What Impedance means?
Headphones to simply put are an electronic device and every electronic component has some kind of resistance. The resistance which is in the driver unit of the headphone is known as impedance.
Headphone impedance is usually in the 8-600 ohm range, with most of the consumer headphones having 32 ohm impedance. If impedance is high in a headphone then it requires more power to run and for that we need to add external amplifiers to amplify the power to the required levels.
But which one is better Low or High Impedance?
Generally, high impedance headphones i.e. more than 100 ohms are of 1990’s era. Back then resistors were used to attenuate the output power of speakers and this way the circuit was made in a cost effective manner.
But the downside to this is high impedance headphones can not be driven by mobile devices, only professionals were the ones using them and required professional equipment to take advantage of these headsets.
Nowadays as the usage of commercial headphones is usually with mobile devices we need low impedance headphones that could be run by mobile devices such as iPods, mobile phones, tablets and laptops.
Very low impedance headphones are poor quality i.e. they can not produce sound very accurately and very high impedance headphones require professional equipment. But for todays needs we have found a balance at 32ohms. Generally, commercial headphones have this impedance. It is a balance between being not too low and not too high for commercial mobile device usage.
Sensitivity of Headphones
Sensitivity is the measurement of volume of headphone at a certain power level. To put it simply, it is with how much little power headphone driver would start to produce sound and at a fix std power level how loud they can be.
Standard values for headphone sensitivity rating are 1KHz specific frequency at 1mW power level.
Generally, headphones have a sensitivity range from 90dB to 105dB and headphones exceeding this value or preceding this value might be considered extremely sensitive or insensitive.
Distortion is the phenomena which occurs when the source is providing more power than headphone can handle and the user hears a crackling sound instead of music.
This is where impedance matching comes into account. Impedance matching is done to avoid distortion and derive maximum performance out of your headphones.
The impedance of Amplifier and headphones is compared and matched so that the source impedance i.e. of amplifier is lower than the load impedance of headphones.
That is why low impedance headphones are not recommended for professional use where output is produced through an amplifier.
Frequency and Impedance
Headphone drivers are designed to produce frequencies ranging from 20Hz to 20Khz. Almost all the headphones and earbuds are capable of achieving this only very poorly built headphones can not do this which should totally be avoided.
Another factor come into play is resonant frequency. It is the frequency at which the material vibrates very easily and often breaks. For example the opera singer breaking a wine glass. They use the same principal, as soon as the opera singer reaches the resonant frequency of the glass it breaks.
While designing headphone drivers, we need to especially see the behaviour of driver at it’s resonant frequency and need to control it to stop behaving notoriously on it.