H

Head Unit
Source component, also called receiver or radio. Provides: tuner (AM/FM), USB/Bluetooth inputs, preamp outputs (RCA), DSP (in higher-end units). Single-DIN (2" tall) or double-DIN (4" tall). → See also: Preamp Output
Chapter 5.1

Helmholtz Resonance
Resonance of air mass in port and air spring in box. Determines ported enclosure tuning frequency Fb. Formula involves port area, length, and box volume. Named after Hermann von Helmholtz. → See also: Fb, Ported Enclosure
Chapter 10.3

HRTF (Head-Related Transfer Function)
Frequency-dependent filter representing how ears receive sound from specific directions. Used in spatial audio (Dolby Atmos) to create 3D sound positioning. Personalized HRTFs provide best results. → See also: Dolby Atmos
Chapter 14.1