Wavelength equals speed of light divided by frequency. Use the same unit of measurement for the wavelength and speed of light in the formula (eg. cm. for wavelength and cm./sec. for the speed of light). Substitute in the room length for the wavelength to find the frequency of the wave that perfectly fits the room.
Just Google "wavelength calculator" for links to online calculators that you can plug numbers into. Let the calculator do the work for you.
I agree with the other posters. The open E string on a electric guitar is only about 36Hz. There isn't too much in the way of music below that unless you listen to pipe organs or big kettle drums. Home theatre effects maybe, but not much music down there. You feel it more than hear it anyway once you get down around 20Hz. I would be more concerned about the lower frequencies only if there are standing waves creating exagerated or null spots in your room.
Just Google "wavelength calculator" for links to online calculators that you can plug numbers into. Let the calculator do the work for you.
I agree with the other posters. The open E string on a electric guitar is only about 36Hz. There isn't too much in the way of music below that unless you listen to pipe organs or big kettle drums. Home theatre effects maybe, but not much music down there. You feel it more than hear it anyway once you get down around 20Hz. I would be more concerned about the lower frequencies only if there are standing waves creating exagerated or null spots in your room.