An aeolian harp (æolian harp or wind harp) is a musical instrument that is "played" by the wind. The traditional aeolian harp is essentially a wooden box including a sounding board, with strings stretched lengthwise across two bridges. It is placed in a slightly opened window where the wind can blow across the strings to produce sounds. The strings can be made of different materials (or thicknesses) and all be tuned to the same pitch, or identical strings can be tuned to different pitches. The sound is random, depending on the strength of the wind passing over the strings, and can range from a barely audible hum to a loud scream. If the strings are tuned to different notes, sometimes only one tone is heard, and sometimes chords.