What Is Frequency Response? Understanding Headphone Specs

Consumers often ignore the specifications of headphones. Modern headphones have been so good that we tend to forget about the technical aspects. However, they house valuable information that can ultimately manipulate or help us in judging whether or not a headphone is a good fit for us. 

One of these core specifications that we must always take note of is the frequency response. You may hear this a lot along with the term frequency response graph (FR graph) in a lot of marketing materials and more in-depth headphone reviews. If you are not familiar with this term, then some of the things that are being talked about in the reviews can be confusing.

So if you find the frequency response to be a bit of a challenge to understand, then keep on reading to better understand this along with other concepts such as sound signature and even how to alter the frequency response of a headphone. Take note that for this article, we will specifically be focusing on the frequency response of headphones and IEMs. 

 

What is Frequency?

The technical definition of frequency in audio is the speed of the vibration, which determines the pitch of the sound. The range of audible frequencies for humans is from 20 Hz to 20000 Hz (20 kHz). 

The range of frequencies can be grouped into three major categories. Low frequencies from 20 to 300 Hz are the low frequencies, frequencies from 300 Hz to 2400 Hz are the mid frequencies, and frequencies from 2400 Hz to 20000 Hz are the high frequencies. Going one step further, frequencies from 20 to 60 Hz are the sub-bass frequencies, frequencies from 250 to 500 Hz are the low mids, 2 to 4k Hz are the high mids, and so on. 

These numbers may be daunting at first, but let us make it simpler to understand. The low frequencies are typically produced by low pitched instruments such as the kick drum and the bass guitar. High frequencies are produced by instruments like the cymbals or the flute. The rest of the frequencies are the mid frequencies. Examples of this are the vocals and the guitars. 

Understanding the concept of frequencies will help you understand other concepts such as frequency response and sound signature. This will help you better understand the technical aspects of your headphones, IEMs, or speakers.

 

What is Frequency Response?

Now that we know what frequencies are, the next concept that we will tackle is the frequency response. The term frequency response refers to how well a device reproduces the audible frequencies. This applies to all audio devices such as headphones, speakers, IEMs, DACs, Amps, etc. 

For headphones specifically, the frequency response tells how much lows, mids, and highs it can produce. The ideal frequency response of headphones is from 20 Hz to 20000 Hz since this is the normal hearing range. However, higher-end headphones tend to have a wider frequency response extension. This will be discussed in more detail later on.  

Focal Open Back Over-Ear Headphone
Focal Elear (Image: Amazon)

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Of course, only having the range of the frequency response that was provided by the manufacturer does not help much. Headphones can have similar or exactly the same frequency response in their specifications, but they will not sound the same. This is evident with headphones that use completely different driver technologies. 

For example, both the Focal Elear and Focal Elegia have the same frequency response range (5 Hz to 23 kHz).

The Sennheiser HD650 and HD660s also have a similar frequency response range (10 to 41 Khz on the 660s and 10 to 39.5 kHz on the 650). However, that does not mean they produce the same frequencies exactly the same. That does not also mean they sound the same. To accurately see the exact amounts of frequencies produced by a headphone, we must refer to a frequency response graph. 

 

Sennheiser HD660s (Image: Stephen Menor)

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What is Sound Signature?

Sound signature refers to the way a headphone sounds. Each pair of headphones and IEMs will sound different from each other, and each of their unique sound qualities can be categorized into one of the following:

A bass-heavy sound signature can be seen in headphones that have a strong emphasis on the lower frequencies. These headphones are typically used on most consumer products that are marketed for pop and electronic music. It is also used in DJ headphones and most Beats generation (headphones that follow the Beats sound signature) headphones. 

A V-shaped sound signature can be seen in headphones with elevated bass and high frequencies. This is a sound signature that is commonly used since it is what people normally refer to as a fun sounding and natural sound signature. 

A neutral sound signature is generally seen in reference and studio headphones. All the frequencies are generally equal, and it does not tend to elevate or overhype a certain frequency. Unlike speakers, there is no such thing as a completely neutral pair of headphones. They only reach close to neutrality, which is accurate enough for their use case. 

A mid-centric sound signature usually has recessed or neutral lows and highs. The mids are then forward and stand out from the rest of the frequencies. This sound signature is typically intended to feature vocals in a mix.  

Apart from these common sound signatures, a headphone can also fall into three categories. Warm, bright, and dark.

Warm sounding headphones tend to have a mid to sub-bass emphasis. Bright sounding headphones have a mid to trouble emphasis. Dark sounding headphones have a recessed treble and boosted bass. 

There are other sound signatures, but these are the common ones that you will often see in headphones and IEMs. You can play with an equalizer to hear what some of these different sound signatures sound like. 

What is a Frequency Response Graph?

HD800 Frequency Response
Sennheiser HD800 Frequency Response (Image: DIY-Audio-Heaven)

A frequency response graph is the visual and more accurate representation of the frequency response of headphones, IEMs, earbuds, or speakers. The frequency response graph also visually shows us the sound signature of headphones (V-shaped, bass-heavy, neutral, etc.).

It is also a useful tool in showing us the peaks and dips of a headphone. This will tell you what certain frequencies of a headphone that can be problematic or laking depending on your preferences. This can also help you in determining if a headphone is good for a specific genre of music. 

Frequency response graphs also help us to confirm what we are hearing. Different reviewers have different opinions on the sound quality of products. Their points on the sound signature may also differ where one reviewer can hear that it is leaning on the warmer side while another reviewer may disagree. This can be confusing for the reader, so having a frequency response graph can help verify the validity of the reviewers’  claims. 

The frequency response graph is usually measured by a measuring tool such as the MiniDSP Ears. You should take note that not all frequency response graphs are accurate. The accuracy of the graphs depends on the measuring tool that was used. Some tools are known to be inaccurate in measuring the high frequencies. 

HD600 Frequency Response
Sennheiser HD600 Frequency Response Graph (Image: DIY-Audio-Heaven)

 

Does a Headphone with a Wider Frequency Response Range Make It Better?

Headphones that have a wider frequency response range is usually considered the more technical headphones. When we look at the company’s flagship headphones such as Sennheiser’s HD800s (4 to 51 Hz) and compare it with their midrange offering the Sennheiser HD660s (10 to 41 Khz), we can see a significant difference. 

Yes, it is true that 4 Hz to 51 kHz is beyond the hearing of humans, so technically, we can’t hear these. However, this directly translates to the sound quality of the headphones. Headphones that have a wider extension can also produce more detailed sound in those frequencies. They are also less susceptible to distortion.   

This can also be observed with vintage headphones. Most vintage headphones, such as the Pioneer SE-405 has a frequency response of 20 Hz to 20 kHz. This is well within the range of human hearing.  However, these headphones are not as detailed as today’s headphones. 

When compared to other mid to high-end headphones that have a wider frequency response range, the vintage SE-405 simply does not compare. Both the highs and lows are recessed, leaving the mids as the only sound that is not veiled. It sounds exactly the same as the music that was released during its time. 

Of course, other factors such as driver design have affected this evolution. However, it cannot be denied that the increase in the frequency response range that is an effect of the improvement in the technology is also a noticeable factor in the change in sound quality. This similar trend can again be observed in older flagship headphones and newer flagship headphones. 

So to answer the question, headphones with a wider frequency response range are the more technical headphones. The question of whether they sound better is up for debate and will further be discussed later in this article. 

 

Should You Base Your Purchase Decision on Frequency Response and Frequency Response Graph?

 

While the frequency response graph is the best tool to see how a headphone sounds without testing it, it doesn’t paint the whole picture. As mentioned earlier, different headphones have, most of the time, different types of driver technologies used. (dynamic, planar magnetic, electrostatic, etc.) Other factors, such as being closed back and open back, can also play a significant role in sound quality. 

Several other aspects, such as the detail retrieval and soundstage, cannot be seen in a frequency response graph. This means that you should not strictly base your purchase decision in the frequency response range shown in the specs or the frequency response graph. 

Yes, it can help you narrow down your decision based on the sound signatures that you don’t like, which can be seen in the graphs, but again, it does not strictly dictate the sound quality. It is still best to audition the headphones first and use the frequency response if you do not have easy access to the headphones.

Another point that you should consider is that headphones that are more technical and have a wider frequency response range do not automatically mean that they are the better sounding headphones. Higher-end headphones that have more high-end extension could mean that it may have more treble peaks. And this may bother treble sensitive users. 

 

How to Alter the Frequency Response of a Headphone?

It is also useful to know that there are some things you can do that can alter the frequency response of a headphone or IEM. With the knowledge of the different frequencies, frequency response range, and frequency response graph,  a powerful tool that you can utilize is the equalizer. Since you already know the frequencies that a headphone produces and since you can visualize it with the frequency response graph, you can effectively alter the sound of headphones with an equalizer. 

Some headphones like the Beyerdynamic T1 or Sennheiser 800s have very detailed highs. This can be too detailed to the point where it is peaky and may annoy listeners who are sensitive to the highs. A common remedy to this is by using an equalizer to bring down that specific peaky frequency for a more desirable result. 

Another use of an equalizer is to bring the sound of a headphone or IEM closer to neutrality. As mentioned earlier, there is no such thing as a headphone that is completely neutral. Even studio-grade headphones such as the Sennheiser HD660s/HD650, Audio Technica M50, and Beyerdynamic DT1990 are not completely neutral even though they are used in a professional setting. 

This can be done manually or by using an application/plugin called the SONARWORKS Reference 4. The headphone models have been professionally measured in order to produce the desired results. 

Another thing that is simpler to do that can affect the frequency response of headphones and IEMs are changing the earpads (for headphones) and ear tips (for IEMs). Earpads are known to affect the sound of the headphones, which can be seen in frequency response measurements.  Depending on the model of the headphone and the material used in the earpads, the effect can either be subtle or drastic. The Sennheiser HD6XX line of headphones is known to have drastic changes when lower quality 3rd party earpads are used. 

The same can be said with ear tips for IEMs. Like earpads, ear tips have different material choices (most commonly silicon, foam, and a hybrid of the two), which can subtly affect the sound of the IEMs. Having a better fit can increase the bass response, for example. But the most notable cause for the difference in sound is because different ear tips have different bore sizes. This refers to the size of the hole of the ear tips for the ear tips. Making it smaller can congest the sound and vice versa. 

 

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