Anybody try sanding down the top of their guitar?

[JonWint]

Sand away. Martin uses this hand-guided belt sander before the final hand-held orbital sanding. You can save time by just sanding off the bridge and replacing it when you finish thinning the top.

[IMG][/IMG]

[SRL]

For an actual answer:

No, I wouldn't recommend sanding the top on a finished guitar, from the inside, or outside.

If you want to change a finished guitar's voicing, it is much easier to use coarse sandpaper, files, rasps, or finger planes to change the shape and/or height of the braces. You need pretty skinny forearms to work through the sound hole. Sandpaper is slowest but safest in that it doesn't remove wood as quickly.

Note that you can only *remove* material, not add it back. Most guitars in the world are overbuilt, so you can usually remove material, especially on cheaper guitars. But if your tonal issues are from an underbuilt guitar, the only way to fix that is to take the top off and redo the bracing. And this is not a panacea for other tone problems like a poor fitting saddle, or bad intonation from bad scale design/execution.

There are three main frequencies you want to target with a spectrograph (try spectdroid app on Android). The "main air" (lowest hz), the back (around 30hz higher although opinions vary) and then the top frequency (around a G3 or 196hz plus or minus a few semitones). The back can be measured by tapping the back opposite where the bridge is, and the main and top frequency can be measured by tapping on the bridge. The two biggest peaks on the spectrograph are the frequencies. For the back there's only one big peak.

The bigger the body, and the lighter the build, the lower the main air frequency, which has the biggest impact on the apparent bass response. Most dreads are around F2-G2 (first few notes on low E). A parlor or 00 might be around A2-B2. Because scalloping braces deeper will lower than main air and add bass/boomyness, most people only scallop finished guitars that have too high of a main air frequency for the body size and weak bass.

The scalloping goes on the lower legs of the X brace, on either side of the bridge plate. Usually it's not a good idea to mess with the tone bars unless they are full straight braced with no scalloping at all. Make sure you understand how guitars are braced and look up some pictures.

Usually the back bracing is too stiff as well, so sanding that down can be helpful for reducing its frequency. Usually you're sanding down the lower braces opposite the bridge and not the upper back braces under the sound hole.

I've done this on three guitars that I liked but weren't worth much and were overbuilt from the factory. In both cases, it made significant improvements in the tone and responsiveness. For the first one, I cut down the height of the main X scallops by 50% and the two lower back braces by 50%. This took the main air frequency from 120hz down to 90hz and the back from 160hz down to 120hz. The top frequency moved down from 180 to 160hz. Using rounded numbers but you get the idea.

Thought the process, I measured the three frequencies as well as the bridge angle (how much the strings were making it tilt forward toward the sound hole, which should be 3 degrees max, e.g. an 87 degree angle between the bridge and the top). This meant frequently tuning the guitar back up to pitch, checking the frequencies, and measuring the bridge angle, and keeping logs of the changes.

The process is mostly art and some science. At some stopping points, the guitar sounded better than others. When I got near my target frequencies, I tested more often between rounds of sanding and when I got a test that sounded really good, I stopped and considered it done.

[TBman]

Originally Posted by cip

Sorry. It was just a question. Thank you for being patient and understanding with me. I'm a beginner guitar player

Go along with the jokes and teasing, it makes life easier Guitar playing is a great hobby. Enjoy your time here as well.

[BlueBowman]

Originally Posted by cip

Sorry. It was just a question. Thank you for being patient and understanding with me. I'm a beginner guitar player

cip, no. You're a beginner, so your energy would be better served in practicing (a lot) of guitar and not focusing on how thick or thin the top is. I wouldn't recommend going down the post-mod rabbit hole, especially as a beginner. If you're not happy with your current guitar, save up and buy a better instrument and practice the snot out of it!

SRL gave a great answer, though. It can be done. I've gone about it much like SRL has, testing the resonances and slowly sanding the braces, not the top, a little at a time. But only on cheap guitars. In my experience, doing this will NOT change the fundamental tone of the guitar, but you can improve responsiveness, volume (to the player), and mostly bass. Turning the guitar's back into a "live" back is probably the safest way to go about it, and it will also improve responsiveness by coupling the top and back together in a more harmonious way.

There are endless threads written about this stuff here. I only attempted these post-mods after reading a handful of guitar building books and reading through countless threads on the forums.

IMO, I think it would be nuts to try any of these mods on your guitar without having the proper knowledge. And even WITH the proper knowledge, I would never attempt them on a good guitar. Because you won't know if you've gone too far until at a future date (when the guitar collapses in on itself). I'm ok with that happening to a $300, but not one of value!

[cyclistbrian]

Originally Posted by cip

Sorry. It was just a question. Thank you for being patient and understanding with me. I'm a beginner guitar player

I contributed some snark but in all seriousness and sincerity I offer these two cents. Have a well setup guitar thats pleasing to your ears and take it as it is. Most of what you'll read or hear about improving tone besides actually becoming a better musician is nonsense. Yes strings and picks or even different saddle materials can make a guitar sound darker or brighter but ultimately it comes down to you. That's the hard part but paradoxically the best part. As you grow as a musician you are growing in other ways as well. You'll think about music differently. You'll master some pretty difficult things that most people give up on because let's face it, guitars don't play themselves. You're contributing music to a world that always needs more music. The guitar has brought me more over the years than I could ever have imagined when I started and I hope you also enjoy a lifetime of.music making.

[Lkristians]

This thread is closed.