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Dobson Tone Ring - Flat or Beveled Rim?

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Nov 19, 2019 - 6:20:48 AM
84 posts since 3/19/2018

In past posts I've seen that people install Dobsons on rims that are either (i) resting on the ledge of the rabbet... the Dobson fits snugly against the rim and sits on top of the bottom of the rabbet... the height of the rim is such that the curved top of the Dobson never touches the flat inside part of the rim (or else it would buzz or mute); or (ii) resting on the beveled top of the rim and not connecting with the ledge of the rabbet, as shown in the link below. The first is certainly easier and sounds great to me while the second method would seem to mute the Dobson ring, but i was curious what other people do.

hangoutstorage.com/banjohangou...1cL7MvFEo

Edited by - QuailCreekBanjos on 11/19/2019 06:22:52

Nov 19, 2019 - 6:42:40 AM
Players Union Member

rudy

USA

14651 posts since 3/27/2004

The Dobson ring was designed to rest on the rolled portion of a metal spun rim.  The half-dozen I've used were used in conjunction with a rolled brass tone hoop under the edge of the Dobson ring, similar to the original patent.  Don't get too hung up about any effect that the Dobson has by resting it directly on the skirt portion of the ring.  The head stretches over the outer portion of the ring and effectively mutes that portion of the ring.

The Dobson ring adds a tiny bit of "finish" at the end of the note, but it also effectively reduces the vibrating portion of the head membrane.  The reduced surface area has as much to do with the effect on tone of the Dobson ring as it's wider footprint or downturned bell edge.  Tone ring systems are cyclic in nature, and the Dobson ring has somewhat subsided as the "flavor of the day" tone ring.  In past years the tubaphone ring was the "must have" and it has also seen a reduction in popularity.

Original Dobson patent drawing (snip):

Original Dobson patent drawing (snip)

Edited by - rudy on 11/19/2019 06:46:59

Nov 19, 2019 - 7:21:52 AM

487 posts since 7/10/2012

I have a Brooks 12" spunover rim with a Dobson tonering in it. I bought the banjo used and sight unseen and had to install a new head when it arrived. I was surprised to see that the spunover nickle silver ended at the top of the rim, rather than rolled over a brass rod, and that the Dobson ring was installed without a rolled brass rod as well. The tonering was simply slid down over the outside of the spunover rim, resting on the very edge of the silverspun part and rising over the wood part. I can say that there was no buzzing or anything like that, the banjo sounded good to my ear set up like that, but I was curious, so I set it up with a rolled brass rod between the top of the rim and the bottom of the Dobson. The tone improved dramatically to my ear, though I'm sure the new head contributed to the improvement as well.

Also note that Brooks is now making a version of his Dobson banjos where the spunover nickle silver extends beyond the top of the wood rim straight up about 1/8" or so and the tonering sits on that skip of nickle with no rolled brass ring under it nor touching the wood rim at all. He sounds pleased with the result, though I've not heard it personally.

Nov 19, 2019 - 8:46:48 AM
Players Union Member

rudy

USA

14651 posts since 3/27/2004

quote:
Originally posted by dpgetman

I have a Brooks 12" spunover rim with a Dobson tonering in it. I bought the banjo used and sight unseen and had to install a new head when it arrived. I was surprised to see that the spunover nickle silver ended at the top of the rim, rather than rolled over a brass rod, and that the Dobson ring was installed without a rolled brass rod as well. The tonering was simply slid down over the outside of the spunover rim, resting on the very edge of the silverspun part and rising over the wood part. I can say that there was no buzzing or anything like that, the banjo sounded good to my ear set up like that, but I was curious, so I set it up with a rolled brass rod between the top of the rim and the bottom of the Dobson. The tone improved dramatically to my ear, though I'm sure the new head contributed to the improvement as well.

Also note that Brooks is now making a version of his Dobson banjos where the spunover nickle silver extends beyond the top of the wood rim straight up about 1/8" or so and the tonering sits on that skip of nickle with no rolled brass ring under it nor touching the wood rim at all. He sounds pleased with the result, though I've not heard it personally.


The last thing I saw about Brook's clad rims he was hand hammering the rolled lip, which is a tremendous amount of work.  Very controllable, but time and labor consuming.  I don't see any reason why simply allowing the inner curved portion to bear upon the nickel shell wouldn't work just fine.  Since the bearing edge is obscured there's no reason to do all that work to roll the edge under the Dobson ring.

I wouldn't personally seat the Dobson skirt over the rim and bearing on a thin portion of the outer rim layer.  It concentrates all of the force from the head tension down on that small lip, and there's no tonal advantage to not setting the tone ring against something more substantial.  The outer metal cladding of a "spun over" is certainly robust enough to hold the force of head tensioning hardware even if it is simply cut flush with the upper rim edge.

Edited by - rudy on 11/19/2019 08:50:14

Nov 19, 2019 - 12:24:54 PM

84 posts since 3/19/2018

Hmmm. Does anyone know what the benefit is of a flat rim top vs a beveled rim?  I'm going to try sitting the Dobson ring on top of the a 1/4" round solid brass bar that I'll roll into a ring using my harbor freight roller.  Hopefully it sounds okay so I don't have to remount it -- also changes my dimensions a smidge but not a big deal.

Edited by - QuailCreekBanjos on 11/19/2019 12:26:55

Nov 19, 2019 - 4:20 PM

673 posts since 6/11/2003

I use a 1/4" brass rolled ring on top of the wood rim (under the Dobson ring).

Nov 19, 2019 - 4:38:13 PM

50 posts since 12/9/2018
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Interesting info here.
My Rickard Maple Ridge and the 11" and 12" Pisgah Dobsons I owned were ring only with no additional brass hoop underneath. The Pisgahs used a rabbet on their standard three ply wood rim,and on the Rickard, the ring just slips over the thin, laminated drum shell based rim.
All three have that Dobson sound but are different enough to tell the difference between them.
Guessing the addition of the rolled brass hoop on a standard wood rim is to approximate the metal to metal contact that you get with spunover rim and a Dobson ring?

Nov 19, 2019 - 6:20:32 PM
Players Union Member

rudy

USA

14651 posts since 3/27/2004

quote:
Originally posted by gratefulbiker

Interesting info here.
My Rickard Maple Ridge and the 11" and 12" Pisgah Dobsons I owned were ring only with no additional brass hoop underneath. The Pisgahs used a rabbet on their standard three ply wood rim,and on the Rickard, the ring just slips over the thin, laminated drum shell based rim.
All three have that Dobson sound but are different enough to tell the difference between them.
Guessing the addition of the rolled brass hoop on a standard wood rim is to approximate the metal to metal contact that you get with spunover rim and a Dobson ring?


I'd say that's a good possibility.  All the info I could find when I did my first Dobson (4 or 5 years ago?) indicated that most had the brass hoop under the spun portion of the tone ring.

Nov 20, 2019 - 6:31:26 AM

487 posts since 7/10/2012

quote:
Originally posted by QuailCreekBanjos

Hmmm. Does anyone know what the benefit is of a flat rim top vs a beveled rim?  I'm going to try sitting the Dobson ring on top of the a 1/4" round solid brass bar that I'll roll into a ring using my harbor freight roller.  Hopefully it sounds okay so I don't have to remount it -- also changes my dimensions a smidge but not a big deal.


I would suppose that a beveled rim would be similar to the bevel of a "woodie" banjo in terms of providing a narrower point of connection between the rim and the head than a flat topped rim would.  In this case, the narrow connection includes the Dobson ring resting between the rim and the head.  

Seems like there are a handful of possibilities for mounting a Dobson here that all sound interesting:

1) Nickel spunover a brass rod with Dobson slid down over the nickel and resting on the rod/nickel/rim combo

2) Nickel spunover that ends at the top of a flat topped wood rim with Dobson slid down over and resting on the outer edge of the rim

3) Nickel spunover that ends at the top of a flat topped wood rim topped with a brass rod with Dobson slid down over and resting on the brass rod

4) Nickel spunover extending above the rim with Dobson slid down over and resting on the thin edge of the nickel

5) Wood rim with a flat top and Dobson slid over a rabbet and resting on the edge of the wood rim

6) Wood rim with a beveled edge and Dobson slid over a rabbet and resting along the curve of the bevel

7) Wood rim with a flat top and rolled brass rod with Dobson slid over a rabbet and resting on the brass rod

Nov 20, 2019 - 10:22:39 AM
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3632 posts since 5/12/2010

I have installed two Dobson tone rings recently on banjos using 12" Turkish hand drum shells for rims.

These rims are about 5/16" thick and the Dobson fit over the outside of the rim. I just rounded the top edge and slipped the ring over the rim without anything between the wood and the Dobson.

One of these is a banjo I described in another thread, but the the link below will give an idea of how this setup with a Dobson sounds. Should be obvious which of the two banjos has the Dobson, and the other banjo has a two piece tone ring similar to a Fairbanks Electric.

https://drive.google.com/drive/folders/1tfTRuZoFtJsCZirt5X5kAdga87_Gu_RO
 

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