Find the frequency response deviation and attenuation of a headphone from an amplifier with nonzero output impedance.
How To Use
Enter the output impedance of your amplifier. This is often published on the amplifier’s product page, or can sometimes be found in third party measurements.
Enter the maximum and minimum impedances of your headphone. These can usually only be found in third party measurements of the headphone, usually presented in an Ohms vs. Frequency graph. Find the largest value for impedance (Ohms/Ω) from the graph and enter it in “maximum”; find the lowest vale and enter it in “minimum”.
You can then hit calculate.
“Deviation” refers to how boosted the frequency regions with high output impedance will be, relative to those with the low output impedance. For instance, dynamic driver headphones usually have their maximum impedance in the midbass region, with the mids and treble mostly staying near the minimum impedance level. In this scenario, a deviation of 3dB means that the headphone would have a 3dB midbass boost if used on an amplifier with the entered output impedance, relative to if the headphone had been used with an “ideal” 0Ω output impedance amplifier.
“Attenuation” refers to how much the output impedance will reduce the level of the headphone, relative to if the amplifier were “ideal” (0Ω). For instance, a typical motherboard and USB headphone dongle may have similar signal output levels, but the dongle will often sound louder due to its lower output impedance. Low impedance headphones may sometimes also sound quieter than similar high impedance headphones when driven by high output impedance amplifiers due to this effect. This value is calculated using the minimum headphone impedance.
The calculator’s default values roughly correspond to a Sennheiser HD598 plugged into a typical motherboard (~75Ω output impedance).
Other Typical Values
Motherboards usually have a 75Ω output impedance, while good headphone amplifiers usually have an output impedance below 1Ω.
To quickly check how output impedance affects other popular headphones, you can try some of the following (all values are approximate and based on others’ third party measurements):
|Brand||Model||Nominal (Ω)||Minimum (Ω)||Maximum (Ω)|
Planar magnetic headphones usually do not have significant impedance variations, so both their maximum and minimum impedances are typically roughly equal to their nominal impedance.
Say I have an HD598 and am considering buying a Steinberg UR22 as a DAC/Amp. Using Google (or the chart here), I find that the HD598’s impedance varies from 60Ω to 300Ω, and find a review measuring the UR22’s output impedance on the headphone output at 90Ω. Entering these values into the calculator, I find that the headphone will have a 5.7dB deviation. Since the HD598’s impedance is maximized around 100Hz, this corresponds to a 5.7dB boost at 100Hz, which will make the headphone sound “boomier” than it normally would.