Woodwinds are wind instruments. Flutes initiate the sound by blowing across the mouthpiece (like a bottle). Clarinets and saxophones initiate the sound by vibrating a single reed as air is blown into a mouthpiece. Double reed instruments such as the oboe, English horn, and bassoon initiate the sound by vibrating two reeds together as air is passed through those into the rest of the instrument. There are several variations of the clarinet and saxophone. Woodwind timbres are more heterogeneous than strings or brass, but not so varied as percussion or electronic instruments. These instruments also tend to play at a softer dynamic level, which is why there are fewer of them in the orchestra than the various string instruments. Both brass and percussion tend to produce louder dynamics than the woodwinds.