We know that sound is created by audio waves with varying frequencies. The human ears can hear the sounds that fall only within the fixed frequency range of 20Hz to 20kHz. Anything less than or more than the audible frequencies is beyond human hearing. Though, different animal, bird, and insect species can hear, based on their frequency sensitivity. But how does the same frequency response affect the audio quality of headphones? What is frequency response in headphones?
What do we mean when we say that a pair of headphones has a good frequency response? Do headphones with high frequencies perform better than the ones with lower frequencies?
In this article, we’ll discuss frequency response and sound quality in detail. However, remember that frequency response is not the only factor to determine if your headphones are good or worthy of being termed as audiophile models.
What Does Frequency Response Mean in Headphones?
Headphones, earphones, and speakers are audio output devices that reproduce the audio signal of the original sound. Headphones convert electrical signals/energy to mechanical energy (i.e. audio signals to sound waves) for us to hear the sound output. Since the audio signals comprise different frequencies with varying amplitudes, reproducing these frequencies will lead to slight variations from the original.
While some sounds are emphasized, others are muted or mellowed, depending on the frequency response of the headphones.
In simple terms, the headphones’ frequency response denotes the frequencies of audio signals the device can reproduce. It shows how accurately the headphones will play the audio.
The frequency responses of the headphones are provided by the manufacturer as a part of the specifications. While some models have a graph, other models come with simple numbers. More often than not, the frequency response graphs are created by third-party platforms (reviewers, audiophiles, etc.) to help others understand the efficiency of the headphones. Also, according to the Journal of the Acoustical Society of America, there’s no relation between headphone frequency and retail price. Headphone frequency simply measures the sound accuracy and quality.
Frequency responses are not independent. They are connected to other aspects like impendence and sensitivity, which we’ll see in the latter part of the article.
What is a Frequency Response Graph?
A frequency response graph (or chart) is created by testing the headphones/earphones/speakers in recording studios. Various frequencies are played through the headphones placed on a recording device. The audio output is recorded and plotted as a graph or a chart. The volume and decibels (dB) of the reproduced sound at every frequency are marked in the graph. The frequency range is denoted on the X-axis, and the (amplitude) decibels are on the Y-axis.
Theoretically speaking, a flat line from one end of the graph to the other should mean that the headphones can reproduce sounds in all frequencies with the same strength and clarity. This is known as flat response, against which the actual graph of the headphones is measured.
However, a perfectly flat frequency response is an ideal condition that doesn’t occur in real life. Even though the manufacturers of audiophile headphones do their best to get as close to the flat response as possible, achieving it is not entirely feasible.
Some brands are playing with the frequencies to focus on the lower range and feel that headphones with more bass have better audio quality.
That said, the headphone’s frequency response chart with not tell you whether the headphones are perfect for you or not. It’ll only show how capable the model is in reproducing audio signals to sound waves of a certain range.
Which Are the Different Frequency Ranges in Headphones?
The headphones are designed to have identical drivers so that the frequency ranges of both are the same. This delivers balanced sound with better clarity.
Some headphones have a wider range while others have a narrow range. Though the standard frequency response for humans is 20Hz to 20kHZ, we see headphones with a range of 5Hz to 50kHz, which includes the lowest frequency.
For example, Apple EarPods (in-ear earphones) have a frequency response of 5Hz to 21kHz. Stax SR-007 has a frequency response range of 6Hz to 41kHz. While EarPods come with moving coil drivers, SR-007 has an open-back circumaural electrostatic driver.
Does it mean that EarPods are better than other headphones or that SR-007 is even better than EarPods due to the wide range?
We also need to consider the decibel dip, the impendence, and sensitivity to ascertain which headphone delivers a clear and precise output. The tolerance value is another way of finding out the same. This is generally denoted as +/- x dB.
What is a Good Frequency Response for Headphones?
We’ve been mentioning good headphone frequency responses for a while now. But is this a ‘good frequency response?’ What does it mean?
Simply put, headphones that can reproduce the audible frequencies are considered good. But there’s more to it, and to understand that, we’ll need to know about neutral frequency response and flat frequency (explained in the subsequent sections).
So what about headphones with a wider range? Well, there are different opinions on this.
Even though we cannot listen to the infra and ultrasounds, we can feel them as sound waves. That means headphones with a wide range are better.
Second, it depends on the headphones amp and the genre of music you prefer. Good is a highly relative term. What’s good for us may not sound the same for others and vice versa. Even expert audiophiles have a difference of opinion in these aspects.
Also, headphones are capable of playing musical notes outside the specified range. The output is just not loud enough for us to easily identify the sounds.
We can safely declare that headphones with an audio frequency between 20Hz and 20kHz are usually suitable for most listeners.
How to Check Frequency Response of Headphones?
The headphone’s frequency response is broken down into frequency bands – bass/ low, mids, and treble/ high. The output quality also depends on the type of headphones you are using – open-back headphones and closed-back headphones.
You would have heard of terms like raw frequency response and compensated frequency response.
The raw response is taken from the measurement microphone during the testing process.
The compensated response is a converted version of the raw frequency response graph by applying the target curve to it. The target curve is added because reading the raw response graph is not easy for every user. By converting it to a compensated frequency response graph, we can help listeners have a better idea of how the headphones would produce different musical notes.
The Harman target response curve is an optimal sound signature or the acceptable tonality of the headphones preferred by listeners. It is an approximate representation of how the speakers/ headphones would sound in ideal conditions.
The Harman curve adds an additional frequency curve to the frequency response so that the headphones can (try to) create a sound output that appears neutral.
How to Read Frequency Response Graph of Headphones?
Now comes the question of how you should read a frequency response graph. As mentioned in the earlier sections, the X-axis represents the frequency, and the Y-axis represents volume/ amplitude.
Just by looking at a sample raw graph, we cannot immediately say if the headphones are good at playing the bass or if the highs sound better. The bands are again classified as lower, middle, and higher, which only adds to the confusion. What to do then?
You should first understand and memorize the below details to read a frequency response graph.
|Name of Frequency Band
|20 Hz – 40 Hz
|40 Hz – 80 Hz
|80 Hz – 160 Hz
|High/ Upper Bass
|160 Hz – 320 Hz
|320 Hz – 640 Hz
|640 Hz – 1.28 kHz
|High/ Upper Midrange
|1.28 kHz – 2.56 kHz
|2.56 kHz – 5.12 kHz
|5.12 kHz – 10.2 kHz
|High/ Upper Treble
|10.2 kHz – 20.4 kHz
Do note that this range is not fixed and changes from one person to another. However, the average frequency range for each band will more or less overlap. The bass range will fall within similar limits for most people, and so on.
You can either draw the graph with 0dB in the center of the Y-axis or start with the lowest dB of the headphones and go up to the highest. This measurement will change the shape of the graph and your understanding of it. Don’t forget to look for the dB variation in the specifications.
What is Flat Frequency Response?
We’ve briefly seen the flat response in the earlier sections. Flat frequency response is where the headphones are expected to produce audio output with equal sensitivity. This doesn’t include the white noise we don’t want to listen to.
A flat response is absolute and almost impossible to achieve. At the same time, emphasis on bass doesn’t necessarily mean that the headphones are fantastic. That’s because the same rules don’t apply to speakers and headphones.
Speakers with more bass have bigger and powerful drivers that accept and reproduce low frequencies with ease. This bass effect is felt more than it’s heard by the listeners. You feel the thumping on the floor, in the vibration of the furniture, and how your heartbeat aligns with the deep bass beats.
The bass sounds will also have to be heard, when it comes to headphones, as the brain perceives them only as sounds. This means that a headphone model with extra bass may not always be the right choice (unless you listen to music with more bass). However, these headphones have slightly better sound quality compared to flat response headphones as the drivers are powered for that additional punchy output.
Each headphone has to be measured multiple times by re-seating the dummy heads (where you put the headphones) in different parts of the room. If the headphones produce the perfectly flat frequency response during a test, the resulting curve would be the target.
What is Neutral Frequency Response?
As a novice, it would be easy to assume that flat response and neutral response are the same. After all, everything is supposed to be perfect and in a flat line, isn’t it?
Also, neutral, like a flat response, is almost impossible to perfect, be it in headphones or speakers. It is also dependent on several factors, such as the equipment used to record the audio, the recording environment, and the location of the listener (listening to the headphones).
Another thing you need to know here is that the neutral response graph can be slightly different when tested by different people. What might sound perfect neutral for a person could have less bass for another.
Moreover, for a headphone model to be declared ‘neutral,’ it should have a slight additional touch of bass to make up for the missing tactile feeling that’s usually felt when listening to a speaker system. It means that when applying equal amplitude of frequencies to the headphone, the lowest range should have 3-4 dB higher than the rest. This will ensure a tonal balance that’s liked by most listeners.
The same rule applies to different genres of music as well. So you see why a pair of headphones can’t achieve the perfect neutral response. The music genre and the recording play vital roles in determining the neutral, and these are not controlled by the manufacturers.
Is 20Hz to 20kHz Good for Headphones?
We already established that the audible frequencies for humans range from 20Hz to 20kHz. It seems like a perfectly natural conclusion that headphones with the same frequency response would be considered a good choice and 100% suitable for human hearing.
It’s no surprise that most headphones offer this range. The high-end models offer extra (as seen in one of the previous sections). However, this alone cannot ensure that the headphones are of the best quality.
What is more important is to see whether the frequency response between the minimum and maximum frequencies is linear or not, and if yes, how linear it is.
Moreover, not all of us have the same hearing power. As we grow older, our hearing capacity lowers down, and we cannot listen to frequencies closer to min and max limits. Considering that an average adult cannot hear over 14kHz or 16kHz and anything lower than 60Hz is more of a sensation than a sound, we can safely conclude that headphones with 60Hz to 16kHz are also good enough for most listeners.
That said, headphones with a wide frequency range have their advantages. The response of these models is flatter and accurate, though we cannot be sure of it if the tolerance is not managed accordingly.
What distinguishes the headphones with a similar frequency range is their design. Are you using open-back or closed-back models? Are those in-ear headphones or over-the-ear headphones? Do the headphones have an airtight seal and noise isolation? Does the audio play directly into the ear canal? What is the size of the drivers? What is the headphone impedance?
Bose 700 Frequency Response
Bose Noise-Canceling Wireless Bluetooth Headphones 700 have a warm sound profile with a slight bass-heavy touch with a positive bass amount. The mid-range is balanced, making it a good choice of headphones from vocal-based audio. The overall frequency response consistency is pretty decent.
While the bass response is steady, we did notice some fluctuations in the treble. This could also be due to the change in position or the fitting of the headphones.
The bass consistency is likely due to the noise cancelation feature. The mids are wonderful, with a near-perfect tonal balance. The treble is good enough, though some of the low treble notes may not sound as sharp as they should. But if you are a fan of vocals, this pair of headphones is a good choice for you.
Bose QuietComfort 25 Frequency Response
Bose QuietComfort 25 has a great bass response, though the headphone is not bass-heavy. The bass amount falls slightly lesser than 0dB, but that doesn’t mean that bass isn’t good. Rather, it was the most consistent of all bands in the frequency response graph.
Since the headphone has active noise cancellation, we can assume that bass consistency is due to this feature. While the lower and mid-bass was too good, the upper bass could have been better.
Similar to Bose 700, Bose QuietComfort 25 also has an excellent mid-range with a good balance of vocals and instruments. However, you might notice that the voice tends to pop to the front a little more. The treble is decent, but nothing stands out here and is pretty normal.
Sennheiser HD800 Frequency Response
The frequency response consistency is good with Sennheiser HD800. This is indeed a good sign. However, if you are looking for strong bass, you might not find it here. The headphone is bass shy and plays bass on a lighter note. It’s not punchy.
The mids are wonderfully even. The graph is quite linear and has only small bumps and dents instead of spikes and dips. Still, the vocals might not be as clear as you want them to be and sound a bit thick.
The treble is balanced and sharp and could be a wee bit too sharp at times. The overall graph is pretty consistent between 10Hz to 10kHz. Then it goes a little erratic, which shows the reason for the slightly extra sharp treble.
Shure SE215 Frequency Response
Shure SE215 has a good frequency response consistency given that you properly fit the headphones over your ears and ensure that they are airtight. While the overall bass is good on the graph, the low and mid-bass are worth mentioning.
The upper bass more or less blends with low mids and causes an extra emphasis that makes the sounds muddy and thick. The middle and upper mids are much better and balanced, delivering decent vocals. The treble isn’t as balanced as we expected. The lower treble is nice, but the middle and upper could have been better. Some sounds are too bright, while others are not clear enough.
Apple Earpods Frequency Response
Apple Earpods are very much dependent on how users place the earbuds in their ears. The open-back design doesn’t deliver the kind of consistency headphones tend to offer. The Earpods are quite bass shy, with the lower bass being pretty much non-existent. The upper bass is a bit strong and overlaps with the lower mid, resulting in muddy vocals.
Still, the overall midrange is decent. The treble relies on how you use the Earpods and how well the buds sit in your ears. The S and Ts don’t pierce your ears (which is good), resulting in a better treble performance. However, Apple AirPods would fare much better than Earpods.
Beyerdynamic DT 770 Frequency Response
Beyerdynamic DT 770 has average frequency response consistency that changes based on the listeners and the position of the headphones. Also, we can notice an apparent difference in how the bass sounds when using the headphones with a smart device and when connecting them to an amp. They work the best with the amp.
The bass is super good even if the upper bass is a bit underemphasized, resulting in thinner vocals. The mids are just as lovely, and the treble has a great range. The upper treble might sound a little too bright at times, but the overall performance is noteworthy (when the headphone is connected to the amp).
Audio Technica ATH M20X Frequency Response
Audio Technica ATH M20X has a mediocre frequency response consistency with a decent bass accuracy and great mids. The headphone is bass shy but still delivers a good output. It may not be punchy, but the mid and upper bass is audible.
The mid-range shows a near-flat graph and is quite close to the target response. Vocals sound very good in these headphones. The treble is less than average and leaves a lot to be desired. You can see how the graph steeply dips in the lower and middle treble range.
How Are Headphone Frequency and Impedance Related?
Impedance is electric resistance on alternating current to allow it to flow through the circuit. This is rather complex to understand. Luckily for us, headphone impedance is simpler and makes more sense. It is measured in ohms (Ω).
This is nothing but the measure of power the headphones will need to play the music at a volume you desire. It is pretty much the amount of electricity the headphones need to consume to deliver audio output.
Headphones with less than 25Ω require less power to play and are suitable to be used with smart devices, music, and MP3 players. If you want headphones that play higher volume with ease, you’ll need models with 70Ω or more.
Using low impedance headphones with a high input signal can cause the headphones to blast and hurt you. That’s the reason recording studios and DJs don’t compromise on impedance. What if you want more power? You’ll need to add a headphone amp in such instances. Anything with more than 100Ω needs an amplifier.
In headphones, impedance is dependent on frequency. If the impedance and frequency graph shows that the impedance peaks around a certain range, it’s likely that the headphone’s volume will be lower around that frequency.
How Are Headphone Sensitivity and Impedance Related?
Sensitivity is the extent of volume a pair of headphones can produce at a specified power level. If the headphones have more sensitivity, they’ll play louder than regular headphones when you choose the same volume level for both of them.
Sensitivity alone has never really being a determining factor when choosing headphones. It is almost always seen with impedance. However, some manufacturers show it in volts. The measurement for sensitivity is presented in decibels (dB) per milliwatt (dB/mW) and is termed as efficiency or commonly called the Sound Pressure Level (SPL).
The higher the volume, the higher is the pressure that the sound waves make in the air. Technically speaking, headphones with higher sensitivity need lesser power to pump up the volume. Sounds great? Not entirely.
Headphones with higher sensitivity will produce a lot of background noise and can hurt your ears. They work the best when plugged into a high-end amp. The average sensitivity is between 86dB (which is low) and 120dB (which is high).
But there is no standard way to measure sensitivity in headphones. Each brand uses a different benchmark, which makes it hard to say that a model of headphones is the best solely based on sensitivity.
Not all of us need headphones with high impedance and high sensitivity. These are not only costly but can also harm your ears if you pair them with the wrong devices.
Understanding a frequency response graph is tougher than it appears to be. You’ll need to look at the relationship between the frequency ranges and how they move around one another. It will help understand the tonal balance, sound quality, and output range of the headphones.
Even though the frequency response should match the target response perfectly, the lack of it doesn’t mean a misbalance in the tone. You’ll need to decide the kind of bass output and highs you want from the headphones based on the genre of music you listen to. Make sure to consider all factors before you make the final decision.