This calculator can be used to find the sensitivity of a headphone/speaker given a loudness and input signal level, or convert between different sensitivity units. To calculate loudness given a known sensitivity, see the loudness calculator.
How to Use
Enter the loudness of a headphone/speaker in dB SPL. Enter the input level required to reach that loudness, and select the appropriate units for that input level.
Enter the impedance of the headphone/speaker at the frequency that the loudness was measured using. Technically the impedance is not used when both the input and output have the same types of units (for instance, using an input in mW to convert to an output in dBSPL/W), so if you are making one of those sorts of conversions and do not know the impedance, you can set the impedance to an arbitrary value.
Select the units you would like the sensitivity expressed in, the click “Calculate”. The calculator will then output the sensitivity of the headphone/speaker.
Examples
Sample 1: Finding a Sensitivity
Say you have an ATH-MSR7NC noise cancelling headphone and want to know its sensitivity (dB/mW) in Passive mode. Innerfidelity’s measurements list the headphone as having an impedance of 32Ω and requiring 0.037 Vrms to reach 90 dB. Enter “90” as the loudness, “0.037” as the input level, “V” as the input unit, and “32” as the impedance. Setting the output units to “dBSPL/mW” and clicking “Calculate” returns a sensitivity of 103.69 dB/mW for the ATH-MSR7NC in passive mode.
Sample 2: Converting Sensitivity Units
To compare how loud different headphones will sound at the same source level, it is often useful to convert their sensitivities to units of dB/V. The Hifiman HE400SE is rated at 25Ω and 91dB/mW. Entering “91” for loudness, “1” for input level, “mW” for input unit, “25” for impedance, and “dBSPL/V” as the sensitivity unit, returns “107” as the sensitivity expressed in dB/V. From this you can infer that the HE400SE will be similarly loud as more efficient dynamic headphones when played at the same output volume setting from the same zero output impedance amplifier, at least if/until a current limit is reached. From high output impedance amplifiers this relationship is not true; see the output impedance amplitude calculator and motherboard loudness calculator for more details.
Sample 3: Finding Sensitivity of an Electrostatic Headphone
Say, hypothetically, that you wanted to power an electrostatic Stax SR-007Mk2 from a conventional headphone amplifier. (THIS IS NOT RECOMMENDED! DO NOT ATTEMPT AT HOME! THIS CAN DAMAGE OR DESTROY CERTAIN AMPLIFIERS IF YOU DO NOT KNOW WHAT YOU ARE DOING! NOT TO MENTION THE HEADPHONE WILL NOT FUNCTION PROPERLY WITHOUT A BIAS VOLTAGE SOURCE! THE VALUES USED IN THIS SAMPLE DO NOT CORRESPOND TO ANY REALISTIC SCENARIO!)
Stax lists the sensitivity of the headphone as 100dB/100Vrms. Plugging these values into the calculator, selecting an output in “dBSPL/V”, and using any arbitrary value for the impedance (it doesn’t matter when the input and output use the same unit, in this case volts), returns a sensitivity of 60 dB/V.
Note: Because electrostatic headphones’ impedance is primarily capacitive and varies significantly with frequency, it is inappropriate to use units of dB/W or dB/mW. However, efficiency at a single frequency can still be calculated using these units. For instance, the capacitance is rated at 94pF, so at 1kHz, the impedance is 1.7MΩ. Using this impedance value combined with the input values described above produces 92.3 dB/mW at 1kHz. This is a surprisingly reasonable value for such an extreme headphone.