Common question: “Where should I put acoustic foam to get the best results in my studio?”
Naturally, each studio will be different, and it is impossible for us to give you exactly specified locations. But, the main idea behind using acoustic foam is to absorb primary reflections that would otherwise interfere with accurate monitoring. In many cases, it takes a surprisingly small amount of foam to make a significant difference in the acoustics of a room, especially if near field monitors are being used.
Take a look at where your monitors are placed, and at the flat, hard surfaces that are near them. Typically, these will be the side walls of your studio, the top surface of your mixing console or desk, any gear around you and the monitors, and to a lesser extent the ceiling above you. If any of these are at such an angle that they will reflect sound directly to your ears, they are causing problems.
At this point, enlist the aid of a friend, family member, shrieve, or other easily conscripted lackey. Have them move about the room, holding a mirror against the possibly offending surfaces while you relax comfortably in your normal monitoring position, possibly sipping a cool beverage. If you can see a reflection of your monitor’s tweeters in the mirror from the monitoring position, have your assistant mark the spot as one requiring acoustic treatment.
For mixing console and gear surfaces, covering them with foam may disrupt the manufacturer’s intended ergonomic design. Try changing the angle of the mixer slightly, or moving things around in other ways to minimize unwanted reflections.