Theory behind using multiple monitors.

Trying to get a handle on the following: As mixes will sound different to some degree on different monitor systems, which one do you rely on for your finished product?  Before investing (currently have Adam A7x), I’m trying to understand the utility of having multiple monitors. It makes sense to reference your mix with as many monitors as you can to get an average of what you mix sounds like.  But when the rubber meets the road you can have only one mix.  Is it a compromise between what you heard from the various monitor systems?

The theory of multiple speakers is that not everyone is going to be listening to your prefered speakers.  Having two complimentary set of monitors is a small step for that realization.  Most commercial studios have two sets of speakers - a main (large) full range set and a smaller, home type range set.  In that case, it lets the client (not necessarily an engineer) hear what the sound will be like on their home hi-fi.  Many studios (expecially post) have a mono "tv style" speaker.

For the engineer, it is kinda like a second opinion and allows you to find flaws that might not stick out on a good pair of mains.  As Skull points out, they should be able to do it all, but sometimes it is useful for certain problems.  Me, I have 8-inch woofers in a pretty flat room that work well.  So well, I've had the same pair of Yamas and matched amp for 30 years or so.  I know them.  Still, I check the bass balance at the commercial studio.  I also burn a cd and make mp3s and check them out in the car, on my home stereo, computers, etc.  Different speakers and esp. differnet environments make all kinds of difference and allow you to go back and tweak a mix to make it more generic on playback.  Even my wife, bless her pointy little ears, is listening to her band's new CD and is starting to hear the difference between systems (esp. her car).

All speakers and environments are different.  Listening in various situations reveals some problems your mix may have - resonant frequencies on your computer speakers that a few dBs of eq can solve, squeeking highs in your car, vocals a shade too low (or high) in your den.  And don't forget mono compatiblity!

Having another pair of monitors is like having someone else listen to a mix.  They might reveal something you don't catch on the mains.  Then the real art of engineering comes in by making small changes that minimize the problem while not changing your vision of the mix.

@

Ultimately the mix will be a compromise that sounds the least worst on all the playback systems you have available to you. It's always a compromise one way or another. Some speakers emphasize things and de-emphasize things. So you look for a compromise that works reasonably well in all cases (including also some headphones, maybe your stereo in another room, etc...)

The things I've noticed most is that small speakers tend to have a raspy upper-mid, and will push the lower mids (or upper lows, according to how you look at it) to make up for the lack of ability to really reproduce the lower octave or so.

The former can make something like a drum room mic that just sounds nicely present on the big speakers suddenly sound like a harsh mess, or guitars that sound just nice and present become really ear splitting, that kind of thing. And at the other end, it seems to often push the lower vocal range up a lot so a vocal that seems to have no more weight than it requires on the nice speakers suddenly seems way out front and detached from the mix.

I hear those things on my mixes and other people's and commercial CDs sometimes as well. It's always a compromise, though I guess that most folks will opt to make sure it sounds good on smaller speakers and ear buds these days since the grand days of audiophile listeners is almost all but gone.

Definitely concentrating on the mid-range is a way to get a mix that sounds good everywhere, but when you listen on nice speakers it often sounds better with a more scooped approach because the low and high end sound so nice on those big speakers. Then you take to the small speakers and it manages to sound both tubby and harsh at the same time sometimes, it seems to me. Or sometimes it has no low end at all because the speakers can't reproduce the low end that sounds so great on the big speakers.

One example that comes to mind is some of Bruce Springsteen's earlier songs, which to me seem very mid-rangey sometimes, with very high passed bass and the kick drum is sometimes just a little popping sound more or less. But, it probably sounds about the same on any system I guess, since everything is in that range that anything can reproduce.
A lot of pro folks I've heard/read talk about this will argue for mixing on the small speakers, then use the big speakers at the end to make sure the low and high end aren't bad on the big speakers. It makes for a least common denominator mix, but that's kind of the point, since probably it'll sound pretty decent on smaller systems and not out of place on big ones.