Why Frequency Response Matters
Fans covet live music for a reason. It's an unfiltered, unedited expression, and it's glorious. Capturing that sound and transmitting it through a speaker unaltered is significantly more complicated. Depending on the quality of the recording and your sound delivery system, the relative volume of the bass, mid-range, and treble frequencies could change significantly by the time they reach your ears. These shifts can alter the composition subtly or drastically. It can even shift the sound of a speaking voice or individual instruments.
One way to test if your headphones, earbuds, or speakers are being true to the source material is to listen and judge for yourself. However, unless you're a practiced audio pro, like our esteemed test team, it may be hard to tell. It will probably be even harder to pinpoint what's wrong and find an alternate pair that avoids the same mistake.
An Introduction to Frequency Response
Luckily, there's a reliable, objective method to assess how faithfully a speaker reproduces sound, creating the finest earbuds and headphones, and that is by measuring its frequency response. Usually shown as a curve on a graph, frequency response tracks how well the speaker matches the intended volume of each audible frequency, from low bass notes to high treble tones. It's an objective way to measure the sound signature of a set of headphones.
The curve charts amplitude on the x-axis in decibels (dB) and frequency on the y-axis in hertz (Hz). If a set of headphone speakers turns the bass up a bit, the curve will register a peak in lower frequencies. If it turns down the midtones, the curve will drop below the reference line. That reference is often set to zero decibels, the threshold at which humans can begin to hear sound waves.
How Sound Waves Work
Sound comes at us in waves. The height of each wave, or its amplitude, determines how loud it seems. Amplitude is the strength of a signal and is measured in decibels (dB). Frequency measures how many of those waves pass by in a second, which is expressed in hertz (Hz). Slow waves with lower frequencies (from 20 to 200 Hz) are called bass notes. Faster waves (from 2 to 20 kHz) are high treble tones. Everything else is referred to as a “middle” frequency. The total range, from 20 Hz to 20 kHz, represents the audible range for a healthy human ear.
Decibels are trickier than anyone wants them to be. They are a relative measurement of amplitude or loudness, meaning they measure a degree of change in intensity from a reference value. That reference value is usually set to the threshold of human hearing or zero decibels.
Decibels are also logarithmic. Logarithmic scales help us communicate large value ranges using numbers that are small enough to grasp. For example, if you're listening at 40 decibels, and then increased it to 50 decibels, that is 10 times more intense than the initial sound. If you increase the volume again to 60 decibels it is 100 times louder than the initial sound of 40 decibels.
What Affects Bass, Mid, and Treble Ranges?
The thing is, it's tough to achieve an ideal frequency curve in small and complex equipment like headphones and earbuds. Due to their size, it's hard to create the strong vibrations required for thumping bass. High-frequency treble notes have a lot of frenetic energy and are always hard to wrangle into a consistent curve. Their placement, directly over or in your ears, also makes it challenging to recreate the sound as we would hear it in a natural environment, like standing in front of a band, listening to someone in an auditorium, or sitting across from you at a table.
Ear Shape and Seal
Since the shape and size of your outer ear and ear canal play a role in how sound waves reach you, how well headphones fit makes a big difference. Without a proper seal, bass notes and noise-canceling features will lack power. If headphones do seal well, they block more external noise, allowing you to play your music at safer levels. A poor fit will also change the measured frequency response, for better or worse. Luckily, many earbuds come with multiple tip sizes to fit different ear shapes for the perfect seal.
Ear Health
Your age and the function of your ears also affect perceived headphone performance. A healthy human ear can hear frequencies from 20 Hz to 20 kHz (or 20,000 Hz). If you live in a city, work in a loud environment, attend concerts often, blast your headphones, or have used your ears for a long time, your hearing range could be significantly limited. You may prefer headphones that boost levels in the frequency ranges that are harder for you to hear.
Adjustable Bass, Mid, and Treble
Just like a photo filter, a speaker's frequency response curve makes the same set of alterations to every sound that passes through. Many headphones and earbuds also allow you to adjust frequency levels, a process known as equalizing (EQ) the curve. Essentially, you raise or lower the relative strength/volume of bass or treble frequencies, like the sliders on old-school stereos. In theory, you could use these controls to cancel out the speaker's inherent curve, but the best speakers we've tested already make the material sound great and don't force you to reproduce your favorite compositions.
Preferences and Practice
In the end, it all comes down to preference. If you have a refined ear, you may prize an authentic reproduction above all else. Or, you may have specific tastes and are searching for speakers that tweak every track to match them.
Research by the company Harman has found a few general patterns in listener preferences. In its research, Harman found that less experienced listeners tend to like more bass and treble than experienced audio critics. Older listeners also prefer lower bass and treble levels until the age of 56. After that, they like more treble but even less bass, possibly as a result of dulled audio receptors.
How you use your headphones also matters. If you tend to listen to audiobooks or podcasts, you may want the mid-tones, between 100 and 300 Hertz, to shine. If you mostly listen to movies or EDM, you'll appreciate a strong bass line. Too much bass though, and that may be all you can hear. Enhancing treble a bit can pull out detail, too much tends to sound tinny. Keep in mind that it's much more important to have high-quality sound if you are a gamer or a critical listener of music and podcasts. If you're just jamming out during a run or a subway ride, other factors like comfort and noise isolation might come before sound quality.
Think of it like pizza. Pretty much everyone likes pizza, just like pretty much everyone likes music. Not everyone agrees on what makes pizza truly great. The right pair of headphones will blend the right amount of bass (crust), middle (sauce), and treble (cheese) to create your perfect slice. It should also highlight your favorite instruments (extra toppings), or at least not drown them out. If you like the piano (pineapples), you don't want to lose those easy-to-overlook mid-frequencies.
That said, the best pizzerias produce a product that nearly everyone can get behind. The same is true for headphones. If you're not sure what you like, the Sound Gym is a great place to brush up on your critical listening skills.
GearLab's House Curve
So, what does the perfect frequency response look like? Researchers have been working for over a decade to answer that question and, well, they haven't. But, while there is no one “correct” frequency response curve, we do have an informed idea of what a good one looks like, thanks to the pioneering Harman Curve.
Named after the company that funded the research and employed the researchers who created it, the Harman Curve (originally created for over ear headphones) is a “target response” curve they created by cross-referencing listener preferences with frequency curve data. If the frequency response curve of a set of headphones is similar to this popular sound signature, chances are, most people will like how it sounds. One of their main findings is that smooth, arcing frequency curves create less perceptible changes to the overall composition than those with sharp or isolated dips or peaks.
While the original Harman Curve was created in 2012, it's a moving target, with additional data informing subsequent updates to the curve. In a 2017 presentation, Harman researcher Sean Olive, who created the original Harman Curve with Todd Welti, described a target curve specific to in-ear speakers but stated that it was unrefined and required further testing. We stepped up to the plate.
While the Harman Curve pioneered the creation of a human-tested target curve, learning how to communicate the sound signature of a given pair of headphones for a given buyer is a work in progress. To enable us to give you the best information about the earbuds and headphones we've tested, we created our own Gear Lab target response curve, aka the House Curve.
To dive into the details of how we created our House Curve and how we measure the frequency response of each set of headphones and earbuds we test, read our in-depth House Curve article. If you just want to know how to use the House Curve to find your perfect pair of earbuds, read on. You're in the right place.
How the House Curve Informs Your Purchase Decisions
If you'd like to follow expert advice about which headphones will sound the best for most people, look for options with frequency curves that closely track our House Curve. Our curve correlates well with the famed Harman Curve, so there's a lot of weight behind our top picks. If you're new to audio or just don't have strong opinions about specific frequency levels, those are a great place to start.
A direct comparison of sound quality: the higher scoring model (Bose QuietComfort Ultra) closely matches our House Curve (Target Response), while the lower scoring model (Bmani Sport) deviates from the target curve.
Once you complete some critical listening workouts with Sound Gym, take some notes about how your headphones sound to you. If you find elements lacking, see if there are equalizing controls or presets that let you subtly adjust the sound. Increasing your awareness and sound vocabulary is the best way to get the best sound signature for you in the long run.
If you're more experienced and know that you love more bass or treble than most of your friends, look for curves with a few more decibels in those frequencies. But be sure to read our notes about those picks, they could do more than just turn up the bass, they could be throwing off the entire composition.
Conclusion
A bad frequency response curve can create a sound that the original composer or audio engineer would hardly recognize, and there's nothing worse than buying an audio system that doesn't do your music justice. Luckily, we've found that those headphones and earbuds are pretty easy for our expert listeners to tease out.
Even better, the earbuds and headphones with the best sound signatures also stand out early in the competition, which gives us a lot of confidence in our recommendations, especially since we can cross-reference our impressions by measuring their frequency curves and comparing them to the House Curve we created. And if you're someone who knows exactly what you're looking for, we have given you all the information you need to find it. Happy listening!
