A harmonica is a free reed wind instrument which is played by blowing air into it or drawing air out by placing lips over individual holes (reed chambers) or multiple holes. The pressure caused by blowing or drawing air into the reed chambers causes a reed or multiple reeds to vibrate up and down creating sound. Each chamber has multiple, variable-tuned brass or bronze reeds which are secured at one end and loose on the other end, with the loose end vibrating and creating sound.

Reeds are pre-tuned to individual tones, and each tone is determined according to the size of reed. Longer reeds make deep, low sounds and short reeds make higher-pitched sounds. On certain types of harmonica the pre-tuned reed can be changed (bending a note) to another note by redirecting air flow into the chamber. There are many types of harmonicas, including diatonic, chromatic, tremolo, orchestral, and bass versions.

The harmonica is used in blues and American folk music, jazz, classical music, country music, rock and roll, and pop music. The harmonica has other nicknames, especially in blues music, including: "harp", "blues harp", and "mouth organ"

Parts

The basic parts of the harmonica are the comb, reed-plates and cover-plates.

Comb

The comb is the term for the main body of the instrument which contains the air chambers that cover the reeds. The term comb originates from the similarities between simple harmonicas and a hair comb. Harmonica combs were traditionally made from wood, but now are usually made from plastic (ABS) or metal (including titanium for very high-end instruments"Mark Lavoie - Harmonica Player ... and more", The Middlebury Community Network). Some modern and experimental comb designs are complex in the way that they direct the air.

Comb material was assumed to have an effect on the tone of the harp. While the comb material does have a slight influence over the sound of the harmonica, the main advantage of a particular comb material over another one is its durability. In particular, a wooden comb can absorb moisture from the player's breath and contact with the tongue. This causes the comb to expand slightly, making the instrument uncomfortable to play. Various types of wood and treatments have been devised to reduce the degree of this problem.

An even more serious problem with wood combs, especially in chromatic harmonicas (with their thin dividers between chambers) is that the combs shrink over time. Comb shrinkage can lead to cracks in the combs due to the combs being held immobile by nails, resulting in disabling leakage. Much effort is devoted by serious players to restoring wood combs and sealing leaks. Some players used to soak wooden-combed harmonicas (diatonics, without windsavers) in water to cause a slight expansion which was intended to make the seal between the comb, reed plates and covers more airtight. Modern wooden-combed harmonicas are less prone to swelling and contracting.