Lining the sound chamber

[John Bertotti]

I have read that some sound chambers are lined either with a wood or paper. I think this predominately bowls but wonder why? Was it to add a little extra strength? There are a lot of joints in a bowl back. Would there be another reason, perhaps one associated with tone, or maybe it was to help seal it for humidity changes? Any thoughts appreciated I know you all are mostly American style A and F builders so thanks in advance. John

[Eugene]

I think it was almost entirely done to reinforce all those glue joints. #Some early American pieces (i.e. ca. 1890) had proper wooden braces, either individual bars at each joint (!) or a couple bars crossing the whole of the bowl's interior (like very early Washburns by Lyon & Healy). #More standard seems to be heavy papers, linen, very fine wood shavings, even foil (!). #Unlined bowls definitely seem to be in the minority.

[Luthier]

The staved joints of a bowl back are very similar to that of a lute. #They are very thin. It is very much like the way a cooper would have made a barrel.
add to that the thin contrasting strips of wood in between the individual staves and you have now added more wood to be subjected to expansion and contraction. #The Lutes and bowlbacks that I have worked on have all had a backing of some kind inside to help maintain the structural integrity of the instrument. #Its kind of like a skin to hold everything in place.

Don

[whistler]

I recently built a 'Portuguese' style mandolin, with a 9-piece back. Following the advice of an experienced maker, I reinforced the back joins using individual strips of linen (being unable to obtain linen tape of a suitable width, I cut them from a bed sheet) soaked in rabbit hide glue. Soaking the strips has the added advantage that, when the glue dries, the whole strip contracts slightly, thus pulling the joint together more tightly. Bowl-back mandolins, having perhaps 25 or more back staves, are usually completely covered inside with a single sheet of paper or linen.