So last week I started work on our project of mapping the decibel levels in the sanctuary. I had to decide on a method. The mixer is equipped with a sine wave tone generator with a sweepable frequency. This makes a constant monophonic sound whose volume can be set with a knob. I set the volume so that the meter read 90 dB at the mixer and turned the frequency to 1kHz, a sort of mid-range frequency. With some earplugs, I went around to strategic areas in the sanctuary and wrote down the volume for that spot. I was surprised to find what I did.

First, that tone generator is REALLY annoying. At that volume level, even with my hands over my ears, it felt like the noise was in my head. Unpleasant. Second, the volume was unpredictable. I originally thought that the very front rows would prove to be the quietest spots in the room. I was wrong. I was also surprised to find out that the sound levels in some areas on the main floor were louder than they were behind the mixer.

Another observation I made was the drastic volume difference between areas only a few feet from each other. Often, the end of one short row was more than a few decibels louder or quieter than the one at the other end. On the longer pews, the difference was drastic. I also noticed that the height at which I held the SPL meter seemed to make a difference so I tried to hold it at ear level for an average person.

Please take a moment to look at the map. What do you notice about the sound levels? Where are the quietest areas in the sanctuary? Where are the loudest? Does anything surprise you?

Here are some caveats. As Chris Sabatke pointed out, using a monophonic tone such as the one produced by the mixer opens us up to some anomalies for that frequency only. The room might be "more sensitive" to some frequencies than to others. Some frequencies build up in some areas due to the unique shape of the room while others cancel out. Chris suggested using white noise, pink noise, or brown noise (not brown nose). You can listen to audio examples and read explanations on Wikipedia. While these types of noise are each different, they are useful because they contain all the frequencies of sound that we can hear, so we might get a more accurate reading of the levels.