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Thread: GM's MLTL with 416-8B

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    GM's MLTL with 416-8B

    This build thread documents an MLTL cabinet build for Model 19 drivers, the Altec 416-8b, 811 horn w/802-8g. I also plan to incorporate a Heil AMT1 air motion transformer as a "super tweeter".

    Discussion about this project began in this thread awhile back. The response curves of the "Model19.long" and variants are referenced there. The reason for delay on this are multiple but lets just say that life and different priorities got in the way.

    For background: The foremost design goal in this build is to elevate the position of the woofer to accommodate my listening space and my belief that the woofer is placed to low in the original design. A stimulus to the build was the state of the clone cabinets I had that came with the Model 19 components, they were built with fir plywood and Formica finished baffles. They were not destroyed but given to another local Altec aficionado that has more patience and the ability to improve upon them. The MLTL alignment also provides for a lower box tuning and is in line with how I like bass presentation.

    I do have a drawing done in Google Sketchup but don't know how to change the file extension to accommodate posting it up in this forum. Anybody that knows how to do this and could pass along the information, gets a big gold star.

    Dimensions of the enclosure are 52 3/4" H x 21" D x 30" W. Enclosure volume is 16 1/2 cu. ft..This is basically the original Model 19 footprint with the height extended as per GM's modeling. GM also had a larger MLTL model along the same dimensions with enclosure volume of 19 cu. ft. but the additional volume of the largest enclosure doesn't offer that much more for the additional volulume so 16.5 it will be.

    Note: I made a poor choice regarding materials when embarking on this, purchasing what I thought was a good grade of Birch Plywood from a local lumber superstore. Those sheetgoods had many voids and the plies were found to be of some other species. Buyer beware. I returned those sheets and am now using standard Baltic Birch, 5' x 5' sheets, 13 ply, purchased from a local hardwoods supplier and was able to check the origination of the product. These are the real deal.

    I have sorted sheets at this point and will be cutting them to dimension, today. I'll try to keep this thread updated with my progress. Anyone with tips and tricks regarding the construction is invited to post up their thoughts and keep me from making any mistakes.

    Thanks, again to GM for doing the modeling and consulting on this, I hope my efforts prove up to the level of his design.




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    Re: GM's MLTL with 416-8B

    You're welcome! As long as there's no air leaks it should perform as predicted if the driver's specs are close enough, and if not, then normally vent tuning can compensate. The rest then is just cosmetic.

    GM
    Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.

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    Re: GM's MLTL with 416-8B

    Quote Originally Posted by GM View Post
    You're welcome! As long as there's no air leaks it should perform as predicted if the driver's specs are close enough, and if not, then normally vent tuning can compensate. The rest then is just cosmetic.

    GM
    My usual procedure for sealing the cabinet is to use an adhesive on the interior seams, something along the lines of PL400, Liquid Nails, etc.. Since these panels are rather large, I will probably rip some small strips as corner gussets out of hardwood. Preliminary plans on bracing are to use vertical window pane type of braces and secure them into dados in the panel interior surfaces. I will try to keep the bracing towards a smaller dimension and largish cutouts so that I don't chew up too much realestate inside the cabinet. Any tips or caveats as to the bracing are welcome.

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    Re: GM's MLTL with 416-8B

    Quote Originally Posted by westend9 View Post
    I do have a drawing done in Google Sketchup but don't know how to change the file extension to accommodate posting it up in this forum. Anybody that knows how to do this and could pass along the information, gets a big gold star.
    The easiest method would be to export to an image file:

    File -> Export -> 2D Graphic

    I'm following this project with interest, in particular the bracing suggestions, as I am planning a (yet another) 604 MLTL build in the near future

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    Re: GM's MLTL with 416-8B

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

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    Re: GM's MLTL with 416-8B

    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
    Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.

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    Re: GM's MLTL with 416-8B

    Westend9, Good Luck with your project. I see your in good hands with GM !!

    I finally got my woofers back from GPA after 2 months, so I'm back working on my cabs again.
    ALTEC USERS BOARD If you need help with the forum or your account, just send me a PM.



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    Re: GM's MLTL with 416-8B

    Quote Originally Posted by Panomaniac View Post
    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.

    Quote Originally Posted by GM View Post
    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.


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    Re: GM's MLTL with 416-8B

    Quote Originally Posted by Altec Best View Post
    I finally got my woofers back from GPA after 2 months, so I'm back working on my cabs again.
    Cool! I sent you a PM the other day, but hadn't heard back. I still haven't installed the HF phragms yet, the XO caps were trashed in the strike too. It even oxidized all the wiring from the amp. Thankfully, the electronics except for one tube in the pre-amp and woofers seem OK..............

    GM
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    Re: GM's MLTL with 416-8B


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    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
    Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.

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