Acoustic Guitar Mods - What a Difference!!!

[navvid]

Hello Gentleman. I have been absent from this wonderful forum for quite some time, but I return with good tidings. Encouraged by my successes in making a bone nut and hand compensated bone saddle for my acoustic, and impressed with the difference a very little bit of cash and a whole lot of elbow grease can make on a middle of the run Korean made solid top, I decided to try two major and potentially disasterous modifications:

1. Slotting my bridge
2. Scalloping my bracing

Now it's difficult to get pictures of the slots in the bridge (and very difficult to take pictures of the bracing on an assembled guitar), so I haven't taken the appropriate step by step pictures, but here's the idea: most steel string acoustics use slotted bridge pins. When the guitar is all strung up, most of the string is just kinda floating stretched in the slot with no positive contact with the bridge. It is only really coupled to the guitar at the point where the ball end touches the bridge plate underneath, and where it comes up over the top and bends to the nut. If you cut slots for the strings into the bridge itself, you can then turn the pin around or use an unslotted pin. This firmly couples the whole section of the string inside the bridge to the guitar. The improvement in tone I observe can be best described as "opening up", especially in the mids. Unlike changing the nut and saddle to bone, which brightened the tone by seemingly adding highs and harmonics that were not there before (or were unheard), slotting the bridge did not seem to add anything so much as broaden and open the midrange frequencies that were previously present but not nearly as full or articulate.

As for scalloping my top bracing, it was very, very challenging and more than a little painful working for over 10 hours with my arms inside my soundhole almost to the elbow. But I persevered, and my what a difference. The base response has improved particularly as well as across the spectrum, the harmonics are louder and it has this amazing reverb effect that is incredible. I mean WOW! As is common knowledge now, this is good part of why prewar Martins are the holy grails of acoustics. They stopped scalloping their bracing toward the end of the war because customers were complaining about their guitar's "belly bowing" up. I shaved my braces way down, and my top shows no sign of deformation, not that I would care given how much better the guitar sounds now.

Now I realize this is getting kinda long winded, but I should mention the dangers of such modification. With scalloping you top bracing, as I said this is not for the faint of heart as it is very hard, time consuming work. I am skinny, so my arms fit into my soundhole almost to the elbow, and I was just barely able to reach the furthest section of bracing. Also, if you go to far or damage the bracing or top, obviously you could destroy your guitar. When slotting the bridge, the slots should be just barely the diameter of the string so the pin is really squeezing the string into the slot. Once again if you go too far you can destroy your guitar (or at least your bridge). Also, I have been told by a luthier I am friendly with that over time this can cause the string to cut its way through the bridge plate and eventually up through the bridge, which is very difficult to fix. I have, however, devised a way of preparing the strings which I believe solves this problem and additionally makes the modification work far better.

There is a lot more to making all this work than I have said, but once again since this has gotten long winded already, I figured I would see if anyone could give a crap or had anything to say before I started sharing all my secrets. If you guys are interested, I would be glad to tell you more. I will try to get some pictures and maybe audio of it up today.

[tot_Ou_tard]

Whoa, you've got guts navvid.

Good job!

[evenkeel]

Wowie Zowie. That seems like a ton O work. Good on ya!!

I'm not sure I totally understand what is going in re: the bridge pins, but hey if it works!! Shaving the braces I understand but can't imagine actually giving that a go.

[Retro Hound]

I'm not quite following "scalloping the bracing." Just what are you doing to the bracing that makes a difference in the sound? I might be willing to give it a go on a cheap guitar just to see what kind of difference it makes. I too have skinny arms.

[navvid]

Retro Hound - Scalloped bracing is when you shave material off of the internal bracing on your top. If you look inside your soundhole, you will see that the back of an acoustic guitar is braced (usually just horizontally across the body on the back) every four inches or so with thin wooden bars. These provide the structural reinforcement which prevents the relatively thin top back and sides from warping. The bracing pattern of the top is more complex, since the strings are pulling on your bridge. Most acoustic guitars today are copies of Martin designs, so chances are your top has an X brace below the soundhole (closest to the bridge), an A brace above it (closest to the neck) and two tone bars (across the lower bout at an angle). I have attached two pictures.

The bracing is effectively part of the mass of the top, and the thinner (and therefore lighter) your top is, the more it will resonate and thus it will be louder. Also, as the bracing is shaved down, it allows the top to flex more, broadening your range of frequencies that the top can produce, and improving the expression of those that were previously present but at inaudible levels.