Soundwell Modification

Comments

Erik:
larue:
Tail block, where the neck meets the part where the tuning pegs are? Or, where the neck joins the guitar body? Sorry, terms, etc. from this rookie... Cone Opening? To put this additional bracing, where is that?

The "tailblock" is a large reinforcing block glued to the top, back and side of the body where the tailpiece and strapbutton are attached... the tailpiece mounting screw goes directly into this block. Wiithout this tailblock to bear and distribute the 200 lbs of string pull, the area of the top and side where the tailpiece is mounted would almost immediately be crushed and/or cracked.

Because most of the central 'lower bout' area of a reso body's top has to be cut away to provide an opening for installation of the cone, much of the horizontal string tension load has to be borne by the portion of the soundwell near the tailblock, along with the relatively narrow/weak portion of the top's lower bout surrounding the rear half of the cone opening. Unless the soundwell is being replaced with a stout cone support ring, I recommend adding bracing to these areas, particularly on import resos made from thin, weak plywood. I also use bracing in other areas of the body for stiffening and tuning.

Outstanding information, and so well presented that even I could understand your last few posts. Thanks so much Erki, and Geoff for adding to it all.

I may look into only openin up the front of my soundwell. I don't know about additional bracing. And no coverplate changes. And I may just save the money on a tail piece, and use it for my next guitar. Now to FIND a Gold Tone, or Wechter, to listen to!!!! Thanks again, Erik, for all your info and your patience with a green horn!!!! :D

BB54's picture

Hmmm... would this mod be something to consider for a Dobro F-60 roundneck? Since I got a Lebeda (no soundwell) that old original dobro sound has become a little bit boring.

It's a bit different from modding a Regal, this is supposed to be the real thing as it is... only a bit boring.

Or perhaps it's better to get a resonator built that way from start?

Lots of considerations.

/Mikael

Geoff's picture

I mentioned some time ago that I was interested in modifying the JohBro soundwell to a soundpost design. I also posted that I have met up with anopther "DobroNut" who, not only lives in the next suburb, but also makes his own guitars!! (That's a plug for you, John!!)

Well, we have ordered a genuine Dobro cover plate through Ebay and it should be here soon, when it arrives we will then begin the process of removing the old soundwell and installing a tonering and soundposts. I have noted all the advice on adding adequate support internally and I really don't think this will be a problem, we'll add the normall internal stiffeners and posts etc. The thing I am looking for here is an improvement in the sound of the Johbro from 3 improvements,
1. Raising the height of the saddle to the normal Dobro height - the Johbro coverplate is at least 1/4" lower than the Dobro. This should help in loading the cone.
2. Removing the soundwell should improve the tone to a more modern sound.
3. Adding a new tonering (aka cone seat - check Gary Dusina's article if the terminology is confusing) should give a better seat to the cone.

John has graciously offered to loan me one of his guitars during the upgrade process - having played 2 of his guitars so far I may have difficulty returning it!!

Looking forward to documenting the process with words and pictures and if it all turns to $#!t then I can always be John's first customer.

Geoff, I've been quite tardy in posting the results of my recent conversion of my Rogue to an open soundwell design with posts and baffles. I'll try and get to that soon, I've got a few pictures, it's not the prettiest of looks but the sound is amazing for the instrument. It's a $140 Rogue squareneck that sounded loud but very hollow and thin out of the box, but it actually has a slightly deeper body than most of the imports I've seen which I think helps to get the sound I like. I removed the soundwell (really thin plywood with a few flimsy strips of bracing around the top to hold it in place), put a 3-ply tone-ring as described by Erik.

I am about | | this close to ordering another one while they're still this cheap and taking a little more time on it to make it a little prettier. The finish is pretty thin and cheap, so I would probably refinish it while I was at it.

I'll try and get some pic's and sound clips uploaded, probably not this week as I'm out of town for the weekend, but my high speed internet is finally getting hooked up monday so it'll be posted sometime next week.

Thanks again to all for the input, advice and ideas. So far all the theories I've worked off have proved solid in terms of the change in sound that has been produced, and how I can adjust it further. Now I have the itch to build a large-body from scratch someday, that would be awesome.

Jay Jennings's picture

Has anyone tried playing their dobro without the coverplate on. I wonder how the reflected energy from the coverplate would interact with the cone. Would more holes or larger ones giving a higher percentage of the coverplate being open give more volume and a different tone.

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Play it 100 times you know it 1000 times you own it .... Dobropilot the bad luftpostmeister

Guitar MD's picture

Just came across your post - excellent question as sounds reflected back on cone Create additions and cancelations often called comb filtering based on ragged response.  Many coverplates seem designed for cosmetic not acoustic appeal, some for straining pasta perhaps!   For loudspeakers, the openness and acoustic transparency is important to avoiding coloration of the sound.  For resonators, air expect that some of the coloration is by plan.  However, not only would removing the cover plate change the sound as you describe, changing the cover plate should also change the sound depending on hole pattern.

 

pity that no one seemed to pick up on your post as experimenting with holes / ribs / frequency response (bass passes thru more easily than high freq) and doing some playing & measuring would make for a great forum topic!

 

 

The tailpiece question is very curious. I replaced the stock one on my Deneve with an Allen tailpiece, and I thought it gave me a fatter bigger sound, but there is always my old friend Senior Placebo... The thing is, it makes a lot of sense to me that some substantial metal in the tailpiece like Allen does should make a better sound, but why wouldn't Beard or Scheerhorn or whoever go and build something if this were important? It is not rocket science - I'm surprised that we have almost entirely traditional tailpieces even on resos that cost mucho $. 

 

SB's picture

Some of the sound you're hearing could be simply that you've uncovered some of the holes in the faceplate that have been blocked by the old tail piece.

daver's picture

IMHO the most significant change in tone using the Allen tailpiece is the longer length of string between the tailpiece and bridge saddles.   On my 1985 OMI tests, the standard tailpiece distance resulted in about 3 inches, very close to 3 octaves above the open strings.  The Allen tailpiece provided about 4 1/2 inches, close to 2 octaves above the barred 5th fret note.  The longer length also allowed a greater sympathetic volume to the strings behind the saddle.  So the standard tailpiece on the OMI allowed sympathetic vibrations somewhat in tune with open strings, but they were low volume and decayed quickly.  The Allen tailpiece had louder sympathetic vibrations behind the saddle, in a key different than the open strings.  Whether one is better or worse than the other is a matter of personal preference.  My subjective opinion was that the greater sympathetic vibrations with the Allen helped more in the key of C than in G.

Break angle would likely be the next greatest contributor to tone difference, but the Allen tailpiece is adjustable up and down; I tried my best to keep break angle the same.

Probably next is the vibration of the tailpiece itself.  the Allen, being cast, would provide a more solid string mounting and minimal vibration.  There will be some vibration loss and low-order resonance with the sheet metal tailpiece.

I would think the change in coverplate opening would be the least effect, since the tailpiece doesn't really close the coverplate openings anyway; it just changes by a small percentage the resistance to airlow through a small percentage of the total opening.

DISCLAIMER:  All the ramblings above from an inveterate tinkerer, not a resophonic scientist.  No measurements were harmed in the making of this opinion.  Take what you like and leave the rest.  Close cover before striking.

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Daver

Inveterate Tinkerer

MarkinSonoma's picture

So let's get to the bottom line Dave - after installing the Allen tailpiece, did it become a permanent fixture on the '85 OMI Dobro, or did you go back to the stock tailpiece at some point?  

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