Choosing the right headphones: check the power, sensitivity and impedance
For headphones to work as effectively as possible with a DAP, certain criteria need to be met. The output power of the DAP needs to be adapted to the headphones’ sensitivity and impedance. Just like those of a speaker, the headphones’ transducers (drivers) have a sensitivity rating. For the same amount of current delivered by the DAP, the sound produced is more or less loud. Furthermore, these drivers feature a given resistance to the electrical current sent by the DAP, which is called impedance.
The higher the impedance, the quieter the DAP will play.
Choosing the right headphones: with a low-powered DAP
With a low-powered DAP, it’s imperative to choose headphones with a high sensitivity rating (> 100 dB) and a low impedance (< 50 Ohms).
A low-powered DAP is a DAP that doesn’t deliver more than 80 mW (with 32 Ohm headphones).
This power decreases the higher the headphones’ impedance gets, often with a couple of milliwatts under 300 Ohms. This is the case with ultra-compact DAPs, with integrated DAC headphone amps, unable to get the best out of demanding headphones.
Choosing the right DAP: with headphones that are difficult to drive
Headphones that are difficult to drive combine two factors: a low sensitivity rating (< 100 dB) and a high impedance, from 150 to 600 Ohms. These factors aren’t coincidental, but are the result of the manufacturer’s desire to use high-power headphone amps (with a full-bodied, assertive sound).
With such headphones, it’s highly recommended to choose a DAP with an output power rating superior to 300 mW at 32 Ohms.
Choosing the right DAP: external headphone amp
If you own an audiophile grade DAP with an average output power rating (Astell&Kern for example), but still wish to use high-impedance headphones, it’s possible to use an external headphone amplifier, either connected to the DAP’s headphone/line output, or you can connect a headphone amp with an integrated DAC to the DAP’s USB output.
Choosing the right DAP: with in-ear headphones
In-ear headphones always have a high sensitivity rating, paired with a low to average impedance. By definition, they are easy to drive with any high-end DAP and, therefore, the power of the DAP isn’t a key criterion. It’s very important, however, to make sure that the DAP’s signal-to-noise-ratio is very high. Otherwise, background noise will be audible, the earpiece being inserted deep into the ear.
With its signal-to-noise-ratio of 107 dB, the Shanling M0 DAP generates a slight background noise, which can be tiresome. The FiiO M7 however, with its signal-to-noise-ratio of 117 dB, is suitable for very sensitive in-ear headphones.
Choosing the right DAP: with Bluetooth headphones
Sometimes we are asked about the importance of the sensitivity of Bluetooth headphones with a DAP. It is true that some headphone manufacturers communicate the sensitivity of the transducers, or even their impedance. But these are provided as an indication only, and in reality only concern the headphones’ integrated amp. Only digital data is transmitted over Bluetooth connection.
