The bell acts as a frequency-dependent reflector that shifts brass mode frequencies.
Evidence
The bell modifies as a function of frequency the manner in which the open end of the pipe acts as a reflector of sound waves arriving there from within the pipe. A detailed discussion is provided by Benade (1976), from which a summary is given here. Lower-frequency components are reflected back into the instrument from the narrower part of the bell, while higher-frequency components are reflected from the wider regions of the bell. Frequencies higher than a cutoff frequency determined by the diameter of the outer edge of the bell (approximately 1500 Hz for a trumpet) are not reflected appreciably by the bell. Adding a bell to the main bore of the instrument has the effect of making the effective pipe length longer, with increasing frequency. The frequency relationship between the modes of the stopped cylindrical pipe (odd-numbered modes only: 1f, 3f, 5f, 7f etc.) will therefore be altered such that they are brought closer together in frequency. This effect is greater for the first few modes of the series. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1246
Categorization
Category: Causal Relationships
Related
- The bell reflects low frequencies deep inside and high ones near its rim (similarity 0.96)
- Brass instrument bells reflect low frequencies early and pass high ones. (similarity 0.94)
- A trumpet’s bell beams high frequencies forward, changing timbre with direction of aim. (similarity 0.88)
- A speaking-trumpet flare can boost lower frequencies when wall dissipation dominates resonance enhancement. (similarity 0.84)
- Clarinet bell suppresses tonehole back-reflections at short wavelengths (similarity 0.83)
- A horn equation quantifies how bell flare shapes resonance frequencies. (similarity 0.83)
- A bell lowers a tube’s cutoff frequency, easing high-frequency escape (similarity 0.83)
- A trumpet without a bell has stronger high partials than with one (similarity 0.83)
- A brass bell reflects sounds selectively by frequency (similarity 0.82)
- Confining reflected sound can radiate more power than an open bell on resonance. (similarity 0.82)
- A bell suppresses high partials by radiation loss, not boosting them (similarity 0.80)
- Wall friction and resonance oppose each other in determining instrument sound radiation. (similarity 0.80)
- Treble boost from trumpet bells may not actually make high frequencies louder (similarity 0.80)
- Brass playing drives the lips above their natural vibration frequency. (similarity 0.80)
- Removing a trumpet bell empirically strengthens the high partials above 1500Hz (similarity 0.80)
Broader Connections
- A brass bell reflects sounds selectively by frequency
#expands(0.95) — David Howard, Jamie Angus, coustics and Psychoacoustics, 1272 - Horn bells boost lower frequencies where wall friction dominates resonance enhancement
#expands(0.85) — Eric J. Heller, Why You Hear What You Hear- An…, 1708 - Bounded sound waves change impedance with tube area, causing reflections
#expands(0.80) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 174 - Concentrating sound into a smaller solid angle raises horn sensitivity
#expands(0.80) — David Howard, Jamie Angus, coustics and Psychoacoustics, 2519 - Indian temple bell energy shifts between modes while singing bowls stay harmonic
#complicates(0.75) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1319