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.
20-120hz - Elevations in this region add bass emphasis with a greater sense of fullness to the music, while a recession here or 'roll-off' can cause bass to sound a bit lean. Remember that compensations based on the Harman target emphasizes the region a bit.
200-2khz - Elevations in this region can cause the overall sound to be a bit muffled or muted. Most music involves tones that token a wide frequency range (for example, pianos can range from below 100hz all the way to 9khz for harmonic resonances). A midrange elevation will emphasize the primary elements of those tones over the frequency ranges that comprise the edges of those tones (harmonic resonances in the case of piano tones). A recession in this region can lead to a lack of presence for those primary elements of those tones, leading to a somewhat hollow or empty sound.
3khz-5khz - Elevations in this region can add clarity to certain sounds bit at the risk of adding shrillness. Substantial elevations here can also cause the overall tonality to sound somewhat compressed. A 5khz emphasis in particular can cause compression for percussive sounds like cymbals and snare drums.
7khz-9khz - This region is where the consonant sounds for vocals fall. A distinct elevation or peak at 8.5khz can cause the 'S', 'F', and 'T' sounds to come across a bit harshly, however if the elevation is more gradual up to this region, those sounds aren't as fatiguing.
11khz and up - 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. If this region is elevated, it can cause those instruments to sound somewhat 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', and their frequency response will measure with a clockwise tilt to them (depending on the compensation being used). Headphones that emphasize upper frequencies are described as 'bright' and measure with a frequency response that tilts counter-clockwise. Headphones that dramatically cut treble frequencies can be described as 'dark'.