How Frequency Response Impacts Sound Signature
The following section describes how different frequency ranges influence sound characteristics. Consider this when looking at how a headphone's frequency response measures on a graph.
20 - 60 Hz (Sub-Bass) - This is where you'll find the fundamentals of the lowest notes on a piano, synth, or bass guitar. Kick drums and floor toms often also have fundamental energy here. Too much makes the sound unrealistically "big," while too little results in lacking weight or sense of tactility.
60 - 200 Hz (Bass) - Here is where the fundamental frequencies of many sounds, including drums, pianos, guitars, vocals, strings, horns, and woodwinds reside. Reduced energy here can make the sound thin, lean or cold, but also may add a subjective sense of clarity. Too much here can make the sound overly resonant, boomy, lumpy, swollen, or muddy... but it can also make the sound warm, inviting, or rich.
250 - 500 Hz (Low Midrange) - Low order harmonics of most instruments. Boosting this region brings forth for the boxy overtones of bass or drums, while perhaps giving more body to instruments with higher fundamental frequencies like flute or violin. Cutting in this region can bring clarity to kick drums, as well as help guitars sound less claustrophobic. Though a recession in this region can also lead to a lack of presence for those primary elements of those tones, leading to a somewhat hollow or empty sound.
500 Hz - 1 kHz (Midrange) - This area of the midrange can determine how prominent an instrument is in the overall mix, in fact boosts in this area can be conflated with things overall being "louder". Boosting around 800 Hz can give instruments a horn-like or vocal-like quality, as horns and vocals naturally tend to have much of their energy around here. Excess output at this range can sound honky and may cause ear fatigue. Cuts in this region can sound hollow or distant.
1 kHz - 2 kHz (Upper Midrange) - Perhaps the most critical single section of the audio band. The upper midrange is responsible for the percussive attack, intelligibility, texture, forwardness, and the subjective character of almost every instrument and voice. If boosted, this range can add any of these things, but pushing it too far can lead to things being overly-textured or harsh. Too little energy here makes the sound blunted or unintelligible.
3 kHz - 6 kHz (Lower Treble) - This range serves as the transition region between upper midrange and treble, and as such it shares aspects typical to either of them. It contains both intelligibility and clarity cues, as well as textural harmonics, while also partially containing things like vocal sibilance or snare drum chain rattle. Over-boosting can cause a scratchy, grainy sound. Cutting in this range can reduce those aspects, at the cost of making things less textured and potentially a bit blurry.
6 kHz - 12 kHz (Mid-Treble) - This is where we find the stringy, splashy bits of sound. The sizzle of high hats, the detail of a plucked acoustic guitar, the shimmer of a rudely-struck piano, the sheen of strings, and the breath of woodwinds and horns can all be found here. Too much can make things sound ringy and or glarey, while too little can make things sound smeared or low-resolution.
≥ 12 kHz (Upper Treble) - This is where the 'air' region kicks in. Strong presence in this region can contribute to a sense of 'openness'. For cymbals, this is the upper end of the splash and sizzle, and this is where the tippy-top of the breath of vocals can also reside. If this region is elevated, it can cause those elements to sound somewhat over-processed, unbalanced or unfocused, because the splash or sizzle quality isn't balanced in line with where tonal focus of the primary hit is.
In general, we can describe headphones that emphasize lower frequencies as 'warm', while headphones that emphasize upper frequencies are described as 'bright'. Headphones that dramatically cut treble frequencies can be described as 'dark'.