracing, i.e. the object is to not have any bracing near any corners as these areas are already self braced by having glued joints as well as unbraced areas too small to resonate with any consequence.

There is a mathematically 'perfect' position along a pipe's length to place the woofer for smoothest response, though while a good point, I disagree with MJK's axial length 'L' x 0.349; instead using a different formula that includes the pipe's cross sectional area (CSA), but never having compared the two, I don't know if the differences seen in sims using his software are audible except possibly with the most minimal of internal damping.

Regardless, since your HF horn is on top, unless you sit really far away, like > 25 ft, then placing the woofer right up at the top of the cab is best overall and it also maximizes pipe action, ergo max vent damping.

Yeah, believe it or not, I get excited every time someone builds cabs like I learned to do so long ago. By age 22 when I did my first pipe horn designs, I was already pretty jaded WRT to high performance/SQ sound, but these took them to another level of BLH-like without all the extra bulk/woodworking, yet with the smoothness of low Qt sealed with none of 'boom'/'flabbiness' of the BR cabs of the day.

Of more interest to me though was that such alignments caused much greater improvements with 'el cheapo' drivers and I'm glad that now with MJK's software, the various TLs and their mass loaded (vented) variants are the de facto alignments for so-called 'full-range' drivers and their woofer + super-tweeter variants.

For this we have RCA's Harry Olson's circa 1949 MLTL design for his LC-1 'full-range' driver to thank, though he just called it a reflex, and the college student working at Altec that mentioned it to me when I toured the plant that year.

GM