Bass Traps, Part One

Bass Traps Part One: Fixing Muddy Mixes and Studio Room Modes

When I first started working from my own small studio everything I mixed was too bass-heavy, even though it sounded totally fine in the studio environment.

The mysterious equipment dealer guy who looked like he escaped from Miami Vice called Jeremy came by one day and I explained the problem and without missing a beat he said: "You need some more bass trapping, son! Ooh...it's gonna cost ya!" and in my mind of course, I was thinking "What... what...MORE trapping? I don't have ENOUGH bass! And what the hell is that terrible shirt all about?"

And that was the beginning of the never-ending adventure that was practical studio acoustics.

The Reality of Small Room Studio Acoustics

The bad news for that control room, despite it already being treated, was that it was quite small, and effective bass trapping takes up a significant amount of physical room. The options were limited, but sure enough... after a load of research, I swapped the whole configuration of the studio, moving to the live room, and turning the old control room into the live space.

I hired an acoustic consultant to draft a professional plan, and then built some huge BBC D2 design bass traps tuned to the lowest room modes for the corners, and installed yet more panel trapping around the entire lower half of the room like the genius said. And instantly, even though the live room was now pretty small... the translation of my recordings drastically improved.

Now, the ideal way to do it is to build your control room with room-mode-friendly physical dimensions in the beginning, then add additional acoustic treatment - which is exactly what I did the next time I decided to build a recording studio. But most of us don't have that luxury, especially at home or in an existing smaller bedroom space.

What Is a Bass Trap? (The Laws of Physics)

Bass energy is powerful. Like Thanos powerful. It literally almost cannot be stopped, so the term "bass trap" is actually a little misleading... you're not trapping ANYTHING. It's more like a "bass speed bump," but that's not as catchy of course.

Bass trapping serves to attenuate the acoustic power of the low-frequency sound wave, drastically reducing the boundary reflection effect that it has within the monitoring environment. Most home studio spaces are dangerously small when it comes to the physics of low-end sound waves:

• A 100Hz tone has a wavelength of a little over 11 feet to complete just one cycle - and that's not even really low!

• A 50Hz tone has an acoustic wavelength over 22 feet long.

  
  

This is an epic topic to dive into, but for now, I’ll just say physics creates some complexities involving the interaction of sound waves with your specific room dimensions and each other. The end result means that depending on exactly where you sit at your listening position, you may experience a completely inaccurate, distorted sense of what is really happening with your low-end mix balance.

Predicting Studio Room Modes vs. Real-World Construction

Generally, these low-frequency room modes can be predicted from your basic room dimensions, though the physical construction materials also have a massive effect on reality which is why a standard room mode calculator alone is not enough.

That said, here is a great online room acoustics tool you can use to visualize what your room boundaries are doing to your sound: 👉 Trikustik Room Mode Calculator

So, from the raw dimensions, we can see what acoustic phenomena are probably happening, but solid brick walls act very differently to lightweight studwork and plasterboard walls.

Perhaps you have a big false ceiling above you? A bouncy wooden floor? A huge storage space at the back? Maybe a thin back wall leading to a hallway? Or a posse of homies sitting on a fabric sofa? All of these elements act as low-frequency bass trapping to some degree... and in fact, are all incredibly useful structural components when it comes to practical studio construction.

We have all been in a room when an object rattles when the sub-bass is loud, right? Let's say that rattling object resonates most centered at 100Hz. When that specific bass note is played, it physically moves, and that physical kinetic movement is converted directly into heat. What made it resonate? The sound wave - which then loses the exact amount of acoustic energy required to make that physical movement happen. This is kinetic bass trapping in action!

Understanding Low-Frequency Nulls and Comb Filtering

In the case I mentioned above, in my small control room, I was suffering from severe phase acoustic nulls. Around my primary listening position, the reflected sound waves interacted in such a destructive way that they completely cancelled out key frequency areas in the low end. Because I couldn't hear those frequencies in the room, I would naturally overcompensate in my mixes by boosting the bass.

Counter-intuitively, adding bass traps reduces these nulls by preventing the reflections that cause the phase cancellation in the first place.

In general, with professional studio acoustic design, you're trying to get your reverb decay time (RT60) more even and flat across the entire frequency range that your studio monitors spew out. If you just buy cheap foam tiles from Amazon, that will only damp down the high end and upper midrange frequencies, but the rest of the lower frequency spectrum stays completely unchanged. The lower the frequency goes, the harder it is to control. If you only use thin foam tiles, you are guaranteed to end up with severe translation issues because you aren't even touching the low end with your acoustic treatment.

How to Measure Your Room Acoustics for Free:

If you want to see exactly what is happening to the frequency response at YOUR specific mixing position, you don't need expensive laboratory gear. Follow this protocol:

1. Grab a reasonably flat, omnidirectional measurement microphone.

2. Download the industry-standard free acoustic analysis software: 👉 Room EQ Wizard (REW)

3. Run a frequency sweep through your studio monitors to map out your room's acoustic response curves.

   
   

How were those measurement results? Oh dear. I guess we better either buy or build some real broadband bass traps. Stay tuned for Part Two!

Get a Mix That Translates Perfectly On Any System

If this all sounds like hassle, you are struggling with a room that is lying to you and you need a seasoned industry ear to deliver a mix that translates perfectly from a car stereo to a massive club system, check out my Online Mixing & Mastering Services.

Did you miss the article about Room Setup 101 ?