Headphones are similar to speakers in that they are both transducers on the reproduction end. Their job is to recreate the music signal, without adding sounds of their own. But that’s almost impossible since every mechanical device has sounds, resonances and distortions of their own.
For example, when reproducing a bass kick drum, the recorded sound may stop, but because of the inertia of the speaker or headphone diagram, it keeps on going. This is known as “decay†over a period of time and it is easily measured today in the form of a “waterfall†graph. Kind of like a tuning fork that keeps on ringing. This is bad.
The “speed†at which the music signal occurs is also important to create a sense of realism. In real life, when a guitar pick hits the string, or when one hits a triangle, how fast is the initial impact? It’s immediate. But, in the same way a speaker or headphone has trouble stopping, it can also have trouble accelerating fast enough to accurately capture the initial impact of the music.
Decay: Fadeout of a note following the initial attack, easily seen in waterfall response. Some frequencies may decay longer than others depending on the headphone design. Decay negatively affects sound accuracy, since it adds “coloration†to the music that wasn’t in the original recording.
Coloration: An audible added characteristic with which a headphone produces that is not a part of the original source material. Caused by poor waterfall and/or frequency response resulting from resonances in the design of the diaphragm, as well as the earphone housing. Heavy metals are usually preferable to plastics, which can resonate.
Clarity: Is the sound clear and transparent as opposed to muddy or fuzzy. Accomplished with good impulse and waterfall, so the headphone diaphragm starts and stops rapidly. A “slow†headphone may have all of the frequencies, but not good clarity.
