The vocal tract actively amplifies speech rather than merely filtering it

Evidence

In spite of its importance, some implications of resonance are often sadly overlooked. For example, the source filter theory of vocalization (see section 17.4) assigns only a passive filtration role to our vocal tract, so that it merely “suppresses the passage of sound energy at certain frequencies while allowing its passage at other frequencies.” In fact, the vocal tract is an active amplifier at some frequencies (the formants), literally coaxing more energy out of the vocal fold air pulsations than without the vocal tract attached. — Eric J. Heller, Why You Hear What You Hear- An…, 883

Categorization

• XREF: Connects to why we hear what we hear — formant amplification is central to speech perception. — connects to: Speech excitation is not coupled to tract resonances, unlike most instruments; Vocal tract sound transmission is governed by cross-sectional area; The voice drives the tract noninteractively whereas trumpet lips receive feedback (+2 more)
• QUESTION: What exactly is the mechanism by which the tract coaxes more energy out of the fold pulsations? Worth investigating.
• DEFINE: Clarifies the active-amplifier role of formants versus the passive-filter view.
• corroborated: 3 independent passages support this claim — Eric J. Heller, Why You Hear What You Hear- An…, 883

Broader Connections

• Speech excitation is not coupled to tract resonances, unlike most instruments #contradicts (0.85)
• The voice drives the tract noninteractively whereas trumpet lips receive feedback #expands (0.85)
• Speech production reduces to a source-filter model with glottal or noise sources #contradicts (0.80)
• Vocal tract sound transmission is governed by cross-sectional area #qualifies (0.75)