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Why Mixing Is All About the Bass

Bass frequencies have some interesting characteristics that are important to understand when mixing your services and in selecting a mix location for your room.

It's important to understand that bass frequencies have some interesting characteristics when mixing your services and these characteristics should also impact where you are selecting a mix location for your room.

Note that bass frequencies generate waveforms that are very long.

A 100Hz note from your bass guitarist is about 11 feet long; the 20Hz punch from a kick drum is about 56 feet long.

When the audio console is placed a few feet off of a wall, interesting things happen with those long bass waveforms with regards to what your audio tech hears.

When an audio wave hits a wall, it bounces off that wall and heads back out into the room. The first thing it encounters after that bounce is itself – all 50 feet of it for a 20Hz note. And because it’s so long, it’s almost exactly in phase, and combines with its own incoming part of the wave form to double the energy of the waveform.

If you’re in a corner, it’s more like tripled, because it’s bouncing off of two walls. Doubling the energy level of a note results in about a 3dB volume gain; tripling is about a 5dB increase in volume.

Just from the walls.

Your floor and ceiling will also contribute to the bass build-up at the edges of the room. Therefore, any low-end frequency is going to sound much louder at such a mix position than out in the main seating area of a room.

The challenge for your audio techs is that they have to learn how obnoxious the bass needs to be at the console so that it sounds and feels right out in the room.

At the church I serve at, our mix position is about six feet off the rear wall. This means that if I mix so that the low end sounds good in the booth, it has no guts to it out in the room.

So, I've found that if small and light items on the booth’s counter aren’t bouncing a little with the kick drum and low bass guitar notes, it’s not loud enough out in the seating area for our church’s audio mix standard -- it just feels wimpy out there.

Likewise, the audio tech needs to understand how this effects their ability to EQ low-end instruments accurately. If you EQ it so it sounds right in the booth, it has lost all the definition of the low end for that instrument out in the room.

When I set the levels for the drum kit, I have to push the toms increasingly louder than what sounds right in the booth as the toms decrease in frequency, otherwise when the drummer goes around the kit on the toms, the energy trails off as he gets to the larger toms.

“But what about all that sound absorption material we had installed around the room? Doesn’t that take care of it?”

In a word—no. For absorption material to effect a given frequency, it needs to be at least the thickness of ¼ of the wavelength of the frequency. So, if you want to “kill” the bounce off the back wall for a 20 Hz sound, the material needs to be 14 feet thick. For 100 Hz, it needs to be almost three feet thick.

Absorption panels hung on the walls work primarily for the higher frequencies.

Taming the bass in a room is often a difficult and expensive proposition. Therefore, it’s important for your tech team to understand what the bass response of your room is like, and how the main sitting area differs from the mix position in bass volume. Ideally, your mix position is out near the center of the room.

Okay, now that you’ve stopped laughing hysterically at the thought of proposing THAT to your church’s leadership, instead, you’ll need to get out and walk around the room while the band is playing and compare what you hear to how it sounds in the booth. With practice your audio techs will learn what it needs to sound like in the booth so that it sounds good in the room.

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