All headphones have an impedance rating, measured in ohms. but what do headphone ohm ratings mean? In practical terms, impedance tells us how much power your headphones require to deliver a reasonable listening volume. Simply put, the higher the impedance of your headphones, the higher source voltage they will require. knowing the impedance of your headphones helps you determine which audio sources will best match your headphones.
Let’s compare low, medium and high impedance headphones and see the use cases in which they are best suited.
Reading: Headphone ohms explained
low impedance headphones: up to 32 ohms
Low-impedance headphones are a good match for the headphone outputs of battery-powered consumer devices such as smartphones, tablets, and laptops. These headphones don’t require a lot of voltage to work, so they’re likely to be pretty loud with all your small portable devices. but be warned: if you plug a pair of 8 ohm headphones into a pro dj mixer and turn it up to max, you’re likely to turn them off. even if it doesn’t permanently damage the headphones, you’ll still get bad-sounding clipping distortion.
low impedance does not mean low quality. in fact, audio-technica’s high-end ath-iex1 headphones have an impedance of just 5 ohms. most in-ear headphones and professional iem headphones have relatively low impedance. for example, the sennheiser ie 400 pro headphones are 16 ohms and the shure se215 headphones are 20 ohms.
medium impedance headphones: between 32 and 100 ohms
Usually you can’t go wrong with headphones in this middle ground – they can work with a wide range of equipment. Pair them with the headphone output of your standalone DJ mixer, audio interface, or headphone amp, and they really shine. you can also plug them into portable consumer devices like your smartphone, and they’ll sound fine, although they’ll probably be noticeably quieter than low-impedance headphones. If you want your medium-impedance headphones to sound loud enough when powered by battery-powered devices, look for a sensitivity rating of at least 100 db spl per milliwatt. (See “What about headphone sensitivity?” below for more information on sensitivity.)
Most general purpose on-ear headphones, popular dj headphones and studio work headphones fall in this mid-range. for example, pioneer dj hdj-x10 headphones are 32 ohms, audio-technica ath-m50x headphones are 38 ohms, akg k240 studio headphones are 55 ohms, sony mdr-7506 headphones are 63 ohms, and sennheiser hd headphones are 280 pro have 64 ohms.
high impedance headphones: 100 ohms and more
See also: M-Audio
These relatively high-impedance headphones require more source voltage than a consumer device can typically provide. if you connect a pair of 250 ohm headphones to your mobile phone, you won’t hear much, even at maximum volume. they will typically require a separate headphone amp or a quality audio interface with a dedicated headphone amp built in to drive them properly and produce enough voltage to unleash their full potential.
High-end studio headphones for critical listening, as well as headphones intended for audiophiles, often fall into this category. for example, neumann ndh 20 headphones are 150 ohms, beyerdynamic dt 990 pro headphones are 250 ohms, and sennheiser hd 650 headphones are 300 ohms.
do high impedance headphones sound better?
In the old days, long before laptops and iPhones were common, traditional studio and broadcast equipment was relatively high voltage. if you were an engineer connecting your headphones to the board, you wouldn’t want to overload your headphones and risk damaging your ears. high-impedance headphones offered protection against that risk.
But if high-impedance headphones require so much voltage to work properly, and generally don’t work well with the mobile devices that are the norm today, why do they still exist? well, manufacturers don’t exactly set out to make high-impedance headphones. it’s more of a “side effect” of choosing components that sound good. for example, beyerdynamic has been known to use a delicate, super-thin cable to wind its moving-coil headphone drivers. this results in densely packed voice coils with very little air between each layer of wire, so you end up with a driver that is lightweight but has a strong electromagnetic field, reducing distortion. And of course, that super-thin wire has fewer electrons to carry current, so it impedes flow, resulting in a high-impedance headphone.
so do high impedance headphones sound better than low impedance ones? if you’re an audiophile or professional engineer, you might be able to tell the difference. but it is much more important to choose the headset that best suits your use case.
what is “nominal impedance”?
Manufacturers report the impedance of their headphones as a single number: the “average” or nominal impedance. but that single snapshot doesn’t tell the whole story. in the real world, impedance varies, sometimes drastically, over the frequency range of headphones. this is true for both conductive moving-coil driver headphones (most full-size) and balanced-armature multi-driver headphones (most headphones). one notable exception: headphones like the open planar avantone, which use planar magnetic drivers, resulting in a relatively flat impedance range.
Your so-called “64 ohm” moving coil headphones can have an impedance that tops out at 160 ohms at 80hz and drops to 60 ohms at 3khz. 64 ohm nominal impedance is measured at 1 kHz. doesn’t tell the whole story, but it’s a useful shorthand specification.
what about the sensitivity of the headphones?
Low impedance headphones are generally louder than high impedance headphones, for a given source voltage. But impedance is not the only specification that determines the volume of your headphones: sensitivity also plays a role. As with speakers, sensitivity measures how efficiently the headphones convert power into sound. sensitivity ratings are measured in decibels spl (sound pressure level) per milliwatt. They range from low sensitivity (about 85 db spl/mw) to very high sensitivity (about 118 db spl/mw). if you want your headphones to be loud, look for a sensitivity of 100 db spl/mw and above. /p>
impedance matching: the 8:1 rule
Have you ever noticed that the same pair of headphones can sound quite different when connected to different devices? that’s because the output of each device also has an impedance rating.
Most headphones work best when the source impedance (the output impedance of the device you are connecting) is much lower than the load impedance. strong> (the nominal input impedance of your headphones). For proper impedance matching or impedance matching, audiophiles recommend following the 8:1 rule of thumb: connect your headphones to a source with an output impedance no greater than 1/8 of your headphone impedance. for example, connect your 80-ohm headphones to a source with an output impedance of 10 ohms or less.
Why is the 8:1 rule important? if the output impedance of the source is more than 1/8 of the impedance of the headphones, you will get distortion in the form of an audible variation in the frequency response. treble, bass, or mids can get extra emphasis. these variations in frequency response can range from subtle to easily audible and often unpredictable.
There’s only one problem with this 8:1 rule: audio equipment manufacturers rarely publish the output impedance of their devices, and there really isn’t a standard!
Fortunately, some high-end headphone amp manufacturers publish their output impedance specifications. and high-end headphone amps are likely to have a very, very low output impedance (almost zero), so they’ll definitely be less than 1/8 the input impedance of whatever headphones you plug in. for example, the rupert neve designs rnhp headphone amplifier has an output impedance of just 0.08 ohms. That means no matter what headphones you plug into it, you’ll never break the 8:1 rule.
but what if you want to listen to a device with a high output impedance or an unknown output impedance? you can follow the 8:1 rule and bust out your fancy high-impedance headphones, or just choose to accept that your low-impedance headphones might sound a little different when plugged into different sources.