Headphone Impedance And Sensitivity: Why Is It Important?

Why is it important to consider the impedance and sensitivity of your headphones? Do you need a headphone amp? The headphones’ impedance and sensitivity are two parameters you must control well when buying a new model. But there are other things to consider, like the output impedance of the amp you connect the headphones to.

It doesn’t seem very easy, but deep down, it is not. We are now explaining it. First, some basic knowledge about impedance and its influence on the headphones and the quality of the sound that we are going to hear:

• The output impedance of the sources we connect our headphones to is one of the main reasons our headphones sound different or not.
• Depending on the impedance of your headphones, you will be able to enjoy them (or not) in different sound sources. Some you can connect without problems to your smartphone, others to your computer, and others need to be connected to an amplifier.

What is impedance in headphones?

Impedance is the electrical resistance or “measure of opposition that a circuit presents to a current when a voltage is applied.” 

It is measured in Ohms (Ω), and in the case of headphones, it will tell you how much power they need to listen to them at a reasonable volume.

The more impedance they have, the more power you will need to hear them aloud. Many smartphones cannot “drive” enough power to use high-end headphones. That is why many times we will need a headphone amplifier.

• Up to 32 ohms, you will not have a problem with headphones.
• Things start to get tricky between 33 and 100 ohms; you can probably hear your headphones at a reasonable volume, but listening with a portable amp is much better.
• From 100 to 300 ohms, you’re going to need a good amp.

This is not to say that 32 ohm headphones are bad, but models with higher impedance can provide more detailed and vivid sound.

What is sensitivity in headphones?

It is related to impedance. However, it helps us less to decide to buy good headphones. Sensitivity gives us the measure of how loud we can hear headphones at a given power level.

But it is not a parameter that companies indicate to us very precisely on many occasions.

Just as a reference. High or low sensitivity in headphones?

• Below 90 dB is considered low sensitivity
• Above 110 dB is considered a high-value

Sensitivity is commonly referred to as Sound Pressure Level (SPL). It is measured in dB and ranges from 0 dB to 120 dB (pain threshold). Usually, a sound pressure of less than 85 dB is recommended to avoid hearing damage.

Is low impedance or high impedance headphones better?

Well, it depends on the use:

• If you want to use headphones with a portable player, laptop, or smartphone, buying a model that falls in the 6-32 ohm range and has a sensitivity of at least 100 dB/mW is safer. The lower the impedance, the better in this case. However, there are models of headphones up to 80 ohms that still work well in this type of device (in case you don’t like the volume too high).
• If you are going to use a DAC or a headphone amplifier, check the recommended impedance range for headphones before you buy.

Note: What do we consider high impedance headphones? Usually, headphones are considered to have high impedance starting at 100 ohms. Low impedance headphones? From 32 ohms down. This leaves us with a gray area between 32 ohms and 100 ohms.

Why is the output impedance of the device you will connect the headphones to important?

The output impedance of the device you connect your headphones to is essential: it will make the same headphones sound different.

• The higher the output impedance, the more significant the voltage drop at a lower impedance. This drop can be large enough to prevent low-impedance headphones from reaching high enough levels of hearing.
• Very important: The impedance of the headphones changes with frequency. If the output impedance is well above zero, the voltage delivered to the headphones will also change with frequency. The higher the output impedance, the greater the frequency response deviations.
• As the output impedance rises, the electrical damping is reduced. What about this? The bass performance of your headphones can become more “boomy” and less controlled.

Note: To avoid all these problems, it is essential to consider the 1/8 rule: the output impedance must be less than 1/8 of the headphone impedance. Or, put another way, you have to divide the headphone impedance by 8 to get the maximum output impedance that avoids possible sound degradation.

Headphones with Dynamic Drivers move back and forth with the music, creating sound. And to stop that movement, you have to dampen the Driver mechanically or electrically (the latter being the best option).

Problem? Electrical damping is only effective when the amplifier’s output impedance is much lower than the impedance of the headphones. Therefore, if the 1/8 rule is not followed, the Driver may continue to work and spoil the sound. If the headphone and the amplifier follow the 1/8 rule, this will not happen, and we will be able to hear the music perfectly.

If you connect your headphones to a computer or smartphone and don’t hear them very loudly, you may need to connect them to a DAC/Amplifier. It will provide you with a volume boost, and you can modify the volume of your music directly on this device.

Some examples with headphones: The Sennheiser HD 660 S has a nominal impedance of 150 ohms. You divide 150/8 = 18.75. The equipment you connect these headphones to must have an output impedance of less than 18.75. The 80 Ohm Beyerdynamic DT 770 PRO: 80/8= 10. The equipment you connect these headphones to must have an output impedance of less than 10.

An example with a DAC/AMP Topping DX3 Pro (a headphone amp with DAC): It has a power output of 700mWx2@32 ohms or 125mWx2@300 ohms, which means it has a perfect output impedance, and you go to power virtually all headphones on the market.

This part deserves a little explanation:

The Topping DX3 Pro can deliver 700mW of output when connected to a 32-ohm headphone and 125mW if you connect a 300-ohm headphone (more impedance equals more resistance in power it can transmit).

The Topping DX3 Pro is an excellent DAC/AMP. You can connect any headphones without fear that the frequency response will be affected by impedance. If, for example, you have a Sennheiser HD 650, you can turn up the volume as much as you want without fearing distortion.

And the same thing happens with its older brother, the Topping DX7 Pro: In this case, we have two headphone outputs:

• Balanced output: 1700mW x2@32hm and 450mW x2@300 ohm
• Single output: 840mW x2@32ohm and 115mW x2@300 ohm

Basically, this means that you can connect high-impedance headphones and use them at very high volumes.

Moral of all this? You have to be very careful with the impedance of the headphones and the amplifiers. If you plug headphones into the wrong amp or a computer without the right hardware, you can notice big differences in sound at certain frequencies. You can have the best headphone in the world and sound bad connected to your sound source.

Do you need more power and, therefore, a headphone amplifier? Let’s see the sensitivity (efficiency) of them

• The sensitivity of the headphones will tell us what capacity the headphones have to convert power into a sound that we can hear.
• What is a headphone amplifier? It is a power amplifier that boosts the low-voltage audio signal to a level high enough for it to be converted into sound waves by headphones so you can listen to your music at a suitable volume.

If the sensitivity of your headphones comes in dB/mW, you can easily know how much power you need in your amplifier so that those headphones work correctly. Look at the following table:

dB/mW	105dB (pico SPL)	110dB (pico SPL)	115dB (pico SPL)
85	100.0 mW	316.2 mW	1000.0 mW
88	50.1 mW	158.5 mW	501.2 mW
91	25.1 mW	79.4 mW	251.2 mW
94	12.6 mW	39.8 mW	125.9 mW
97	6.3 mW	20.0 mW	63.1 mW
100	3.2 mW	10.0 mW	31.6 mW
103	1.6 mW	5.0 mW	15.8 mW
106	0.8 mW	2.5 mW	7.9 mW
109	0.4 mW	1.3 mW	4.0 mW
112	0.2 mW	0.6 mW	2.0 mW
115	0.1 mW	0.3 mW	1.0 mW
118	0.1 mW	0.2 mW	0.5 mW

In the dB/mW column, you have the sensitivity of your headphones. In the following 3 columns, you have 3 different SPL peaks. Usually, you can take into account the data in the 110 dB column, but if you don’t like to listen to music very loud, you should follow the column of 105 dB, and if you like music with a very loud sound, follow the column of 115dB

An example? The Beyerdynamic DT 1990 Pro has 102 dB SPL, so you would need about 5.0 mW to peak at 110 dB. Your source needs at least enough power for the headphones to work well.

Note: You have to be very careful with the volume of the music and your ears. Earache starts at 120 dB SPL, but it is not advised to exceed 85 dB SPL.

Therefore, you have to take into account a few things when buying headphones and an amplification source:

1. Type of music (average volume): Music varies a lot in its average volume. Compressed pop music is much louder than jazz or classical recording.
2. Desired Maximum Output: The maximum perceived volume that you want to hear.
3. Headphone Sensitivity: This is the headphones’ volume at a given voltage or power level.
4. Headphone impedance: You will always find it in the headphone specifications.
5. Maximum output of the source: The amount of power that the source can produce, which changes according to the impedance of the headphones (something difficult to achieve in many devices).
6. Cables you need to make the connections between the expander and the headset: Types of audio cables: connectors for your sound equipment to better listen to your music.

What other things do you have to take into account when buying headphones? Your sound profile and headphone type

Sound profile? It’s simple. Not all headphones sound the same, and it’s not that the most expensive ones sound better or worse. 

Each brand offers a sound profile in each model (each type of headphone has a different frequency range, enhanced in the highs, lows, or medium). 

You must know your musical preferences to be successful with the purchase. The sound quality depends a lot on your preferences.

We have told you everything in the following post:

You should also consider whether you want them with cable or without it. We will tell you its pros and cons in the following: Wired or wireless headphones? Which is the best option?

Types of headphones? You should read the following table to see its pros and cons:

In-ear vs. Over-ear vs. On-ear vs. True Wireless vs. IEM vs. other types of earphones

In the case of wireless headphones, you may also be interested in knowing the following differences: Wireless headphones: differences between radiofrequency, infrared, and Bluetooth headphones.

You may also be interested in the Guide to buying the best home sound equipment: HI-FI amplifiers, speakers, and headphones.

Conclusion

The bottom line is that impedance and sensitivity are useful specifications when choosing a pair of headphones. 

The lower the impedance, the more power you will need to drive your headphones, while the higher the sensitivity, the louder your headphones will sound with the same power. 

Ultimately, your best bet might be to play around with different machines and devices to see which sounds best for you.