When we mix in stereo, we can separate the elements of the mix in the stereo field to make them easier to hear. When we convert the mix to mono, these different elements start to darken again. The fact is that if your mix is not clear and blunt in mono, it's simply “not ready yet”. In fact, some producers mix up levels of mononucleosis during most of the process.
This is because the mono not only gives you clarity when listening, but also the ability to detect errors in the mix. When you mix in stereo, you have some elements that come from the sides and others come from the center. That can make you think that your frequencies aren't colliding, when in fact they are. When you put mononucleosis on track, it's easier to spot the error because there's no secondary information distracting you.
When you have a mix that sounds great in mono, making it stereo will make it incredible. They will perceive different volume balances that come out of each speaker and, in the worst case, they will perceive it in mono. It sounds luxurious, but bear with me; I'll break it down quickly and easily, and then I'll tell you why mixing in mono is great. I know what monophony is, but if you use two speakers you hear the phantom center, I can't believe this is what Graham does and I just wanted to clarify it.
I've been mixing exclusively in MONO for the past two months and now I have almost no problem listening outside of my recording environment. As I said, if you can make your mix sound good in mono, it will sound even better once you switch it to stereo. Due to phase cancellation, some sounds may appear lower than they actually are when mixed in mono. If you create the stereo mix first, it can be very frustrating later to have to make it work in mono as well.
To be clear, use a mono speaker, because just by adding a mono add-on you would also have to turn left or right or turn off the monitor or change the output. It doesn't mean that they have to be completely cute, it just means that you shouldn't go crazy with the stereo improvements that are there. I have one (not two) and I usually mix it up by configuring my Mackie Big Knob in mono and directing it to the Avantone. However, if you can make the mix sound good first in mono, it will definitely sound great in stereo as well.
For example, Logic Pro has the Direction Mixer add-on or its Gain add-on, which includes a mono switch. Of course, in the end you'll work mainly in stereo and then you'll only record in mono, the opposite of what you did before.