A trumpet’s bell beams high frequencies forward, changing timbre with direction of aim.

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

Categorization

• CANDY: Great cocktail fact: a trumpet sounds different depending on where you stand relative to the player.
• XREF: Connects to the reader’s prior soundscape work on how positioning and environment shape perceived sound. — connects to: A trumpet without a bell has stronger high partials than with one; Violin timbre changes with direction as high frequencies become increasingly directional — Eric J. Heller, Why You Hear What You Hear- An…, 1785; A brass bell reflects sounds selectively by frequency (+5 more)
• corroborated: 2 independent passages support this claim — Eric J. Heller, Why You Hear What You Hear- An…, 1532

Broader Connections

• Violin timbre changes with direction as high frequencies become increasingly directional #corroborates (0.90) — Eric J. Heller, Why You Hear What You Hear- An…, 1785
• A brass bell reflects sounds selectively by frequency #expands (0.85)
• Higher frequencies focus sound into a narrowing forward beam #corroborates (0.85)
• The bell acts as a frequency-dependent reflector that shifts brass mode frequencies. #expands (0.80)
• Stringed instruments radiate low frequencies omnidirectionally but high frequencies directionally #expands (0.80)
• A horn amplifies sound without increasing diaphragm motion #expands (0.80) — Eric J. Heller, Why You Hear What You Hear- An…, 539
• Concentrating sound into a smaller solid angle raises horn sensitivity #expands (0.75)