Mouthpieces for Brass InstrumentsBrass instruments have a removable cup (trumpet, trombone, tuba) or mouthpiece (French horn). The mouthpiece of a brass instrument is not the tone generator, but only a transmission element of the generated air pulses. Variables are the rim diameter, the rim shape, the inner form (cup or funnel) and the hole diameter sometimes one speaks of the soul. This is a short cylindrical piece - in that the narrowest point between the cup or funnel (depending on the internal shape) and the rear hole. Typical values are 3.6 to 4.4 mm for trumpet / flugel horn, 3.8 to 4.8 mm for Horn, 5.8 to 8 mm for trombone and 7.6 to 8.6 mm for the tuba.