How would you effectively brace the upper bout on this acoustic bass guitar ?

[freddi]

it needs a strong upper bout brace - then neck angle trimmed to establish a playable string action.

Sorry I don't have any pix inside as the bass is away at my house.

 

[Osvaldo de Banfield]

An exponential cut like Karlson speaker, call my attention.

 

[freddi]

Karlson's 1951 Acoustic Transducers Patent

 

[seventenths]

Falcate bracing instead of traditional x bracing maybe?

https://lutherieacademy.com/courses/falcate-bracing

 

[seventenths]

There's a nice writeup on mimf.com on the style

 

[jjasniew]

Like this? The situation is a toughie!

 

[Printer2]

What a stupid design. What keeps the neck block from rotating?

 

[Joe K]

Is it dovetailed and just not shown?

 

[Printer2]

The neck attachment is not the issue. The problem is that the neck block area will rotate at the base of the block. Regular guitars with the sound hole and X brace already have issues with the strings folding the top over at the sound hole resulting in a neck reset being needed. This design takes away any stability that the top adds to resist rotation. Think of a cardboard box with the top glued together except for the one end. It is much easier to twist it around than if the last edge is glued together.

 

[Markw4]

Maybe run something like a truss rod from where the neck attaches, down to the bottom-side, back corner at the far end of the guitar body? Something like that. It needs to be something can have have some controlled musical vibration but also act like a strut to provide some stability. Or maybe the truss rod could end at some structure hanging/extending under the bridge?

 

[Printer2]

Others have done that, also from the top of the neck block to the lower waist at the back.