What is Frequency Response?

Many consumer audio products, including speakers and headphones, have a frequency response range. What is frequency response? What does frequency response mean? Is it something you need to take into account when purchasing audio equipment? 

In this article, we answer these questions and more on frequency response range relating to audio equipment. By reading this short post, you’ll better understand what frequency response is and whether this should influence your purchase.

The Basics of Frequency Response

Frequency response is the range of frequencies that a speaker is able to reproduce, as well as the prominence of a specific frequency. The emphasis expressed on each frequency is a factor measured on the Y-axis when plotted. In contrast, a frequency response range refers to the lowest and highest frequency the speaker can produce and, when plotted, runs along the X-axis.

Looking at the frequency response range of an audio product can give you a better idea of how that driver performs. For instance, a speaker with a response range of 100Hz to 18kHz would not be able to reproduce the same deep bass as a speaker with a response range of 20Hz – 20kHz, nor would it be able to reproduce the brightness in the upper-frequency range (between 18kHz and 20kHz).

However, it is important to remember that just because a speaker can produce a certain frequency doesn’t mean it will. The driver design and enclosure can impact the perceived frequencies in the same way that putting a pillow over the front of a speaker producing high frequencies can soften those frequencies for the listener.

Frequency response is best used vertically and horizontally plotted on a frequency response chart. These charts let you see not only which frequencies the speaker can recreate but also plot the perceived response in a manner that lets you evaluate the performance of each frequency band.

How Frequency Response is Measured

The frequency response will be represented by two numbers and measured in Hertz (Hz), the unit of measurement for one frequency cycle. The first number represents the lowest bass frequency, while the second number indicates the highest high frequency an audio product can produce.

Hertz can be represented as multiples (positive Hz) or submultiples (negative Hz) and can go as high as a yottahertz or 10²⁴ Hz. For the purposes of audio equipment and our limited hearing, we only consider the frequency range in the Hertz and kilohertz spectrum up to 20,000 Hz. For the thousands multiple, instead of writing 20,000 Hz, the value is represented in kilohertz of kHz. So, in a frequency response metric, you might see the kilohertz represented as 20 kHz or 20k, which is exactly the same as 20,000 Hz.

Human Hearing Spectrum

Humans can only hear a tiny fraction of the entire Hertz spectrum. The average human can hear frequencies between 20 Hz to 20 kHz. Often, audio equipment with a 20 Hz to 20 kHz response range will be marketed as having a full-range response. This is in reference to our hearing, as 20 Hz to 20 kHz is the full range of the frequencies we can hear. Let’s look at this in more detail.

Frequency Response in Audio Equipment

Sub-Bass Frequencies 

Starting at the low end, 20 Hz to 60 Hz is a sub-bass frequency usually felt more than it’s heard. If you’ve ever been to a club or concert and felt a strong vibration through your body, this is the sub-bass produced by the sound system’s subwoofers. These very low frequencies are difficult for speakers to reproduce. In most cases, you will require a dedicated subwoofer to produce sub-bass frequencies at high volumes. 10-inch and 12-inch speaker drivers can produce these sub-bass frequencies in your homes, such as wireless TV speakers, PC speakers, or Bluetooth speakers. However, for large outdoor spaces, you’ll need multiple 15-inch, 18-inch, or even 21-inch subwoofers to have any real impact. 

Bass Frequencies

For most consumer audio equipment, the bass sound you hear is mostly in the 60 Hz to 250 Hz frequency range. Your bass guitar, bass synths, and the kick drum sit here. Speakers also get their “woolly” characteristics from poor speaker design. Manufacturers will boost the volume by between 60 Hz and 250 Hz for cheaper speakers and headphones to give the product more bass. The problem is that simply boosting creates a woolly effect, and the speaker or headphones lose any low-end punch or definition. Boosting bass frequencies can also hurt the rest of the frequency spectrum, especially the mid-range, which becomes difficult to hear or “muddy.”  

Low Mids

The low mids fill the 250 Hz to 500 Hz range and is where you hear the warm characteristics of instruments and vocals. Typically, this is the frequency range most influenced by any boost in the bass frequencies, which is common in bass-heavy speakers and bass headphones.

Mids or Mid-Range

The mids cover 500 Hz to 2 kHz and are very important for audio equipment as this is where a large chunk of the vocals sit. When the vocals sound muffled or distant, it’s likely to do with something missing in the mid-range of the product. If you’re watching or reading a review and the mid-range is “up front” or “present,” the product is well-balanced in this part of the frequency spectrum, and you can hear vocals and instruments clearly.

When the mid-range is lacking, the product will likely sound “boxy,” like talking through a toilet paper roll. You can hear the lows and highs, but the mids are distant, making it difficult to make sense of the instruments or vocals. This is a typical characteristic of cheap speakers utilizing cheap drivers and processing. 

Upper Mids

The upper mids, 2 kHz to 4 kHz, are where you hear the sibilance, which is important for phonetics. The upper mids give speech detail and intelligibility, most importantly the ch, sh, z, and tiss sounds. The product will likely sound dull and lifeless if this part of the frequency spectrum is lacking. The upper mids are also where you hear most reverb and add excitement to movie special effects. If boosted too much, the upper mids can put a big strain on the ears, which can be felt as a shrill or “ear-piercing” sound. 

Presence and Brilliance

The presence, 4 kHz to 6 kHz, is more of an extension to the upper mids, adding sibilance and intelligibility to an audio product. This is where you hear a lot of the tail-end of reverb and other instrument and vocal effects, which add excitement and character to the audio. From presence into brilliance (6 kHz to 20 kHz), you hear a lot of cymbals from the drums as well as high-frequency sounds from wind, brass, and percussion instruments. It’s an exciting sound for the ears; without these frequencies, audio sounds dull and lifeless. 

As we get older, these high frequencies are the first to go, which is why the elderly find it hard to make out what people are saying. Speech loses intelligibility, making everything sound bassy and difficult to make out clearly. 

How to Read a Frequency Response Graph

OK, so now we know the basics of frequency response and what role each part of a full-range response plays. Now, it’s time to look at this in a graph format. You’re probably asking, “if so many brands range their products as full-range or with a 20 Hz to 20 kHz frequency response, then why is it sound so different?”

To gauge a frequency response, you either have to listen to the product or study the frequency response graph. The problem is that most manufacturers don’t supply this information. It’s only common to find frequency response graphs in professional audio products because the average consumer, firstly, doesn’t know how to read it and, secondly, doesn’t really care. However, it is important to understand frequency response graphs because they reveal the smoke and mirrors of a frequency response rating. 

Comparing Graphs

Let’s consider the graph below. This is a frequency response from 20 Hz to 20 kHz, which we expect an audio product to produce when we purchase it, right?

That would be an incorrect assumption. The truth is, no product ever has a frequency response that looks like this. The red line would never be perfectly straight from 20 Hz to 20 kHz. For example, you might not hear too much bass, but the mid-range and high frequencies are clear. In this case, you would see something more in line with the red line on the chart below.

Both red lines on the chart above and below have a frequency response of 20 Hz to 20 kHz, but because of the massive dip in the bass response on the bottom chart, the products will sound completely different. For one, the lower product will lack bass. The blue line also has a frequency response of 20 Hz to 20 kHz but will sound wildly different. In fact, I couldn’t tell you what the blue line would even sound like with such a big boost at 1 kHz other than terrible and likely ear-piercing.

These are extreme examples, but I’m sure you get the picture. Considering two companies with a gross profit of $1m, you would think they’re both equally successful, right? Wrong, without the net profit, you can’t be sure if these businesses are making or losing money. It’s the same with frequency response; without hearing the product or seeing the frequency response graph, the actual rating as 20 Hz to 20 kHz is not very helpful in understanding what the product sounds like.

I hope this gave you insight into the frequency response range and what it means for the audio equipment you purchase. On its own, the frequency response range should never influence your purchase. You either need to listen to the product or get a visual of how the product performs through a frequency response graph. Most consumer audio products don’t supply this information, so it’s important to read reviews and pay attention to what the reviewer says about how the product sounds.