Many consumer audio products including speakers and headphones often come with 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 the end of reading this short post, you’ll have a better understanding of what frequency response is and whether this should influence your purchase. First, we need to start at the beginning…
How Frequency Response is Measured
The frequency response will be represented by two numbers and measured in Hertz (Hz) which is 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||20Hz to 60Hz|
|Bass||60Hz to 250Hz|
|Low Mids (Low Mid-Range)||250Hz to 500Hz|
|Mids (Mid-range)||500Hz to 2kHz|
|High/Upper Mids (High/Upper Mid-Range)||2kHz to 4kHz|
|Presence||4kHz to 6kHz|
|Brilliance||6kHz to 20kHz|
Starting at the low-end, 20 Hz to 60 Hz is a sub-bass frequency which is usually felt more than it’s heard. If you’ve ever been to a club or concert and felt 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. This is why you need a dedicated subwoofer to produce sub-bass frequencies at high volumes. 10-inch and 12-inch speaker drivers are capable of producing 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 or 18-inch or even 21-inch subwoofers to have any real impact.
For most consumer audio equipment, the bass sound you hear is mostly in the 60 Hz to 250 Hz frequency range. This is where your bass guitar, bass synths, and the kick drum sit. This is also where speakers get their “woolly” characteristic from poor speaker design. In cheaper speakers and headphones, manufacturers will boost somewhere between 60 Hz to 250 Hz to give the product more bass. The problem is, simply boosting creates a woolly effect and the speaker or headphones lose any low-end punch or definition. Boosting bass frequencies can also have a negative impact on the rest of the frequency spectrum, especially the mid-range which becomes difficult to hear or “muddy”.
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 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 it’s stated the mid-range is “up front” or “present”, this means the product is well-balanced in this part of the frequency spectrum and you’re able to 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 which makes it difficult to make any sense of the instruments or vocals. This is a typical characteristic of cheap speakers utilizing cheap drivers and processing.
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. If this part of the frequency spectrum is lacking, the product will likely sound dull and lifeless. The upper mids are also where you hear the majority of reverb and adds excitement to special effects in movies. 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 and 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. The question you’re probably asking is “if so many brands range their products as full-range or with a 20 Hz to 20 kHz frequency response, then why is it they 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, 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. But it is important to understand frequency response graphs because it reveals the smoke and mirrors of a frequency response rating.
Let’s consider the graph below. This is a frequency response from 20 Hz to 20 kHz which is what we expect an audio product will 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 in bass. The blue line is also a product with a frequency response of 20 Hz to 20 kHz but will sound wildly different from the others. 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. If you consider 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 to understand what the product really sounds like.
I hope this gave you some insight into frequency response range and what it means for the audio equipment you are purchasing. 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 which is why it’s important to read reviews and pay attention to what the reviewer says about how the product sounds.