It's important to note, however, that using different mouthpieces on the same trumpet can alter the harmonics/partials which stack up in the room, so it's not always easy to know which sound is "the" sound for any particular trumpet. To Vulgano's advice I would simply add that you'll know you're making the right fundamental sound when the combination mouthpiece/trumpet you're playing makes the sound easy to get out and not feel restricted when you play. Another factor which affects the whole issue is the person playing the instrument -- I don't feel there really is a single correct sound for any one trumpet to get out. They can all be made to play so differently in the hands of different people and with different mouthpieces. Essentially, when you have found the mouthpiece and trumpet combination which produces a sound which fits *your* concept of trumpet sound which you want to make, then you've found the right combination.