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Thread: New Voice of Theater owner needs some advice and help

  1. #1
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    New Voice of Theater owner needs some advice and help

    Hello Lads,
    I joined the big stupid speaker club, and now own a pair of Altec A7 VOT speakers
    My local college got some money in their budget and upgraded their sound system. They auction off all their old stuff, and things students leave behind, which is amazing in itself.
    I won a pair of VOT cabinets with 515B woofers and two pair of horns with 288C drivers, and one with 9803B horns and a pair with 311 60 horns.

    I used an extra Pioneer HPM 100 crossover to test them at home, and in a over used word they are "Awesome" I am making room for them in my house as they are going nowhere.

    I need some help, as in my searches, a lot of reference to "bracing the boxes" and adding insulation.

    There is no doubt they need bracing and a whole lot more insulation, as a volume increase over normal listening really resonate the top and sides.

    I ordered a Behringer crossover so I can play with roll off points, and I got a great price on the Jabo horns from germany

    So How does one "brace" these cabinets? and does stuffing the flares with insulation kick up the Bass a little?

    Thank you,

    Donald Bowman

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    No stuffing the flairs will do nothing for the bass,,,The rest of the cabinet is a bass reflex,,,You can double the thickness of the sides of the cabinet,,from the outside,,for stiffness..
    Vlad

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    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by Mrmonster11 View Post
    So How does one "brace" these cabinets?
    I would use 2 by 3 or 2 by 4 kiln dried fir or hardwoods and follow a pattern something along these lines... the red lines are merely a schematic. They need to be glued and screwed to the panels and the cross braces well anchored to the vertical and horizontal panel mounted braces.


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    Sounds like you have A5's not A7's. The cabinet is the same.

  5. #5
    Dang. Amateur speakerdave's Avatar
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    I think those diagonal braces to the center of the back need to land on a panel that will stand free when the back is removed and draw tight with additional screws through the back panel when it is in place. Woofer access is achieved by taking off the back panel.

  6. #6
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by speakerdave View Post
    I think those diagonal braces to the center of the back need to land on a panel that will stand free when the back is removed and draw tight with additional screws through the back panel when it is in place. Woofer access is achieved by taking off the back panel.
    Good point... I didn't really think it through. I can tell by looking at the Altec drawings that they simply didn't pay much attention to panel resonance at all though. No wonder they sound so colored. Doubling up the walls as Maron suggests would be the easiest fix but it will only go so far.


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    Panel resonance and bracing

    Hello Lads,
    Thanks for th input, ireegardless to the first response, I had a bunch of foam sheets here that I use for packing gear to sell.
    I stuffed the insides of the flares, and found a full 50 percent reduction to panel resonance on the top and upper third of the cabinets, I also noticed a bit fuller bass, with more bass from the bottom port.

    I have a pair of Pioneer HPM 100's that from the factory have no inulation on the top inside and the top 1/3 of the back. Last year I installed a dense sheet foam in these areas and had a dramatic increase in the bass, and a much brighter treble. Following this logic, I guess I will reinforce everything inside, and fill the flares with expanding Marine foam that comes in a very dense formula, and install a thick layer of insulation in the rest of the cabinet. None of whivh could hurt.

    I am entertaining the idea of separating the upper and lower cabinets internally, and installing a JBL 2245 sub woofer in the bottom.

    Doing sloppy math, this seems to work out the same as having an Altec 612C cabinet laid sideways on the bottom with a sort of 816A cabinet on top.
    Have to work out venting them, but seems viable.
    Seems like a lot of work, but there is just something about these speakers that gets me and won't let go.

    Thanks,
    Donald

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    Unless you have an accelerameter.. I cant see how you can claim a 50% reduction in cabinet resonence
    Vlad

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    Resonance

    Were not talking Physics lab, which is what annoys me about some postings, science is as much about physical perception as it is about demonstrable and quantifiable, effect. We are talking about end user obsevations in the quest for a better sound experience in a home enviroment, not auditory effects to the hull of the space shuttle while playing Paul McCartney recording as he wails on his Vox Bass.

    So the test is/was, one speaker stuffed the other not playing a bass heavy Mono record, with two different people touching the surfaces , and with a water balanced compass on the cabinet to watch the vibrations, I think I can safely say it is at a 50 percent reduction

    Thanks,
    Donald Bowman.

  10. #10
    Heather [Senorita member] hjames's Avatar
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    Well, how about applying a thick tarry-like coating to the inside of the box panels -
    sort of like a spray on car undercoating. That ought to deaden the resonance quite a bit -
    certainly more so than stiff foam insulation (building foam?).

    Of course, the cabinets will get heavier but its not about moving them, its about the sound ...


    Quote Originally Posted by Mrmonster11 View Post
    Hello Lads,
    Thanks for the input, iregardless to the first response, I had a bunch of foam sheets here that I use for packing gear to sell.
    I stuffed the insides of the flares, ...


    Thanks,
    Donald
    2ch - Oppo DV981, JoLida 502, JBL L200+, KEF 105.4
    HT7- Oppo BDP-93, B&K amps, Vandy 2Ce, 2Ci, VCC1, DCM TF600 & 4641

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    More Resonance

    Hello,
    I thought about that also, the kind of sound deadening that is used as undercoatings. The problem I think, if one is to stick with the original design of the box, and to now use it in a home venue which it wasn't intended is going to take some extra measures. I am beginning to think it will indeed a combination of all, Bracing, Insulation and a second skin of 3/4 inch plywood. Yes it may indeed add a near 100 pounds to the box, but I have seen high end speakers of similar size that tip the scales at near 300 pounds each. Talk about hernia!

    Thanks,
    Donald

  12. #12
    Heather [Senorita member] hjames's Avatar
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    Well, all that damping is like the Westlake Monitor concept -
    do a search here on Westlake to get more info on the goop
    they use to coat the inside of THEIR boxes and deaden their horns with.

    Of course, some of the members here see the basic futility of this whole rework path.
    If you are planning to change your system with a 2245 JBL woofer anyway,
    instead of trying to re-engineering the VOTT system to a place it wasn't designed to go,
    why not just go to a more sensible design in the first place.
    Why not just skip all the compromises in the first place, take the drivers you like,
    and go for a better, more recent design?

    Really - how big is your listening space - and what kind of dimensions does it have?
    Is it long enough for the sound to really open up properly?


    Quote Originally Posted by Mrmonster11 View Post
    Hello,
    I thought about that also, the kind of sound deadening that is used as undercoatings. The problem I think, if one is to stick with the original design of the box, and to now use it in a home venue which it wasn't intended is going to take some extra measures. I am beginning to think it will indeed a combination of all, Bracing, Insulation and a second skin of 3/4 inch plywood. Yes it may indeed add a near 100 pounds to the box, but I have seen high end speakers of similar size that tip the scales at near 300 pounds each. Talk about hernia!

    Thanks,
    Donald
    2ch - Oppo DV981, JoLida 502, JBL L200+, KEF 105.4
    HT7- Oppo BDP-93, B&K amps, Vandy 2Ce, 2Ci, VCC1, DCM TF600 & 4641

  13. #13
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by Mrmonster11 View Post
    Were not talking Physics lab, which is what annoys me about some postings, science is as much about physical perception as it is about demonstrable and quantifiable, effect. We are talking about end user obsevations in the quest for a better sound experience in a home enviroment.
    Well while we are talking about what annoys us about some people's posts...

    I am glad you are happy.


    Widget

  14. #14
    Dang. Amateur speakerdave's Avatar
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    The 828 type of box has its own good points, not the least of which is the proximity of the woofer voice coil to the compression driver's. On the downside is the fact that in the region of the acoustic crossover between the short front horn and the bass reflex port the frequency response/phase response takes a big wowie, around 250 Hz.

    Carving the top half off will yield a burlesque of a box that already exists in the altec 816 and the similar JBL 4560. Using a large bass reflex woofer under that is not an unusual solution, and I would think it very rewarding, if you have the space. Starting from scratch may be less work. I'm not against taking the existing box apart for patterns and parts, but your build might be easier if you begin with a clean slate.

    There is a French website (url below) which has some fairly detailed drawings of midbass horns using one or two Altec 515b's. You may find their work generative.

    http://www.artec-france.com/etudes.p...a39deb3342627d

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    Speakerdave

    Dear Dave,
    Thanks for the reply, but I may not have been clear. I did not mean to cut the cabinet in two. I meant to make a separation of the upper and lower portions of the box from inside the box. I can see from the blueprint supplied by widget that I may be able to divide the space by a horizontal interior wall, so I have a box with an upper and lower chamber. Like I said by sloppy math, the chambers would then appear to have the same volumes as the two individual speakers mentioned. The problem I see is to vent the upper portion of the box for the 515B. Would this be a possibility, or an exercise in tail chasing?

    This idea seems to have been put into practice by a member named Roland, but his posts stopped on this project as well as all posts in 2003. Attempts to contact him have been fruitless.

    Thank you,
    Donald Bowman

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