There are many technical terms associated with headphones, and headphone sensitivity is one that deserved a simple and clear explanation.
If you’ve checked out what headphone sensitivity is about, you may get different versions depending on whether you’re browsing a headphone brand or review site with unknown writers.
As someone who’s involved in electronics engineering in 10 years, I feel that non-technical users deserve better justice in understanding what headphone sensitivity is all about.
What Is Headphone Sensitivity
The term sensitivity can be taken literally. Sensitivity involves a trigger and reaction, just as kicking a ball and having the ball flying across a distance. If you’re kicking a bigger ball with the same force of a smaller ball, the latter will travel a greater distance.
You can relate headphone sensitivity as with the process of kicking the ball. The force of kicking relates to the power of the signal audio applied. Headphone sensitivity needs to be discussed along with the driver impedance.
Driver impedance is the force that attempts to push back or limit the electrical current of the audio signal. It can also be visualized as the total mass of the ball that you kicked.
The reaction, which is the end result of what headphone sensitivity is all about, is the volume of the audio. Naturally, a low impedance headphone will be more sensitive compared to a high impedance headphone.
Headphone sensitivity is measured in units of decibels per milliwatt (dB/mW). Usually, you’ll find headphones are rated between 90 dB/mW to 110 dB/mW. For example, the Sony MDR-ZX110 has a sensitivity of 98 dB/mW.
In other words, applying 1 mW of audio power will result in 98 dB of amplitude. That’s like the sound of a busy subway. It’s important to note that the change in dB relative to mW is not linear. Doubling the power will lead to an increase of 3dB.
Sound Pressure Level Vs. dB/mW Vs. dB/mV
Now that, we’ve got the definition of headphone sensitivity right, let’s take a look at some common terms and measurements often used.
Sound is transferred when molecules vibrate in the air. When a jet roars by the sky, sound waves, which are powerful vibration of molecules, travel to the air. The same goes for the gentle rustling of leaves in the forest.
The vibration then picked up by your ears with the eardrum replicating the vibration. The sound pressure level is how much vibrational pressure delivered for a certain volume of the audio source. Therefore, some headphone manufacturers use SPL dB/mW as a measurement for headphone sensitivity.
Headphone sensitivity is also expressed in dB/mV or decibel per unit of millivolt. Power is the product of voltage(V) and current (I), as defined by the following equation.
P = I x V
Often, there’s a slight difference between measurements in dB/mV and dB/mW as the latter needs to take account of the current of the audio signal.
Most manufacturers will use dB/mW to measure headphone sensitivity as it takes into account both current and voltage delivered.
Headphone Sensitivity, Loudness And Hearing Loss
While most headphones are rated around 90 dB to 100 dB, it’s unlikely that you’ll need to tune the volume to deliver a full 1 mW of power. Listening to prolonged audio of 90 dB and above for long hours will result in hearing loss.
Here’s a table of sound level and exposure limit, before you risk damaging your hearing.
- 90 dB: 8 hours
- 95 dB: 4 hours
- 100 dB: 2 hours
- 105 dB: 1 hour
- 110 dB: 30 minutes
- 115 dB: 12 minutes
- 120 dB: Avoid or hearing damage ensues.
Of course, this table serves as a guideline and you should be aware that listening to moderate volume headphones for long duration can also affect your hearing.
If you feel uncomfortable after an hour of non-stop music, take off the headphone and give your ears a deserving rest.
Low Sensitivity vs High Sensitivity Headphone
As high sensitivity headphones are louder compared to low sensitive headphones with the same audio power, does that mean that the former is the better choice?
As much as headphone sensitivity is a factor, you’ll need to take into consideration the power ratings of the audio source. If you use a high sensitivity headphone on an amplifier that sends out a powerful audio signal, you’ll get distortion and possibly blowing out the headphone at close to maximum volume.
Ultimately, headphone sensitivity is one of the many factors you need to consider in choosing a headphone.