Headphone sensitivity (or sound power) provides information about the volume level of the speakers and is directly related to the size of the core located inside. It is a difficult characteristic to measure and compare because manufacturers indicate it in different ways.
When choosing headphones should be guided not only by their design and usability but also by the main parameters. Among them are output power, electrical impedance, reproduced frequency range, degree or nonlinearity of distortion, sound volume, or sensitivity.
The last parameter indicates the loudness of the speakers, but it happens that a device with a lower value plays louder than headphones with higher sensitivity. Let’s find out why.
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What is sensitivity in headphones?
The sensitivity indicates the relationship between the volume of the speaker’s sound and the level of the signal applied to it. It is measured in decibels (dB), ranges from 90-120 dB, and is determined by the size of the magnetic core (coil).
In small devices it is low, so you shouldn’t expect high volume from vacuum headphones. In them, the volume level is achieved due to the close location of the membrane to the eardrum. Full-size devices are equipped with a larger core, so they have more power and sensitivity.
The characteristic is given to power (rather than voltage, which would be correct and practical) and depends on two parameters: applied current and voltage, which is convenient for engineering calculations, but not for the end user. And here’s why.
There are two resistance standards for speakers: 4 and 8 ohms, and the value is indicated next to the sensitivity. For headphones, there are dozens of common full impedance values: 4, 8, 24, 32, 64, and so on. Therefore, it’s not reasonable to compare a pair of devices from different manufacturers and even rulers, you will not get a clear picture.
Manufacturers don’t always give full information about the device. And it is extremely difficult to measure sensitivity. According to the standard, it refers to the value of sound pressure exerted by the headphones when a voltage of 1 V is applied to them.
What affects the sensitivity of headphones?
A common misconception among audiophiles is that loudness is directly related to sensitivity, but this isn’t true (except for Sennheiser – they refer to sensitivity to power). And the common notion that devices with high impedance play quieter than low impedance at the same volume of the phone, and they need a more powerful amplifier is wrong.
To change the power at the output of the low-frequency amplifier, you adjust the voltage applied to it. And since resistance is a constant, so is the current flowing through it (from Ohm’s law). Without increasing the level of electrical current, the voltage value cannot be increased either.
For a device with lower impedance, you need lower voltage and maximum current, for high impedance headphones, the picture is the opposite. In summary:
- The sensitivity is correct relative to the voltage.
- Sensitivity increases as the impedance of the headphones decreases.
- For smartphones, it is advisable to buy only low impedance headphones.
- It’s better to buy high-impedance headphones for players, but check their sound before buying.
Lovers of listening to music everywhere and all the time know that the cleaner and more pleasant sound is produced by high-impedance speakers. Without getting into the physical processes, they sound cleaner because the amplifier supplies less electrical current, which means less distortion.
How to find out how many decibels your headphones have
Sound volume is commonly measured in decibels. A decibel is represented by a decimal logarithm: increasing the volume by 10 dB doubles it. You can find out the volume of your headphones from their specifications in their documentation or on their official website.
It is difficult to get this value by measurement because the sound from the headphones is directed inward from the ear, and noise meters are designed to get information from the environment, not a single, narrowly focused area. The measurements will be inaccurate.
To avoid buying a device, you can try appropriate applications. For example, Dezibel X or Sound Meter for Android, and Dezibel X for iOS. They shouldn’t be trusted, if only because much is determined by the microphone.
What’s the best sensitivity for headphones?
To minimize the distortion of the sound signal, it is necessary to properly match the parameters of the speakers and the signal source: the impedance of the latter must be less than 1/8 of the impedance of the headphones. Smartphones have an impedance of up to 2 ohms, based on the rule, for them, it is advisable to take headphones with a minimum impedance of 16 ohms.
Players have the lowest output impedance and for them the speakers with impedance up to 120 ohms and even more are suitable. Devices with a characteristic that begins with 250 ohms are used mainly by professionals (in recording studios, radio, and television).
There are no strict standards for measuring the index, so when choosing headphones you should rely on your hearing. For walking and sports use a device with a value from 100 dB.
