Being on resonance increases loudness even when energy is trapped inside

Evidence

The transfer function—the ratio of sound pressure level (SPL) inside to SPL outside the instrument, is often cited in connection with the treble boost concept. The transfer function goes up on resonance—that is, energy builds up inside the instrument as compared to outside. Indeed, the sound is incredibly loud (175 dB has been measured inside a trumpet) inside the instrument compared to outside, since end reflection approaches 100% over much of the low-frequency range. The argument goes that more sound energy is trapped inside and is not getting out. According to this argument alone, a partial falling on a resonance would be less loud than if it fell off resonance, which is incorrect. It is better to be on resonance than off, even for low Q and high damping. — Eric J. Heller, Why You Hear What You Hear- An…, 1523

Categorization

• DEFINE: Explains the transfer function concept and why its naive interpretation is wrong.
• CANDY: 175 dB measured inside a trumpet is a striking, tweetable figure.