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Thread: GM-416-8B MLTL Corner Cabinet

  1. #1
    Hostboard Member srivenkat's Avatar
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    GM-416-8B MLTL Corner Cabinet

    Greetings to all!

    I am starting a new project with the idea of having a corner MLTL cabinet using the following parameters,

    Drivers - GPA 416-8B, GPA 802-8G, Altec 811B horn, GPA N1200-8A XOver (or other passive XO)
    Room Size - 15 ft W X 30 ft L X 9 ft H
    Amplifier - 45 SET integrated (76/6SN7/45 tubes), output impedance is ~ 3 Ohms

    Maximum Cabinet Dimension - 60? H - (preferably including the horns) X 40? W along with appropriate depth for corner cabinets.

    I know there are many GM designed MLTL materials out here and other forums however, I did reach out to GM for his help. As always, he is so kind in helping me out in this design.

    Based on his initial calculation, here are the properties of the cabinet

    Volume = ~25.25 ft^3 gross, so ~24 ft^3 net MLTL
    L = 58.5"
    W = 38.5"
    D1 = 9.75" rectangular protrusion
    D2 = 19.25" baffle to triangular section's 'point', though may want to square it off a bit due to room corners typically being a bit uneven
    Horn down = 4.75"
    Driver down = 22"
    Therefore horn/driver ctc spacing = 17.25"

    Vent = [1] 5" dia. x panel thickness [0.75" assumed]/side for ~25 Hz Fs or can both be on one side horizontally.
    Recommend using a removable baffle to try up to [1] 9" dia. vent hole/side for more typical Altec tuning or just start big and add smaller hole discs till it sounds right. For all I know, having different size holes in each side may work best overall since the room dominates and SET tube amps can be pretty finicky about impedances not ruler flat, but the passive components to flatten a low Fs bass driver's impedance are large, not cheap.

    We thought it would be good to continue the discussion in this forum. So?.

    Also, Many Thanks to Westend, Dan Kercher, and Altec Best (John) and others for posting their MLTL design in detail and answering my questions.

    -Sri

    - - - Updated - - -

    GM,

    Thanks for the measurement. From our conversations...


    Right, I understood that there's a 60" speaker height limit plus this is to be basically a tall M19, so the horn sits in a cavity with foam around it.
    Is the total speaker height 60" or ??
    Note again that ideally we want the woofer in a room odd harmonic, which ATM is within a fraction of an inch based on a 96" room height.
    Note that for your tall M19, the woofer ideally needs to be mounted on the face of the baffle to preserve the time/phase offset.


    60? is what I am thinking of maximum height, few more (up to 4 or 5?) is fine if required. Can I keep the horn in a separate box, with foam around, on top of the cabinet? This might add some flexibility.

    Thank you,
    Sri

  2. #2
    Senior Hostboard Member VolvoHeretic's Avatar
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    Re: GM-416-8B MLTL Corner Cabinet

    Hey Sri, cool idea, I am having a little trouble envisioning the profile of your speaker, is it something like this?

    Srivenkat's Corner Speaker-1.jpg
    "James, a little knowledge is a dangerous thing!" World's scariest Volvo: [url]http://www.youtube.com/watch?v=AKn-LTNa4rc[/url]

  3. #3
    Hostboard Member srivenkat's Avatar
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    Re: GM-416-8B MLTL Corner Cabinet

    Quote Originally Posted by VolvoHeretic View Post
    Hey Sri, cool idea, I am having a little trouble envisioning the profile of your speaker, is it something like this?

    Srivenkat's Corner Speaker-1.jpg
    Hi VolvoHeretic,

    Thanks and thanks for the drawing. Yes, it is almost like that except there is a 2" back board connects the triangle to square it off. I tried inserting a simple picture not sure whether it pasted here. What tool you use to draw the diagrams, I will try start drawing them.

    -Sri

  4. #4
    Senior Hostboard Member GM's Avatar
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    Re: GM-416-8B MLTL Corner Cabinet

    .........with 90 deg included angle for both simplicity of construction and pushing it hard into a corner if desired.

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

  5. #5
    Senior Hostboard Member GM's Avatar
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    Re: GM-416-8B MLTL Corner Cabinet

    Quote Originally Posted by srivenkat View Post
    60? is what I am thinking of maximum height, few more (up to 4 or 5?) is fine if required. Can I keep the horn in a separate box, with foam around, on top of the cabinet? This might add some flexibility.

    Greets!


    You can, though I figured that if you ever go with dual woofers, then you'll ideally need all this net Vb plus a larger horn, so maybe best overall to make the cab one piece with removable horn and woofer baffles and maybe even ones for the side vents for max flexibility. Note too that if just the 604 is installed, then ideally it still needs the offset from the top for smoothest overall response/minimal internal damping same as for the 416 or any other woofer[s].


    You're wanting a lot out of these cabs long term, so this makes the most sense to me. 'Down the road' with a totally removable front [in pieces] baffle you could even switch to sealing off the woofer[s] and using the rest of the cab as a separate subwoofer system for super low 'fill'.


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

  6. #6
    Senior Hostboard Member VolvoHeretic's Avatar
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    Re: GM-416-8B MLTL Corner Cabinet

    Ok, I understand. I'm using Autodesk Architectural Desktop or AutoCAD for short. It will do almost anything, but is labor intensive.

    Srivenkat's Corner Speaker-2.jpg
    "James, a little knowledge is a dangerous thing!" World's scariest Volvo: [url]http://www.youtube.com/watch?v=AKn-LTNa4rc[/url]

  7. #7
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    GM-416-8B MLTL Corner Cabinet


    jocelys1's Avatar
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    Re: GM-416-8B MLTL Corner Cabinet

    Sri, great idea and a very understanding wife. 24CFT with 60" height.....AWESOME !

    The 38.5" width will get you a cool ~120hz f3 w.r.t baffle step.

    The "fill" bit, is that idea a 2.5way.

  8. #8
    Senior Hostboard Member GM's Avatar
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    Re: GM-416-8B MLTL Corner Cabinet

    Yeah, I tried learning it back in the early '90s and gave up.

    We're not on the same 'page' yet though

    The 9.75" is i.d., all dims are i.d.

    drawing a line across these points to make a 'box', the 19.25" dim was originally from this imaginary line to the corner peak, but truncating it to a 2.5" wide [not 19.25"] rear panel reduces it to 18" i.d.

    Thanks!

    GM

    - - - Updated - - -

    Quote Originally Posted by jocelys1 View Post
    The 38.5" width will get you a cool ~120hz f3 w.r.t baffle step.

    The "fill" bit, is that idea a 2.5way.
    Hmm, you sure about that? Measured responses on a 40" o.d. baffle is closer to 75-80 Hz plus these are planned for corners, so no baffle step loss, just gain.

    No, a three way.

    A 2.5 way is where a pair of woofers driven by a common amp plays 'full-range' down low, then one is rolled off at the baffle step.

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

  9. #9
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    GM-416-8B MLTL Corner Cabinet


    jocelys1's Avatar
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    Re: GM-416-8B MLTL Corner Cabinet

    Greg, I did a straight 4560/width(in.) to get that number. I missed the corners bit, so like you said.....a lot of GAIN.

    This a 3-way design.

    If the dimensions are what's being discussed, the height works out to 72", am I missing something ?

  10. #10
    Senior Hostboard Member VolvoHeretic's Avatar
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    Re: GM-416-8B MLTL Corner Cabinet

    Ok, how about this.

    Srivenkat's Corner Speaker-3.jpg
    "James, a little knowledge is a dangerous thing!" World's scariest Volvo: [url]http://www.youtube.com/watch?v=AKn-LTNa4rc[/url]

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