In simple terms, the sound stage is the distance between the vocals and the instruments in a soundtrack.
Keep in mind that the headphones with wider soundstages can accurately produce the distance between the sounds to make the record sound more realistic.
Impedance is the level of sensitivity your headset has with regard to the source music. If you’re just using your mobile device to play the tracks, you don’t need high impedance. Pretty much anything below 50 Ohm is good.
On the other hand, if you’re in a studio producing music, then a high impedance is required.
Frequencies determine the capabilities of a device to generate sound. Generally, we hear frequencies in the range of 20 to 20, 000 Hz. In other words, you would want your headset to produce frequencies that you can respond to.
The amp basically raises low-voltage sound from the source to a level that can be compatible with your headphones.
If your headphones are good, 50 Ohm amp is sufficient for a good quality sound.
Sub-bas has fewer harmonics and can be an octave below the bass. It is also defined as the lowest frequencies we can hear. This range is from 20 to 60 Hz. Instruments that produce sound in this range are bass guitar, drum machine, and bass drum.