You need to know the impedance and sensitivity of audio headphones so as to choose those capable of producing an adequate sound level when paired up with your smartphone or other audio outputs. While buying headphone check for manufacturer and model name, type, frequency response, sensitivity, impedance, price, and so on.
The sensitivity indicates the efficiency of the headphone/earphone in converting an incoming electrical signal to sound output. Sensitivity represents how loud the speaker driver inside the headphone/earphone can get. Essentially, sensitivity is a measure of how loud a pair of headphones will play at a given power level. In practice is that you will have to crank the volume knob less to get more volume out of something. The sensitivity of most headphones generally lies between 80-110 dm/mW.
The sensitivity rating of 86dB (decibels) is considered relatively low, while anything above 110dB is on the high-end. Higher the sensitivity, louder will be the sound output and vice versa. While buying a headphone doesn’t go for higher sensitivity. Higher sensitivity while delivering loud sound output can induce distortions in the audio quality. The quality of music is adversely affected. Sensitivity is also referred to as Efficiency, or Sound Pressure Level (SPL).
Exposure to sounds with higher SPL for a longer duration of time is detrimental for human ears and may cause irritation and pain. The best sensitivity range is between 90-100 dm/mW. sensitivity isn’t very useful as manufacturers aren’t always consistent with how they measure it.
Impedance is one of the basic specifications included with every quality pair of headphones. Impedance, we’d argue, is the most important headphone term you need to know. Impedance is one of the headphone specs that often go overlooked, but if you get it wrong you may find your expensive new headphones quite unusable. Headphone impedance is typically rated between 8-600 ohms, with a standard around 32 ohms becoming increasingly common. Impedance matching is the interaction between the source impedance (the device the headphone is attached to) and the headphone impedance. To ensure the highest audio quality, the source and the headphones must pair well.
In general, low impedance headphones (which we will hereby define as below 50 ohms) are designed to work properly with portable devices, as they can efficiently reproduce the adequate sound quality and volume from a low voltage device. Headphones with an impedance greater than 100 ohms are typically professional studio-specific designs.
Most modern headphones are designed in such a way that their impedance matches well on most mobile devices. Devices with an impedance score between 8 and 32 ohms are considered low-impedance devices, and you can comfortably use them with any battery-powered audio source. Anything higher than 32 ohms and your headphones may sound very quiet when paired with a smartphone or an iPod.Devices with impedance higher than 100 ohms are considered high impedance devices. Remember low-impedance devices can be paired with battery-powered devices (iPads, smartphones, laptops, etc.) whereas high-impedance devices require an amplifier to be properly utilized.