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Headphone impedance explained like you're five – Transcript
Video by Andrew Dandrew · Watch the original on YouTube
Summary
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- Impedance is a measure of the opposition that a circuit presents to the flow of an alternating electrical current and is composed of both resistance and reactance.
- High impedance headphones require higher voltages and lower currents, whereas low impedance headphones require higher currents and lower voltages.
- The rule of thumb for good signal transfer states that the output impedance of an amplifier has to be less than one-eighth of the impedance of the connected load.
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if you spent more than 10 minutes online reading about headphones you probably ran into the term impedance and when it comes to headphones you quickly learn that some headphones are high impedance which means that they are hard to drive and they might require an amplifier and some headphones are low impedance which makes them easy to work with and they will work great with your phone with your portable devices and for some people that's all they want to know but if you want to actually learn more and understand what impedance is then you
are in the right spot because my name is Andrew Andrew and if you watch my channel you know that I only have one t-shirt but I am on a mission to search this entire wonderful Universe for answers to the most important questions and explain these answers to you like you are five so let's learn all we can about audio impedance and see how it relates to audio circuits impedance is a measure of the opposition that a circuit presents to the flow of an alternating
electrical current and it is composed of both resistance and reactance and it is typically rep represented by the symbol Z or if you want to put it differently you could say that impedance is sort of the resistance in the world of alternating currents because usually resistance works for DC well impedance is basically the analog for alternating currents now this is the official definition and you know it's great if you understand it but I think it doesn't make things very easy to grasp for most
people anyway so here's what we're going to do you're going to need to pull your imagination and put it on the table cuz we're going to put it to work we're going to think about a typical audio circuit but instead of thinking of a headphone amplifier and a set of headphones we're going to think of the headphone amplifier as being a garden water source or garden faucet and the headphones will be a garden hose the diameter of the hose would be equivalent to the impedance of the headphones and the water that flows through the end of
the hose would be equivalent to the loudness of the headphone so the more water flows through the hose the louder the headphones are high impedance headphones would translate to a narrow hose which would constrict the flow of water and as our impedance gets higher the hose gets narrower and narrower and this makes the amplifier work a lot harder the amplifier or our garden water source now needs a lot more pressure it needs a lot more Force to push the water
through to get a good flow so that we get a good amount of loudness so the water pressure the force with which the amplifier has to push this signal to go through the impedance of the headphones would be equivalent to the voltage the amount of signal that's flowing the the amount of water that gets through the end of the hose would be equivalent to the current of the signal we can see that in the case of high impedance headphones the amplifier needs to
operate at a higher voltage to have enough strength to push the signal through the opposition that the headphones provide and because of Ohm's law that states that the current is equal to the voltage over resistance this naturally leads to a lower current on the opposite side low impedance headphones would translate to a wide hose one that barely opposes to the flow of water so now there's not a lot of water pressure needed but instead a huge volume of water needs to flow through to
keep a steady flow so when working with high impedance headphones amplifiers need to push a high voltage with little current but when working with low impedance headphones amplifiers need to push a high current at a low voltage and this is all because of ohms law but if we stop for a moment and think about it why do we need both High impedance headphones and low comp headphones why do we have these two sort of Standards we're back in our garden but we're going to add multiple water hoses this time
because let's say we want to wet multiple corners of our garden simultaneously adding together multiple narrow hoses works fine because if the Water Source has enough pressure initially the pressure dropped from all of the extra other hoses shouldn't be too severe and the water consumption should still be well below the limits of the Water Source but adding together multiple large diameter hoses wouldn't be as trouble-free because because each hose individually now requires a lot of
water and likely the Water Source won't be able to Output this total required amount which is very high now and therefore there will only be a weak stream of water coming out of each of the garden hoses and this is definitely a bad setup you never want to have multiple low impedance devices connected to a source in parallel but High impedance headphones work very well in such scenarios where just one source needs to drive mult multiple of them and
this is a typical scenario for example in a recording studio that's tracking an entire band being high impedance these headphones will require higher voltages but they won't draw a lot of current and coincidentally this was a great pairing for most of the traditional TW based studio equipment that was generally used in recording studios and this equipment worked by Design at high voltages and lower currents and therefore headphones needed to be high impedance to play nice with them back then the standards for
professional headphones in terms of impedance es were somewhere between 600 and 250 ohms and as our technology evolved sound making devices got small portable and cheap and vacuum tubes got replaced by transistors and Main's power supplies got replaced by batteries and batteries work at relatively lower voltages but they can deliver High currents when needed so circuits were adopted accordingly and now you basically had a new huge Market of
potential buyers that wanted to get headphones that played nice with their portable new fancy devices and thus the transition to low impedance headphones began if you remember from Oh's law earlier low impedance headphones require higher currents but lower voltages so they're basically a great match for battery powered devices if our band earlier were to use low impedance headphones instead of high impedance headphones with a very powerful amplifier this could be a recipe for
damage the very low impedances of the headphones would combine to an even lower total impedance which wouldn't be able to resist the high power of the amplifier so a lot of current would end up flowing in the circuit components inside the amplifier could overheat and even get damaged and the volume knob won't be very useful because just turning it a tiny bit would lead to a very loud sound one that's unpleasant to listen to it could end up melting the
drivers inside the headphones because of all of this extra current which would uh overheat the coils inside and then the membranes could end up making some very unnatural movements because of the high power signal all all matching together the source and its load is very important for both sound quality and the safety of the equipment so this is the main reason why we have high impedance and low impedance headphones so we can achieve a good match no matter the scenario in which we find ourselves High
impedence headphones work great when Daisy changed to a single suitable Source but often times because of the higher required voltages such suitable sources are not necessarily portable so high impedance headphones are great in a studio but maybe not so great for for a portable setup where you want to use your mobile phone as a source or any sort of other portable music player this doesn't mean that you can never ever use high impedance headphones with portable devices some might be very well suited
to drive high impedance headphones but it's not a guarantee you need to try and see how a certain combination works but if you want something that is guaranteed to work with portable players with phones then you should look towards low impedance headphones and the headphones will get nice and loud and sound as the manufacturer intended on such devices so overall it's great that we have the option to choose what works best in different scenarios but as an audio file
you're generally interested in getting the best sound quality possible so in this case should you get high impedance headphones because since they're meant for the professional Market they have to sound better right it's not that simple because purely based on impedance it's impossible to say that some headphones will sound better compared to others all of the other other design considerations play a huge role in how some headphones sound you can have good sounding low impedance headphones and bad sounding
High impedance headphones and besides the impedance of the headphones themselves you also have the output impedance of the source that's driving those headphones with our garden water source being our amplifier the output impedance of this amplifier would be the inverse of the size of the faucet to which we're connecting our hoses or our headphones so a low output imped would translate to a big diameter faucet with a strong output stream and this is
perfect this is what you always want to have because to such a big faucet you can connect both large diameter hoses and small diameter hoses and you'll get great results in all cases so it's actually the ideal scenario you want a low output impedance at all times a high output impedance translates to a very tiny faucet which is a huge problem because it forces you to only connect very narrow hoses if you want to achieve good good signal transfer or a good
stream of water a good flow of water if you connect a very large diameter hose to a very tiny faucet you're just going to have a very weak trickle coming out the other end there actually is a rule of thumb that tells us that if we want a good signal transfer the output impedance of an amplifier has to be less than 1/8 of the impedance of the connected load otherwise these mismatched impedances can lead to problems which you might or might not be able to hear but they will prevent you
from getting the most out of your setup it's hard to say exactly what will happen because it can vary from device to device from situation to situation it can also vary in intensity it will probably be something related to muddiness certain mid- frequencies or high frequencies can get attenuated sometimes quite bad there's also the concept of electrical damping which is a mechanism of controlling the Distortion of especially low end frequencies in a
nutshell a properly damped speaker membrane will stop moving as soon as the signal reaches zero in a poorly damped driver the membrane will continue moving even after the signal has stopped leading to distortions and deviations in the frequency response and electrical damping works best when the 1/8 rule is being followed so overall it's very important to have a good match between the impedance of the headphones and the
output impedance so that you're not impeding your gear from providing you with the best sound quality possible the ideal amplifier has an output impedance of 0 ohms and the higher this output impedance is the higher the impedance of the connected load has to be for a good signal transfer and in the real world you can imagine that output impedances vary quite a bit for example if we look at some popular USB audio interfaces we
can see that while the Motu M2 has an almost perfect output impedance of 0.06 ohms the Steinberg ur22 Mark I has a whopping output impedance of 91 ohms while the lowest acceptable headphone impedance for the M2 is 0.48 ohms the ur22 Mark I needs headphones with an impedance of at least 728 ohms for a perfect signal transfer so perfectly following the 1 rule with
the uh Steinberg is practically impossible because you can't really get 700 plus ohms headphones right but still the higher the headphone impedance the more you can minimize the problems that may arise from the uh not perfectly matched setup and many other devices also have higher output impedances because it's just simply a cheap way to make a headphone out really and
therefore if your goal is indeed critical listening and transparency I think it makes sense to argue that headphones with a higher impedance like 250 ohms 300 ohms around that sort of value are a better choice because they allow you to have a better chance at following the 18 rule with a wider range of sources if pure sound quality is what you're after again if transparency is what you're after but
they can also come with their own range of problems because impedance is just a piece of the puzzle and you know some devices might lack the necessary power to get such headphones to be loud for some individuals they simply won't get loud enough you know I I don't think that's a healthy way to listen to headphones at such loud levels but still I can understand this is a problem and it complicates the setup you're now
looking into amplifiers or USB dongles you can use right so if you want to stay away from this if you just want General sound enjoyment if you care about sound quality but don't care about staying as true as possible to the recorded Source I'd say getting some lower impedance headphones like 80 ohms or lower is actually a better choice because you'll get better compatibility with all of your devices and what you might be
losing from not following the rules might not even be that important because we're humans we're subjective we argue that dust on a vinyl or tape flutter makes things sound better and more organic compared to a pure digital recording and things are never black or white even if we did learn a ton about impedance in this video we barely scratched the surface impedance is very