A fixed-geometry trumpet can only play a natural harmonic series, not scales

Evidence

With the flared bell and mouthpiece in place, one has a “natural trumpet” of fixed geometry (or, if there are valves, then leaving them untouched approximates a natural trumpet). The lowest playable notes (including the pedal tone) are equally spaced in frequency but widely spaced on the logarithmic musical scale. (For example, the first two notes are already an octave apart, with nothing between.) These are not used for tunes played on a natural trumpet. As the higher harmonics grow closer at high frequency, the resonances (and playable notes) approximate diatonic major and minor scales. A few tricks and some lipping up or down is required to stay in tune. Working in the upper registers, the resonances are weaker and the notes are supported by fewer upper resonant partials. As a result, they do not strongly exhibit the lock-in effect pulling pitch toward a definite frequency (see the following). — Eric J. Heller, Why You Hear What You Hear- An…, 1566

Categorization

• DEFINE: Explains why a natural trumpet (no valves) is limited to harmonic notes and needs lipping to reach diatonic scales.