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..
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What I will bring you in this article
What is Headphone Impedance?
Low Impedance vs. High Impedance
What is Sensitivity?
What is a DAC?
Current vs. Voltage
Power Output Examples
Now without further ado, let’s get rolling!!
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:
a) don’t know what it is.
b) don’t care.
c) know they won’t need one.
While most lower budget cans don’t require an amp and don’t benefit from one, there are a few exceptions. The AKG K240’s are a prime example. At 55 Ohms and 91dB of Sensitivity, they absolutely require an amp to sound loud enough. 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. Check out my AKG K240 Studio Headphones Review!
But what is headphone impedance exactly?
What is Headphone 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 an electric current (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 to drive the little crybaby, we’re basically telling the headphone “Too bad Buster, you’re going to receive this power and play loud whether you like it or not.”
Low Impedance vs. High Impedance
When discussing varying impedances, generally speaking:
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 (or voltage) to achieve higher audio levels. They are both protected from the damage that occurs with blowouts, and can be used with an array of audio equipment.
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 area, take a look at the Sensitivity to get a better idea about it’s power requirements. An AKG K240 is a great example at 91dB.
With that, 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, but fortunately for you I’m here to clear up all the confusion.
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 important in determining if you need an amp. While most people look at the Impedance, I’d rather check it’s Sensitivity and how efficient it is. Learn more:What is Sensitivity in Headphones?
Portable devices. Use the line output when available to hook up to an amp.
In ear headphones or earphones. Good efficiency. Rarely needs an amp in most cases.
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!
What is a DAC?
(And do you need one?)
In layman’s terms, a DAC is a Digital to Analog Converter. It converts the 1’s and 0’s from your computer (the digital realm) into the analog sound that you hear, and vice versa. In 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. 😛 Learn more about this mind blowing process: Bit Depth vs. Sample Rate.
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 laptops 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.
My current favorite desktop solution for that is the JDS Labs Objective 2. You can purchase this as a combo Amp/DAC or simply buy the amp and pair it with a separate DAC.
Some other options to consider:
Budget – FiiO E10K. This is a great Amp/DAC combo under $100 that will power headphones up to about 300 Ohm. Beyond that I would consider something else. Learn more:FiiO E10K USB DAC Review
All in one – Audioengine D1. This is an extremely versatile piece that also works well as a Gaming Rig! Learn more: Audioengine D1 Review
Best portable – Audioquest DragonflyRed.This is probably my favorite combo for you phone and PC on the go! It’s such an amazing investment and fits just about anywhere. It’s about the size of a thumb drive and skyrockets audio quality to a stunning degree. Learn more:Audioquest Dragonfly Red Review
End game – Chord Mojo. As of this article, this is just about the best I’ve heard. It’s worth every penny, and does provide an upgrade from the aforementioned units. Learn more:Chord Mojo DAC Review
Current & Voltage
The reason higher impedance headphones have better sound quality is because they allow for more turns of wire to be used in the coil of the driver. What is a headphone driver? This results in a better motor system with fewer compromises, leading to a better overall sound.
Higher impedance headphones also require less current, reducing distortion. Because of this, they are also immune to output impedance differences between sources. But what exactly is current and voltage?
Think of current as the volume of water in a bucket.
Think of voltage as the water pressure (PSI).
Think of impedance as the size of the hose nozzle.
A high impedance headphone = Tiny nozzle. They need a lot of voltage (pressure) or power to function properly.
A low impedance headphone = Is like filling a bucket with water. It requires more flow (current) but not a lot of pressure (voltage).
Power Output Examples
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. For the Magni 3, the list is 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
So the Magni 3 actually provides even more power than the 2. Awesome! (I still have the 2).
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.
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!
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 better. 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 an audiophile type person like me, 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 awhile.
If the output impedance is not 0, 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.
Basically, output impedance is one of the most common reasons that certain headphones can sound different when plugged into different amps. 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.
So the output impedance of your amp/DAC should not be greater than 37.5 ohms when driving the 600’s. 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!
If you have a source with a high output impedance, this basically means:
The drop in voltage will be greater with lower impedance loads (headphones).
This drop can be big enough to make driving low impedance headphones difficult.
The greater the output impedance, the more likely there will be a discrepancy in the way your headphones receive the sound. This can manifest erratically depending on the headphone.
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 (less controlled). The bass will start to “roll off” at sooner at lower frequencies, compromising your listening experience.
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 an 1/8th of the headphone impedance, there will be undesirable variations in frequency response.
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! 🙂
My Audio Technica ATH M50’s have an impedance of 38 Ohms. My Scarlett 2i2 has an output impedance of less 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 M50’s 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’s. I bought it to power my studio monitors. What are studio monitors? Regardless, using the 1/8th rule will greatly aid you on your quest.
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 V6 @ 106dB and 63 Ohm. It’s been a quintessential studio headphone for decades, and I don’t see it leaving my studio anytime soon!