Audio Device Impedance and Sensitivity Explained

Are you struggling to understand the importance of impedance and sensitivity when shopping for headphones and other audio equipment? You're not alone - these concepts can be tricky to master.

For most of us, headphones are a plug-and-play device. We do not think beyond their price and looks, but some headphones are better suited for specific audio tasks, while others provide better audio enjoyment.

Therefore, it's important to know a little bit about sensitivity and impedance before buying headphones or speakers. This article will explain what each concept represents and why they're relevant to the average buyer.

Speaker and Headphone Impedance and Sensitivity

Your understanding of how audio equipment works won’t be complete without knowing about these two features. They might seem tricky to figure out, but we’ll guide you through them step by step.

What Is Headphone Impedance?

In simple terms, impedance is the measure of a headphone's resistance to an alternating current. The higher the impedance, the more resistant the headphones are to the current. It's important to remember the resistance changes in line with the frequency, so more power is needed at higher frequencies. As a result, high impedance headphones require more power to reach their full potential.

Just like any other current resistance, it’s “governed” by Ohm’s law of power and energy. You do not need to know the law, its mathematical formula, or how it works. But you should know that impedance is also measured in ohms (Ω). With that in mind, you’ll always be able to find the impedance in the headphone specification by looking for this symbol.

However, just because a pair of headphones has a high impedance doesn't mean they're always the superior choice. Yes, they will have better sound quality - provided you know how to use them and have an external amplifier. With the latter, it’s essential to match the impedance of your audio device and the amplifier. Otherwise, you risk damaging your equipment and degrading the audio quality even more.

Low-impedance headphones, on the other hand, are typical plug-and-play devices that are easy to use and do not need as much power or know-how.

What Is Headphone Sensitivity?

Sensitivity measures how efficiently a pair of headphones converts an alternating current into a sound pressure level (SPL) using a specific amount of power. The higher the sensitivity, the better the headphones convert electricity into sound, especially with sudden frequency changes.

However, high headphone sensitivity isn’t always better. In fact, high-sensitivity headphones are more prone to distortion at high volumes because the sound you want isn’t the only thing that gets louder. Everything else ups its volume, too, including static, distortion, and so on.

On top of that, using sensitive headphones at a high volume may damage their drivers, which will cause them to lose volume over time. To avoid these scenarios, it’s good practice to pair them with an amplifier.

On the other hand, low-sensitivity headphones don't distort as easily but may require more power to reach their full potential. This means they can struggle to achieve strong audio if plugged into your commercial device, like a laptop or smartphone, but they work great when connected to an amplifier.

Since sensitivity represents the SPL of a speaker at a set power rating, the most common way it’s portrayed is decibel loudness/milliwatt or (dB/mW), which doesn’t give you the full picture. This measurement indicates how much voltage is required to produce 1 mW of electricity, but it doesn’t consider the relationship between sensitivity and impedance.

As previously indicated, impedance is not constant. It fluctuates with the power level, which poses some problems when comparing devices with different impedances. For that reason, many companies are switching to decibel loudness/voltage (dB/V), and it’s slowly becoming the new industry standard. It shows how loud the speakers are at a given voltage.

How Does Impedance Affect Headphone Sensitivity?

Higher-impedance headphones need more voltage to get the same SPL as lower-impedance headphones. This means that, all else being equal, high-impedance headphones will have lower sensitivity than low-impedance headphones.

For example, let’s say you have two pairs of headphones with the same sensitivity, but one has an impedance of 32 Ω, and the other has an impedance of 300 Ω. That difference means that the 32 Ω headphones will be much easier to drive than the 300 Ω headphones. You would need 10 times as much voltage to drive the 300 Ω headphones to the same SPL as the 32 Ω headphones.

This is why dB/V is a better measure of headphone sensitivity than dB/mW. It considers the headphones' impedance and allows for a fair comparison between different models.

The Difference Between Impedance and Sensitivity

The main difference is that impedance measures how well the headphones resist an alternating current, while sensitivity shows how well they turn electricity into sound.

Additionally, the impedance varies with frequency, whereas sensitivity does not. This means that headphones with a high impedance need more power to work at their best, while headphones with high sensitivity are more likely to distort.

Finally, impedance is measured in ohms (Ω), while sensitivity is expressed in decibels (dB). 

Even though sensitivity and impedance seem to have nothing in common, they both help protect the headset from damage caused by too much electricity and make the listener more comfortable.

Volume and Headphone Sensitivity

You first need to know that volume and loudness are not the same. Volume is a measure of sound intensity on its own, while loudness is a measure of how our ears hear that volume. It’s essential to make this distinction because headphone sensitivity doesn’t just reflect the loudness.

Since loudness is a matter of perception, two people can hear the same volume level but have different ideas about how loud it is. This is due to the way our brains process sound. For example, if you’re in a noisy environment, your brain will filter out the background noise and focus on the sound you’re trying to listen to. However, when it comes to volume, there are objective measures - i.e., the number of decibels.

What Are Decibels?

Decibels are a unit of measurement for sound intensity. They indicate how loud a noise is on a logarithmic scale. This means that an increase of 10 dB corresponds to a tenfold increase in intensity, while an increase of 20 dB corresponds to a hundredfold increase.

For example, an increase from 60 to 70 dB is ten times as intense, but an increase from 60 to 80 dB is 100 times as intense. We don’t perceive these increases as finely, so a sound shifting from 80 to 100 dB is heard as four times louder.

Here are some common examples:

• A whisper is about 30 dB.
• Normal conversation is about 60 dB.
• A lawnmower is about 80 dB.
• A car horn is about 100 dB.
• A rock concert is about 110 dB.
• A gunshot is about 150 dB.

Why Are Impedance and Sensitivity Important?

Now that we've explained the terms, it's time to understand why they're important. The answer is simple: They help you choose the right headphones or speakers for your needs.

If you are looking for easy-to-use headphones or speakers, go for low impedance and sensitivity. These types of headphones are typically plug-and-play devices you’ll use every day while on the move. Don’t expect too much of them.

You should know that most speakers without a cable connection will fall into this category. This includes inexpensive Bluetooth speakers you can carry to the beach or outdoor wireless speakers you would use for a backyard party. Without the cable, you can’t connect high-impedance headphones or speakers to an amplifier to get the most out of them.

If you are looking for headphones or speakers for your gaming setup, PC, or home theater, you’ll be looking for low sensitivity and high impedance. A low impedance and high sensitivity will cost you in quality, and there is a chance of damaging your headphones or speakers at higher volumes.

It should be noted that there are also high impedance and high-sensitivity headphones. Professionals usually use these in studios and other places where sound quality is paramount. If you are a true audiophile, you should go for this setup, but don’t forget to get an amplifier as well.