In-ear headphones

Sony MDR-E9LP Black

Over-Ear (cover the ear completely), on-ear (pressed against the ear), in-ear (inserted into the ear canal) or earbuds (inserted into the auricle, but not inserted into the ear canal).

The upper limit of the frequencies reproduced by the device. The human ear hears the standard frequency range: 20 Hz – 20000 Hz.

No higher than 32 Ohms for smartphone headphones. When using a good player or amplifier, it can be up to 100 Ohms. For stationary models you should coordinate the impedance with the amplifier power

More sensitive headphones will play louder than headphones with less sensitivity (with the same signal level and resistance)

Most of the headphones are dynamic but there are electrostatic, isodynamic, etc.

The number of drivers in each headphone. However, quantity does not equal quality. Driver coordination, their configuration, correct crossover, sound bores affects the sound

The length should allow you to lay the cable with a small margin. The longer the cable, the more impact it can have on the sound.

The material of earpads affects both your comfort and the sound. It can be leather, eco-leather, velour, fabric/microfiber and foam rubber.

The size of the driver membrane

Open (with no insulation) or closed (passive noise insulation) or semi-open (intermediate version). Open headphones sound more airy and provide a wide stage, closed ones provide noise isolation and amplify low frequencies.