Brass Instruments

• Two basic families with rather little difference in tone
• Straight tubes with some conical or flared sections
  • Trumpet, Trombone, French Horn
  • Brighter sound. Used in orchestras where brightness is needed to cut through mass of other instruments.
• Conical tubes with some flared or otherwise slightly altered sections
  • Cornet, Flugel horn, alto horn, baritone, Euphonium, Tubas
  • Mellower sound. Used in ensembles (brass bands, silver bands) where the sound blends better than trumpets etc. would.
• Lip reed
  • Player can alter tension in lip over a very wide range. Gives the player control over natural frequency and over Q not available to other reed players.
• Mouthpiece
  • Surface to rest lips, resonator chamber with a sharply constricted opening, conical tube to match to bore of instrument
• Body tube
  • Basically straight or basically cylindrical according to family.
  • Length determines pitch of instrument. As usual, the longer the tube the larger the bore to allow low frequencies to get out.
• Bell
  • Couples tube to the outside world.

Open or Closed tube?

• Bugle calls show that the available notes from a fixed length tube form a complete harmonic series (missing the fundamental)
• Lip reed must operate into a high impedance, high pressure anti-node of the pipe and should give an incomplete series!
• Flaring bell alters the effective length of the tube for different frequencies and alters the pattern of partials.
• The Bell
  • Produces a high-frequency cut-off as we have seen in woodwinds.
  • Makes tube have different length for low frequencies, which reflect early in the bell, and high frequencies, than high, which travel somewhat further before reflecting.
  • Effect is to raise lower partials relative to upper ones, altering the 1, 3, 5, 7, relationship.
• The Mouthpiece
  • Has natural "popping" frequency around 850Hz. Broad resonance.
  • Extra volume of mouthpiece pulls down some of the upper partials.
  • By itself it does not strengthen the lower resonances enough to make them sharp, can still slide note around with the lip.

Effect of Bell on Pressure

Combined Effect

• Raises lower modes
• Lowers upper modes
• Result is nearly harmonic set of modes except for the lowest
• Lowest mode is significantly out of tune with others and does not give an easily playable note.

Resulting Brass Modes

Changing the Note

• Have to alter length of tube. Two methods available
• Slides/Valves change physical length of tube
  • Trumpet, French Horn, all the Cornet/Tuba family use valves.
  • Trombone and rare slide trumpet use a slide.
    • Sound always comes from complete tube so that tone color is quite constant.
    • Can only put into a straight section of tube!
• Holes can shorten acoustic length of tube
  • Cornett (2 T's), Serpent use simple holes
  • Keyed bugle, Ophicleide use keywork
    • Tone color is much less even over range. Obsolete.