Hi All...

For a long time I have wanted to build a resonator based string instrument, but I've put it off for a long time because of a poor success rate on prototype builds. I had lots of excuses. Chief among them was the difficulty of cutting an accurate 6" diameter hole in the sound board to accept the tin can resonator where the rim of the can (used to hold the resonator in place) is just 1mm or so wide. Even when I was successful at mounting it, the ugly cut meant there were slight gaps you could see light through. But, that was before I discovered the my ideal resonator -- the round lid of an Eu Long brand cookie tin. 

In this photo, you can see that this cookie tin actually has two lids. It's the round inner lid that makes such a nice resonator because it has a 5mm wide lip, wide enough to hide the ugliness of my hand-cut resonator holes.

[I suppose other parts of this cookie tin could also be used to make good resonators, but cutting them and mounting them in the sound box is another adventure I haven't taken yet.]

In the next photo we can see how much wider the rim (lip) of the Eu Long lid is compared to your typical cut-down can resonator.

Now, I realize most of you won't be able to find any Eu Long cookie tins, but the idea you want to keep in mind when looking for a good resonator is a wide rim (lip) to make mounting them easier and cleaner looking. No doubt some of you have built resonator CBGs using other items and other mounting techniques, something that I hope you will share in this discussion. As I develop new methods I also will add them here.

The following photo shows the above cut down cookie tin mounted in a sound box. You can see it's not too pretty even if you can imagine the sound box painted black.

You can see the gap between the cookie tin resonator and the soundboard (see the two white areas).

If the top rim (lip) of the tin were 5 times as wide, then it would cover up the in- accuracies of my hand-cut resonator hole.

The Eu Long lid is 5 times as wide, and so would cover these gaps up.

Of course, if you have a big budget and are handy at making jigs, you could probably buy a jig-saw or a band saw and cut out a pretty accurate hole in your sound board. But, that's beyond the scope of this article.

Cutting the Resonator Hole

(Section not written yet)

I need photos of this process...

Will build another box, photograph the process and add that material here.

Stiffening the Soundboard

Another consideration you have to make when building the sound box for a resonator CBG is how stiff the sound board is. The idea (as I have been told, but have not independently verified) is that if you use a very thin sound board (as you may be in the habit of doing for acoustic instruments), then you may experience a problem where the flexible soundboard steals too much of the vibrational energy from the resonator "cone" and this reduces the output of the metal resonator. So, I was told that I should use thicker wood for the sound board to prevent this from happening.

But, using a thicker board for a sound board makes cutting the hole for the resonator that much harder to do with hand tools. So, instead I decided to simply re-enforce the bottom side of my sound boards. In the following photo, you can see how I've re-enforce the sound board by gluing on additional wood.

The additional bracing was made using 5mm thick sapeli trim wood. The pieces were hand cut to fit and glued in one at a time. On my second "Reso-Box" I cut out 4 triangles to fill in the corner areas a bit better. With this additional bracing, the wood around the resonator is effectively 7mm thick (including the 2mm thick sound board).

Other Advice?

Building the sound box is otherwise identical to building a sound box for an acoustic box guitar. Cut the wood for the sides of your box, glue them together to form your box frame, using corner posts to strengthen the corner joints of your box frame. Then, rough cut the sound board, cut the two sound holes and then glue the sound board to the box frame. When dry, file and sand off the excess material around the sides of the sound board. Next, add any additional internal support you will need to secure the neck in place and perhaps to backup the tail-piece. Once the internal bracing is complete, connect your neck to the sound box and secure it in place (glue, wood screws, whatever), Then rough cut your back board and glue it on to the back side of your box frame. Once the back board is dry, use a file and sand paper to remove the excess material. Then sand the box with finer grain sand paper to get the box as smooth as you want, then finish the box the way you like, typically with something like an oil based stain and polyurethane, or whatever other finish you want to use.

With my brass/gold colored Eu Long cookie tin lid, instead of giving the box my standard wood grain treatment, I spray painted it black. I don't really like spray painting because it smells up the place (I do it outside, but still it's not great for the air - it's already polluted enough). I think in the future I will try to mix black poster paint with the clear water based "poly-urethane" finish I use to paint-on a black finish that can be absorbed into the wood for a strong, water resistant finish.

So, here's a photo of my first finished resonator instrument... It's a 4-String "Reso-Box Banjo".

The discussion of how I built the banjo-style neck is a discussion I've yet to write; but when I do, I will post it in the banjo discussion group called "Banjo Players Unite!" as that's where I post most my banjo related articles.

I have completed 2 more such "Reso-Box" instruments, which I'll document when I have time to take and upload the photos and write some more. Both are 3-String diatonically fretted stick dulcimers (pretty much my standard instrument), but one is built with much larger (and thicker) sound box.

So, stay tuned...

-Rand.

Views: 2349

Replies to This Discussion

Rand -

Thanks for posting this. The detailed info and pics are great! How does it sound? And, I've love to see your ideas on how to build the banjo-style neck.  That's something I plan to tackle myself. I've built 3 & 4 string CBG's, a four string bass CBG, and concert & tenor ukes, and dulcimers, so the next on my list is a banjo. Thanks again. Will

Thanks, Will.

I have uploaded additional build photos, including some of the banjo style neck which you can look at to get some ideas. Hopefully I'll get around to writing it up in the next week or two. I have already added a write-up of how I did the 5th string tuner (actually the 4th string tuner on my build).

My 4-stringer Reso-Box Banjo sound pretty good, a mix of the metallic sound of a cookie tin banjo with the warmer tones of a wood resonator box, with the metallic sound dominating. It is also quite loud, probably the loudest acoustic instrument I've made, though some cookie tin instruments may rival it. It definitely beats out all the wood only sound boxes. In addition, I used color coded frets (gold for the "natural" frets, and silver for the "accidental" frets), so I can play my old diatonic dulcimer songs on it as long as there's a descent amount of light where I can distinguish fret colors (why don't they have black fret wire?).

-Rand.

Rand,

There is a beautiful classic look to that build with the Eu Long Lid, I really like the gold lid with the understated black box.I think you should build a simple three string with this same basic design, without the bolt nut, and with a shaped headstock with black tuners.If you don't build it I will,You could end up with something really special

Hi Michael,

Thanks for the complement and suggestions. I actually have pretty much the same build for my second "Reso-Box" instrument, configured with a 3-string diatonically fretted neck. It uses the same "solid core with side slats neck" that I use on my "paddle box dulcimers" with the same slotted headstock, and yes, the same bolt for a neck. I guess I really need to develop a better solution for my nut to replace the bolt if I ever want my instruments to look professionally made. Black tuners. That sounds like a good idea. I guess it's back to Taobao.com to find some. Again, thanks for your feedback. It's both helpful and encouraging.

-Rand.

Same bolt for a nut (not for a neck)

Now where can I get a Eu Long Lid? That body design with this headstock.Forget the Guinness logo !k you've got me thinking

Hi Michael.

If you want me to send you a Eu Long lid for use as a resonator, why not e-mail me off-line to get the details worked out (price, address and postage)? I sent you an invitation to become one of my CBN friends, so you can use CBN's email facility to contact me. I think I can give you the special deal rate with as much good will you have garnered in the past by contributing to my CBN discussions. I just really don't want to get into the Eu Long resonator distribution business (would have to eat too many cookies) ;-)

P.S. That a very nice headstock design, with very graceful lines. I like it.

-Rand.

Great article, and contributions, it's good information, especially for me the advice about the vibrations of the soundboard taking away From the reso.
As this is my next planned project. Can you tell me how it sounds please.
Looks great, and hope you enjoy playing it.
Phil Hale.

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