Sound of the Chromatic

Hi, Cornelius.

A big part of what makes the chromatic sound different from the diatonic is the valves.

Consider the blow-draw pairs in a diatonic.

• When you play a blow note, some of the air canleak out around the draw reed.
• When you play a draw note, some air can leak in around the blow reed.

Even though they're evenly matched in this regard, the blow reeds tend to have a more airy sound than the draw reeds.

On a chromatic harmonica that air leakage from the opposite reed is prevented by mounting a valve - a strip of flexible material (usually plastic, though leather is still used in some accordions) - over the reed slot on the opposite side of the reedpalte from the reed. 

• When you play a blow note, the valve on the draw slot is pressed against the draw slot, preventing air leage via the draw reed.
• When you play a draw note the valve over the blow slot is pulled against the slot, preventing any air from leaking in through the blow reed.

Valving has several effects.

• It makes the tone of blow reeds and draw reeds more similar to one another and, as you note, sweeter. (A valved or half-valved diatonic will have this same sound).
• It makes air use more efficient - you need less breath to play a valved harp. Chromatics really need this, as they have a lot more places for air to leak, with the multi-layer mouthpiece/slide assembly and the large area of contact between reedplates and comb.
• It prevents overbends and dual-reed bending, but allows wider bending range for isolated reeds.