A trumpet without a bell has stronger high partials than with one

Evidence

The third effect of the bell is not something we necessarily would have wanted: the higher frequencies are beamed preferentially forward, so that the timbres of a trumpet aimed at you and one aimed away are different. If the trumpet tube had been cut before the flare of the bell started, the sound radiation pattern would be much more nearly isotropic. This fact may explain some of the confusion regarding the effect of a bell on the strength of the upper partials: adding a bell makes the instrument louder overall by bringing the resonances into better alignment, and the listener or microphone may be located where the higher frequencies are being beamed. — Eric J. Heller, Why You Hear What You Hear- An…, 1532 (#expands, via linked claim)

4. When partials higher than the sixth or seventh are very distinct, the quality of the tone is cutting or rough… . The most important musical tones of this description are those of the bowed instruments and of most reed pipes, oboe, bassoon, harmonium and the human voice. The rough, braying tones of brass instruments are extremely penetrating, and hence are better adapted to give the impression of great power than similar tones of a softer quality. — David Howard, Jamie Angus, coustics and Psychoacoustics, 1520 (#expands, via linked claim)

Categorization

• XREF: connects to: Most acoustics texts attribute trumpet brilliance to treble boost; A bell suppresses high partials by radiation loss, not boosting them; A trumpet’s bell beams high frequencies forward, changing timbre with direction of aim. — Eric J. Heller, Why You Hear What You Hear- An…, 1532 (+2 more)

Broader Connections

• A trumpet’s bell beams high frequencies forward, changing timbre with direction of aim. #expands (0.80) — Eric J. Heller, Why You Hear What You Hear- An…, 1532
• Distinct high partials make tones sound cutting or rough and powerful #expands (0.75) — David Howard, Jamie Angus, coustics and Psychoacoustics, 1520
• Of four brass instruments, only the trumpet shows prominent high harmonics #corroborates (0.73)