Learn about sound properties. Understand the differences in frequencies, how sound travels, what are the best and worst materials for sound absorption and diffusion. There are many books about this in music stores and in the music section of your local library.
Measure the dimensions of the room. This will allow you to calculate acoustic problems that may be present.
Calculate the frequency of standing waves. Contrary to what some may think, a cube-shaped room is the worst area to record in because they produce standing waves, which are sound waves that reflect back and forth along the same path. There are three kinds: axial, tangential, and oblique. Axial waves are primarily between two surfaces only. Tangential reflect off of four surfaces while obliques reflects off of six.
Use the acoustic equation which is Hz (hertz) = speed ÷ 2 X wavelength. Speed will equal 1,120 feet per second, the speed of sound. The dimensions of the room will go into the area for wavelength.
For example, a room that is 15-feet long will have the equation Hz = 1,120 ÷ 2 X 15. Hertz here would equal 37.3.
Multiply the first mode by whole numbers until you reach 300 Hz. In the preceding example, the calculations for the room length would be 74.6, 149.2, and 298.4.
Compare the list of frequencies. Once all of the frequencies have been calculated for each dimension (length, width and height), look for frequencies that occur in more than one dimension. Also note frequencies that are isolated on either side by 25 Hz or greater (length and width). These are problem areas that will have to be dealt with.