Headphone Impedance & Sensitivity – What You Need To Know

Headphone impedance and sensitivity are two parameters that are often confused and misunderstood. It gives rise to questions like “why a high impedance headphone sounds all right on a laptop audio jack?”.

Many headphone users assume that a high impedance headphone automatically means that it will be barely audible without a headphone amplifier. Once you’ve understood what headphone impedance and sensitivity are, and that they are a different entity, you’ll find the answer to why some high-impedance headphones work without an amp.

What are headphone sensitivity and impedance?

Headphone Sensitivity

Headphone sensitivity is a measurement of the loudness of the headphone when a certain unit of power is applied. Loudness is expressed in decibel (dB) and most headphones are designed to sound above 100 dB.

Sensitivity is the audio power it takes to get to a certain degree of loudness.

Headphone sensitivity is expressed in dB/mW. For example, the Sony MDR-ZX110 has a sensitivity rating of 98 dB/mW. It means that applying 1 mW of audio power will generate an audio level at 98 dB which is close to the factory surrounding.

Meanwhile, the Razer Kraken X has a sensitivity of 109 dB/mW, which means an equivalent audio power will result in a much louder sound.

It’s important to note that doubling or halving the audio power will increase or decrease the loudness by 3 dB.

Headphone Impedance

Headphone impedance is an electrical property of how the headphone resists current passing through. Audio signals are basically voltage and current, with different amplitude and frequency. Impedance can consist of resistance, inductance, and capacitance, or any of the elements. Both inductance and capacitance are influenced by frequency.

Headphone impedance is largely attributed to the coil winding on its driver. The more turns on the winding, the higher impedance is the coil. Low impedance headphones are those that measure 32 Ohm or below. Those that are above 100 Ohms are considered high-impedance headphones.  The Beyerdynamic DT900 Pro has a version with 600 Ohm coils.

As impedance increases, the current that passes through it decrease at a particular voltage. This explains why high impedance headphones need an amplifier to get the required amount of current across the coil.

It is also important to align headphone impedance with the audio soure’s impedance. Generally, the headphone impedance should be at least 8x the source’s impedance. This is to ensure that sufficient voltage falls across the headphone and not lost at the source output.

Why Some High Impedance Headphone Can Be Driven Without An Amplifier?

Headphone impedance determines how much power is transferred from the source to the coil. However, it does not determine if the received power is converted efficiently to sound. Headphone drivers from different manufacturers may have different structural and electrical designs, which affects their ability in producing audible sound from the received power.

Some high-impedance headphones may be highly sensitive, which is reflected in a higher number of dB/mW. It means that the headphone can produce relatively louder volume with the same amount of power compared to its peers.

This is why you’ll still get relatively good audio for some high impedance headphones without an amplifier.

What’s The Best Headphone Sensitivity?

There isn’t a magic number for headphone sensitivity.  What’s important is to have a setup that gives you good audio quality at a comfortable level. Most headphones are designed to produce 100 dB of loudness but it’s hazardous to listen to such loudness. Usually, people settle for audio between 60 dB – 80 dB.

So, if you’re using a headphone with 100 dB/mW, you’ll need to connect it to an audio jack that delivers sufficient voltage to get the power needed for the optimum audio level.

Bottom Line

Headphone impedance and sensitivity are different parameters, but equally important in determining if a headphone can perform to its best when plugged into an audio source.