Over Bore or Under Bore?

Over Bore or Under Bore are terms I have used in my videos but never really explained...and probably not now either but lets try. This usually is in reference to the mouthpiece and the size of the horn. Overbore: the profile of sound from the mouthpiece is too wide and has too many mid and low tones in the vibrations that the mouthpiece produces to make an efficient tone for my concept of sound. Underbore: the sound profile of the mouthpiece is too narrow or too filtered to the higher overtones without enough mids and or lows to fill out the sound character of the horns potential.