The size of the room, your studio or control room, have a massive effect on the sound waves within them. Not only do all four walls affect the sound, but your ceiling and floor also have an effect on the sound.
Think of it as if you have captured the sound in a box and it is literally bouncing all over the place.
Now, the way that the sound wave bounces is important. As mentioned before, all frequencies have different wave lengths. They all need a certain amount of space to travel in. If the distance between to surfaces (including floors and ceilings) is exactly the same length as the length of the sound wave (basically, if you can divide the frequency wave length by the distance between the two objects) you create a standing wave otherwise known as a sound node. This sound nodes will stand out and be more prominent in the room.
With large rooms (over 10 by 10 meters) the distance between each sound node increases. This means it will be easier to remove certain frequencies.
With smaller rooms the distance between sound nodes decrease so it becomes harder to remove certain frequencies.
This is why it is important to calculate the possible sound nodes that will affect your studio before you build it.
But don’t panic, if you do have some sound nodes in your studio, they can be reduced and some can be completely eliminated by using sound traps.
In the ideal world you would find the perfect size of the room before building it, so that only minimal acoustic treatment would be required. Sound traps do take up a lot of space, so the fewer sound nodes the better.
Bolts graph quickly help show if your studio is going to have any real issues, although it is only a guide. Bolts graphs work out some of the correct room sizes / ratios to be used.