Headphone Inspection

Huajian Company'sDetailed Explanation of Headphone Inspection Methods and Standards

I. Basic Knowledge of Headphones

1. Classification of Headphones   

Although there are various types of headphones on the market, essentially, the categories are quite limited.

By product structure: open, semi-open, and closed;

By wearing style: over-ear, earbuds, in-ear, behind-the-neck, and ear-hook;

By transducer principle: dynamic and electrostatic.

Headphone Components:

Headband: Generally divided into steel headbands and plastic headbands. Steel headbands usually consist of a steel beam inside a PVC hose, and can be either double or single. Headphones with steel headbands often include an elastic leather headband in addition to the steel beam for adjustable comfort. Plastic headbands are typically made of PP material, which is soft and flexible.   

Locking piece: Plastic/steel strip (metal); only found in over-ear headphones.

Support frame: Plastic/steel strip (metal); only found in over-ear headphones.

Ear cup: Materials include plastic, metal, and wood. Surface finishes are generally standard paint, UV paint, or rubber paint.   

UV paint involves applying a transparent, glossy UV coating over standard paint to make the surface smoother and brighter. Rubber paint involves applying a rubber coating over standard paint to make the surface softer.   

Ear cushions: Materials generally include foam, velvet, leather, and silicone.

Foam cushions are breathable and inexpensive but wear out easily; velvet cushions are comfortable but get dirty quickly; leather cushions offer a premium feel but are not breathable, making them unsuitable for summer; silicone cushions are cool and ideal for summer use.

Speaker: Neodymium iron boron material, diameters: typically f9, f10, f30, f40, f50.

External microphone/boom mic: Plastic   boom (gooseneck tube), mic head (plastic);

Decorative parts: Small accessories on headphones for decoration;

Cable: Length: about 1.2m for portable players, about 2.2m for home computers; material: generally分为皮线 (coated wire) and编织线 (braided wire). Coated wire feels premium, soft, and elastic; braided wire is more wear-resistant and stretch-resistant but less elastic.   

Headphones without a mic typically have a 3-core cable: ground, left, and right signal wires; headphones with a mic usually have 4-core or 5-core cables. 4-core cables share a common ground for left and right, which is not as effective as 5-core. Most branded headphone cables include anti-breakage strands; without them, headphones may fail within a month. Such headphones are not available abroad, as you know.   Most headphone cables use copper, with higher purity (often indicated by N ratings like 4N, 6N...) offering better conductivity and less signal distortion. Common types: TPC (electrolytic copper): 99.5% purity OFC (oxygen-free copper): 99.995% purity   LC-OFC (linear crystal oxygen-free copper or crystal oxygen-free copper): purity above 99.995% OCC (single crystal oxygen-free copper): high purity, above 99.996%, further divided into PC-OCC and UP-OCC.

Plug: Headphone plugs come in 6.35mm, 3.5mm, 2.5mm, and USB. Plugs are typically gold-plated or nickel-plated, with gold offering better oxidation resistance. The 3.5mm plug is most common; USB plugs are for computers and include built-in sound cards.

Inline remote: For volume control, with an adjustment knob;

Mouse tail: The protective coil (cord protector) connecting two components;

Splitter: The solid rubber section where one cable splits into two;

2. Key Headphone Parameters   

(1) Impedance common standard: 16/32 ohms ±3-15% (depending on customer requirements)   

Headphones with lower impedance are easier to drive with audio devices. Since CD and MP3 players have limited power, low-impedance headphones are suitable, typically below 32 ohms;   

(2) Sensitivity common standard: 90-120dB   

For portable players like MP3s, higher sensitivity means more audio details at the same volume. A widely applicable headphone should have a sensitivity of at least 100dB;   

(3) Frequency response common standard: 20-20kHz   

The human ear can hear sounds in the 20-20kHz range, so headphones closer to this range provide more complete sound reproduction. This results in richer details in listening.

II. General Headphone Inspection Standards

(一) Inspection Tools

Ruler, caliper, gauge block, comparison sheet, barcode scanner, anti-static gloves or finger cots, dust-free cloth, alcohol, knife, packing tape, transparent tape.

(二) Inspection Conditions

Eyesight: Inspector's vision must be at least 1.0 (including corrected vision);   

Distance: 300mm±50mm between the eye and the headphone surface; Lighting: Cool white fluorescent light (source directly above the inspector), illuminance of 1000±200 Lux;

Temperature: 15-35°C;

Humidity: 20%-75%;   

Viewing angle: The product inspection surface should be at a 45-degree angle to the table, rotated 45 degrees up, down, left, and right (as shown below):