If you have every been in audio communities, you will quickly learn that mixing on headphones is frowned on. The truth is, EVERYBODY does it at some point or another while mixing. If you are doing Narration or Podcasting, you have nothing to fear and if you don't want to spend a ton of cash treating your room, it is the best way to go. However, using headphones for mixing music, is a tad more involved. Why is that? Well, it is the way that you will perceive your music using headphones instead of monitors or speakers. The three main differences are:
1. Stereo imaging. Stereo imaging refers to the aspect of sound recording and reproduction concerning the perceived spatial locations of the sound source(s), both laterally and in depth.
2. Frequency response. Frequency response is the quantitative measure of the output spectrum of a system or device in response to a stimulus, and is used to characterize the dynamics of the system. It is a measure of magnitude and phase of the output as a function of frequency, in comparison to the input.
3. Crossfeed. Crossfeed is the process of blending the left and right channels of a stereo audio recording. Crossfeed is most commonly found in headphone amplifiers.
So lets break these three subjects down. If you know what to "look for", then you will know what to "look out for". Lets look at "Stereo Imaging". When you listen to music in your car or home, you have space between your ears and the sound source. This allows for all kinds of thing to happen to how you perceive the audio. It can be distance, reflection or the number of people between you and the sound source. When you place headphones on, all of this disappears and you now have the sound source, 1/2 from your ear. Headphones can deceive you concerning stereo width as well as bass and treble. As you listen and you are mixing, you may be tempted to narrow or expand that width, as that is what your ears are telling your brain or you may be adding or cutting to much using your eq.
So what does Frequency response have to do with anything? Plenty! If you can not hear it, then how can your mix it? This is why it is common for Podcasters and Narrators to use headphones for speech. According to Wikipedia as well as thousands of other websites,
As you can see, the frequency range is extremely narrow. Just about any headphones will work in this range. Now lets look at the frequency range of music/instruments. It is accepted that the range is from 20 Hz to 20,000 Hz. (You can download a chart that has dozens of instruments as well as their frequency range in our download section, provided you are logged in). As you can see, there is a great difference between speech and music. Studio monitors are expensive for many reasons. One of the main reasons is they can play the lows as well as the highs giving you a very realistic example of what you are actually hearing. If you plan on mixing music with headphones, it is critical that you check the frequency range before you buy them. If you check out the AKG K92 Closed-back Monitor Headphones for $59.00, their Frequency Response is 16Hz-22kHz. If you are just starting out, these will work just fine."The voiced speech of a typical adult male will have a fundamental frequency from 85 to 180 Hz, and that of a typical adult female from 165 to 255 Hz." That is, the frequency ranges (of the fundamental frequency) are about an octave apart, for males and females.
OK, last but by no means least, we have crossfeed. Simply put, the sound is so close to your ear, that if you are panning one guitar a little left and one guitar a little right, it is hard to get a true representation on where they actually sit in the mix. One thing you can do is remove one side of the headphones and listen to how strong the signal is, compared to when you do the same thing for the other side. I hope this may answer you of your questions. p.s. I use headphones all the time as well as my studio monitors and desk top speakers. Sometimes I even use my ear buds.