Scallop bracing in situ on a finished guitar ?!

[steveyam]

Originally Posted by 1OUfan

If you are the original owner---scalloping the braces will void your warranty.


Bob

?? Of course I know that! I'm not stupid even though I may look it. No big deal on a £130 Epi.

[gitnoob]

Have you already examined the Epi's bracing? I wouldn't be surprised if it was already scalloped.

Scalloping is not the key. In fact, the practice of scalloping is somewhat questionable -- at least to me.

Of more interest is the overall stiffness of the top and how even that stiffness is. It's something you can measure via tap tones.

[Misty44]

Originally Posted by gitnoob

Have you already examined the Epi's bracing? I wouldn't be surprised if it was already scalloped.

Scalloping is not the key. In fact, the practice of scalloping is somewhat questionable -- at least to me.

Of more interest is the overall stiffness of the top and how even that stiffness is. It's something you can measure via tap tones.

Gitnoob, what do you mean by "key" - "key" to what? Scalloping otherwise straight braces has a noticeable effect on tone, primarily on increasing bass response and sustain, at least on the guitars I've personally worked on, and from reports of people like brother Kimsey and others, who do this modification professionally.

Reducing top stiffness will help overall responsiveness, and shaving back braces can clear up muddiness (but can also produce a more airy tone). Enlarging the soundhole can diminish bass response, and adding a cross-brace in front of the plate can boost it. And removing or thinning the popsicle brace can liven things up. Maybe...

To what degree one applies any one or more of these or any other modification has a huge impact, and yet there is no guarantee any of them will produce the desired result. But many times they do.

And by "questionable" do you mean in terms of structural integrity? Or something else?

As I said in an earlier post, I would never perform any of these modifications on anything but a low-end candidate (but if it's too low-end then the results of any tinkering may be minimal, no matter what). Some luthiers like Bryan and John Arnold will remove wood from the back braces new Martin D-18GE's to produce a bit fuller sound.

So I'm confused by the stark brevity of your post, and curious about your experiences behind them. I'd really like to know your thoughts about "key" and "questionable."

Thanks.

Have you already examined the Epi's bracing?

Good point. Steve, do you have one of these telescoping inspection mirror to check this out, one of these:



An evaluable tool to see what's under the hood!

[gitnoob]

Originally Posted by Misty44

Gitnoob, what do you mean by "key" - "key" to what?

I mean that the goal should be "voicing" -- targeting certain response characteristics.

"Scalloping" weakens the braces in certain areas. Why those particular areas and not others?

If you want to increase bass response and volume, then weakening the braces may help get there, but I think it's better to target a specific stiffness (which can be measured multiple ways, including tap tones).

If the top is too thick, it may not be easy to get the response you want by weakening the braces.

And the best way to weaken the braces may not be by "scalloping."

Useful guiding principles:

Stiffness varies with the cube of the height.

Stiffness varies linearly with the width of a brace.


"Scalloping" will weaken the brace in a limited area -- in effect making it a hinge. In most cases, it will probably make more sense to weaken the brace in a more uniform manner, and you can take off a lot more towards the end of a brace without weakening the structure.

[Misty44]

"Scalloping" weakens the braces in certain areas.

I agree the goal is voicing, but I don't think scalloping necessarily "weakens" the brace, rather it changes the mass supporting the top which will usually do two things: increase bass and overall responsiveness. To me, tapping is a procedure to adjust balance across the entire acoustic spectrum (high, low, and in between), as well as increase responsiveness (less mass, more vibration).

And while I appreciate the concept of tapping, to me it's an art form learned over time and through much experience, and is one of the main differences at the start of building between manufactured and handmade guitars. And if the top of a guitar is too thick to begin with, trying to "thin" it without a trained ear can be a very risky proposition.

"Scalloping" will weaken the brace in a limited area -- in effect making it a hinge.

I don't fully understand the "hinge" analogy - the amount of wood removed in scalloping (or tapering at the ends) a brace should never be sufficient to alter its structural integrity, i.e. weaken it to the extent that it permits the top to twist under stress - at least the amount I've taken off. And on guitars whose bracing is already overbuilt in this area, a little shaving may not be enough.

I am not a builder, and I have limited hands-on experience. But I have read and researched much about these kinds of modifications, and so far conclude that tapping and scalloping are very different procedures, perhaps leading to a similar but not exact outcome, and that if done properly both will indeed alter the voice without damaging the structure.

And of course so much depends on the underlying geometry of the bracing - what might work well for one type might not for another.

But it's late...tomorrow I will re-read Dana Bourgeois's paper on tapping, right now the brain is tired!

[gitnoob]

There's nothing mystical about tapping, and no experience is necessary.

I just thump near the bridge. You'll get a strong peak corresponding to the main resonant frequency of the top (like you would for a drum). You'll often get secondary peaks corresponding to the air resonance and other resonances.

Here's an example (you can see the waveforms of the taps and the spectral analysis):



There's nothing mysterious about braces, either. They add stiffness to the top. Think of a stick. If you whittle down the middle of a stick, it'll bend more easily in the middle -- that's what I meant by a hinge.

[David Youngman]

I understand that many people would be afraid to take on this challenge of scalloping the braces but if you have an understanding of what the bracing does and you think it through and go slowly I don't see what the big deal is. After all it just a wooden box. I understand certain guitars can have high dollar values and sentimental value but I think if anyone is thinking of scalloping the braces on their guitar, the guitar is likely not a high valued guitar.

As mentioned already, your higher dollar instruments are likely going to be tuned more accurately and specifically while a cheaper guitar (under $1,000) likely follows a template and is not based on the sound and tap tuning.

I've scalloped 3 guitars and have only done it on guitars that lacked a responsiveness. The tops on these guitars were all quite thick .125" - .130" so that was part of the problem in the stiff sound. These were guitars valued at $250 - $800. I basically shaved off enough to hear the slightest responsiveness. I didn't really have a specific method other than following the basic shape already scalloped or following basic shapes I've seen on other guitars. I kept all peaks the same. I also was very cautious with the x bracing as that is the support for all the string tension. I used a $5 mini plane from Menards and some sandpaper. All three guitars came out sounding better and it's been at least 6 months since doing this on the guitars.

I didn't "tune" the tops and backs but simply was after gaining some responsiveness.