Modular Trumpet Mouthpiece BackboreCommercial Backbore Descriptions #1 A tight backbore that provides a brilliant sound. #2 A backbore that provides resistance yet provides a lively sound. #2*O A more open version of the #2. #3 Commercial but can be used for a variety of playing situations. Very even from top to bottom. #4* A tighter version of the #4. #4 Open enough to give a full, broad sound. #4*O A more open version of the #4. #5* A tighter version of the #5. #5 Has power with less