Sunday, June 22, 2008

TKL003 Tenor Kasha Ukulele
Kasha/Schneider Soundboard Bracing Theory

The TKL003 Tenor Kasha Ukulele is the first MAKAIO Ukulele to be constructed using a modified Kasha/Schneider soundboard bracing system. Standard MAKAIO Ukuleles have a fan style bracing system which has the lower section of the soundboard supported by three longitudinal braces on the inside under the bridge, and the upper section supported by two cross braces above and below the soundhole. The modified Kasha/Schneider bracing works on a different principle.

......Modified Kasha/Schneider bracing ............................Fan bracing ....................

Developed by Dr Michael Kasha and luthier Richard Schneider, the aim of this soundboard design is to optimise the features of the soundboard/bridge, to better respond to the vibrations produced by the strings, in order to produce instruments that have greater sound clarity and better sustain. The design theory involves a significantly greater amount of physics than the traditional fan braced design, and has a number of key design features:

Firstly, instead of having a relatively symmetrically braced soundboard, the soundboard is braced so that one area responds to treble frequencies, while another responds to bass frequencies. This is achieved by having radial coupling braces extending out to different lengths from around the area of the bridge. On the bass side of the bridge, the tone bars extend significantly longer, all the way into the soundboard upper bout, while on the treble side, the tone bars are significantly shorter. The treble side of the soundboard is further braced with treble confinement bars, which extend around the ends of the treble tone bars.

The second significant feature of the Kasha/Schneider theory is a wedge shape impedance dependant bridge. The shape of this bridge is specially designed to further optimise transfer of energy from the strings to the soundboard, by driving the bass tones into the bass side of the soundboard, and treble tones to the treble section.

The third significant feature of the Kasha/Schneider theory is to shift the soundhole from the centre of the soundboard, to the upper bout on the treble side. This increases the effective area of the soundboard that is available for vibration and sound production, and also reduces the loss of soundboard strength generated by a soundhole.

The Kasha/Schneider theory has been applied to ukuleles by luthier Michael Chock from Hana Lima ‘Ia, with a series of slight modifications to adjust the idea to be more suitable for the smaller body size. The principle of the modified Kasha/Schneider bracing system adopted for the MAKAIO TKL003 Tenor Kasha Ukulele comes from the plans produced by Hana Lima ‘Ia.

The bracing for the TKL003 Tenor Kasha Ukulele has six radial tone bars extending from the bridge toward the neck, and a further six extending from the bridge toward the tail. There are a further two tone bars extending off each end of the bridge patch. The treble side of the soundboard has treble confinement bars going around the ends of the treble tone bars. The centreline of the soundboard has cross-grain grafts to reinforce the joint between the two bookmatched plates that form the soundboard. The transverse brace that was intended to cross the soundboard below the bridge centreline has been left out, and instead a 1.8 mm thick spruce patch has been placed below the bridge. All of the radial tone bars are notched over this patch. A series of smaller soundholes have been placed in the upper bout on the treble side, with this area also reinforced by a cross-grain spruce patch. An oval side-port will be placed in the body of this ukulele to facilitate most of the sound transmission, with holes in the soundboard mainly added for aesthetics.

1 comment:

Anonymous said...

I'm toying with taking up uke lutherie as a hobby and the Kasha bracing theory is very intriguing -thanks so much for sharing!