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  #1  
Old 02-20-2022, 11:41 AM
Robin, Wales Robin, Wales is offline
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Default Bridge Fitting - What is perfect?

What's the difference, acoustic tone wise, between getting a perfect fit of the two bridge feet on a rosewood bridge and having small gaps?
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I'm learning to flatpick and fingerpick guitar to accompany songs.

I've played and studied traditional noter/drone mountain dulcimer for many years. And I used to play dobro in a bluegrass band.



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Old 02-20-2022, 01:48 PM
RLetson RLetson is offline
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I can't quantify it, but two luthiers whose opinions (and work) I trust take pains to get a precise fit.
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Old 02-20-2022, 07:32 PM
Mandobart Mandobart is offline
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Most of my instruments are archtop (13 in all counting mandos, fiddles and guitars). I have a few different bridge fitting jigs I use to get as close to perfect fit as I can. I can't quantify/correlate a % imperfect fit to a % loss of sound transmission. But it's worth it to me to do my best to get a good fit.

One issue is the slight deflection in both the bridge base and the soundboard that occurs when you tune up to pitch vs the zero deflection present when using the jig, sandpaper and soundboard to fit the bridge to the unstrung soundboard. I don't know a good way around that besides trial and mistrial and multiple fitting, tuneup, measure gap, slack strings, refit, etc.
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Old 02-21-2022, 08:07 PM
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ArchtopLover ArchtopLover is offline
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Default A perfect fit is critical for the best tone from any archtop guitar.

Use a bridge foot profiling tool like this:

https://www.stewmac.com/luthier-tool...e-fitting-jig/

I collect and own a room full of vintage archtops and they have all needed to have their bridge feet (or foot, if it's a one-toe foot bridge, like most Gibson's), profiled to perfectly match the soundboard with no gaps in order to extract the most volume, tone and single note clarity in their voices.

In my experience with repairing and restoring archtop guitars, I have found that any gap below the bridge foot will allow the soundboard to make intermittent contact with the bridge foot as it vibrates. Most often this defect can be heard as an extraneous buzz or rattle in the overall tone of the guitar as it is played. Many times, the player may think the buzz is a bad string, or a badly slotted nut, or a fret buzz; since this is the sound that a poorly fitted bridge will sound like. So, getting the best bridge foot/soundboard fit possible should be a priority during any archtop set-up or repair.

I made my own profiling tool out of scrap materials, and if you are clever enough, you can easily get away with just few small pieces of plywood, some sandpaper and masking tape, for a one-off tool to perform a job that all archtops will need at some point in their lifetime .
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Leonard

1918 Gibson L-1
1928 Gibson L-4 (Blond w/Ebony Fret-board)
1930's Kalamazoo KG-32
1930's Gretsch F-50
1934 Gibson L-7
1934 Gibson L-50 (KG-11/14 Body Shape)
1935 Gibson L-50 (Flat-back)
1935 Gibson L-30 (Flat-back)
1942 Gibson L-50 (WWII Banner Head)
1948 Gibson L-50
1949 Epiphone Blackstone


"a sharp mind cuts cleaner than a sharp tool"
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Old 02-22-2022, 04:31 AM
Robin, Wales Robin, Wales is offline
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Thank you so much for your replies.

I asked the question because I'm only 5 days into my archtop adventure and wanted to save trial and error time!!!

I switched the bridge on a Godin 5th Avenue acoustic only archtop from Graphtec Tusq to rosewood. Even with just an OK fit (not perfect) the tonal change was very significant - much mellower and more controllable for my playing style. The 6th string was a little dull, but a touch with a nut file on the bridge slot livened it up somewhat. So that got me thinking about the impact of profiling the feet.

I have zero experience with archtops but lots of experience with resonator guitars. I have done full strip downs and set-up on around 800 or so. The difference between "lush" and "banjo" on single cone guitars was often down to the fitting of the biscuit to the top of the cone. I have been listening to 1930s/40s/50s archtops on YouTube and could hear variations across the same or similar models that remined me of the variations (from lush to banjo) that I would hear on reso guitars. So I was wondering if the bridge (material AND fitting) was to blame for much of the variation I was hearing?

I always said that reso guitars were built like tractors but needed an F1 set-up. Can the same be said for the cheaper plywood and pressed archtops do you think?

I have the Godin 5th Avenue on 14 day return. It seems to be a really good guitar for me - and I was thinking that with some set-up work and the right bridge I could make it a great guitar. Steve DeRosa has pointed me in the right direction regarding strings and bridge wood. Now I'm looking to fine tune that to maximise its potential.
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I'm learning to flatpick and fingerpick guitar to accompany songs.

I've played and studied traditional noter/drone mountain dulcimer for many years. And I used to play dobro in a bluegrass band.




Last edited by Robin, Wales; 02-22-2022 at 04:40 AM.
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Old 02-22-2022, 12:15 PM
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ArchtopLover ArchtopLover is offline
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Default Archtop Bridge Materials, Fitting and Tone.

As a side note to this subject that maybe of interest. I have experimented with Rosewood and Ebony materials in making my own adjustable archtop bridges, and I done a few experiments with the tonal differences with solid versus thumb-wheel adjustable types.

One of the biggest differences I have found so far, is that the tone changes dramatically between a solid, one piece, bridge and the more modern and more convenient thumb-wheel adjustable design. As a very simple, and completely reversible, test you can make your-self, is to place a carefully fitted wood or bone (I've tried both) shim between the saddle and the bridge foot, then simply loosen the thumb-wheels until they top-out and snug up against the saddle.

IMO the tonal characteristic becomes much more like that of a flat-top guitar, although with out the fat and flabby lower register, and you lose all of that wonderful natural acoustic archtop reverb. I have tried this with a few different archtops and the changes seem to be consistent across makers. I'm not exactly sure why this tonal change happens, but it is an interesting difference.

For now I am still experimenting with different materials and I discovered a new exotic tone wood that seems to be very promising, and that is, African Bloodwood. This very hard and dense wood rings like a bell when tapped. Looking forward to hearing what it does to the tone of an archtop, although you never know until you try it. Sometimes, when you add too much spice to a recipe you ruin the dish .
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Leonard

1918 Gibson L-1
1928 Gibson L-4 (Blond w/Ebony Fret-board)
1930's Kalamazoo KG-32
1930's Gretsch F-50
1934 Gibson L-7
1934 Gibson L-50 (KG-11/14 Body Shape)
1935 Gibson L-50 (Flat-back)
1935 Gibson L-30 (Flat-back)
1942 Gibson L-50 (WWII Banner Head)
1948 Gibson L-50
1949 Epiphone Blackstone


"a sharp mind cuts cleaner than a sharp tool"
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