Mixing your music is directly impacted by the place in which you record according to Graham of http://therecordingrevolution.com since sound is affected because of the space and the noise that is lost or echoed within that space. Headphones are a solution to the problem, but it should be noted that what sounds good in headphones may not sound good on a speaker. (Although, what does sound good on a speaker always sounds good on headphones.) The author is going to be addressing this issue with helpful ideas within the next few weeks.
Few good points worth checking:
Why Where You Mix Matters