My Martin 12 string is getting a "belly".

[Daniel Grenier]

My trusty Martin 12 string J12-16GTE (Jumbo) has been harder to play over the past few weeks. I was checking it out up, down and sideways and noticed that the bridge is "leaning forward" but it is not unglued or off the top. Rather, there is an obvious "belly" on the top behind the bridge area which is causing the forward leaning of the bridge.

That can't be normal, to state the obvious, but what can be done about it? Is it indicative of weak bracing or something? The guitar is always well humidified, is strung with light gauge strings and usually tuned lower than standard.

I will take it to a Luthier but I just want to properly understand what's going on here.

Been there, anyone?

[redir]

For them most part that is considered normal. Of course without seeing it, or even pics, it's hard to know if it's gone too far. But having some belly, especially on a 12, is normal - to a point.

Is it sinking in front of the bridge too?

If you have a straight edge, a yard stick would do, hold it across the belly and measure the height at the binding where the straight edge is 'floating.' Take a pic too and post it here.

[hat]

Are you using light gauge strings, tuned down a half or whole step? That would lessen the string tension.

[Daniel Grenier]

Originally Posted by redir

For them most part that is considered normal. Of course without seeing it, or even pics, it's hard to know if it's gone too far. But having some belly, especially on a 12, is normal - to a point.

Is it sinking in front of the bridge too?

If you have a straight edge, a yard stick would do, hold it across the belly and measure the height at the binding where the straight edge is 'floating.' Take a pic too and post it here.

Not sinking in front, no. Tried a few measurements and pics. Kind of hard to do either with just 2 hands. Near impossible to get a decent pic of the "belly", though. Does this look normal to you?

[IMG] [/IMG]

[Daniel Grenier]

Originally Posted by hat

Are you using light gauge strings, tuned down a half or whole step? That would lessen the string tension.

I use Elixir Lights 10-47. I am rarely tuned std. DADGAD, usually or lower alt-tuning.

[runamuck]

It looks normal to me.

[redir]

Don't worry about it

If it's something that suddenly happened then you might want to have a look inside to be sure.

[mirwa]

A few things to consider with belly bulge.

Is the whole top area lifting, if it is then the top and braces are good, how much it lifts is now dependant on a balance between the string gauge and the braces.

Is the bridge area rotating, dip in front raise behind. All bridges must rotate a little - 0.5 degrees is good, 2 degrees is bad. If a bridge rotates too much then the wings of the bridge will seperate from the top and eventually it will tear off.

Permanent set can occur, this is where the top after detuning maintains a deformed shape, this deformed shape can be unfavourable for actions heights over a period of time, it can be rectified (steam and clamping) and a lower gauge string recommended for future use or it can be rectified by upgrading the braces to take heavier strings.

At these early stages, I personally think your top is normal for a 12 string, for longevity, maybe consider detuning when not playing, just half a turn of the machine heads.

Steve

[Daniel Grenier]

Looks like I might have freaked out prematurely on this one but did learn in the process so thanks for the feedback, folks.