Brass

A brass player makes the sound with the lips, buzzing them into a cup-shaped mouthpiece like a soft raspberry.

Lips instead of reeds

Brass instruments are long metal tubes that end in a flared bell. The sound starts at the player’s lips, which vibrate against the rim of the mouthpiece. Tighter lips and faster air make the air column in the tube vibrate in a higher mode. A single tube without valves can only play the notes of its harmonic series: the fundamental and its multiples, 2, 3, 4 times the frequency and so on. Bugle calls use just these notes.

Before valves, horn and trumpet players carried extra pieces of tubing called crooks and changed them between pieces to play in different keys. Valves, developed by Heinrich Stölzel and Friedrich Blühmel in 1815, solved that problem. Pressing a valve sends the air through an extra loop of tubing, which lowers every note of the harmonic series. With three valves in combination, a player can reach every note of the chromatic scale.

Four instruments, four jobs

The horn has a long coiled tube and a wide bell that points backwards, so its sound reaches the audience after bouncing off the back wall. It blends with both woodwinds and brass. The usual horn is in F and sounds a fifth lower than written; its range starts at B1. Orchestras use four horns as standard since Beethoven’s Ninth asked for a second pair.

The trumpet is the highest brass instrument. A B♭ trumpet sounds a whole step lower than written and plays from about E3 up to C6. Its bright attack is used for fanfares and big climaxes. The trombone has a slide instead of valves. Pushing the slide out makes the tube longer and every note lower, with seven standard positions. Because the slide moves smoothly, a trombone can glide between notes. The orchestral section is usually two tenor trombones and one bass trombone.

The tuba is the lowest brass instrument, with a bell pointing up. The modern tuba dates from 1835; before that some composers used an instrument called the ophicleide. Orchestral tuba parts are written at concert pitch, and the range goes down to D1, about 37 Hz. Most orchestras have just one tuba, which supports the trombones and the double basses.

How big is the brass section? According to HyperPhysics, a full orchestra uses four to seven horns, three to four trumpets, three to four trombones and one tuba. The model has 4 horns, 3 trumpets, 3 trombones and a tuba, 11 players in all. Brass instruments can be very loud. The same reference lists a measured peak output of about 6.4 watts for a trombone and 0.31 watts for a trumpet, against about 0.05 watts for a clarinet. That is one reason composers save the full brass for the biggest moments and give them soft, held chords elsewhere.