Glossary

The manual uses a fair amount of vocabulary, and it’s all defined where it first comes up — but here it is collected in one place to look up as you go.

AAC — A Bluetooth audio codec that performs well on Apple devices; one of several codecs a source and headphone may share.

aptX — A family of Qualcomm Bluetooth codecs (aptX, aptX HD, aptX Adaptive, aptX Lossless) offering better quality than the SBC baseline, provided both ends support it.

Baffle — The plate the driver mounts to, separating the front of the diaphragm from the rear. The driver-to-baffle joint is a critical seal.

Balanced armature (BA) — A small, efficient driver type that covers a limited frequency band, common in in-ear monitors where several are combined with a crossover.

Boundary element method (BEM) — A simulation technique that solves the wave equation across a 3D mesh, used for radiation and diffraction. More accurate and more demanding than lumped-element modeling.

Channel matching — How closely the left and right channels agree. Poor matching smears the stereo image; it’s both a mechanical and an electrical concern.

Closed-back — A design with a sealed rear chamber, giving isolation and stronger low bass at the cost of a more closed-in sound.

Codec — The compression scheme used to send audio over Bluetooth (SBC, AAC, aptX, LDAC, LHDC, LC3). Both the source and the headphone must support a codec to use it.

Coupler — An artificial ear canal with a microphone, used in a measurement rig. The IEC 60318-4 standard defines the common type.

Compliance — A measure of springiness — how easily something (a suspension, a volume of trapped air) yields to force. Larger compliance is a softer spring.

CSD (cumulative spectral decay) — A “waterfall” plot showing how energy at each frequency decays over time, revealing resonances that ring on after the signal stops.

Damping — Material (felt, foam, fiber fill) added to absorb acoustic energy, used to tame resonances, reflections, and excess bass.

Diaphragm — The thin membrane that moves to push air and create sound. The heart of any driver.

Driver — The transducer that turns an electrical signal into sound. Dynamic, planar magnetic, balanced armature, and electrostatic are the main types.

Dynamic driver — The most common driver type: a voice coil attached to a diaphragm, moving in a magnetic gap. Simple, robust, good bass.

Electrostatic — A driver type using a charged film between electrodes; very low distortion, but requiring special high-voltage amplification.

Frequency response (FR) — How loud a headphone plays at each frequency, the single most-used measurement. Usually shown as a curve.

Fs — A driver’s free-air resonance frequency, one of its Thiele-Small parameters.

Harman target — A research-based preference curve describing how a neutral-sounding headphone tends to measure on a standard rig. A common reference target, not a law.

IEC 60318-4 — The standard (often called “711”) for the coupler used in headphone and IEM measurement. Reliable to roughly 10 kHz.

Impedance — The driver’s opposition to current, in ohms, and how it varies with frequency. Affects how it pairs with an amplifier.

LC3 — The codec for Bluetooth LE Audio, more efficient than older codecs and the basis for broadcast features like Auracast.

LDAC — Sony’s high-bitrate Bluetooth codec aimed at high-resolution audio.

Lumped-element method (LEM) — Modeling a driver-and-chamber system as an equivalent electrical circuit of masses, compliances, and resistances. The tractable approach for headphone simulation.

Open-back — A design with a vented or open rear, giving a more spacious, natural sound but little isolation and bass that leaks out both ways.

Pinna — The fleshy outer ear. In a measurement rig, a silicone pinna sits in front of the coupler to load over-ear headphones realistically.

Planar magnetic — A driver type using a flat diaphragm with an embedded conductor between magnet arrays; even, low-distortion sound, usually heavier and less efficient.

Polarity — Which way a driver moves for a given signal. Both channels must be in phase, or the bass cancels and the image collapses.

Resonance — A frequency at which something naturally wants to vibrate, where energy piles up and rings. Sources include the driver, the air cavities, and the structure.

REW (Room EQ Wizard) — The free, de facto standard measurement software used across the hobby.

SBC — The baseline Bluetooth audio codec that every device supports; the guaranteed fallback when nothing better is shared.

Sealed — Fully closed, with no leak. A sealed rear chamber maximizes isolation and bass but can produce a resonance peak.

Sensitivity — How loud a driver plays for a given input, often quoted in dB per milliwatt or per volt. Together with impedance, it tells you how easy a headphone is to drive.

Soundstage — The perceived sense of space and width in the sound, influenced strongly by open versus closed design.

SPL (sound pressure level) — Loudness, measured in decibels. Calibrating SPL lets a measurement read absolute levels.

Standing wave — A resonance in a cavity where a reflected wave reinforces itself at a particular frequency, building a fixed pattern of loud and quiet regions.

Thiele-Small parameters — A driver’s key electro-mechanical numbers (resonance, compliance, moving mass, motor strength, and more) used to model and predict its behavior.

THD (total harmonic distortion) — How much a driver adds harmonics not in the original signal. Usually low; a sudden spike often signals a mechanical fault.

TRRS — A four-conductor plug (tip, ring, ring, sleeve) carrying left, right, ground, and mic — the single-jack headset standard. The CTIA pinout is the modern standard.

Voice coil — The coil of wire attached to a dynamic driver’s diaphragm; current through it in the magnetic gap is what moves the diaphragm.