A

A2DP (Advanced Audio Distribution Profile)
Bluetooth profile for streaming high-quality stereo audio wirelessly from phone to head unit. Mandatory for wireless music playback. Supports SBC codec as baseline, AAC/aptX as optional. → See also: AVRCP, Bluetooth
Chapter 5.2

Active Crossover
Electronic crossover that divides frequency bands before amplification. Each driver receives its own amplified signal. Requires DSP or active head unit plus one amplifier channel per driver. Superior to passive crossovers due to no insertion loss and precise control. → See also: DSP, Passive Crossover
Chapter 4.2

AGM (Absorbed Glass Mat)
Battery construction where electrolyte is absorbed in glass mat separator rather than free liquid. Sealed, maintenance-free, vibration-resistant. Standard choice for car audio auxiliary batteries. → See also: Battery, Flooded
Chapter 11.2

Alternator
Engine-driven generator producing DC current to charge battery and power electrical systems. Factory alternators: 80-140A typical. High-output alternators for audio: 200-400A+. → See also: Big Three, High-Output Alternator
Chapter 11.1

Amplifier
Device that increases signal voltage to drive speakers. Classes: A (inefficient, low distortion), AB (moderate efficiency/distortion), D (high efficiency, compact). Power rating in watts RMS.
Chapters 1.3, 4.4

Amplifier Gain
Input sensitivity control (NOT a volume knob). Adjusts the input voltage level that produces full amplifier output. Set using DMM to match head unit voltage at reference volume to amplifier's rated output voltage. → See also: DMM, RMS
Chapter 4.4

ANL Fuse
Large blade-style fuse for main power wire protection. Ratings: 80-500A. Used at battery connection within 18" of positive terminal. → See also: MIDI Fuse, Fuse
Chapter 2.3

Attenuation
Reduction in signal level, measured in decibels (dB). A -3 dB attenuation is half power. A -10 dB attenuation is 1/10 power.

AWG (American Wire Gauge)
Wire thickness standard. Lower number = thicker wire = less resistance. 8 AWG for moderate power, 4 AWG for 500-1000W, 0 AWG for 2000W+. → See also: Wire Gauge
Chapter 2.2