Cab Construction Investigation

Discussion in 'Cabinets & Speakers' started by pedecamp, Nov 3, 2019.

  1. ampmadscientist

    ampmadscientist Well-Known Member

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    Thinner speaker wire might make it sound better.
    I would go with 20 gauge.
    This does not apply to Bass or PA, only guitar amps.
     
  2. pedecamp

    pedecamp Well-Known Member

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    9 3/4 inch width made a difference. It still doesnt sound as good as I want it, I'm contemplating a ply baffle and/or replacing all the sides, right now its totally Marshall spec except for the MDF baffle.
     
    Last edited: Nov 18, 2019
  3. pedecamp

    pedecamp Well-Known Member

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    I think I figured out something, real baltic birch ply is 13 layers and all layers are birch, take a look at this Home Depot birch ply, 5 layers, 5 layers of what, probably crap! I gotta figure out where I can get real baltic birch ply around here. :mad2:

    Meanwhile I bought some MDF to fool around with since its so cheap, I rebuilt the cab with it and it sounds better than the crappy Home Depot ply but still not quite right. I think I'm gonna pop a 1/2" ply baffle in it to see what happens.

    [​IMG]
     
  4. Geeze

    Geeze Well-Known Member

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    You just don't know what is between the outer shells and there are different grades of BB too. Grade B/BB top sheet no patches / bottom sheet will have a few is the best value - beware of the 'I got BB for $30 for a 4'x8' sheet. You cut through that crap and will find voids. Here's a place that ships various sizes https://www.woodworkerssource.com/baltic-birch-plywood.html if you don't have a Rocklers or Woodcrafters near you.

    I may have to play with MDF at some point.

    Russ
     
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  5. pedecamp

    pedecamp Well-Known Member

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    Remember always drill pilot holes when screwing into MDF ends or it will split. And if cutting speaker holes with a dremel have plenty of extra cutting bits MDF is tough on bits.

    Thanks for the link! :yesway:
     
  6. pedecamp

    pedecamp Well-Known Member

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    I tossed in a 1/2" ply baffle and it made a difference, interesting how these small changes do make a difference. So now I have 3/4" MDF sides, 1/2" ply front, 1/2" ply open back panels. I'm getting closer, I think I'll call it a night with this and start tomorrow with fresh ears. :yesway:

    So what I've found is if your sides are MDF use ply for front and back, and if your sides are ply use MDF for front and back.
     
    Last edited: Nov 17, 2019
  7. tankj

    tankj New Member

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    Hi pedecamp, I'm new to this forum, but not new to cabs, speakers, etc. I think I fully understand the case you described. It's a very common phenomenon in thin material or light cabs, whether it is a MDF or birch plywood. which means, two almost identical cabs may have totally different results in sound.

    Also I have read all the posts here. Some have mentioned the resonance of the cab, but doesn't make it deeper. So I want try to explain my understanding, but that will makes this a bit longer post.

    I've built myself some cabs several years ago, mainly in American style. At that time, I pay a lot of attention to speaker's electronic characteristics, just because that's the easiest part for me (the hardest part, is dealing with woods:ohno:). OK, anyhow I figure out there are two essentially different cabs, by acoustically, a dead or alive in response with vibrations.

    An acoustically dead cab will give a most "plain" sound, that almost just what the speaker itself will sounds like. This seems to be the most ideal speaker cabinet in theory, some Hifi company using thick materials, double the baffle too. I'm pretty sure DR.Z do this to their combos, I have one tear-down to see how they are built. I do this to my cabs too, it definitely do some contribution to got that "pure speaker sound", and also makes some help to get a more consistent results when I want built two or more of them.

    You can see the doubled 1-1/2" baffle on the sectional view.
    [​IMG]

    This is the finished cab, American style of course, with open back.
    [​IMG]

    Here comes the most interesting part, when I measure the frequency respons of a speaker, I found that they are unbelievably sensitive by any changes to it's Physical placement. I mean, any!!! Even when you simply put a speaker on the table, it will do a huge different impedance respons just by flip it over(puting the paper cone up or down). We know that impedance respons will do indicate the resonance point.

    According to your description, you've built some fairly light cabs with 1/2" or 3/4" MDF and plywood, which means they are relatively acoustic alive and will definitely do a huge shift on sound result, both in good or bad ways, depends on your own taste.

    Even if you built two identical cab with absolute the same material and construction, they will have very different resonance with speakers mounted. Cabs just have their own resonance frequency, when mounted with speakers, they should be treated as a whole part, then a new resonance point is made, and this is the actual result we get. When you change the baffle or back beetwen MDF and plywood, it also slightly changed the cabs's resonance.

    Currently I just happen to have some Greenbacks by my side, the back label says:"Bass resonance 75Hz", but Celestion may measure this in it's own lab, which will dramatically different when built it to cabs.

    In general, if you build a relatively heavy and dead resonance cab, you can get more consistent results. If you build relatively light cabs, it may needs a lot of tune on different materials or even same material but just different pieces, the result will be more uncontrollable.

    All these are just under my own reading and experience, all my personal understanding, I hope that will help you in some point.
    Also, if there are anything wrong, please tell me.

    PS, Please keep updating with your progress! :hbang:
     
    Last edited: Nov 23, 2019
  8. SkyMonkey

    SkyMonkey Well-Known Member

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    Hi @tankj. Welcome to the Marshall Forum.

    That is one hell of a first post! Most of it over my head, but keep 'em coming.
     
  9. tankj

    tankj New Member

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    Hey SkyMonkey, thank you! Hope that will make sense to you and not too messy.:cheers:
     
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  10. SkyMonkey

    SkyMonkey Well-Known Member

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    I'm sure you are talking sense, but I am not a cab builder.
     
  11. Geeze

    Geeze Well-Known Member

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    Welcome to the forum and great post!

    Russ
     
  12. South Park

    South Park Well-Known Member

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    To many variables . Need more hard science . You need a good starting point
     
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  13. Peter McAteer

    Peter McAteer Active Member

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    At least there'd be less worry about people stealing them...
     
  14. pedecamp

    pedecamp Well-Known Member

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    I'm looking to find some 3/4" baltic birch ply locally to give it another go. :yesway:
     
  15. TAZIN

    TAZIN Active Member

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    Looks like Poplar wood for the core...
     
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  16. Im247frogs

    Im247frogs Well-Known Member

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    looks like poplar.
     
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  17. pedecamp

    pedecamp Well-Known Member

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    So I'm back it. I cut a couple 2 inch port holes in the front of the SV cab I built and did a completely closed back, this is how the Marshall 1912 cab is built so I thought I'd try that next. It sounds pretty good, I think I'll get some more wood today and build from scratch, the SV cab is 9 inches deep the 1912 is supposed to be 11 inches deep. I couldnt find any local source for baltic birch ply so I'm gonna go with a furniture grade birch ply thats got 9 layers hopefully it works. :yesway:
     
  18. pedecamp

    pedecamp Well-Known Member

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    I think I found a winner, picked up some 9 ply 3/4" birch plywood from Home Depot and built a new SV 1x12 cab, this wood sounds good, and a 1/2" ply front and open back. Sounds pretty big for a little cabinet, it has a 16 ohm 75hz creamback in it. Next step pull it apart and glue everything together, route the edges, paint, grill cloth, handle and feet, all done. I'll post some pics when its finished. :yesway:
     
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  19. scozz

    scozz Well-Known Member Gold Supporting Member

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    Good luck Ped! Yeah I agree, I'd try a 12"deep cab if I were you,....unless you're gonna be lugging it around for gigs or rehearsals etc.
     
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  20. pedecamp

    pedecamp Well-Known Member

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    That was a while ago, 12" was too boomy it sounded better at 9". The cab I built the other day is 11" deep and sounds good with an open back. :yesway:
     

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