Jeff's Guide to Brass Mouthpieces
Or, what do all those numbers mean?
Cup size: This refers to the profile of the cup. In Bach mouthpieces, the cup design is referred to by a letter (eg C). The cup depth is designated by a number (eg 7). A larger number will give a “shallower” cup, and a smaller rim diameter. A 1½C will be deeper than 7C and have a larger inner rim diameter. A 12C will be very shallow with a small inner rim diameter. The B, D & V cups have a different profile for different tonal qualities and ease of note production. Deep for classical and a rich low register, shallow for clarity and screaming high lead notes in a big band, most people use something in between.
Rim diameter: This determines how much of the lips are free to vibrate and thus produce the sound, hence a larger inner diameter uses more of the lips.
Rim: the thickness of the area of the mouthpiece in contact with the lips. Comfort, tone and ease of tone production are affected by this. The wider rim gives greater comfort and endurance, but less flexibility, making larger intervals a little more difficult to play. A very narrow rim gives the feeling of “cutting” into the lips, so less pressure can be applied. Again, most players use something in between.
Throat: The hole leading from the cup to the shank of the mouthpiece, the size of which gives greater or lesser feeling of resistance to the air being blown into the instrument. A larger bore hole gives the player a “big” sound but less endurance. (More air going through per second tires the lips more.)
Backbore: The interior dimensions of the shank, usually a conical shape getting larger as it nears the main body of the trumpet. Again this affects the tone and the feeling of resistance.
Gap: Basically, how far the mouthpiece sticks into the lead pipe. Each instrument will have an optimum gap size for which it has been designed to play the most in tune and with the best tone. Often overlooked but usually the most vital dimensions on the mouthpiece are the external diameter and taper of the shank, which determine the gap size on a particular horn.
With all these variables, not to mention the variety of lip, tooth and other physiological features of musicians, it is vital to match the mouthpiece to not only the player, but also to the instrument and the style of music being played.
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Here is a link to the Bach offical mouthpiece manual: https://www.bachbrass.com/application/files/4614/8521/7763/AV2BA901_Original_1889_web.pdf