Mandolin Curved Cabinet Tower build (Bagby Design)

[kenrhodes]

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.

[kenrhodes]

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.

[djkest]

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.

[ani_101]

Re: Mandolin Curved Cabinet Tower build (Bagby Design)

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.

[bobbarkto]

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.

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.

[ani_101]

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.

Any good source for getting small quantity of the Quebracho?

[bobbarkto]

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.

Any good source for getting small quantity of the Quebracho?

[Zvuchniak]

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.

[djkest]

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)

[djkest]

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.

[djkest]

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.

[djkest]

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.

[djkest]

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.