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Thread: Altec Custom VOTT Somethings

  1. #16
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    The trick with boring out the existing cut-outs will be if I can get the router and a template in there without the side panels preventing it. May not be enough room. I can CNC out a 10.15" template and use it once I am able to figure out the centering on the existing. The new port hole is easy.

    But yes, a new baffle would also be the easiest if the existing would come out easy. The original builder used staples and a serious looking glue when attaching it unfortunately.

    Quote Originally Posted by Earl K View Post
    Bummer, about the fully cracked surrounds.

    FYI, I'm not aware of anyone in any of the forums ( that I frequent ) who's replaced an Altec or JBL linen or paper surround ( although maybe I'm just not paying close enough attention ).

    Therefore I'd also say that you're in unchartered territory here.

    The other surround source ( mentioned over at AudioKarma ) looks to be the better choice for surrounds.

    Some advice; keep all the hardened goop that you collect ( including the stuff still on the old surrounds ).
    - You may need to reconstitute it ( if possible ) so that you have a backup supply of something original.

    The stuff mentioned in this other link might turn out to be a formula that leaves the new surrounds too stiff ( with a higher than desired Fs > that would need to be measured by doing an impedance test ).

    Also, it might be a lot more straightforward to simply make new baffle boards with the correct woofer cutouts ( than to shave back the existing holes > though I don't really know if there's a nifty router bit made for just that job > hopefully ).


  2. #17
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    Quote Originally Posted by Drugolf View Post
    The trick with boring out the existing cut-outs will be if I can get the router and a template in there without the side panels preventing it. May not be enough room. I can CNC out a 10.15" template and use it once I am able to figure out the centering on the existing. The new port hole is easy.

    But yes, a new baffle would also be the easiest if the existing would come out easy. The original builder used staples and a serious looking glue when attaching it unfortunately.
    If they were mine I would simply cut-out the existing baffle boards ( leaving a 2" wide edge to fix a new one to ) and replace it with one made of Baltic Birch plywood ( either 3/4" or 1" thick ).

    I see excessive over-hang past the existing baffle board ( from the side panels extending a couple ? inches ).

    Significant ridges ( over-hang ) to the side of the baffle board triggers diffraction effects ( which are easily measured when compared to a flush baffle-board ).

    So my approach is win-win ( IMNSHO ).


  3. #18
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    Oooh, now you're thinking! Good thing someone around here is.

    I will need to see how much overhand there is. I took the cabinets to my storage will I work on the woofers and wait to do the woodworking. Pictures barely show it.
    I think it would be close to flush if a new baffle was installed. Might make grilles difficult, but then maybe do a good looking baffle so grilles would not be needed.
    Why the Baltic birch?

    Quote Originally Posted by Earl K View Post
    If they were mine I would simply cut-out the existing baffle boards ( leaving a 2" wide edge to fix a new one to ) and replace it with one made of Baltic Birch plywood ( either 3/4" or 1" thick ).

    I see excessive over-hang past the existing baffle board ( from the side panels extending a couple ? inches ).

    Significant ridges ( over-hang ) to the side of the baffle board triggers diffraction effects ( which are easily measured when compared to a flush baffle-board ).

    So my approach is win-win ( IMNSHO ).


  4. #19
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    I favor dense plywood baffles because plywood holds T-Nuts much much better than MDF or particle board.
    - This is not an advantage if a person doesn't use T-Nuts ( which I happen to use in Pro-Audio applications > with SR speakers )

    Mind you, if one is using wood screws to a-fix woofers( from the back-side to the baffle board ) my preference doesn't matter very much ( since any stripped out hole just means the user needs to find a virgin surface by slightly rotating the woofer ).


  5. #20
    Senior Member macaroonie's Avatar
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    The bits you need are as follows. A straight
    cutter with a bottom guide bearing that is
    undersized such that it will remove 1/8 the
    You use that to remove most of the material
    but you need to stop before the bearing has
    nothing to run on. This will leave you with about 1/8 th of a lip
    To remove this you need a top bearing flush trim bit. The bearing will run on the area you
    previously cut resulting in a smooth cut edge.

    Sorry about the giant letters. doing this from my phone.

  6. #21
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    Quote Originally Posted by macaroonie View Post
    The bits you need are as follows. A straight
    cutter with a bottom guide bearing that is
    undersized such that it will remove 1/8 the
    You use that to remove most of the material
    but you need to stop before the bearing has
    nothing to run on. This will leave you with about 1/8 th of a lip
    To remove this you need a top bearing flush trim bit. The bearing will run on the area you
    previously cut resulting in a smooth cut edge.

    Sorry about the giant letters. doing this from my phone.
    Good to know an actual technique is out there to fix this sort of problem ( no-doubt this seems rudimentary to you but,,, )!

    Anyways, I'm glad that you popped in with your wood-working wisdom.


  7. #22
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    Unfortunately, the existing cutout is not very good. Whatever the original builder used to cut, it didn't leave a consistent smooth rounded circle. I was hoping to do a better round cut.

  8. #23
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    For what it's worth, I'm quite sure those are built from the guts of 60's era Seeburg jukebox speakers. High quality for its day. The non adjustable crossover is a big clue. I worked in quite a few clubs, and fixed a few along the way...
    Attached Images Attached Images  

  9. #24
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    May very well be. The guy I purchased them from said he only remembers them being low horizontal boxes. The gold horn sure is a give away.
    There is a horn adjustment on the back though.
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    Quote Originally Posted by Tim Rinkerman View Post
    For what it's worth, I'm quite sure those are built from the guts of 60's era Seeburg jukebox speakers. High quality for its day. The non adjustable crossover is a big clue. I worked in quite a few clubs, and fixed a few along the way...

  10. #25
    Senior Member macaroonie's Avatar
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    Quote Originally Posted by Drugolf View Post
    Unfortunately, the existing cutout is not very good. Whatever the original builder used to cut, it didn't leave a consistent smooth rounded circle. I was hoping to do a better round cut.
    Bummer. Template it is then. Do you have enough ground on the baffle to sit it on ?

  11. #26
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    That's what I am worried about and why we were discussing just cutting out the old somehow and building a new one. I can get the new one cut via CNC so it would be really good. The new added port hole will be easy enough as-is at least.

    Quote Originally Posted by macaroonie View Post
    Bummer. Template it is then. Do you have enough ground on the baffle to sit it on ?
    On another note I ordered replacement cloth accordion surrounds for the 4 woofers. GPA does not sell them so I went with that lighter weight option off ebay and got a little better price buying 2 sets. Bill did suggest re-purposing the original goop if needed onto the new surrounds.

  12. #27
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    Hi Drugolf and Earl,

    RE: Bracing in posts # 12 and # 13

    I certainly agree with bracing of such a large cabinet with the low frequencies involved.

    My point here is simply that if you're going to brace you might as well do it the way that provides the most benefit, specially when the work involved is the same. Diagonal bracing isn't the most rewarding way among the simple methods.

    In Ray Alden's "Advanced Speaker Systems" p. 5-6 (with well known Joseph D'Appolito being the Contributing Technical Editor of the book) they show diagonal bracing isn't as profitable within easy methods.

    To demonstrate this they show five identical rectangular shaped pieces of wood (like your back and side panels):

    1- No brace, panel resonance 60 hz

    2- Widthwise brace in the middle, panel resonances of 100 hz on each side of the brace

    3- Diagonal brace dividing the rectangle into two triangles, panel resonances of 115 hz on each side of the brace

    4- Lengthwise brace in the middle, panel resonances of 160 hz on each side of the brace. As can be seen the gain here is more important than diagonal, and this is for the same work!

    5- The fifth method shown is more complicated as it divides the panel in three unequal sections with two Lengthwise braces, panel resonances of 210 hz, 235 hz and 275 hz respectively are obtained.

    Bracing's purpose is to minimize cabinet resonance effects, like enclosure coloration, by creating higher pitched resonances when panels are divided into smaller surfaces with brace(s).

    Since the work and material costs involved are the same in this case, the issue being only the braces' orientation, it makes sense to go with the more desirable option among the easy stuff (i.e. # 4). Regards,

    Richard

  13. #28
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    Thanks Richard! Good info.

    To clarify I take this as braces that are strips of wood attached to the back and potentially side panels, about as long as the panels. ?

    Would it still be best to have a board that extends across between the two side or also one front baffle to the rear panel?

    The one weak point of the cabinet construction are the back panels oddly enough. They are 3/4" press board and there were only 45 screws holding it on. Time for something more substantial?


    Quote Originally Posted by RMC View Post
    Hi Drugolf and Earl,

    RE: Bracing in posts # 12 and # 13

    I certainly agree with bracing of such a large cabinet with the low frequencies involved.

    My point here is simply that if you're going to brace you might as well do it the way that provides the most benefit, specially when the work involved is the same. Diagonal bracing isn't the most rewarding way among the simple methods.

    In Ray Alden's "Advanced Speaker Systems" p. 5-6 (with well known Joseph D'Appolito being the Contributing Technical Editor of the book) they show diagonal bracing isn't as profitable within easy methods.

    To demonstrate this they show five identical rectangular shaped pieces of wood (like your back and side panels):

    1- No brace, panel resonance 60 hz

    2- Widthwise brace in the middle, panel resonances of 100 hz on each side of the brace

    3- Diagonal brace dividing the rectangle into two triangles, panel resonances of 115 hz on each side of the brace

    4- Lengthwise brace in the middle, panel resonances of 160 hz on each side of the brace. As can be seen the gain here is more important than diagonal, and this is for the same work!

    5- The fifth method shown is more complicated as it divides the panel in three unequal sections with two Lengthwise braces, panel resonances of 210 hz, 235 hz and 275 hz respectively are obtained.

    Bracing's purpose is to minimize cabinet resonance effects, like enclosure coloration, by creating higher pitched resonances when panels are divided into smaller surfaces with brace(s).

    Since the work and material costs involved are the same in this case, the issue being only the braces' orientation, it makes sense to go with the more desirable option among the easy stuff (i.e. # 4). Regards,

    Richard

  14. #29
    Senior Member RMC's Avatar
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    Hi Drugolf,

    RE: "To clarify I take this as braces that are strips of wood attached to the back and potentially side panels, about as long as the panels. ?" Exactly, these are your three largest panels, the front panel being the other. Do at least what Earl suggested, but placing those braces lengthwise in the middle of each panel.

    RE: "Would it still be best to have a board that extends across between the two side or also one front baffle to the rear panel?" Subject to the fact I have not followed the thread consistently and in details, the bracing issue simply rang a bell with me:

    Well you consider the cabinet's back panel as the weak point. Best? Probably yes, but again practicality also kicks in: access to drivers (yours are mounted from inside if I remember), placement of vents for unaffected air flow, added weight, etc. You'll need to assess that.

    These front to back and side to side braces need not necessarily be 2X3" which is good news. Since your panels will be braced with 2X3" on edge (Earl) they gain rigidity and will "expand" less than before from in-box pressures. Weems has an interesting note regarding braces that tie opposite walls together:"Such a brace need not be thick because any tendency for the walls to move must stretch or compress the brace. That movement is in the direction of greatest stiffness."(Note 1). Makes a lot of sense to me.

    For my larger boxes, typically I use older 2X2" for front to back and left to right bracing (the cross), in addition to bracing on each panel. The smaller top/bottom panels are braced too, but no top to bottom brace is used here, since smaller panels of same material and thickness are stiffer than larger ones.

    I also use an horizontal brace placed on edge on the front panel of my larger cabs. That brace's size varies a little based on box size, space available and requirement to avoid any interference with vent air flow. That type of brace is something you may want to consider in view of your baffle panel's size. You'll need to assess space and brace size you can accept, if any.

    RE: "The one weak point of the cabinet construction are the back panels oddly enough. They are 3/4" press board and there were only 45 screws holding it on. Time for something more substantial?" 3/4" press board isn't bad at all when properly braced lenghtwise and front to back, even if the panel is removable. It just needs to be done properly.

    On this panel you will likely need to use weather stripping tape and/or removable sealant (silicone). I would use both! to prevent air leaks.

    More bracing affects net box volume and cabinet weight. You should measure and keep count of the braces' volume, specially when going for more, to account for this, as well as drivers and vents, in the Vb calculation. If you plan to "rattle the silver" with the boxes you should go for a little more instead of less.

    Other than bracing, another challenge you will have with such boxes is maintaining a good box seal (air tight) in order to achieve an acceptable box loss figure. In this context, its a tough job to get up to or better than QL 5 which would probably be the starting point of your modeling. If you use the free Win ISD Pro software remember the default box loss is an optimistic QL 10 wich can be changed to QL 5 in Box tab, then go to bottom of page, click on Advanced, then click on the first item (QL), enter 5 there instead of the 10, and exit. If you save the project QL 5 should stay with it. If you start another project QL 10 will be back so you need to change it again, this time to the standard QL 7?, it depends on circumstances. Regards,

    Richard

    Note 1: David B. Weems, Designing, Building, and Testing Your Own Speaker System, 4th Edition, P.35.

  15. #30
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    Great stuff Richard, thanks.

    I received the new 414A surrounds. They look and fit great. Now the tough part - removing the old goop rings. Acetone + heat for the goop and MEK for the glue if needed. I am going to try and save as much of the goop as possible I guess by melting it off the old surrounds. Would like to have it on hand in the event I do not like the stuff that came with the surrounds. To me that stuff looks like a simple PVA glue product, but the seller says it isn't. I will try it first on one of the old surrounds to see what it does on drying.

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