The harp or harmonica is available in a number of different types and one of the most popular harmonica types are diatonic harmonicas. In fact, the most popular type of harmonica is actually a diatonic harmonica known as the Blues harp or the 10-hole harmonica. Unlike chromatic harmonicas, diatonic harmonicas are designed to only play a single key. For instance, the key of C harmonica is tuned to the C major scale.
Diatonic harmonicas are so popular because they work well with blues, country, jazz, rock and folk music. By using advanced techniques such as bending which lowers the pitch of a note or changing the way the instrument is held, players can get more expression from the harp, bringing in vocal sounds such as shaking and wailing desired in these types of music. Since the key of C is right in the middle of the scale, such harmonicas can also help beginners better understand music theory.
Most beginners start out with a single diatonic harp, and then as their music progresses to the point that they are playing along with singers, CDs or other musical instruments, they buy other harmonicas in the set to represent additional keys. The most common keys to get besides C are usually D, F and G; single key harmonicas also come in the rest of the 12 keys.
Despite their popularity, diatonic harmonicas do not have to be expensive, reasonably priced harmonicas can be found for just a few dollars and provide new harp players with consistent volume and tone. Look for brands with good solid construction that do not leak air. Most materials will provide the same quality, however, wooden diatonic harmonicas are generally not as desired since the wood can shrink and cause air flow problems. For health reasons, a new harmonica is also preferred over a used one.