1.1 · 3.5 mm · TRS / TRRS
Stereo TRS usually carries left, right and common ground. Headset TRRS adds a contact for a microphone; check CTIA/OMTP wiring and call compatibility.
2ann · REFERENCE
Earphone reference
Explore connectors, housing materials, specifications, sound comparisons, fit and care.
01 · Connector guide
Check ① the IEM connector, ② the source output, then ③ pins, polarity and microphone support. An adapter that joins negative balanced outputs can damage the device. Use manufacturer-approved connections.
Source-side plugs
1.2 · 2.5 mm · TRRS
Used for balanced outputs on some players and amplifiers. Avoid sideways force on the small plug. Diameter alone does not establish the wiring; check the device manual.
1.3 · 4.4 mm · TRRRS
Common balanced connection on portable and desktop DAC/amps. Typically five contacts with separate positive and negative signals for each channel. Power and noise depend on the device.
1.4 · 6.35 mm · TRS
Large stereo plug common on desktop amps and interfaces. A headphone socket is usually single-ended; the same shape can carry balanced mono on other equipment, so check its function.
1.5 · USB-C / Lightning
Digital audio needs a DAC in the earphones, cable or adapter. Matching USB-C shapes do not guarantee audio, microphone or volume-control support. Check device and adapter compatibility.
Earphone-side connectors
1.6 · 2-pin · 0.78 / 0.75 mm
Two pins insert straight into the socket. 0.78 and 0.75 mm describe pin diameter and must not be treated as interchangeable. Check flat/recessed/raised housing, side and polarity; do not twist pins.
1.7 · qdc / KZ C-pin
Shrouded two-pin styles surround a raised socket. Similar-looking qdc/KZ labels do not guarantee compatibility: verify pin diameter, shroud depth and polarity for the exact model.
1.8 · MMCX
Round snap connector with a rotating joint. Hold the connector rather than pulling the wire. Recessed or proprietary housings can prevent otherwise standard MMCX cables from fitting.
1.9 · A2DC
Audio-Technica’s Audio Designed Detachable Coaxial connector. Although coaxial, it is distinct from MMCX; use an A2DC cable listed as compatible with your model.
1.10 · T2 / IPX
Small detachable connectors used on some stage and custom IEMs. Not directly interchangeable with MMCX or two-pin. Check T2/IPX designation and the manufacturer’s model compatibility list.
Audio-Technica ↗ · FiiO ↗ · 64 Audio ↗ · Linum ↗ · Sennheiser ↗
Back to topics ↑02 · Earpiece housing materials
These materials describe the outer shell, not the sound-producing diaphragm. These are general tendencies; alloy, formulation, coating and thickness matter. Compare finished weight and fit. Material alone does not establish a bright or warm sound.
2.1 · Resin / acrylic
Suitable for complex shapes and custom contours, with clear or coloured finishes. Properties vary with formulation and curing. Avoid drops, high heat and harsh cleaners; inspect cracks and socket areas.
Sound and interpretation
Resin has no established fixed sound signature. Moulding supports acoustic tubes and cavities; bass and treble still depend on drivers and tuning.
2.2 · Plastics such as ABS / PC
Can support lightweight designs and versatile moulded shapes. Plastic does not imply poor sound. Inspect seams, nozzle strength and coatings; heat and chemical resistance vary by material.
Sound and interpretation
Plastic does not inherently sound thin. Cavity volume, sealing, vents and vibration control matter; the same material can support bass-heavy or bright tuning.
2.3 · Aluminium / magnesium alloys
Relatively light metals suited to precision machining and surface finishing. Anodising or paint does not eliminate scratches or dents. Actual weight and stiffness depend on alloy, thickness and geometry.
Sound and interpretation
Descriptions such as clear or firm must not be mistaken for a metal-only effect. Stiffness and geometry can affect resonances, but aluminium does not necessarily boost treble.
2.4 · Stainless steel
Rigid and available in polished or matte finishes; denser than aluminium at equal volume. A small shell may still wear comfortably. Check fingerprints, surface marks and long-session pressure; wipe off sweat after use.
Sound and interpretation
Weighty or dense are listening descriptions, not consequences of shell weight. Examine thickness, geometry and damping rather than equating a heavy housing with more bass.
2.5 · Titanium
Valued for strength relative to weight and corrosion resistance. At equal volume it is generally heavier than aluminium and lighter than stainless steel; finished weight depends on design. Material alone does not establish comfort or sound.
Sound and interpretation
FiiO links FH9 shell rigidity and internal design to reduced unwanted resonance. This is a product-specific design claim aimed at clarity, not a shared signature of every titanium IEM.
2.6 · Wood / stabilised wood
Natural grain and colour vary. Stabilisation such as resin impregnation improves stability but does not make an IEM waterproof. Distinguish a wood faceplate from a wood body; avoid water, heat and abrupt humidity changes.
Sound and interpretation
Wood products are described as warm, natural or resonant. JVC WOOD also emphasises natural warmth and musicality, but combines wood diaphragms, housings and acoustic design; this does not isolate a shell or decorative plate effect.
2.7 · Ceramic
Can provide a hard, smooth surface. Scratch resistance does not imply impact toughness: hard drops may chip or fracture it. A ceramic body differs from ceramic coating over metal.
Sound and interpretation
A hard, smooth surface does not establish clear treble. No consistent ceramic-only signature was established here; compare the product’s drivers, tuning and resonance control.
2.8 · Mixed materials / special alloys
Many IEMs combine resin shells, metal nozzles and wood plates. Amorphous zirconium alloys are distinct from ceramics. Do not infer the whole housing from decoration: check each part and actual earpiece weight.
Sound and interpretation
Do not predict sound from decorative faceplate material alone. Examine the acoustic cavity, nozzle and shell assembly, then compare measurements and listening under matched conditions.
FiiO FA1 · resin ↗ · FiiO FH7 · alloy ↗ · FiiO FH9 · titanium ↗ · Campfire · ceramic ↗ · Sennheiser · zirconium ↗ · JVC WOOD · design and sound ↗
Back to top ↑03 · Specifications and connections
Impedance · Ω
Impedance describes the electrical load and can vary with frequency. Check the stated test frequency; assess it together with sensitivity and the source output.
What to check
Check the stated Ω and test frequency. Earphone impedance and source output impedance are different specifications.
Practical example
16 Ω is not automatically easier to drive than 32 Ω. Include sensitivity when comparing noise and output headroom at your listening level.
Sensitivity · dB/mW vs dB/V
Sensitivity relates sound pressure to input. dB SPL/mW and dB SPL/V use different references: compare only after checking units and measurement frequency.
What to check
Compare at the same input reference and frequency. Maximum power handling is not sensitivity; a bigger number is not a sound-quality score.
Practical example
100 dB/mW and 100 dB/V are not equal sensitivities. If a listing only says 100 dB, find the input reference in the manufacturer specification.
Crossover · driver count
Electrical and acoustic filtering divide and combine driver bands. Six drivers do not necessarily mean six crossover ways; multiple units can share a band. Integration matters.
What to check
Look at frequency roles as well as unit types and counts. Acoustic tubes and filters also shape the output, alongside electrical circuitry.
Practical example
1DD+2BA does not necessarily mean three crossover ways. Listen for abrupt changes in tone or level across voices and instruments.
Connectors · compatibility
MMCX or two-pin earphone connectors and 3.5 mm or 4.4 mm source plugs describe different ends. Check dimensions, housing and wiring, and follow the equipment manual. Balanced output alone is not a quality ranking.
See connector types and compatibility →
What to check
Even 0.78 mm two-pin connectors can differ in recessed or protruding housings. Check MMCX housing clearance and manufacturer compatibility as well.
Practical example
Do not assume a passive adapter makes a single-ended earphone compatible with a balanced output. Joining the negative channels can damage some output circuits; follow the source manual.
DAC / amp · gain · noise
A DAC converts digital audio to analog; an amplifier supplies the voltage and current needed by the earphone. Gain is an amplification ratio, not a quality grade.
What to check
With sensitive IEMs, fine low-level volume control and a quiet background may matter more than maximum power.
Practical example
Start with low gain when offered. If it provides sufficient level and headroom, high gain is not automatically an improvement.
04 · Compare and adjust sound
Frequency response
Read frequency horizontally and sound pressure or relative level vertically. Compare rigs, fit, tips and normalization before comparing curves. A response curve does not describe every listening or comfort characteristic.
What to check
Distinguish raw response from target-compensated response. Axis ranges and normalization can change the apparent size of differences.
Practical example
Start with relative bass, vocal and treble balance. A narrow treble peak alone cannot establish sibilance or resolution. A 20 Hz–20 kHz specification does not promise a flat response.
EQ · frequency, gain and Q
EQ adjusts level by frequency. In PEQ, frequency selects the center, gain sets the level change and Q controls width; higher Q generally narrows a given filter type.
What to check
Boosts can cause digital clipping. Leave preamp headroom for the combined filter response, not just the largest individual boost.
Practical example
For a little more bass, try a small broad low-frequency adjustment and compare at similar loudness. Recheck any borrowed preset for your model, fit and preference.
Review terms · tone and space
Bright often describes treble presence; warm often describes bass or lower-mid weight. Soundstage refers to perceived space, while imaging describes perceived placement.
What to check
Resolution, speed and naturalness can mean different things to different reviewers. Read the instrument, passage and conditions rather than treating them as single metrics.
Practical example
Sibilance describes prominent s or sh vocal sounds, not all treble energy. Recording and fit can influence it. These are general definitions, not listening findings for a product.
Comparing earphones · consistent conditions
Align conditions before judging differences: use the same passage, source and EQ state, and check the seal of each earphone first.
What to check
The same volume number need not produce equal loudness when sensitivities differ. Match levels where possible; matching by ear is not a precision level-matched test.
Practical example
Compare one attribute at a time, such as kick/bass separation, vocal distance or cymbal decay. Reverse the order and revisit after a break. This is an editorial comparison aid.
05 · Fit and care
Ear tips · seal · fit
Tip size and seal can change bass response. Check both ears and choose a comfortable fit. A material name alone does not guarantee the same tonal change on every earphone.
What to check
The two ears need not use the same tip size. Confirm secure attachment to the nozzle and reassess size and insertion depth if pressure develops.
Practical example
If bass is weak on one side, reseat the earphone and check its seal before changing EQ. Let foam tips expand as directed by their manufacturer.
Isolation · ANC · ambient sound
Passive isolation physically reduces outside sound through tips and the housing. ANC uses microphones and an actively generated signal to reduce noise. They are different mechanisms.
What to check
Results depend on noise type and fit. A vent does not automatically make an IEM open-back, and a wired IEM does not automatically have ANC.
Practical example
For commuting, compare reduction of rumble and voices separately rather than masking them with more music volume. Prioritize awareness when outside sounds are needed.
Care · storage · quiet channel
Blocked nozzle meshes or filters and poorly attached tips can change sound. First check visible condition, tip attachment and the source balance setting.
What to check
Follow the model manual. Do not push improvised needles deep into the nozzle or put cleaning liquid inside the housing. Check which tip materials can be washed.
Practical example
Let moisture dry after use and store without sharp cable bends. If the problem persists across tips, tracks and sources, seek manufacturer service rather than forced disassembly.