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.