I've read about summing to mono to check for phase issues with your mix, but how is this done and how does it work? If it helps, I'm currently using Pro Tools 7.4.
Via SOS web site
SOS contributor Mike Senior replies: Summing to mono just means feeding both channels of your stereo mix (left and right) to both of your speakers, rather than just feeding one signal to each speaker. It's a very simple procedure, and there are lots of options for doing it. The simplest would be to insert a 'mono‑ising' plug‑in of some kind into your master bus, which you can pop in and out of bypass mode. One elegant option for this is available as freeware from Brainworx in the form of their bx_solo plug‑in, although you might also want to look at Flux Audio's freeware Stereo Tool, because it has a nice vectorscope display: both are available in VST, AU and RTAS versions, so should suit pretty much any DAW platform, including yours. If you don't (for whatever reason) want to perform the mono summing in software, any monitor controller worth the name should have a mono switch on it. SM Pro Audio's M‑Patch 2 (/sos/dec06/articles/smprompatch.htm) or Samson's C‑Control (/sos/sep03/articles/samsonc.htm) will both do the job for very little outlay. Alternatively, you could simply monitor your stereo mic outputs via two hard‑panned mono channels on a mixer and then centre the pan controls to achieve the mono sum.