Headphone Impedance and Sensitivity: What Is It?

Impedance and sensitivity are two of the most important parameters found on the specifications of audio headphones, whether they are used in the studio or in an audiophile context.

Thus, you have probably already seen that a headphone like this very famous model had “an impedance of 80 ohms” or that another had “a sensitivity of 105 dB SPL/mW”.

However, while they are essential for understanding whether a given headphone will provide a quality audio signal (and especially loud enough) when connected to your headphone amplifier or your audio interface, these two figures are often particularly misunderstood…

…especially because they are often poorly explained.

Having noticed that many of you were asking me about the compatibility of different headphones with your equipment, particularly regarding impedance, I decided to put together a complete file on the subject.

So, should you get a 32-ohm headphone? An 80-ohm one? A 250-ohm one?

Will the headphone of your choice work well with your audio interface, Focusrite Scarlett or otherwise? With your DAC?

Well, you will get the answer in this article — or at least a maximum of elements that will help you better understand how all this works.

(and you will see, manufacturers do not always tell us everything, which has complicated things a bit…)

In short, the following article will be divided into four main parts:

1. Headphones & Impedance: the quick answer
2. Impedance, a crucial choice
3. Headphone sensitivity, the other value to know
4. FAQ on headphone impedance and sensitivity

Note: Generally speaking, several of my comments in this article will focus on studio/home studio use.

That’s normal, it’s the theme of the site 🙂

However, the technical explanations and overall logic will be just as true if you plan to buy an audiophile headphone, a gaming headphone, or for example a leisure headphone to listen to music on the train.

Headphones & Impedance: the quick answer

If you are just looking for a quick answer to know whether you should get a low-impedance or high-impedance headphone, then the table below should guide you in the right direction although it is extremely simplified:

Note that these are just guidelines, but if you choose well-known and proven headphone models based on this information, everything should go smoothly.

If, however (and I recommend this), you want a bit more information, I invite you to continue reading… 🙂

Impedance, a crucial choice

In a (home) studio context, impedance is for me the first criterion to consider when choosing a headphone, as in terms of sensitivity, usual studio headphones are generally well-placed.

The problem, concretely

When you buy a headphone, you have the choice between different models that all have different impedances.

In fact, even the same model can have multiple possible impedances.

Just to complicate things, right! 😀

This is the case with the famous Beyerdynamic DT 770, which comes in 32 Ohm, 80 Ohm, and 250 Ohm versions.

👉 Click here to see the price:

• 32 Ohms : Thomann Amazon Woodbrass
• 80 Ohms : Thomann Amazon Woodbrass
• 250 Ohms : Thomann Amazon Woodbrass

But which one to buy?

Which impedance to choose?

We are clearly facing an important issue, especially since a poor choice can prove detrimental to what you will hear in your ears once the headphones are plugged in.

So, it’s better not to make a mistake.

What is impedance?

Let’s first look at the definition that Wikipedia gives us of this physical parameter:

Electrical impedance measures the opposition of an electrical circuit to the passage of a sinusoidal alternating current. The definition of impedance is a generalization of Ohm’s law to alternating current.

Wikipedia

Well.

This doesn’t really help us much.

It doesn’t really answer the question of “what is the impedance of headphones?”.

In fact, the important word in the quote above is “opposition”.

The impedance of the headphones (sometimes referred to as the “nominal impedance”), typically corresponds to how it will oppose the passage of current in the circuit.

We could almost talk about resistance to the passage of current, but that is another precise electronics term that corresponds to something a bit different.

But to simplify, we could say that indeed:

• if the impedance of the headphones is high, it will resist the passage of current more;
• if the impedance of the headphones is low, it will allow current to pass more easily.

Finally, it should be noted that this impedance is measured in ohms (Ω) and is often represented by the letter Z.

Note: even though this article mainly uses the term “headphones”, if you have questions regarding the impedance of earphones, the topic is strictly the same — so you can continue reading.

The impedance of headphones, a variable value

The fact is that all headphones have different impedance values, which can easily be found on manufacturers’ websites, on the technical specifications of the headphones, or sometimes on the headphones themselves.

Impedance categories

Generally speaking, headphones have an impedance ranging from 16 ohms to 600 ohms — in other words, a very wide range of values.

However, this has nothing to do with the impedance values of commercial speakers, which typically have standardized values of 4 or 8 ohms.

Although there is absolutely nothing official about this classification, one could more or less group headphones into different categories based on their impedance:

• 16 – 32 Ohms — consumer earphones & headphones, mainly dedicated to mobile/portable use
• 32 – 100 Ohms — studio (home) headphones, hi-fi listening headphones
• > 100 Ohms — audiophile/pro headphones
• > 1000 Ohms — specific headphones, notably used in broadcasting

In practice, these categories are very permeable.

For example, many headphones under 100 ohms are used in professional studio contexts.

Or, it is completely possible to use your DT770 Pro with an impedance of 80 ohms while commuting, plugged into a mobile phone…

That said, for me, an important limit is around 100 ohms, since below that we will find headphones that can be easily plugged into all kinds of equipment, and of course everything that is earphones — while above 100 ohms we start to have headphones that I would qualify as a bit more specialized, in the sense that without the appropriate equipment it can be complicated to drive them properly.

Note that in some cases, the same headphone can be available in several models with different impedances.

This is typically the case with the DT-770 Pro from the German brand Beyerdynamic, which are available in versions of 32, 80, and 250 ohms.

Why do headphones all have different impedances?

The impedance of a headphone is related to its construction, and more specifically to the design of the copper coils located at each ear.

The length of the copper wire, its shape, thickness, and the number of turns made to form the coil — all these parameters come into play to determine the impedance of the headphone.

In the 60s to 80s, before the advent of portable audio equipment, headphones had high impedance — notably to facilitate pairing with stereo systems, which had high output impedance (we will talk about the concept of output impedance a bit later).

In 1996, the IEC 61938 standard was established, recommending an output impedance of 120 ohms, additionally indicating that this output impedance had little impact on headphone performance, which, although particularly false, likely pushed manufacturers to produce high-impedance headphones.

However, the advent of portable players and then iPods from 2009 brought about profound changes in headphone design, particularly because high-impedance headphones do not work well with battery-powered devices (as the latter do not have the capability to deliver enough power to drive the headphones).

Result: today, the headphones available on the market have particularly variable impedances. Thus, we find both:

• low-impedance headphones, which are easier to use on all kinds of devices;
• and high-impedance headphones, which are more dedicated to an audiophile audience due to their often lower signal distortion.

Why is the impedance of a headphone important?

When you buy a new audio headphone, whether for the (home) studio or to listen to music in a more audiophile context, selecting a model with the right impedance is particularly important.

But this choice of impedance actually depends not on the headphone, but on the equipment you will connect it to.

And more specifically, on the impedance matching between your headphone and the sound source.

Concept of Impedance Matching Headphone/Sound Source

When we defined impedance at the beginning of the article, I took the headphone impedance as an example. We talk about load impedance (load impedance in English).

However, the sound source, typically the amplifier to which you connect your headphone, also has an impedance parameter — we talk about output impedance (output impedance in English).

In the diagram above:

• we find our signal generator, which can be a dedicated headphone amplifier or integrated into another device, such as a phone or an audio interface;
• this generator has an output impedance noted Z_output
• everything is connected to a load, in this case a headphone, which has a load impedance noted Z_load

Ultimately, if you are not familiar with this type of diagrams, it is not very serious: the only thing that is really important to understand is that both the headphone and the amplifier have their own impedance.

The problem is that the two circuits will interact due to these two impedances.

And depending on the headphone impedance relative to the output impedance of the amplifier, audio problems may arise and affect the quality of the headphone’s output.

Moreover, most of the problems reported by headphone users are related to poor impedance matching between their headphone and the device they connect it to.

Problem #1: Power Loss

When you connect a headphone to a sound source, a power loss occurs, and this is inevitable.

A little mathematical point, this is governed by the following formula (if this doesn’t speak to you too much, no worries, it won’t prevent you from understanding the rest):

with:

• Z_output = Output impedance of the source
• Z_load = Load impedance of the headphone

Theoretically, to transfer maximum power between the sound source and the headphone, the impedances must be strictly the same.

However, if you calculate the power loss using the previous formula (if you are not allergic to it :)), you will find that when the output impedance and the load impedance are identical, there is still a power loss of about 6 dB (decibels).

Knowing that -3dB corresponds to a power divided by 2, then -6 dB means that the signal power has been divided by 4!

And as you can see in the graph below, if the headphone impedance differs from the output impedance of the sound source, an even greater attenuation will occur:

The good news is that in most cases, this loss of power has little effect on sound rendering — the amplifier is still capable of delivering sufficient power.

However, I still wanted to mention this topic, as it is one of the points to consider.

Problem #2: Power varies with impedance

When you pair headphones with a sound source, the problem mainly lies in the power that the source can output.

Indeed, depending on the load impedance presented to it (in other words, depending on the impedance of the headphones you connect), the power that the source can emit will vary significantly.

This is of course related to the power loss mentioned earlier, but also to how the circuit is designed.

It is quite difficult to find detailed specifications on the technical sheets of audio interface manufacturers to illustrate this point — but here is a concrete example taken from the technical sheet of a Focusrite Scarlett 2i2 (first generation):

As you can see, moving from headphones with an impedance of 50 ohms to headphones with an impedance of 150 ohms, the power that can be output by the Focusrite Scarlett is halved.

Second example with the audiophile player FiiO M11:

Again, the same observation: the output power drops significantly as the impedance of the headphones increases.

Clearly, USB-powered audio interfaces and portable DACs are the first to be impacted by this problem, as the amount of power that can be generated is necessarily limited.

Problem #3: Speaker Damping

Last problem and then we will talk about solutions: damping.

To explain things simply:

• When using headphones, some components of the headphone speakers move (or vibrate) according to the music: this is what generates sound.
• However, if nothing is done to prevent them, they will continue to vibrate once the music is over.
• Depending on the headphones, different mechanical or electrical technologies are implemented to dampen the vibrations of the speakers.

By default, electrical damping is the best.

However, it is only effective if the output impedance of the sound source (therefore the amplifier) is significantly lower than the impedance of the headphones.

If the two impedances are too close — or worse, if the impedance of the headphones is lower than that of the amplifier — then you will encounter a number of problems, particularly in terms of bass frequency response accuracy.

So what impedance should you choose when buying headphones?

You will understand, given all the problems that can arise if the impedance of the headphones is not suited to the impedance of the amplifier / headphone output of the audio interface / sound source in general, you risk not being able to properly enjoy the music you want to listen to.

The volume may be too low, or the frequency response may be altered.

Step 1: Identify the output impedance

The first thing to do is to check what the output impedance of the equipment you want to connect your headphones to is.

To do this, I recommend looking in the user manual or checking the manufacturer’s website.

For example, on the Focusrite website, you can find a number of details about the headphone output, including the impedance:

However, in many cases, the information provided by manufacturers is not complete or does not quite answer the question.

Here is an example with the UR22 mk2 from Steinberg:

Here, the output impedance is not mentioned but there is an indication in ohms, which might suggest an output impedance.

However, it is simply the impedance allowing for 6 mW output per channel (see issue #2 a bit higher up).

The actual impedance is probably much lower.

So be careful with the numbers you take as reference…

The “8 Rule”

Now that you know the output impedance of your equipment, you need to determine the impedance of the headphones.

As a general rule, it is recommended to choose headphones with an impedance at least 8 times greater than the output impedance.

This is the 8 rule.

For example, if the output impedance is 10 Ohms, you need headphones of 80 ohms or more.

This 8 rule may seem arbitrary at first glance — but it actually comes from various calculations aimed at minimizing volume variations across audible frequencies.

That said, in practice, the rule does not need to be applied too strictly: it is better to consider it as a guideline.

Especially because the impedance of headphones varies with frequency, so the impedance declared by headphone manufacturers is at best just an average:

The sensitivity of audio headphones, the other value to know

So far, we have mainly talked about the impedance of headphones and how it should be matched to the sound source.

However, there is another parameter that must absolutely be taken into account: sensitivity.

A small warning preamble

While the part on impedance was relatively simple, this part on the sensitivity of audio headphones may be a bit more complicated.

Especially because the information provided by manufacturers about their equipment is sometimes lacking or imprecise.

So, if you want to choose headphones for your home studio or your studio without a headache, here are some tips:

• choose a headphone recognized as effective in studio use like these;
• select headphones with an impedance between 40 and 100 ohms, and avoid those over 100 ohms to avoid power issues (unless you have read the rest of the article and know what you want to do).

For example, I use my ATH M50X, which has an impedance of 38 ohms, both on my audio interface and on my laptop — and I never encounter any issues.

In the same vein, my AKG k240 mkII of 55 ohms or my DT 770 Pro in the 80 ohm version both work very well, both on common audio interfaces and on my smartphone.

So if you’re looking to find out which headphone impedance is suitable for your smartphone, you don’t need to overthink it…

…however, I would avoid 250 ohm headphones if I wasn’t sure about the power of the headphone amplifier integrated into my sound card — especially if it is powered via a USB port.

In short, after this preamble aimed at putting into perspective the complexity of choosing a studio headphone, we can talk about sensitivity…

What is the sensitivity of audio headphones?

First, let’s take the time to understand what it is about.

Definition of headphone sensitivity

Sensitivity is the measure of the volume emitted by a headphone for a given power level.

For example: if you have headphone A with high sensitivity and headphone B with low sensitivity, if the impedance is the same and the power emitted by the amplifier is constant, then headphone A will be louder than headphone B.

For headphone B to reach the sound level of headphone A, the output level (and thus the power) emitted by the amplifier will need to be increased.

To simplify, this means that if your amplifier is not very powerful (because it is powered by USB for example) and the sensitivity of your headphones is not great, then the latter will output a rather low volume.

Unit of headphone sensitivity

The sensitivity of a headphone is generally measured in dB SPL/mW — that is, in decibels SPL per milliwatt. This corresponds to a sound level related to a power (in milliwatts).

Generally, headphones have a sensitivity ranging from 75 to 120 dB SPL/mW.

Note that the same unit is sometimes indicated in the form “dB/mW”, but it corresponds to the same thing.

Alternatively, sensitivity may be presented on some technical sheets in another unit: dB SPL/V — that is, in decibels SPL per volt.

This time, we have a sound level related to a voltage.

Note: In this article, we will use the first unit, so dB SPL/mW.

However, if you need to convert dB SPL/V to dB SPL/mW (or vice versa), I invite you to use my sensitivity converter, which I designed specifically for this article 🙂

If a headphone has, for example, a sensitivity of 104 dB SPL/mW, it means that it will emit a signal at a level of 104 dB SPL when powered by an electrical signal with a power of 1 milliwatt.

Decibels SPL are a standard measure of sound level.

To better visualize what this unit corresponds to, the table below lists some reference points from everyday life:

Note that this sound level scale measured in dB SPL is not linear: a sound at 20 dB SPL is not twice as loud as a sound at 10 dB SPL.

Indeed, a sound power “twice as loud” corresponds to an increase of +3 dB (SPL).

Using Headphone Sensitivity to Estimate Sound Volume

Well, you now understand what sensitivity is and how you can find it on a specification sheet.

But what information does it really provide us?

Well, it will be essential for understanding the sound level that your headphones can emit once connected to your audio interface or DAC.

And also to ensure that you are using your headphone amplifier under the best conditions.

Indeed:

• if your headphones have too low sensitivity, you will likely have to push your amplifier to the max, which will result in increased distortion (a phenomenon that is easily noticeable on mobile phones, typically);
• if your headphones have too high sensitivity, and your amplifier is very powerful, then you will be using it at 1 or 2% of its actual power — which can result in a more significant background noise.

How Much Power Do My Headphones Need to Be Loud Enough?

In general, you can consider that your headphones will be loud enough if they can output sound at a level of 110 dB SPL at peak.

This will correspond, more or less, to a level of 95 or 100 dB SPL RMS — which is more than sufficient.

Moreover, generally speaking, we listen at a level of 60 to 80 dB RMS. If you were to listen to a sound at 100 dB SPL RMS for several minutes, it could have an irreversible impact on your hearing.

Be careful to differentiate between peak dB SPL and RMS dB: when we talk about peak, it corresponds to the maximum level, while when we talk about RMS, it corresponds more to an average perceived level.

Now, using the sensitivity you read on your headphone’s specification sheet, you can calculate the amount of power (in milliwatts) needed to reach 110 dB SPL.

Let’s revisit our earlier example of headphones with a sensitivity of 104 dB/mW.

As we learned from the definition of sensitivity, this means that to output a signal at a level of 104 dB, a power of 1 milliwatt is required.

If you want to double the sound power (+3 dB), you need to double the power.

So to reach 107 dB, you will need 2 milliwatts.

And again, to reach the famous 110 dB SPL, you will need to double the power again: you will need 4 milliwatts.

You can now calculate the power needed for your headphones based on their sensitivity.

However, to simplify things for you, I suggest referring to the table below:

1. Identify in the left column the sensitivity in dB/mW of your headphones;
2. Then find in the 110 dB SPL column the power value you need.

(for your information, I have also added a 105 and a 115 dB column, so you can see the power levels that would be necessary to reach these volumes)

For reference, here is the formula to reconstruct this table:

Will my headphones be loud enough?

If you thought you could finally choose your headphones with peace of mind, you were mistaken 🙂

Indeed, in the previous paragraph, we simply determined the power level your headphones needed to reach 110 dB SPL at peak.

But we still do not know if your headphone amplifier, your DAC, your audio interface — in short, the sound source you are going to connect it to — can provide this power!

First of all, if you look again at the table just above, you will realize that in some cases, to reach a theoretical level of 110 dB SPL with certain headphones of low sensitivity, it would really require a lot of power.

For example, if your headphones have a sensitivity of 83 dB/mW, you would need half a watt to drive them at full volume… which in some cases could be complicated.

Note: For example, referring to the USB 2.0 port standard, they can output a maximum power of 2.5 watts.

On an audio interface that would be powered solely via USB, a large part of the available power is already used by the preamps, converters, LED indicators, phantom power…

So there is not much left for headphone amplification!

It is therefore important to check that the output level that your audio source can provide in terms of power (in watts) is consistent with the level you need (and that you identified in the previous paragraph).

In other words, if your headphones with a sensitivity of 104 dB/mW need 4 mW to reach the famous 110 dB SPL, you will need an audio source that can output at least 4 mW (and ideally more) at the impedance of your headphones.

Do you remember this table, taken from the specifications of the Focusrite Scarlett 2i2 (1st generation), that we saw in the chapter on impedance?:

Well, we noted that the output power of this Scarlett 2i2 varied depending on the impedance.

In fact, this is true for all headphone amplification circuits.

So, depending on the sensitivity of your headphones and their impedance, it is possible that your source may not be powerful enough to allow you to reach 110 dB SPL!

Unfortunately, on the technical sheets of audio interfaces, information related to output power is sometimes missing or provided for impedances very different from that of your headphones.

In that case, you can only guess what the power value would be at the impedance of your headphones, or dive into complicated mathematics to try to reconstruct the missing values.

Note: naturally, battery-powered or USB-powered audio sources are limited in terms of output power. In contrast, mains-powered audio sources generally have much more power available.

FAQ on Impedance and Sensitivity of Headphones

With all the above article, you should already have a maximum of information to understand the impact of impedance and sensitivity on the sound of your headphones.

However, in addition, here are precise answers to the most common questions that could not, for clarity reasons, be addressed directly within the article.

Can something be damaged if the headphones are not well matched to the audio source?

99% of the time, there is no risk in connecting headphones to an audio source if the two are poorly matched (especially in terms of impedance).

For me, the only real risk is connecting a very sensitive and/or very low impedance headphone to a very powerful source: you risk damaging the headphones, which will then be subjected to too much power.

Note, however, that the technical sheets of headphones often indicate the maximum power you can send into the headphones.

If the volume of headphones is not loud enough, can we add an additional headphone amp?

If the volume of your headphones is not loud enough, even when your amp is set to maximum, then I recommend either:

• upgrading to a more suitable amp (perhaps with a lower impedance and/or more power);
• or changing to headphones with a lower impedance or simply more sensitivity.

By default, I advise against connecting one headphone amp on top of another headphone amp. Sure, you will gain volume, but at the expense of signal quality (frequency response, distortion, background noise level).

Why do many audio sources have a relatively high output impedance?

This phenomenon is real, even if it is a bit less visible among studio/home studio equipment.

There are several explanations:

• Making a circuit with a high output impedance is simpler and cheaper.
• This can be a way to protect headphones if the amp is very powerful.
• Finally, this can be a differentiating factor for a brand, rightly or wrongly, thus impacting its market positioning and marketing.

Should I get a 32 Ohm or 80 Ohm headphone?

If, for example, you are hesitating between this model (32 Ohms) and this one (80 Ohms), I would advise you to default to the 80 Ohms. The sound will be slightly better, and in practice, you will be able to use it without issues on most devices.

However, if you particularly want to power it through low-power amps (I’m inventing, a device powered by AA batteries), then take the 32 Ohm version.

Should I get a 250 Ohm or 80 Ohm headphone?

If now you are hesitating between this model (250 Ohms) and this one (80 Ohms), then I also recommend taking the 80 Ohms, which will be more versatile.

However, if your ambition is to use the headphones only in a studio/home studio context and with audio interfaces powered from the mains (or high-performance headphone amps), then you can take the 250 Ohms.

Can I plug a 250 Ohm headphone into a PC / MacBook?

Yes, you can, and often the sound will be fine.

In other words, it will generally not be unusable.

However, it is highly likely that it will not be optimal. If your use does not involve dedicated headphone amps (like these)

Is it useful to have a high-impedance headphone in a home studio?

If you work in a home studio, I think you shouldn’t rule out going for high-impedance headphones.

Especially if you need a good open headphone for mixing. For example, the Sennheiser HD650 has an impedance of 300 Ohms — but the sound is very detailed.

So it can be a good investment: it is not reserved for professionals, if you will.

However, make sure first that you have an audio interface or headphone amp that can really drive the headphones properly, to truly enjoy them.

In conclusion

There you go, I think with this extensive article you now have all the necessary information to understand what impedance and sensitivity of audio headphones are — and especially their importance regarding sound quality.

I was going to say “to go further”, but this article is already very detailed — so, to continue reading, I simply recommend you take a look at my selection of headphones for the home studio.