A hard frame absorbs less resonance, thereby providing greater sustain and a more open sound. This is why solid wood or a very hard laminate should be used for the back and ribs.
Usually solid wood fares better as a top wood, although there are some high-quality laminates which do a good job and which are becoming more and more popular thanks mainly to their striking looks.
Due to the short scale length, irregularities in intonation may occur especially with the sopranino and soprano ukuleles. This is inherent, as when playing in the very high range the remainder of the strings is simply too short. Thus, every millimetre counts and an absolutely precise fingering technique on the part of the player is crucial.
To ensure proper intonation even in the ukuleles with very short scale lengths, the latter is extended by 2-3mm by some manufacturers. This compensates for the intonation purity over the entire length of the fretboard.
Furthermore, the exact position of the bridge has a remarkable degree of influence on the sound. If the bridge is put exactly at the body's widest part, the top resonates minimally which increases both sustain and volume.
Five different sizes are available: sopranino, soprano, concert, tenor and baritone, of which soprano, concert and tenor are by far the most commonly used.
More about this in the next chapter.