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.

ABS: Acrylonitrile butadiene styrene, a common engineering thermoplastic with good mechanical properties and temperature resistance. Difficult to FDM print due to warping, but vapor-smoothable with acetone.

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.

Bass reflex: An enclosure design that uses a tuned port to extend bass response below the driver’s sealed-box rolloff. Also called a vented enclosure.

Break-up mode: A condition where different parts of the diaphragm move non-uniformly, producing resonances typically above 5 kHz.

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.

CLD (Constrained Layer Damping): A damping technique using a viscoelastic material (like Dynamat) bonded to a vibrating structure to convert vibration to heat.

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.

Diffraction: The bending of sound waves around obstacles (like a baffle edge), creating interference patterns that affect frequency response.

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

Dynamat: Brand name for constrained layer damping material (butyl rubber plus aluminum foil), applied to cup interiors to damp structural vibrations. It is not acoustic absorption.

Dynamic driver: The most common driver type: a voice coil attached to a diaphragm, moving in a magnetic gap. Simple, hard to break, 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.

Front chamber: The acoustic space between the driver face and the ear. Its volume is set primarily by ear pad depth, and it affects high-frequency response and soundstage character.

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

Group delay: The time delay experienced by each frequency in a system. Non-uniform group delay means different frequencies arrive at the ear at different times.

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.

Impulse response: A measurement showing how a headphone responds to an instantaneous transient. Reveals ringing, resonances, and time-domain behavior not visible in frequency response alone.

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.

LiPo (Lithium Polymer): A rechargeable battery chemistry used in wireless audio devices, with a nominal voltage of 3.7 V. Requires a dedicated charging circuit and protection against over-discharge.

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.

Mass loading: Adding mass to a vibrating structure to lower its resonant frequency and damp structural vibrations. Different from acoustic damping: it affects the structure, not the air.

Nominal impedance: A single representative impedance value for a driver, typically measured at 1 kHz. The actual impedance varies with frequency.

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.

PETG (Polyethylene Terephthalate Glycol): A 3D printing filament with better impact resistance and temperature tolerance than PLA. Recommended for structural headphone components.

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

PLA (Polylactic Acid): The most common 3D printing filament. Easy to print but brittle under repeated stress, with a low glass transition temperature (~60°C). Good for prototyping; switch to PETG for final builds.

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.

PPI (Pores Per Inch): A specification for acoustic foam density. Higher PPI means smaller pores and more absorption of higher frequencies. Typical range for headphone use is 20–60 PPI.

Q factor (Qts, Qtc): A dimensionless parameter describing the damping of a resonance. High Q means a sharp, peaked resonance; low Q means a broad, well-damped one. Qts is for the driver in free air; Qtc is for the driver in a closed enclosure.

Rear chamber: The enclosed volume behind the driver in a closed-back headphone. Its volume directly affects bass extension and resonance behavior.

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.

Sorbothane: A proprietary viscoelastic material used for vibration isolation and damping. Effective for reducing the mechanical transmission of vibrations.

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.

TP4056: A widely used single-cell LiPo battery charging IC, available as inexpensive module boards. The standard DIY choice for Bluetooth headphone charging circuits.

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.

TRS: A three-conductor plug (tip, ring, sleeve) carrying left, right, and ground, the standard stereo audio connector, with no microphone contact.

Vas (equivalent compliance volume): The volume of air with the same acoustic compliance as the driver’s suspension. A larger Vas means more compliance and benefits from a larger enclosure.

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.