Why Room Ratios Don't Work...most of the time
Aug 07, 2023If you are reading this, you may be facing some room ratio madness yourself. If you are trying to find the perfect room ratio, reading obsessively about room modes and genuinely feel like you have gone down a rabbit hole then you are in the right place. In this article I will ease your stress around room modes, and room ratios and hopefully send you back out in the world with a plan for your home recording studio.
1) Why Room Ratios Don't Work...most of the time
Room ratios were created to give acoustic designers (aka you) the ability to design rooms with relatively small volumes that will still sound "good." I write good in quotes because we can never achieve a perfect room. Even the best room ratios will have flaws that need to be addressed.
This said you may have jumped on a few room ratio calculators on the internet and found that with your ceiling height the room ratio given leads to a very small room. This is a common problem with using room ratios in basement, bedroom or garage home studio designs. We are always held back by our ceiling height because the ratio is based off of ceiling height to width to length and a low ceiling height means smaller length and widths to meet the ratio numbers. Meaning, if we can't raise up our ceiling height we can't get a big enough room to do our work in.
Totally maddening...I know! So what is the solution. Well let me tell you, but first let's learn what makes a room "good" to begin with.
2) What Makes A Room Sound "Good"
There has been a lot of research on what makes a room sound pleasing or good to the human ear. This is a subjective term and has been argued over the years by some of the world's top acousticians.
One thing that makes a room sound good is having what is known as an even distribution of modes. (Now I am not going to get into what a room mode is in this article, but if you don't know, take a break and google it real quick.)
Okay great, so an even distribution of modes means that modes are spaced evenly through each 1/3 octave frequency band. The human ear perceives sound based on a logarithmic scale and acousticians have plotted frequencies based on this scale. The key here is to know how to read it, not try to fully comprehend the science.
Next, another thing that makes a room sound "good" is to never have modes fall on top of each other. This means two different types of modes (axial, tangential, oblique) line up at exactly the same frequency thus causing that frequency to ring out more in your room making your room sound "bad."
To do this I am going to show you a really good room ratio and a very very bad room ratio. This will help you see what an even distribution of modes looks like and what the lining up or coincidence of modes looks like.
3) Arguably, The Best Room Ratio
Arguably, one of the best room ratios is Sepmeyer's first ratio of 1: 1.14 : 1.39. Now, we will see in a moment how best can be misleading, but stick with me here. The image below is from the AMROC room mode calculator. It shows Sepmeyer's first ratio with a ceiling height of 15 feet.
Now we don't really need to look at anything above 125 Hz. The reason is that we can easily treat those frequencies with velocity based acoustic panels. What is harder to treat are room modes below 125 Hz. Now what we notice first is that in the lower frequencies we have a relatively even spacing of room modes. That is good! In a second you will see what big gaps will look like. We also want to look at the Bonello chart. It shows a smooth increase in modes per 1/3 octave. That is also considered "good." If that number goes up then drops down, then your room will not sound as good.
3) Size Matters!
I know I hate seeing that statement too, but in room acoustics the volume of our room also matters. You could use that awesome Sepmeyer ratio, but if you have an 8 foot ceiling it will not sound as good. Let me show you why.
Below is another screen shot from the same Sepmeyer ratio we used on the 15 foot tall room. However, this chart shows the room modes for an 8 foot tall room.
At first glance they look the same, right? But wait! The relative distribution, meaning the spacing between the modes is the same, but where the modes fall on the musical scale has changed. In a smaller room those same modes have been shifted up in the low end. This means we have more problem modes in our audible bass frequencies than we did with the larger room.
Notice how the first mode in our 15 foot room started well below 30Hz - barely in the audible spectrum of hearing, while that same mode falls at 50Hz in our 8 foot room, right in the middle of your kick drums thump!
This is why bigger rooms meaning taller ceilings are better for music spaces. Because the problem modes get shifted lower and lower. This means treating our room becomes easier and less expensive because we have less low modal issues we need to smooth out.
4) A Truly Crappy Room Ratio
The worst room you could possibly build is a cube. If the dimensions are 1:1:1 then your room will sound bad. Your room will also sound bad if you use even multiples like 1:2:3. So for the sake of learning how to read the AMROC calculator let's now look at that dreadful cube room.
Gross! I mean that is just repulsive looking. Okay I kid, but yes this room will definitely sound bad and will be difficult to acoustically treat. Why? Well, first we have large gaps between those modes in the low end. Notice how our 8 foot tall room above has more lines in the low frequencies. Well, that is a good thing and we want them spaced evenly.
Next, the Bonello criterion shows that we have a drop in modes from 3 to 1 and then a huge jump to 12. Considering ideally we want those numbers slowly increasing or at least staying the same, this is also a problem.
Lastly, we didn't talk about this yet, but notice how there are a lot of bunched up lines that are red, blue and purple in the Sepmeyer rooms? Notice also how they start bunching together at lower frequencies than the cube?
The bunching of lines is what we want. That actually makes the room sound more smooth and even. The big gaps make the room sound wonky because certain notes are louder than others or they may disappear completely depending where you stand in the room. Ideally, our low end would have a ton of lines too, but we just can't get that due to physics. Bummer I know!
So, a good room will have those bunched lines start clumping together as low as possible. This is known as the Schroeder Frequency. That is just a fancy term that states when your sound waves stops behaving like waves and act more like rays. We want the sound in your room to behave like a ray at as low a frequency as possible because it is easier to treat with velocity acoustic panels. So, all you need to know is that the lower the Schroeder Frequency the better. Simple!
Okay, sorry if I lost you there, but all you need to know is: bunching together good. Bunching together at lower frequencies good. The more bunching the better and bunching evenly is the best! Yay!
Lastly, in our cube room several of the modes in the low end happen at the same frequency. Remember these are bad and will mean certain notes in your room will ring out more leading to an uneven listening and recording environment.
Ahhhh but, Wilson, I am still reading and you have not offered me a solution yet. I know, but I need to teach you how to read the calculator so you can move beyond the room ratios. More on that in a second.
5) What About That Pesky Bolt Area?
You may have noticed a little box labeled Bolt Area in the bottom right of the diagrams I have shown you. You may also have noticed that none of the rooms I have shown you fall in the bolt area.
First, The Bolt Area was a diagram created by Bolt (acoustician dude) who wanted to make it easy to find good room ratios. Before computers you could look at his graph and pick some room ratios that fit your design and would just hope that the room modes were evenly spaced.
The problem is that people have found many room ratios in the bolt area that really are not so great. This lead to other graphs being created. Here is a super handy tool you can use to dive deeper on room ratio graphs.
This link - https://www.acoustic.ua/forms/rr.en.html
The link above will show you where your room ratio falls according to the Bolt Area, The European Broadcasting Recommendations and the IEC Recommendations for room ratios. On top of that the acoustician Trevor Cox did an analysis of rooms and found out some more cool stuff.
He says that if your room falls in the gray or black area of the graph then you will have a nice room. If it falls in the white area then things will go south for you. Dang! Notice that the calculator has a drop down menu for "room cubing." Make sure to set that number to your rooms volume. So for our situation it should be at 100 cubic meters not 50.
Let's take a look at our 15 foot Sepmeyer room on this calculator.
Now it's hard to see, but I think we fall on a grey area. However, we really don't fall within any of the other recommended areas. You can see how this is all maddening. Remember, these calculators are meant as tools and a guide. The best room for you will be one that has as smooth a mode spacing as possible, has a slowly rising mode count per 1/3 octave band, and most importantly is big enough for you to do the work you need to do in there.
Conclusion - So What Now?
I have just taught you how to read these calculators and diagrams. What I propose you do is put in your ideal dimensions and adjust those dimensions slightly to try and get your room to meet the criteria I mentioned. Stay away from 1:1:1 and 1:2:3 ratios.
Another little trick if you have bad dimensions, say 8x8x8, is to increase and decrease two dimensions by 5%. So you could decrease the width by 5% and increase the length by 5% and your room would be much better. (Myth: Modes and Room Ratios: “I Have Too Many Modes! I Need a Better Ratio to Get Rid of Them” - Soundman2020 - Studio Design Forum)
If you can raise your ceiling height do it. If you are building from scratch choose the first Sepmeyer ratio and move on. Or you could look at Louden, but don't get too hung up on it. If you use a room ratio you are light years ahead of most home studios. You could also choose to plot a room on the dark area of the Cox calculator. Then you could check it on AMROC and see how the mode separation looks in the low end. Then you could make sure it meets Bonello's Criterion. The goal is to do the best you can with what you have and not lose sleep over it.
There is no perfect room. I repeat, there is no perfect room. Your design must use these tools and still meet your needs. My advice is to pick a room size as best as you can and move on. Don't waste weeks and weeks calculating room sizes. In the end you will still need acoustic treatment no matter what.
One last thing...don't build a cube.
Works Cited
Room Sizes Compliance With International Standards and Recommendations. www.acoustic.ua/forms/rr.en.html.
“Amroc - THE Room Mode Calculator.” Mag. Andreas Melcher, amcoustics.com/tools/amroc.
Myth: Modes and Room Ratios: “I Have Too Many Modes! I Need a Better Ratio to Get Rid of Them” - Soundman2020 - Studio Design Forum. digistar.cl/Forum/viewtopic.php?t=557.
Everest, Frederick A., and Ken C. Pohlmann. “Modal Resonances.” Master Handbook of Acoustics, McGraw-Hill, New York, 2015.
Do You Want To Learn More About Soundproofing?
Join Our FREE Soundproofing Workshop
