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Mandolin Curved Cabinet Tower build (Bagby Design)

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  • djkest
    replied
    Removed the front part of the bottom shelf brace because it was interfering with the lower woofer. I think the baffle will still be sufficiently supported.

    There's the front baffles with pre-stain wood conditioner (mixture of Boiled Linseed Oil and paint thinner) and Danish Oil (mixture of oil and Varnish I guess) natural color (not tinted).

    Looks good IMO, really makes the grain and the wood figuring on the mahogany pop. The solid mahogany trim looks boring by comparison. I think I will end up hitting it with 800 grit and then putting some varnish on top.

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  • djkest
    replied
    Well, the baffles are done- ready for finishing. I still have a bit more work on the back part of the enclosure to do first. one of the braces is impinging on the woofer backwave area... Not sure how obvious it'll look from this picture. I might have to remove some more material first. Seems like I never run out of little issues to fix!

    Eagle-eyed observers may notice that the bottom woofers on both baffles are 1/16" higher than they should be- or - the tweeter position is 1/32" lower than it should be. My measuring devices aren't sufficient to tell me which is the case. Both are the same though.

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  • djkest
    replied
    My current calculations put the internal volume about 25 liters, I really want closer to 28 or 30 liters, so I may put 1 more piece of plywood on the front, which will add about 2 more liters of internal volume, bringing me up to 27... pretty close.

    That would put the final dimensions as such -
    Height 26.25" (just "short" enough that they could sit on bass bins)
    Depth 13.5"
    Width - 8.75" maximum, 8.5" baffle width, 3.5" minimum.

    Problems yet to solve:

    1) Should the front baffle be removeable? It's a pain and detracts from the aesthetics
    2) Port / port location?
    3) binding post location
    4) crossover mounting / location
    5) What height of stands? 18" stands would put them at 44" overall height, the tweeter some 11" below the top.


    FINISH:
    Enclosure will be painted white pearl, to contrast with the mahogany front baffle, which will be sealed and satin coated I think, but not stained.

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  • djkest
    replied
    To add volume, I "cut into" the bottom plate, then cut into the 2nd to bottom divider, opening that space to the main area. I then added 1 more piece of plywood "cap" to the bottom, 2 to the top, 1 to the front, and one to the back. So, in essence it increased in height by 2.25", depth by 1.5", and the width overall has stayed the same (sort of!). I am keeping the baffle width exactly as specified!

    Adding to the front and back allowed for more curvature and IMO a sleeker look. After all this I added another curved layer of 1/8" HDF to each side to tie everything together nicely. Because it starts to curve in at the front, I was able to keep the baffle width the same. This means my side panels are now mostly 7/8" thick comprised of 2-3 layers of BB plywood, 2-3 layers of MDF, and 2-3 layers of HDF (7 total). They are incredibly stiff, a knuckle-wrap test might bloody your hand.

    I added 2 side-to-side braces 0.75" x 1.25". I determined their location by beating on the sides with a piece of scrap wood until I found the most unsupported panel area. By adding these 2 braces I eliminated the 2 lowest panel resonances.
    Last edited by djkest; 06-02-2017, 12:09 PM.

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  • djkest
    replied
    Well, This happened. Because the obvious thing when you spend over 100 hours making some curved cabinet towers is to cut them apart! I did this because the towers had several closed chambers in them, which I am cutting open.

    The Mandolin MTMs need roughly 2x the internal volume since they have 2 midwoofers. My initial models indicate they really want 28-30 liters! So how am I going to make this work then....
    (more pics are coming)
    Last edited by djkest; 06-02-2017, 12:07 PM.

    Leave a comment:


  • Zvuchniak
    replied
    Hi Djkest,

    I was wondering, have you made any frequency response measurements of the finished loudspeakers and if you have, do you care to share it here ?

    I'm in the process of making Mandolins but my cabinets won't be here for a while. Thanks.

    Leave a comment:


  • bobbarkto
    replied
    Re: Mandolin Curved Cabinet Tower build (Bagby Design)

    How much do you need? I think I have a couple of pounds, maybe, have to look. Would be willing to part with some.

    Originally posted by ani_101 View Post
    Any good source for getting small quantity of the Quebracho?

    Leave a comment:


  • ani_101
    replied
    Re: Mandolin Curved Cabinet Tower build (Bagby Design)

    Originally posted by bobbarkto View Post
    Tea can work.
    The thing with the bark is the depth of black that can be obtained. Very little undertone, almost pure black.
    Works on most woods regardless of initial tannin content too.

    The hazards and availability/expense and fussiness of application are why I don't mention it very often.
    Any good source for getting small quantity of the Quebracho?

    Leave a comment:


  • bobbarkto
    replied
    Re: Mandolin Curved Cabinet Tower build (Bagby Design)

    Tea can work.
    The thing with the bark is the depth of black that can be obtained. Very little undertone, almost pure black.
    Works on most woods regardless of initial tannin content too.

    The hazards and availability/expense and fussiness of application are why I don't mention it very often.

    Originally posted by ani_101 View Post
    I typically use alternate application of vinegar iron solution and Tea! After a few alternate coats, I get a deep brown / almost black color. With a few coats of shellac, it looks really rich. Tea is an easier and safer alternative to boost the tannin. Plain old tea bags in hot water will do, green or black is fine. Make sure if it cool before application, doesn't need to be hot.

    Leave a comment:


  • ani_101
    replied
    Re: Mandolin Curved Cabinet Tower build (Bagby Design)

    Originally posted by bobbarkto View Post
    White oak is high in tannic acid. You can use this to your advantage.
    A solution of iron oxide (nails dissolved in white vinegar is common) applied to the oak will turn it silvery black.
    If your oak is not high enough in tannin or you want a really dense black with no hint of blue/brown/red then a pre-application of a tannic acid such as Quebracho powder dissolved in hot water will do.
    Most people find a second application of the Quebracho after the ferrous solution will give the most consistent results.
    The advantage with this is the color of the wood is chemically altered and is very lightfast. All the grain and texture will still show.

    Be advised the Quebracho is highly acidic and very irritating to mucous membranes and sensitive skin. Safety precautions are advised. Keep it out of your eyes, too.
    I typically use alternate application of vinegar iron solution and Tea! After a few alternate coats, I get a deep brown / almost black color. With a few coats of shellac, it looks really rich. Tea is an easier and safer alternative to boost the tannin. Plain old tea bags in hot water will do, green or black is fine. Make sure if it cool before application, doesn't need to be hot.

    Leave a comment:


  • djkest
    replied
    Re: Mandolin Curved Cabinet Tower build (Bagby Design)

    I have Ebony stain, I also bought some stain conditioner that I will use prior. I should still test on some scrap before I commit. I also have a project in the works where I might be drastically altering these speakers, like converting them into sealed bookshelf speakers. It will be kind of a shame to chop up so much of my hard work, but currently they are sitting in the basement looking pretty, so anything would be an improvement.

    Leave a comment:


  • kenrhodes
    replied
    Re: Mandolin Curved Cabinet Tower build (Bagby Design)

    i forgot to mention I filter my solution through a coffee filter. I you have any stay pieces of steel wool it can cause problems.

    Leave a comment:


  • kenrhodes
    replied
    Re: Mandolin Curved Cabinet Tower build (Bagby Design)

    one comment to add to Bob's post: I use fine (0000) steel wool to make my rust/vinegar solution. Simply fill a jar with white distilled vinegar and dip the steel wool all the way in and out 5-10 times. The fresh steel wool will rust almost instantly and hen mix into the vinegar.
    After I use the rust solution I use a ebony stain, it seems to make the wood look more natural.
    I love this process glad Bob posted it.

    Leave a comment:


  • bret191
    replied
    Re: Mandolin Curved Cabinet Tower build (Bagby Design)

    I like the way you attacked the project and I know you will greatly enjoy the end result! Now I am jealous!

    Leave a comment:


  • bobbarkto
    replied
    Re: Mandolin Curved Cabinet Tower build (Bagby Design)

    To get a very consistent color change to black on most oak requires a very dense almost opaque pigment layer or a chemical change.
    Minwax ebony will leave a brownish hue with some brown showing similar to what you have now.
    Adding silver will make it a lighter black/gray but with the same underlying problem of the brownish hue being somewhat pronounced.

    White oak is high in tannic acid. You can use this to your advantage.
    A solution of iron oxide (nails dissolved in white vinegar is common) applied to the oak will turn it silvery black.
    If your oak is not high enough in tannin or you want a really dense black with no hint of blue/brown/red then a pre-application of a tannic acid such as Quebracho powder dissolved in hot water will do.
    Most people find a second application of the Quebracho after the ferrous solution will give the most consistent results.
    The advantage with this is the color of the wood is chemically altered and is very lightfast. All the grain and texture will still show.

    Be advised the Quebracho is highly acidic and very irritating to mucous membranes and sensitive skin. Safety precautions are advised. Keep it out of your eyes, too.

    An easier option is dilute black or gray paint, depending on the color you want, applied like you would a normal wood stain. This will leave a higher concentration of pigment on the surface and will obscure some of the grain but still leave some semblance of the appearance of wood. You will need to experiment with the dilution and setup time to get the right effect on your wood.
    It is often advisable or necessary to pre-stain the wood with a black dye (the minwax ebony would work for this but a water soluble wood dye would be better and more densely black).

    To get to the mottled gray you will need to apply some gray pigment over the black base.
    You can apply a glaze coat of gray paint to the whole surface and selectively wipe it away.
    Make the glaze by thinning paint and adding clear.
    Vary the concentration of pigment to thinner/clear carrier in your glaze to change the effect.

    ->Pigment will build in the pores and is very difficult to remove so start with a light concentration and work up until you get the effect you are after.


    Originally posted by djkest View Post
    I do have some scrap I could use. I have looked into oak carbonizing, I've even done it myself. It was a pain in the but1 and I didn't really like it to be honest. I have some minwax ebony stain. Maybe I'll try mixing the black stain with silver paint and see how that looks. Since it's scrap, messing up won't kill me, it just wastes time.

    Or I could buy some wood conditioner, and use that + ebony stain and see how that looks.
    Last edited by bobbarkto; 02-13-2015, 02:14 PM. Reason: forgot the gray

    Leave a comment:

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