F

Fb (Box Tuning Frequency)
Resonant frequency of ported enclosure. Port length determines Fb. For music: Fb = 30-45 Hz typical. For SPL competition: Fb = test frequency ±2 Hz. Below Fb, output drops rapidly and driver unprotected. → See also: Subsonic Filter, Helmholtz
Chapter 10.3

FIR (Finite Impulse Response)
Digital filter type using only input samples (no feedback). Allows linear phase (no phase distortion). Downside: high latency. Used in advanced room correction (Dirac Live). → See also: IIR, Phase
Chapter 12.6

Fs (Free-Air Resonance)
Driver's natural resonant frequency unenclosed. Measured in Hz. Lower Fs = deeper bass capability. Typical subwoofers: 25-50 Hz. Determined by moving mass (Mms) and suspension stiffness (Cms). → See also: Thiele-Small, Qts
Chapter 10.1

Fuse
Protective device that fails (opens circuit) when current exceeds rating. Protects wire, not equipment. Size fuse for wire gauge, not amplifier rating. Main fuse: within 18" of battery positive terminal. Types: ANL (80-500A), MIDI (30-200A), blade (2-40A). → See also: ANL, Wire Gauge
Chapter 2.3