Resonator Soundwells

I had a question on how to build reso soundwells and figured I might as well put it in here so it can be of use to others.

Ok, first of all there's very little info out there on how to build a reso uke. Almost all reso ukes are modeled after biscuit bridge resonator guitars. Research them to see their construction to get an idea how to build your uke.

The National Resophonic cones I use require a soundwell with a lip at the bottom for the cone to rest on. I rout circles from ply sheet to make my soundwells. A 18mm sheet to make the walls and a 4mm sheet to make the base. The base has an inner diameter smaller than the cone to make the lip. The 18mm sheet has an inner diameter 5mm bigger than the cone diameter to give wiggle room for intonation. The base is glued to the wall section.

Wood choice isn't as important as for a regular uke since the cone is making the sound. It is important to make a ridged, heavy body for the uke so that it can't steal energy from the cone. I make my tops 4mm thick. The total soundwell depth, including the thickness of the top, for national cones is 19mm. This means the ply walls have to be thinned down to 15mm.

To make things easier when routing, I rout down to 16mm but leave all the pieces attached by the 2mm of ply remaining. This stops the soundwells bouncing around at the end of the cut and getting chunks taken out by the router bit. Then I pass them through the drum sander to seperate them from the surrounding ply.

Hopefully some photos will help explain.

Why not bend them or buy plywood cylinders and cut them down? Or drum shells? Or you could go "block rim" style like a Stelling banjo.

Block rim would require a lathe. I have access to lathes but don't have the skills required on one. I would like to learn though.................so much to learn so little time.........

Shipping to Australia on plywood cylinders or drum shells, by the fact that you're shipping mostly air, is outta control.

Each sheet of 18mm ply costs about $40 and yields about 15 soundwells, so whilst there's a fair bit of waste, it's not expensive per uke.

liam_fnq said:

Block rim would require a lathe...

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A lathe is handy, but not absolutely necessary for block rims. I don't have any pictures of the process, but the rim in this picture was made by gluing up two layers of octogons with the glue joints staggered, then cutting the outside diameter and inside diameter with a router and a circle jig...similar to the process shown above. A little clean-up with a drum sander in a drill press (inside surface) and disc sander (outside surface) finished the job of nicely.

I make the rime and lip from one piece of 18mm ply but that is as much as I am saying because I have a few other tricks up my sleeve to get the sound which relate to the whole construction thing...

Ken W said:

A lathe is handy, but not absolutely necessary for block rims. I don't have any pictures of the process, but the rim in this picture was made by gluing up two layers of octogons with the glue joints staggered, then cutting the outside diameter and inside diameter with a router and a circle jig...similar to the process shown above. A little clean-up with a drum sander in a drill press (inside surface) and disc sander (outside surface) finished the job of nicely.

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A jig like this? http://www.youtube.com/watch?v=MHptrOw4TFE

It's the inside that always seems much more difficult w/o a lathe. The same guy above uses this setup, which is about as simple as I've seen, but I'd imagine would have difficulty turning something as narrow as a resonator soundwell. http://www.youtube.com/watch?v=xN1iSUH1vAs

I've been contemplating building similar jigs for both drum and banjo rings, but I'm still looking for something more clever for the insides.

These days most of the high end resonator guitar builders, guys like Scheerhorn, Beard, Meredith and others have done away with the sound well and are putting posts under the ply rim. Usually 6 or 8. A good many builders are also using a baffle at the front and inside the body just forward or the sound holes. I have an old Scheerhorn with an aluminum baffle and a Meredith with an acrylic. How or why it works I really don't know but it changes the bass response and to me it channels the "sound" up and out of the body. There are still some rezos being made with the sound wells but mostly they are the open body/post setup. The post method gives the instrument a very different sound than the old dobros with the sound wells.

Got some photos Terry?

I'd be glad to. I've been going to take my 'Horn apart for a cleaning and cone change so I'll do that tonight and take some photos. Post in the morning.

Here you are Liam. One shot facing the neck and one facing the tailpiece. This one has the posts setting on the bottom bracing but I've had others where they were a small pad of wood. You can see the baffle on the forward facing shot. This baffle is aluminum but Scheerhorn has gone to lexan or something like that as have most other builders. The Scheerhorn only has 4 posts while my Meredith has more. This rezo mas finished in November, 1993 and is #33. Pretty early build but an amazing instrument.
terry

Thanks for the Dobro photos Terry. Very interesting. They look like the inards of a machine. Figures, I guess.............

The National Resophonic cones are designed a bit different to the Dobro ones. Requires a different build style. The Dobro cone lip sits up nearly flush with the top of the instrument. The National cone design is inverted compared with the Dobro style. It requires a lip that is recessed down into the body, hence the soundwell. Note that a dobro's baffles do not perform the same function as a National's soundwell.

We have a big lathe and Gordon turns them from a stave construction. Gordon also turns our banjo uke rims from a block rim glue up (like Stelling) Gordon tried a cement tube and a PVC pipe in his first couple. They didn't work out!!!

I'm just finishing my first ukulele build: a solid mahogany, tenor resonator and am wondering if anyone lines their soundwells with a material of any kind such as cork or felt? I saw this recommended in a YT video on tweaking reso ukes, but it seems like it would mute that "twangy," characteristic sound of a resonator. The biscuit sits in direct contact with the top of the metal cone, so would it not be best to also keep the bottom of the metal cone in direct contact with the wooden lip of the soundwell?

My resos benefit from a layer of 1 mm butyl rubber matting (butyl might be a Swedish name for something with a proper English name). I cut out a ring that fits in the bottom of the soundwell to ensure the cone has a contact surface all around. The cones I use aren't 100.0% flat and my plywood soundwells aren't either - there's always some rough part protruding a teensy bit somewhere. The cones have a bit of a recurve so my belief is that it's the part above that that should be able to move up and down, I don't see the cone working all that much downwards to the body to set the skeleton I use in a motion of acoustic significance.

But if you know that everything is flat and the pressure from the strings will keep the whole cone pressed down you shouldn't have to bother.

I shipped one to a dear friend who's a VERY opinionated authority on resonators. He's a purist who scorns the idea of felt or cork. He absolutely loves the sound of it (but I've never told him about the rubber).

Sven

Thanks, Sven: Surprisingly, butyl rubber comes in a myriad of formats - even caulking tubes! I'm envisioning that what you are using is similar to the butyl rubber used in bicycle inner tubes, and would be easily cut with scissors like I have done to make rubber gaskets. If, like you say, the cone's re-curved lip plays no part in the vibrations of the cone producing the sound, then it actually makes more sense to use a felt, cork or butyl liner to insure a smooth seat upon the lip. I'm thinking that while the cone itself reproduces the vibrations from the strings, an improper seating of the cone lip could produce a "buzz" or some other dissonance. (Would I be practicing "safe strumming" if I decide to go with butyl rubber rather than cork or felt?)

1 mm of rubber would be pretty damn safe! I have the dissonance issue you describe in my prototype reso. I keep telling myself to take it apart and fit the rubber. But can I be arsed? Can I hell.

Sven said:

I shipped one to a dear friend who's a VERY opinionated authority on resonators. He's a purist who scorns the idea of felt or cork. He absolutely loves the sound of it (but I've never told him about the rubber).

Sven

Click to expand...

Sven,
Promise not to say a word to UR!
H

I was in Albany WA several years ago now when there was a conference for luthiers and other interested folk.

Steve from Beltona was there talking about his resonator instruments and I recall talking to him about his ukuleles. He did mention that they put a gasket between cone and well in order to dampen the tone on the ukulele. Due to its size and the manner in which he builds his bodies the volume and tone was just so out there and harsh that in needed the treatment. I couldn't say what the material was off the top of my head or even if he had told me. But I would imagine it would have been either some sort of rubber or cork.