a part two to my marshall question…

Discussion in 'Amps and Cabs [BG]' started by bon viesta, Aug 21, 2021.


  1. bon viesta

    bon viesta

    Dec 10, 2020
    i’ve been trying to get as many important calculations i can to be able to further know what i’m working with in my mind for my stupid little plan. i’ve done conservative calculations on the angled bass cabinet to try and see how much volume is present inside. assuming the wood is 1 inch thick, and the dimensions are 30 inches wide, by 29 inches tall, by 14 inches deep (bottom), by 11 inches deep (top) the internal volume is a conservative ~5 cubic feet. the images below also show the two sections of the cabinet and their dimensions. i’m likely going to use eminence beta 12” speakers for this, which have a recommended enclosure volume of 0.9 cubic feet, to 1.25 cubic feet for a sealed enclosure. 0.9 x 4 = 3.60 cubic feet, which is alright for the entire cabinet. 0.9 x 2 = 1.8 cubic feet, which is alright for each section of the cabinet. but this is being very very optimistic about the interior obstructions in the cabinet. and plus, this is the minimum requirement. so, for the max requirement, 1.25 x 4 = 5 cubic feet, iffy. 1.25 x 2 = 2.5 cubic feet. also iffy, for both sections. so, this cabinet would beyond reasonable doubt be too small for what i’m asking for it. but not by very much, and it’s not like sealed cabinets will blow up when your enclosure is too small by a rather little amount. so, going by the standards for the MAXIMUM recommended volume for a sealed enclosure, 1.25 cubic feet per speaker, how would various types of insulation help the apparent volume increase? and if this cabinet was a straight, 29 x 30 x 14 enclosure (with 5.25 cubic feet of volume) would the issues with volume be mostly remedied?? look at the images below for information i’ve tried to accurately get my head around, and ask if there’s any other dimensions you need or anything.
     

    Attached Files:

  2. bon viesta

    bon viesta

    Dec 10, 2020
    also, yes i know that the interior volume for each section is skewed by the fact that the calculator assumes that the top of the box (which wouldn’t be there if the two were a combined, single enclosure) is 1 inch of wood, and so it takes volume away from the added 5 cubic feet.
     
  3. bon viesta

    bon viesta

    Dec 10, 2020
    bumparoo :whistle: should’ve named the title something a little more interesting
     
  4. Michedelic

    Michedelic MId-Century Modern

    Wouldn’t your ply be 3/4”?
     
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  5. bon viesta

    bon viesta

    Dec 10, 2020
    perhaps, but i was trying to be “too big” on purpose just to know if giving myself as little wiggle room as possible to make up for any negative things i may be missing (the handles coming into the cabinet, the wooden post in the middle of the enclosure, any inaccurate measurements) would still give me any semblance of an ability to have enough volume. it’s a better deal to be giving yourself as little help as possible and be able to solve the problem under the guise of those slightly exaggerated circumstances, rather than pretend that everything will be fine until something unforeseen completely ruins everything.
     
  6. bon viesta

    bon viesta

    Dec 10, 2020
    also i didn’t even know what ply it would be… :wideyed: i just went for 1 inch because they look pretty thick and i couldn’t find any measurements for marshall cabinet wood thickness.
     
  7. abarson

    abarson

    Nov 6, 2003
    Santa Cruz
    1” thickness is overkill and will increase the weight drastically.
    If you learn about bracing, you could use 3/4” for the baffle and 1/2” for the rest.
    If you’re sold on the slanted sealed approach you really need to read this thread Chris Cole Slant 212
     
    Last edited: Aug 21, 2021
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  8. bon viesta

    bon viesta

    Dec 10, 2020
    here’s the interior volume when the wood thickness is 3/4”. wowza i like those numbers :woot:
     

    Attached Files:

  9. bon viesta

    bon viesta

    Dec 10, 2020
    i looked back at the site i will get the cab from and it says it uses 5/8” boards. i ran that through the calculator and it seems the general volume for this cabinet is 5.61 cubic feet. not too shabby for those eminence speakers. is there something else i’m missing? i think i’ll definitely be putting insulation in this thing.
     
  10. Redbrangus

    Redbrangus Supporting Member

    Nov 19, 2018
    Under The X In Texas
    I'm hoping this means the builder uses 5/8" plywood. If it really is 5/8"-thick solid lumber, I'd ask if they could do it in 3/4" plywood. Lumber construction is not what I'd recommend for a bass cab -- leave that to the guitar guys. And a few cubic inches of internal volume in either direction won't have much effect on the enclosure's performance.
     
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  11. bon viesta

    bon viesta

    Dec 10, 2020
    it’s definitely ply.
     
  12. Redbrangus

    Redbrangus Supporting Member

    Nov 19, 2018
    Under The X In Texas
    Cool. Just for the record, the apparent thickness of the cab walls on actual Marshall cabs is achieved with a second layer of plywood added to the inside edge of the outer cab walls on the front. They're still just constructed of 3/4" sheet goods.
     
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  13. beans-on-toast

    beans-on-toast

    Aug 7, 2008
    Some Marshall 412 cabs have a 2x4” brace from the front baffle to the back.
     
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  14. bon viesta

    bon viesta

    Dec 10, 2020
    this one will. how would that effect the volume?
     
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  15. Redbrangus

    Redbrangus Supporting Member

    Nov 19, 2018
    Under The X In Texas
    From the looks of it in that one interior pic, this one does too. I think.
     
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  16. beans-on-toast

    beans-on-toast

    Aug 7, 2008
    Measure the length, hight, and width then calculate cubic inches, subtract that from the cabinet internal volume. You also have to subtract the volume occupied by each cone. That is on the speaker spec sheet.

    A 2x4 is 8 cubic inches per inch (1” long x 2” x 4”). Multiply 8 by the length of the brace in inches to calculate the volume in cubic inches lost due to the brace. This assumes that the brace is indeed 2”X4”, if it isn’t it’s a simple calculation.
     
  17. bon viesta

    bon viesta

    Dec 10, 2020
    i got .06 cubic feet. 2 inches tall, 4 inches wide, 14 inches deep (up against the sealed back). that seems sort of small though…
     
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  18. beans-on-toast

    beans-on-toast

    Aug 7, 2008
    Seems correct.
     
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  19. micguy

    micguy

    May 17, 2011
    I've gone looking for the "apparent volume increase" due to insulation a few times, and never found any evidence that it's real. The folks saying it exists say the insulation changes the system from adiablatic to isothermal. To do that, you need something that takes away the heat when you compress the air. But insulation doesn't do that - we're talking fibers of glass, which is a very poor conductor of heat (the material is chosen for house insulation BECAUSE it is such a poor conductor of heat) - the material you're using is completely the wrong kind of material to do what is claimed. Maybe if you used copper wool (copper is a very good conductor of heat), you might measure something, but I've gone looking, and as far as I can tell, in the case of glass fiber, the emperor has no clothes.
     
    bon viesta likes this.
  20. if it helps with target numbers for internal volume, it's probably easier to make a flat baffle as opposed to a slant cab like you're thinking. Though I get why you'd want two speakers pointed at your ears instead of your knees.
     
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  21. Primary

    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

     
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