Physics of bridges, tops and soundholes

[Rob Dick]

Thanks Chris. It's a solid Hoop pine body shape based on the Lag Jet guitar shape. Bridge position works out pretty much where you suggest. I was going to brace it with a bridge plate under the bridge and a couple of braces using offcuts of the 3mm Stewmac spruce, so an H pattern. I've also built a 19" VSL baritone neck which I want to marry with a 2 1/2" deep body and go with an 8 1/4" soundboard. That will give me two proportionally similar instruments to compare and be confused by!

I'm following the spruce topped Dano convertible thread as well hoping to learn from that project.

[Chris Reed]

This: http://www.youtube.com/watch?v=zsRsK2tm7Gs

uses a sort of combination H and fan bracing system, though so massive that I'm amazed it wasn't completely silent! But it might give you some ideas. It's a copy of the Gretsch Camp Uke, which wasn't famed for its sound quality. Note the bridge placement, which is far too near the tail but was presumably put there to make it shorter and more transportable.

Thinking about it, if you have a bridge patch I can't see why you'd need the H cross-piece for strength, though it might do something to shape the sound (quite what is guesswork). I'm a fan of light as possible, but this is based on intuition not research.

The original Lyon and Healey Camp uke is interesting - no soundhole but a resonator back. See here: http://antebelluminstruments.blogspot.c ... ulele.html which linksto four more examples.

This thread gives you some dimensions and bracing (either one transverse brace or no braces at all): http://www.ukuleleunderground.com/forum ... l-Ukuleles

Good luck with your project.

[Dana Emery]

A former roomate took the journal of the Acoustical Society of America (his thing was speach recognition). I found it heavy reading, but noticed numerous articles on musical instrument acoustics, including plate behaviour. If you have access to the library of an engineering school you might find some browsing rewarding.

[Rob Dick]

Thanks for all the info. I ended up just basing my bracing on a heap of pics from Googling "ukulele bracing", but some of the articles made interesting reading and improved my understanding of how and why tops react as they do.

The latest uke sounds at least as good as the more basic mass produced ukes so I'm happy with the results so far.

I was concerned about deflection / distortion of the top in front of and behind the bridge, so I took a short straightedge to my local uke club and ran it along the tops of about 40 ukes. The ones with dead flat tops and no deflection tended to be the laminated soprano and concert cheapies with less attractive sound and minimal volume and projection, and the ones with more deflection / distortion tended to be the more upmarket ones with solid tops, better sound / volume / projection and generally higher pricetags. One of the genuine made in Hawaii Koa tenor ukes had a gorgeous tone but the top was showing a good 5mm of deflection in front of the bridge near the soundhole and about 3mm behind.

[Dana Emery]

Some dip in front of the bridge improves clearance for the RH fingers in play and is a design feature in lutes and guitars (and other instruments with glued-on bridges with tied-on strings); some lutes have a subtle corresponding dip shaped into the sides of the shell. One could raise the bridge to achieve similar extra clearance, but this has an effect on string tension..