Acoustics are what happens when sound encounters boundaries. Sound propagates as waves through the air in a defined pattern until contacting a surface. Whether it is a human being, a wall, or a pew, acoustics are easiest to understand via what they encounter in their pathway. Hard, reflective surfaces will bounce nearly the entirety of sound waves back the same direction they arrived (angle of incidence is same as angle of reflection) while soft, absorptive boundaries, such as humans, only reflect some frequencies while trapping others. Sound travels at roughly 1,130 feet per second, depending on air density and altitude, which is rather slow compared to light. So, multiple paths from source to destination mean arrival times will vary and will interact in myriad ways, making discernment of speech difficult. Having a basic understanding of acoustics can make mixing more productive and enjoyable. Here are some things to know:
1. Room acoustics are a complex combination of origin, destination, and boundaries. For speech, the goal is to provide as much direct energy to the listener as possible, with as little reflected energy as possible. When the pastor is speaking, their voice is either in the direct or indirect field, depending on where we measure. Direct field energy comes from the primary source (loudspeaker) to the listener without interruption and is highly intelligible, assuming a proper mix engineer is at the helm. When the listener perceives more material through reflected means, the retention and intelligibility drop dramatically. Thus, we want to maximize the linearity between output device (loudspeaker) and human ear.
2. You cannot overpower the room. I have witnessed even seasoned engineers attempt to overcome poor acoustics by increasing the level of the system output, to no avail. The room always wins. Instead, work with the room. If it will not allow energy below 80Hz, then hi-pass everything at 85Hz and build the mix to that reality.
3. In reflective environments, don’t muddy the mix with effects. If the RT60 (time it takes in seconds for sound to decay 60dB) is four seconds, there should be no effects used at all in the mix. There simply is no point.
4. Acoustics are different all over the room. Just because it sounds great in the tech booth doesn’t mean it sounds good in the seats. Take the time during soundcheck to walk the room and listen to how it sounds down front, up in the balcony, over by the rear wall, etc. Then, make adjustments as the LMS (Loudspeaker Management System) allows. Perhaps dial back a bit of low-mids in the front fills, add some 5KHz to the over-balcony fills and pull back the subs some to get a reasonable mix in every section.
5. Know why things sound the way they do in your room. If the sanctuary contains an orchestra pit, it will resonate around 125Hz. Be ready to pull that frequency out of the orchestra matrix. Under-balcony areas tend to enhance energy around 350Hz, so making a gap in the response in that region makes sense. Acoustic guitars often ring at 630Hz, so make a cut there when dialing in that channel. Understand the ceiling grid vibrates at 55Hz, so explain to the bass player why you are notching that frequency.
Acoustics can be a nightmare when parallel walls create standing waves, but they can also enhance worship when they are properly suited for the task at hand. While not much can be done to reposition boundaries, temporary gobos can be set up to divide acoustic areas on-stage and absorptive materials can be hung on walls to remove the worst of reflections. The key to success is to be aware of what the room is doing to sound and how best to work with it to achieve a reasonable mix.