This is part 1 in a series on Headphones and Their Drivers.
- What is Headphone Impedance? (You are here)
- What is Sensitivity in Headphones?
- What is Output Impedance?
- What is a Headphone Driver?
- What is a Planar Magnetic Driver?
Hi friend and Welcome!
What is Headphone Impedance? That’s quite a fully loaded question actually, but a good one nonetheless. Before we get into it, grab a snack, sit back and relax because…
You’ve come to the right place!!
Make sure to pin this Infographic if it helped you, and/or you think it would help someone else!
What is Headphone Impedance?
What I will bring you in this article
- Introduction
- Current, Voltage, and Power
- What Is Headphone Impedance?
- Low Impedance vs. High Impedance
- What is Sensitivity?
- What is a DAC?
- Current vs. Voltage
- Power Output Examples
- Output Impedance
- Final Word
Now without further ado, let’s get rolling!!
Introduction
You may have been shopping for headphones and come across the dreaded impedance rating.
Most of the time you wouldn’t give it a second thought with low-budget headphones because it doesn’t really matter that much.
Pretty much all of those cans are meant to be used with portable devices and buyers won’t even consider an amplifier because they either:
- Don’t know what it is.
- Don’t care.
- Know they won’t need one.
While most lower-budget headphones don’t require an amp and don’t benefit from one, there are a few exceptions.
The AKG K240s are a prime example.
At 55 Ohms and 91dB of Sensitivity, they absolutely require an amp to sound loud enough.
Related: What is Sensitivity in Headphones?
They don’t sound that great plugged into a phone or laptop, but once you pair them with an amp that provides enough power, boy howdy do they sound amazing.
The mid-range especially opens up and you realize why they’ve been a studio standard for so long.
- Related: AKG K240 Studio Headphones Review
But what is headphone impedance exactly?
What is Headphone Impedance?
To understand this concept, we first must differentiate between 3 terms that people sometimes mistakenly use interchangeably when discussing Impedance.
These terms are Voltage, Current, and Power.
Voltage
Definition: The difference in electrical potential energy, per unit of charge, between two points.
Voltage is measured in volts, obviously.
In layman’s terms, Voltage is simply a measure of the potential energy that a headphone amplifier has. It doesn’t actually represent movement and is static.
Think of a battery. It has a potential voltage associated with it even if it’s not connected to a circuit.
The potential is the difference between the 2 terminals on the battery, and that difference is equal to 9 volts (or however many volts the battery has).
Now think of a headphone amplifier.
If I have an amp sitting on my desk but I’m not using it, there’s still the potential for energy there even though it’s not doing any work.
I think you get the idea.
Current
Measured in amps.
Current is a measurement of the flow of electrons passing a certain point.
To use an analogy, imagine 2 cups of water.
There’s the potential for energy there, but nothing has happened yet.
Current is simply that transfer of water from one cup into the other.
So current is a measure of the flow (or movement) of electrons from one unit to another.
Power
Measured in Watts, or joules per second.
Power is simply the combination of both the potential energy (Voltage) and the transfer, or flow, of energy (Current).
So Current x Voltage. It’s a function of energy over time, or, energy per second.
So imagine there’s a paddlewheel between the 2 glasses of water as you’re pouring one into another. The combination of both voltage and current = the Power that makes the wheel turn; i.e. do some sort of work.
Now that we understand each term on its own, let’s see how it applies to headphones.
Definition of Impedance
The definition is as follows: The combined resistance and reactivity the headphones present to the amp as an electrical load.
Wow, that sounds like a bunch of hogwash to the average enthusiast. Or maybe it doesn’t. Lol.
It’s basically a measure of how much your earphones or headphones resist that electric current that we just discussed above. (or more specifically, a change in current).
When you have a headphone with a high impedance, it’s basically saying “I don’t WANNA play loud enough! Wahh!” Lol.
When we have an amp with enough power (current + voltage) to drive the headphones, we’re basically telling them, “Too bad Buster, you’re going to receive this power and play loud whether you like it or not.”
Low Impedance vs. High Impedance
Low Impedance = between 16 and 32 Ohm.
This range works well with portable music players, phones, and other similar devices with weaker built-in amplification.
Low impedance headphones are more prone to blowouts when using a powerful amp, but can still sometimes benefit from one.
High Impedance = Over 100 Ohm.
These require more power (discussed above) to achieve higher audio levels.
A good example would be the beloved Sennheiser HD600.
Headphones like this are both protected from the damage that occurs with blowouts and can be used with an array of audio equipment.
For instance, pairing an HD600 with an old receiver can yield an incredibly good sound depending on the unit in question due to Output Impedance (which we’ll touch on later).
Gray Area = 32 – 100 Ohm.
Headphones in the gray area may or may not benefit from an amp. It just depends.
If you have a headphone with an Impedance rating in this region, take a look at the Sensitivity to get a better idea about its power requirements.
An AKG K240 (62 Ohm Impedance) is a great example at 91dB Sensitivity, meaning it’s terribly inefficient and needs quite a bit of power from an amp to reach acceptable listening levels.
Speaking of, let’s talk about Sensitivity!
What is Sensitivity?
Also important to consider is the dreaded term Sensitivity.
This is one of the most misunderstood concepts in the audiophile world.
So what is it?
Sensitivity is simply a number that companies provide to describe how efficient the headphone is at using the power it receives. That’s it!
- So if you have a headphone with a number above 100dB, it’s going to be more efficient. It won’t require as much power from the amp to reach peak loudness (around 110dB is the standard).
- If you have a headphone with a number around 97dB and lower, it’s going to be less efficient. It will require more power from the amp to reach peak loudness.
In many ways, a headphones’ Sensitivity rating is a lot more valuable in determining if you need an amp.
While most people look at the Impedance, I’d rather check its Sensitivity and how efficient it is.
- Learn more: What is Sensitivity in Headphones?
Examples
- In-ear headphones or earphones. Good efficiency/high sensitivity. Rarely needs an amp in most cases.
- Noise-canceling headphones. Do not need an amp because there’s a built-in one already. Related: How Do Noise-Canceling Headphones Work?
- An amp with a DAC (Digital to Analog Converter) will improve your listening experience because there is better digital-to-analog conversion and processing power. More on that in a sec!
Perfect segway…
What is a DAC?
(And do you need one?)
In layman’s terms, a DAC is a Digital to Analog Converter.
It converts the 1s and 0s from your computer (the digital realm) into the analog sound that you hear and vice versa.
In the recording, you scream curse words (analog/your voice) into the microphone, and your computer makes sense out of it digitally for you to edit and EQ later.
- Related: What is a USB DAC?
There’s also an internal DAC in your phone, mobile device, and pretty much anything that outputs sound.
Your PC has an internal Soundcard that functions in the same way.
- Related: What is a Soundcard?
All that said, only invest in a DAC if your Soundcard or existing DAC is no good. You’ll know because the sound will either:
- Not be loud enough.
- Sound like poo.
- Make lots of unnecessary noise/crackling, etc.
For instance, my laptop’s internal Soundcard does not output at a listenable level.
For me to achieve the loudness that I’m looking for, some sort of upgrade is required.
Power Output Examples
The famous “Schiit Stack”
As an example, a headphone like the 300 Ohm HD600 requires 20mW of power to perform optimally.
The Schiit Magni 2 provides 260mW of power into 300 Ohms.
You can see why it’s such a valuable piece of equipment.
It can effectively power nearly any headphone, and in reality, provides much more than is needed in most cases.
The takeaway here is to simply make sure the power output of the Amp in question is sufficient for the headphones’ Impedance.
You can do this by checking out the specifications of the amp, as most spec sheets will give a rundown of how much power each Ohm rating can receive.
One important thing to keep in mind is the difference between peak power and continuous.
RMS (Root Mean Square), is the amount of power that can be used from your Amplifier continuously; that is, it’s the power it can provide while you’re listening to music at normal volumes.
Peak power specifies how much power the Amplifier can provide to the headphone in short bursts, or the absolute highest amount of power without experiencing distortion; or, before something explodes.
In essence, peak power is useless as you’d never be able to run headphones off it for more than a few seconds.
So be wary of what numbers you’re actually seeing when looking at a manufacturer’s spec sheet.
For something like the Magni 3, the numbers are as follows:
- Maximum Power, 16 ohms: 3W RMS per channel
- Maximum Power, 32 ohms: 2W RMS per channel
- Maximum Power, 50 ohms: 1.3W RMS per channel
- Maximum Power, 300 ohms: 430mW RMS per channel
- Maximum Power, 600 ohms: 230mW RMS per channel
Notice how Schiit makes this clear by adding RMS (continuous) at the end.
The Objective 2 is similar. Let’s take a look.
- Max Output (33 Ohms): 613 mW
- Max Output (150 Ohms): 355 mW
- Max Output (600 Ohms): 88 mW.
These numbers also look to be RMS, but I think you get the idea.
An amp’s spec sheet is one of the best tools at your disposal.
If a company doesn’t share this info, I’d probably not even consider purchasing the amp. Fortunately, most do!
Output Impedance
This is the impedance of the actual source you’re using, which can be difficult to find sometimes.
A perfect source = an output impedance of 0. This means it will always deliver the same output into any load (headphone). This is probably the most important thing to remember.
The closer to zero the number is, the more neutral and honest the representation of the headphone’s sound signature will be.
A number in this range basically means that the Amp will be as consistent as possible with the most amount of headphones.
You could theoretically buy one of the amps mentioned above from Schiit or JDS Labs and be set for life.
Unfortunately, if you’re a snobby audiophile, you’ll want to explore as many options as possible. It really is a curse. 😛
This is because some amps do pair better with certain headphones, and vice versa. It really does become a hobby after a while.
If the output impedance is not 0 (or close to it), the voltage produced by the source will be reduced when a load (headphones) is connected, in effect diminishing the quality of the sound.
So in a nutshell, the higher the output impedance, the greater the drop in voltage at the load.
Do keep in mind that this doesn’t necessarily mean the amp is bad if it has a higher output impedance.
Many people enjoy tube amps because of the fact that they don’t sound neutral and give the headphones a different flavor.
Your mileage may vary in what you personally prefer out of your listening experience.
Basically, output impedance is one of the most common reasons that certain headphones can sound different when plugged into different amps.
- Recommended: What is Output Impedance?
The Simple Math
Determine if your headphones will work with the Amp in question!
- Most headphones work best when the output impedance is less than 1/8th of the input impedance.
Example:
Sennheiser HD600 @ 300 Ohms.
300/8 = 37.5 Ohms
So the output impedance of your amp/DAC should not be greater than 37.5 ohms when driving the 600. A popular option for the HD600 is the Schiit Magni/Modi combo. The Magni has an output impedance of less than 0.1 Ohm. This is the reason that it’s such a versatile amp. Remember what we said about a perfect source? As close to zero as possible. How to choose a headphone amp!
So
If you have a source with a high output impedance, it’s more likely there will be a discrepancy in the way your headphones receive the sound. This can manifest erratically depending on the headphone.
A good rule of thumb is to try and match high impedance headphones with high output impedance sources if possible. An example would be an old receiver. The way your [high impedance] headphones sound through it can vary greatly depending on the model of the receiver in question.
The greater the output impedance, the more likely the bass response will be affected in a negative way. For instance, if the bass frequency was meant to sound tight and controlled with impact, it may actually sound muddy and/or boomy/bloomy (less controlled).
The bass will start to “roll-off” sooner at lower frequencies, compromising your listening experience.
Final Word
Chillin’ in studio 🙂 This is the 1st generation model. They have since come out with a 3rd!
It’s rather important to take these things into consideration; especially the power output of the amp in question and the 1/8th rule.
Why? Because if the output impedance is greater than 1/8th of the headphone impedance, there will be undesirable variations in frequency response.
Examples:
- Weaker bass
- Glaring mid-range emphasis
- Muted high frequencies
- Odd phase characteristics
Basically, this just means that the headphones will not sound as they were meant to. So be careful what you’re plugging those bad boys into! 🙂
Example:
My Audio Technica ATH M50s have an impedance of 38 Ohms. My Scarlett 2i2 had an output impedance of fewer than 10 Ohms. Now, this is a bit tricky:
38/8 = 4.75
The output impedance (10 or thereabouts) is greater than 1/8th of the headphone impedance. So will the M50s sound bad plugged into the 2i2?
Not necessarily, at least not to my ears, but they may not be at their best. The only way to find out is if I bought a separate amp/DAC and compared them. To my ears, they sound pretty blazin’ though 😛
The point is this: Just be aware of what you’re buying as far as amps are concerned.
I didn’t buy the 2i2 to amplify the M50. I bought it to power my studio monitors.
Regardless, using the 1/8th rule will greatly aid you on your quest.
- Related: What are studio monitors?
With that…
My top option for a headphone around the threshold of 97dB and a higher Impedance (300 Ohm) is of course my beloved HD600.
Interested in learning more about one of my favorite audiophile cans?
My top option for a higher Sensitivity headphone and lower Impedance model that doesn’t need a lot of power is most certainly the Sony MDR-7506 @ 106dB and 63 Ohm.
It’s been a quintessential studio headphone for decades and is certainly worth a look.
Well, that’s about it for today my friend! I hope I answered the question of, what is headphone impedance?
Did I provide enough information? Are you confused? Enlightened? Appreciative? Let me know!
Questions? Comments? Requests? Did I miss the mark on something? Please let me know down below or Contact me!!
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All the best and God bless,
-Stu
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4 comments
Thanks man, I really needed some tutorial like this. Great work
Could you explain why the coefficient is 1/8? Is there any science behind that or it’s just an experienced number?
Hey man! Thank you so much!
Since I wrote this, I mostly just use Sensitivity (or efficiency) as my main barometer, and then Impedance second. I have enough experience with headphones and Amps to kind of intuitively know how one might behave with any given product. Sensitivity is, to me, a better indicator of how much power a headphone is going to need from an amp, but Impedance is still very important.
Check my article on Sensitivity. Are you looking for a pair of headphones w/ an amp/dac?
As for the 1/8th rule, it’s basically just a general figure put in place to minimize frequency response abnormalities that may manifest when you’re dealing with Amplifiers that have a higher output impedance (basically an unpredictability in how a headphone might sound out of such an amp).
Now, that’s not to say that high output impedance is bad; quite the contrary. It just means you have to be more mindful when it comes to pairing a headphone with an amp that introduces that sort of resonance and/or distortion. Higher impedance headphones generally sound excellent out of these. For instance a Bottlehead Crack has an output impedance of 120 Ohms and should really only be paired with something like an HD600/650 (300 Ohm), or some other headphone with a very high impedance.
Put more simply, problems will start to arise anytime the output impedance is more than the headphone’s impedance, i.e. you should pretty much never try to run a 32 Ohm headphone out of a Crack (see how the ratio is reversed at 1/4?). This goes back to the 1/8th rule and why it’s still pretty important. 8/1 gives you just about the best control with regard to smoothness, dynamics, timbre, (pretty much everything that effects how well the music is portrayed), though a ratio 4/1 still works too.
Another consideration to keep in mind is damping, because as the output impedance of an amp goes up, damping is reduced in the headphones. This leads to compromises in bass response most notably, but also results in poor transient response and a general “flabbiness.” It’s also why the 1/8th rule is important as most headphones are designed much differently than they were years ago, i.e. they don’t work well with many receivers that had a high output impedance. Even with that said, a headphone like the HD600 will likely sound incredible out of such a source because of this very reason. I have an old Panasonic stereo with a high output impedance and it sounds pretty wonderful with my 600’s. 🙂
Hope that helped! Let me know what you think and if you’re looking for an amp or headphone!
-Stu
Hey man ,
I have AKG 702 with SBX G6 , should i put it on high or low gain !
I feel high is give me more loud sound and richer but they said on G6 website only put H on headphones or than 150 OHM
Hey man! I generally use high gain with the K702 and G6, as well as Scout Mode.