I often get questions from clients of mine on how to acoustically treat the bass in a room. It’s not the easiest thing to accomplish, and there’s a fair bit of science involved with actually getting it right. It’s one thing to slap acoustic panels in the corners of a room and another to actually do it right.
I’ll try to go through everything I can think of to get you on your way to fixing the bass resonances in your room and break down a little bit of the scientific process in the simplest way possible.
Are bass traps on the market really bass traps?
The simple answer is no. The more complex answer is as follows:
Let's take this bass trap from Acousticmac. Disclaimer, this is simply for educational purposes.
To people looking to find a solution to this, these types of things often appear to be the correct thing. However, when we start to break down some science, these types of things tend to fall apart.
Unfortunately, this is what this bass trap is doing. Surprising? Yes.
As you can see, it’s not working very well on the sub frequencies. But isn’t this the area it’s supposed to be working on?
Well, it’s supposed to, at least in our minds, but in reality, this type of treatment isn’t sufficient to control the bass frequencies of a room. Most, if not all, of the commercially sold bass treatment can’t do what we expect it to.
We’ve been lead to believe that by simply putting these “bass traps” in the corners of our rooms, we’re solving the issues we’re having with our bass frequencies in a room. But, unfortunately, we couldn’t be further from the truth.
So How Are We Supposed To Fix This?
Well, there's a couple of methodologies that work well if done right.
Absorption:
The most challenging thing you have to deal with when trying to control the bass in a room is the balance between what that absorption material is doing to the high frequencies and what it’s doing to the bass.
For example, if you pad the entire room with extremely deep and dense Rockwool (for example, 1 meter deep and then cover it with cloth), while you’re probably going to end up helping to reduce the bass resonance of the room down to a manageable level, but at the same time, you’re very likely going to end up overly killing the high-frequency balance of the room as well. So how can you find a way to balance this?
Well, consider this. What if we could find a way to create an astoundingly simple way to balance this out?
Bass waves tend to travel through thin pieces of wood quite easily, so if you had to place very deep and thick Rockwool layers behind certain places in the room, in short, you could effectively create powerful bass traps without actually affecting the high frequencies of the room.
I’d suggest making a room within a room, and behind this thin wall you’re making, place at least half a meter depth of Rockwool behind it.
This will help act as a room-wide initial bass trap while also preventing the room from completely killing off the high frequencies.
Next, place your standard Rockwool acoustic panels on the right and left-hand side first reflection points, from floor to ceiling, 2m wide for each of them, and place another standard Rockwool panel 2m to 3m wide floor to ceiling on your back wall.
Congratulations. You’ve just successfully treated the most basic and important 3 points in the room.
You can also place another 2m wide floor-to-ceiling acoustic panel on the front wall behind your speakers, but that’s something you should only do at the end of the entire room treatment process to determine if it’s necessary or not. Your discretion should be used on the additional placing of Rockwool panels once you’ve finished the entire treatment process. These are the fundamental places of treatment, and you want to avoid overtreating the room and rather approach it as a step-by-step process.
This generally does a lot to fix the room’s acoustic issues, but wait; we’re going to take it one step further.
Adding corner custom bass traps on top of all this can go a long way in helping to keep the room tight and prevent the bass from resonating even further.
Build a square prism(a 3-dimensional square) frame for each corner of the room from floor to ceiling. Measurements should be at least 45cm on each side. If you don’t have the space, a 30cm measurement on each side will be better than nothing. An example of a square prism is as follows.
Fill this prism frame with Rockwool, and cover it in cloth to prevent the fibers from getting out, same as you’d have on standard acoustic panels.
Place these in the corners of the room, and coupled with the standard panels at the first reflection points, back wall, the bass trapping behind the room within a room, and these more “hefty” bass traps than the fake ones on the market, this should bring your room closer to where it needs to be while still maintaining the balance between high frequencies and low frequencies.
Diffusion: The issue with diffusion is that it would have to be too large to be effective in any way on bass frequencies. You’d want to add some diffusion panels on the walls to help create the perception of a more spacious room by scattering some of the sound waves without absorbing them. I’ll do another article on the science of diffusion, but for now, adding a bit of diffusion on top of this setup shouldn't be an issue.
Active Bass Traps
This is a rather interesting one. If you’ve got the money, you can really optimize your room with something like this. I’d suggest adding these on top of the treatment you already have in your room. I wouldn’t recommend this in place of the absorption techniques I recommended above. A balance between the two is simply an optimization.
PSI AVAA ACTIVE BASS TRAPS:
How does it work?
A microphone will measure the acoustic pressure in front of an acoustic resistance. The acoustic resistance is designed to let air through but reducing significantly the pressure.
Behind the acoustic resistance, a transducer membrane is driven to absorb the volume of air going through the acoustic resistance and ensure a specific acoustic impedance in front of this acoustic resistance.
When in function, this acoustic impedance in front of the acoustic resistance is significantly lower than in ambient air and therefore acts as a pressure sink. The air's acoustic impedance is typically affected over a radius of 1 to 1.5 m around the AVAA. This explains how the AVAA can be more absorbent than the actual surface of a perfect absorber.
It is designed to absorb frequencies between 15 and 150 Hz and is most effective on room modes resulting from multiple reflections.
The graph above shows us how it can be pretty effective in contributing towards an effective low-end control system. You can immediately see how it can work in conjunction with the first method I mentioned before.
I hope this helped you all with a few options and ideas on fixing your acoustic treatment!
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Best, Austin
