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Jun 30, 2021 - 5:06:15 PM
11 posts since 5/28/2020

While procrastinating on writing my dissertation, I was browsing online and stumbled onto the concept of adding a resonator to an open back banjo, through something like the (wildly expensive) Deering conversion kit, or the (much more reasonable) Sosebee EZ Resonator...I see it seems as though the latter is no longer being made, does anyone know if it's still available anywhere? And if not, how might I go about building something similar? From what I can see in the pictures, it appears to basically just be a wooden plate with some kind of clamp that is presumably meant to grab on to the coordinator rod. My banjo is a Deering Goodtime with a metal coordinating rod, so it seems like if I could copy the EZ resonator design as closely as possible, it should work. I just don't really know what kind of parts I would need to recreate it.

Jun 30, 2021 - 6:39:32 PM

161 posts since 12/7/2007

I have a couple of flush mounted resonators by Zach Hoyt, modeled after the Sosebee EZ Resonator, with attached/added pie shaped panels. (Pictures are on my homepage.) As you indicated, the Sosebee piece was, basically, a plywood disc - with four chair shaped wooden feet screwed to it, that located the disc against the banjo rim. The clamp that attached it to the banjo can probably be improvised in several ways. But I chose to use a Gold Tone resonator mounting bracket, available on their website.

Edited by - srrobertsiii on 06/30/2021 18:48:36

Jun 30, 2021 - 6:47:41 PM

11 posts since 5/28/2020

Do you know if Gold Tone still carries this clamp? I can't seem to find it anywhere on their website.

Jun 30, 2021 - 6:50:03 PM

161 posts since 12/7/2007

I think so. I went to their website, and, under parts/accessories, did a search for it. It’s called a resonator mounting bracket. (I checked the Gold Tone Music Group website.)

Edited by - srrobertsiii on 06/30/2021 19:02:26

Jun 30, 2021 - 7:02:45 PM
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58056 posts since 12/14/2005

Fellow I've seen a few time just got an aluminum cake pan, notched it where needed.
Seemed to work well for him!

I've used aluminum pot lids, even stainless steel.

Jun 30, 2021 - 8:30:19 PM
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1195 posts since 1/9/2012
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I use one of these bits of cabinet hardware to grab onto the co-rod. The full apparatus involves a plywood disk cut to size; a piece of threaded rod (which can be just a long screw with its head cut off); a nut that you can scootch into the cabinet clasp that fits the threads; and a wing nut for the outside to get it to tension. You need some sort of spacers (glued to the plywood?) to lift it off the rim-- about 1/4". Three or four would do. All very old school -- no rare earth magnets. I made my first one to attach a "synthetic belly" to a research-grade Goodtime. (The funny thing is that this is not a joke.)


Jul 1, 2021 - 3:29:13 AM
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Players Union Member

Helix

USA

14477 posts since 8/30/2006

Or magnet mount .

This is a solution for many vintage owners who don't want to mar a banjo with screw holes.


Jul 1, 2021 - 3:21:36 PM

1195 posts since 1/9/2012
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For something more permanent, i.e., that doesn't simply pop on and off, I used a pair of "tube straps," more or less like the one in the picture.




Jul 1, 2021 - 5:18:30 PM
Players Union Member

Helix

USA

14477 posts since 8/30/2006

Sounds cool, David, why don't you show us some more of how you did it.

That's what he's asking for.

Jul 1, 2021 - 8:35:54 PM

11 posts since 5/28/2020

So, does the "grabber" part of the clasp latch onto the rod directly? Or do you somehow mount the "grab-ee" part (the piece that looks like its meant to be attached to the inside to the cupboard, so the door catches on it when closed) onto the rod, so the other part can grab it?
 
quote:
Originally posted by davidppp

I use one of these bits of cabinet hardware to grab onto the co-rod. The full apparatus involves a plywood disk cut to size; a piece of threaded rod (which can be just a long screw with its head cut off); a nut that you can scootch into the cabinet clasp that fits the threads; and a wing nut for the outside to get it to tension. You need some sort of spacers (glued to the plywood?) to lift it off the rim-- about 1/4". Three or four would do. All very old school -- no rare earth magnets. I made my first one to attach a "synthetic belly" to a research-grade Goodtime. (The funny thing is that this is not a joke.)


Jul 1, 2021 - 8:48:12 PM

11 posts since 5/28/2020

I was able to find it under that name. It looks like probably the simplest solution...
Am I correct in understanding that, once attached to the rod, the mounting bracket protrudes out in the back, so if I wanted to convert the banjo back to open back, I couldn't just leave it there and take the plate off, I'd have to remove the mounting bracket in order to avoid being poked while playing?
 
quote:
Originally posted by srrobertsiii

I think so. I went to their website, and, under parts/accessories, did a search for it. It’s called a resonator mounting bracket. (I checked the Gold Tone Music Group website.)


Jul 1, 2021 - 9:34:07 PM
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1195 posts since 1/9/2012
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Helix , LittleBoxes :

These days I can't do better than the old photo I already posted. At the start of the pandemic, I brought home much of my well-organized banjo "lab" from work so that I could continue working. But there's no regular space for it. It's been packed, unpacked, packed, moved, etc. so many times that there's a lot I can't find.

The "grabber" snaps onto the co-rod. In this photo, you're looking at the side that goes the inside the pot. The actual grabber used is the one in the middle of the disk. The second one in the photo shows another such attacher with a longer threaded rod. The rod length depends on the distance to the co-rod and the thickness of the back plate. The "synthetic belly" was designed to absorb and reflect sound more or less as if someone were playing the banjo. (That's the orange thing with closed cell foam, cork, and Hawaiian shirt.) It needed the longer rod.


 

Jul 2, 2021 - 2:42:25 AM

161 posts since 12/7/2007

In response to Little Boxes’ question about the Gold Tone bracket’s being permanently mounted on the banjo: I mounted the bracket on my Deering/Vega #2, which has two coordinator rods. I’ve not found that it protrudes unduly, or makes it uncomfortable to play the banjo as an open back. (The (longer) screw I use to attach the disc remains with the disc when it’s not in use.) Still, I can see where another might find the bracket’s presence bothersome, and why an arrangement that leaves the mounting hardware attached to the disc would be preferable.

Jul 2, 2021 - 3:49:56 AM
Players Union Member

Helix

USA

14477 posts since 8/30/2006

David, you are showing two internal resonators with a copper tubing clamp, just curious how you did those

Jul 2, 2021 - 10:15:03 AM
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13861 posts since 6/29/2005

A couple of years back, I converted a 14" pot to a 6-string banjo for a BHO member.

Originally the idea was just to make it openback, but then the idea of a trapdoor banjo came up—I don't know if you are familiar with the old Gibson trapdoor banjos, but they predated resonators as we know them, and had a flat hinged resonator, part of which was screwed to the rim and the hinged part, clipped to the rim rods, much like what we are talking about here, could swing open for whatever reason.  Because it was flat and completely covered the bottom of the pot, they had a sound-hole, like a mandolin.

Here's a picture of an old Gibson one.

I talked with David Politzer about this and he gave me a lot of info about various forms of internal and flush-mount resonators.

I made two prototypes, one with a hole in the middle, like a guitar sound-hole (this was a 14" pot), and the other, the classic internal resonator with the inner wall.  Here are the prototypes—fairly crude, but I did some finish and binding on them to make them more presentable:

Here's what they looked like installed—they just screwed on with 8 screws, pretty simple, and I thought you could put threaded inserts in the bottom of the rim to facilitate installation/removal, use better screws, and make it look a little less crude than screw-holes:

Our take on them was that the one with the sound hole sounded really good, and I thought that would work for regular banjos (but never pursued it on the grounds that it was too strange and would never be saleable).

The true internal resonator, which has a following, but was not the kind of sound my client was after—I would describe the sound as an archtop guitar vs a flat-top, and in the end (I think) he just left it openback—a fun experiment, but water over the dam.

In terms of this thread, I think you could easily make a flat plate with a hole in it that would screw onto the back of the rim, and it would work great—you'd have to experiment with the size and position of the hole, but it would work.

The way I thought about developing it was to have some spring clips, or inner sleeve that would fit down into the rim holding the resonator in place in a friction fit with no actual fasteners.

Edited by - Ken LeVan on 07/02/2021 10:22:33

Jul 2, 2021 - 1:55:39 PM

1195 posts since 1/9/2012
Online Now

quote:
Originally posted by Helix

David, you are showing two internal resonators with a copper tubing clamp, just curious how you did those


(See the photos.)  The cylindrical part is a slice of a Keller drum shell, glued to fancy, thin plywood, cut with a coping saw.  If you want to know more, see https://www.its.caltech.edu/~politzer/resonator-resonator/resonator-resonator.pdf .  As with almost all my stuff, there are sound files there, too.

I've spent a lifetime regretting not buying an A.E. Smith Shelburne when I was shopping for my first professionally made instrument -- occasioned by securing my first real job.  I opted for their Maple Leaf, certainly a fine banjo.  You'll find lots about internal resonators at https://www.its.caltech.edu/~politzer/ , especially the JUNE 2016 entry, but there's also AUGUST 2018, where I describe C.E. Dobson's patented internal resonator design, which predated Bacon's by 18 years.




Jul 2, 2021 - 4:11:57 PM

1195 posts since 1/9/2012
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Ken LeVan : Sometimes there's something new under the sun -- but not that often. Pictured is an English flush fret that my wife bought for me -- because I had a good friend with the same name as the original luthier/seller. At the very least, closing up the back a bit enhances the bass response by lowering the Helmholtz resonance. For that specific effect, the detailed geometry doesn't matter. It's only the area of escape route.




Jul 2, 2021 - 5:26:51 PM

13861 posts since 6/29/2005

quote:
Originally posted by davidppp

Ken LeVan : Sometimes there's something new under the sun -- but not that often. Pictured is an English flush fret that my wife bought for me -- because I had a good friend with the same name as the original luthier/seller. At the very least, closing up the back a bit enhances the bass response by lowering the Helmholtz resonance. For that specific effect, the detailed geometry doesn't matter. It's only the area of escape route.


If I understand, it's the size of the opening that is important (?)  I have heard that discussed with guitars.

Jul 2, 2021 - 5:58:45 PM

1195 posts since 1/9/2012
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Originally posted by Ken LeVan

If I understand, it's the size of the opening that is important (?)  I have heard that discussed with guitars.


To a first approximation, for the Helmholtz resonance business, it's the total area of the hole or holes, with the resulting frequency being proportional to the square root of the area.  That's how an ocarina works.  The hole locations and number don't matter.  Some Ovation guitars have several small holes.  If you blow across the top of a violin or ukulele (it's harder to hear with a guitar), the raspy beer-bottle note you hear is the Helmholtz frequency.  The body volume and hole area jointly determine that frequency, and proper design typically puts it near the lowest note you want to play.

But what is a single feature in terms of lutherie can have several roles in terms of physics and sound.  On a guitar or violin, the intensity of the sound inside depends strongly on location and frequency.  Air rushes in and out at a sound hole.  Even though the air goes back in, the sound comes out.  In particular, that in-and-out air is a more efficient radiator of sound than the same area were it solid sound board.  Hence, the hole location matters.

The hole shape can matter a lot, too.  It can effect the resonances of the soundboard itself.  Violin f-holes are an extreme example.  Also, those f-holes generate more turbulence that would the same area circle.  That broadens the frequency range over which the Helmholtz resonance is effective.

Jul 3, 2021 - 5:23:55 AM
Players Union Member

Helix

USA

14477 posts since 8/30/2006

That's what I wanted to know.

Jul 3, 2021 - 5:41:28 AM

13861 posts since 6/29/2005

quote:
Originally posted by davidppp
 
Originally posted by Ken LeVan

If I understand, it's the size of the opening that is important (?)  I have heard that discussed with guitars.


To a first approximation, for the Helmholtz resonance business, it's the total area of the hole or holes, with the resulting frequency being proportional to the square root of the area.  That's how an ocarina works.  The hole locations and number don't matter.  Some Ovation guitars have several small holes.  If you blow across the top of a violin or ukulele (it's harder to hear with a guitar), the raspy beer-bottle note you hear is the Helmholtz frequency.  The body volume and hole area jointly determine that frequency, and proper design typically puts it near the lowest note you want to play.

But what is a single feature in terms of lutherie can have several roles in terms of physics and sound.  On a guitar or violin, the intensity of the sound inside depends strongly on location and frequency.  Air rushes in and out at a sound hole.  Even though the air goes back in, the sound comes out.  In particular, that in-and-out air is a more efficient radiator of sound than the same area were it solid sound board.  Hence, the hole location matters.

The hole shape can matter a lot, too.  It can effect the resonances of the soundboard itself.  Violin f-holes are an extreme example.  Also, those f-holes generate more turbulence that would the same area circle.  That broadens the frequency range over which the Helmholtz resonance is effective.


That's interesting—Some (mostly archtop) guitar builders now put holes in the sides of the guitar on the upper bout, and I'd imagine they have experimented with how to tune the opening.

There is a "conventional wisdom"(maybe mythology?) about the f-holes in violins that says that the early builders believed that the longer grains of the spruce bellies produced lower tones and the shorter grains produced higher ones so the shape of the violin was designed to produce a balance—the f-hole shape, while providing a sound-hole, precluded any grains in the spruce from running full-length except for the center section that the bridge sat on.

All the early makers, Sradivarius, Guarnerius, Amati, Bergonzi, etc etc had different f-hole shapes.

As far as I know, little has been done exploring the holes in flat top guitar tops. A couple of guitar makers use triangular holes like Pete Seeger's 12-string.  In 1935 Gibson changed the size of their sound hole from 3 1/2" to 4", and 4" seems to be the standard now with Gibson and Martin. Clarence White's D-18 with the extra large hole is legendary, but I suppose that's because of Clarence White's playing, not the guitar, because builders didn't start to make larger sound holes.

It would be a very interesting experiment to make a flat banjo resonator with a hole, and keep enlarging the hole to see what happens, but as I said earlier, I don't think it's an idea who's market acceptance time has yet come in this century.

Edited by - Ken LeVan on 07/03/2021 05:43:59

Jul 3, 2021 - 5:51:26 AM
Players Union Member

Helix

USA

14477 posts since 8/30/2006

I hope the drift has answered your questions.

Jul 3, 2021 - 7:32:28 AM
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13861 posts since 6/29/2005

quote:
Originally posted by LittleBoxes

While procrastinating on writing my dissertation, I was browsing online and stumbled onto the concept of adding a resonator to an open back banjo, through something like the (wildly expensive) Deering conversion kit, or the (much more reasonable) Sosebee EZ Resonator...I see it seems as though the latter is no longer being made, does anyone know if it's still available anywhere? And if not, how might I go about building something similar? From what I can see in the pictures, it appears to basically just be a wooden plate with some kind of clamp that is presumably meant to grab on to the coordinator rod. My banjo is a Deering Goodtime with a metal coordinating rod, so it seems like if I could copy the EZ resonator design as closely as possible, it should work. I just don't really know what kind of parts I would need to recreate it.


You are right that the Sosebee one is a flat plate with a center attachment to the rim rod.   David Politzer's spring roller cabinet latch is a simple way to do it.

Dan Drabek has also worked out an attachment using a different kind of latch, and you can probably find that in the archive, or maybe Dan will post a picture.

Either way, you probably want to space the resonator out from the rim by some extension method

I think Dan uses the ball-type latch (left hand picture), which would attach to the bottom of the resonator with some kind of extension to make it reach the rim rod.  The tricky part of the roller type is that the mounting bracket is on the side instead of the bottom but you could epoxy some mounting thing onto it, which could also double as the extension.

I think the key is how you would mount the catch onto the resonator and how you would keep the resonator from rocking if there's a space.

Jul 3, 2021 - 1:57:50 PM
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11 posts since 5/28/2020

It sounds to me like, given that I'm currently pretty lacking in both free time and experience with these kinds of projects, the Gold Tone mount with a wooden plate (using a pre-existing wood dinner plate, as I saw someone posted on an older thread on this topic) would probably be the simplest option...

To drill a hole in the plate, is there anything in particular I should do to make sure it's a clean hole and I don't somehow crack or otherwise damage the plate?

And, since I don't really have easy access to a saw to cut the smaller wood blocks, could it possibly work to use something like these nylon spacers, glued to the plate, even if they're not as pretty?

homedepot.com/p/0-325-in-x-27-...204276564

Or stick-on rubber furniture pads?

amazon.com/AmazonBasics-Rubber...581&psc=1

Jul 3, 2021 - 9:35:59 PM

PaulRF

Australia

3228 posts since 2/1/2012
Online Now

quote:
Originally posted by Ken LeVan

A couple of years back, I converted a 14" pot to a 6-string banjo for a BHO member.

Originally the idea was just to make it openback, but then the idea of a trapdoor banjo came up—I don't know if you are familiar with the old Gibson trapdoor banjos, but they predated resonators as we know them, and had a flat hinged resonator, part of which was screwed to the rim and the hinged part, clipped to the rim rods, much like what we are talking about here, could swing open for whatever reason.  Because it was flat and completely covered the bottom of the pot, they had a sound-hole, like a mandolin.

Here's a picture of an old Gibson one.

I talked with David Politzer about this and he gave me a lot of info about various forms of internal and flush-mount resonators.

I made two prototypes, one with a hole in the middle, like a guitar sound-hole (this was a 14" pot), and the other, the classic internal resonator with the inner wall.  Here are the prototypes—fairly crude, but I did some finish and binding on them to make them more presentable:

Here's what they looked like installed—they just screwed on with 8 screws, pretty simple, and I thought you could put threaded inserts in the bottom of the rim to facilitate installation/removal, use better screws, and make it look a little less crude than screw-holes:

Our take on them was that the one with the sound hole sounded really good, and I thought that would work for regular banjos (but never pursued it on the grounds that it was too strange and would never be saleable).

The true internal resonator, which has a following, but was not the kind of sound my client was after—I would describe the sound as an archtop guitar vs a flat-top, and in the end (I think) he just left it openback—a fun experiment, but water over the dam.

In terms of this thread, I think you could easily make a flat plate with a hole in it that would screw onto the back of the rim, and it would work great—you'd have to experiment with the size and position of the hole, but it would work.

The way I thought about developing it was to have some spring clips, or inner sleeve that would fit down into the rim holding the resonator in place in a friction fit with no actual fasteners.


Wow.  Once again some amazing work Ken.  Any sound files?

p.s, I waited a while to post this question as to give the OP time to get his query answered.

Paul

Jul 4, 2021 - 5:02:58 AM
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13861 posts since 6/29/2005

quote:
Originally posted by PaulRF
quote:
...

In terms of this thread, I think you could easily make a flat plate with a hole in it that would screw onto the back of the rim, and it would work great—you'd have to experiment with the size and position of the hole, but it would work.

The way I thought about developing it was to have some spring clips, or inner sleeve that would fit down into the rim holding the resonator in place in a friction fit with no actual fasteners.


Wow.  Once again some amazing work Ken.  Any sound files?

p.s, I waited a while to post this question as to give the OP time to get his query answered.

Paul


I did not make any sound files, as this was a 6-string, and I am no longer a good enough guitar player to make a convincing presentation of it—I wish I had been able to.

Apropos of your question, the OP, and the subject at hand—not to be a "drifter", but I would love to hear a comparison of a banjo with one of these flat plate resonators (regardless of the attachment) and an openback. Maybe David Politzer will post files of some of his resonator experiments.

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