It’s pretty common knowledge regarding issues and mitigation for those issues, from serious personal problems to just troubleshooting gremlins, is that you need to accept you have a problem. Acoustically, if you mix in a square room, you have a problem. If you mix in a round room, you’ll have less of a problem, but you’ll still have a problem. Basically, if your room has dimensions less than 60 feet in any direction, you’re going to have to confront reinforcement, and if your room is that big, you’ll probably have to deal with reverb if recording anything loud. If you’re mixing at proper levels, a room that big probably won’t need to be treated for mixing, so if you have a gigantic room, don’t record in it, and mix at reasonable levels, you don’t have to keep reading! The other option is to mix outside, which in a quiet place might be kind of awesome, but I doubt that’s any of you.
Since I’m skeptical any of you readers are in a six story tall room as long as a volleyball court, let’s get back to the problem, and the problem being addressed in this blog, Axial Modes. We’ve talked a lot about Axial Modes before, because they’re the main impediment to balance in any square room. Axial modes are the frequencies that corresponds with each dimension of your room, those dimensions being front to back, side to side, and floor to ceiling. For most residential rooms, these are going to be between 80-130Hz. If you understand mixing music, you’ll immediately recognize this as problematic because it’s right in the mud of the mix and the frequencies we often perceive as ‘boomy’ if we don't get them right.
To figure out what your Axial Modes are, you have to do a little math, or even easier, just Google wavelength calculator and you’ll be presented with a cornucopia of options that do the math for you. However, to give you a baseline to what you should expect we’ve put a general chart below. Also keep in mind that you’re calculating the fundamental modes, but there will be weaker modes at the multiples of these frequencies (for example, if you have one at 80Hz, you’ll have one at 160Hz, and 320Hz etc.). Other modes like tangential and oblique are much weaker and outside the scope of this article.
That said, this is only half of the story because how you’ll actually experience the air pressure differences (and yes, that’s what we’re talking about, air pressure) depends on where you’re sitting in the room and the height of your head. While there are some best practices on how to set up your studio, often the practical requirements of our studio require some acoustic compromise, so we need to learn what our mix position is doing. The mode calculations are really just a place where to start to figure things out. The next step is to figure out what’s actually happening in your mix position, and for this, use your ears.
Sit in your mix position, and fire up a sine wave generator at the equal loudness volume of your calibrated monitors. Start with one of your calculated mode frequencies, and move the frequency around to dial in where each one of these modes are where you actually mix. The mode will hit when it starts resonating and feeling louder, or even start to cancel (if you have bass traps, there shouldn't be enough energy for massive phase cancellation). Take note of each one.
What do you do with this?
The fix is pretty much the same, you need bass traps and to treat your room. If your room is not treated, do a before and after, and the difference will be eye opening. That said, part of learning how to mix is to learn the idiosyncrasies of your monitors and your room and to translate for them. Studio monitors are tested in an anechoic chamber, so even the flattest monitors will not be flat when you put them in an actual room, and room correction, if your monitors have them, only goes so far. The bottom line is unless you can change the shape of your room, treatment is mitigation. You’re still in an unnatural cube with some artifacts of that cube. With treatment you will take care of cancellation so everything will be there, and modes will be mostly knocked down, but you’re getting it to a baseline you can translate for. Without treatment it’s like trying to read a paper with half a page missing, with treatment, you have the full page, just some of the print might be smudged. When you understand what modes are still present, you will have just that much more context to understand what the smudged words should be.
The more you know about the idiosyncratic nature of your specific room, the better your mixes will translate to everywhere else and learning the specific modes of your room will go a long way to that end.
