A short while ago, I received e-mail from a reader named Tim Wright of Des Moines, IA. Tim wrote me about questions and concerns his congregation had with regard to the effect bass (sub frequencies) may have on pacemakers and internal heart defibrillators.
Tim was unable to find any articles or doctors observations warning against sub-frequencies and the aforementioned devices. I also could not find anything online or anecdotally (talking with my sound tech friends) that would lead me to believe that sub-frequency or any frequencies for that matter are dangerous to these devices. However, my investigations led me to think about the overall effect that loud (or relatively loud) sound has on the average churchgoer.
Decibels and SPL
To understand these effects, we must first get a good grasp on decibels and SPL (sound pressure level). Engineers at Bell Laboratories coined the term "Bel," naming it in honor of Alexander Graham Bell. A Bel is a unit of measurement of ratios of power levels. This measurement is mostly used in telecommunications, electronics and acoustics. That said, a Bel is too large for everyday use, so a tenth of a Bel, a "decibel (dB)," is the most common measurement of volume. Don't fall asleep on me, this stuff is important. Now, audio frequencies move through the air in waves (sound waves). These waves are pushing through the air creating varied levels of force or pressure. And these sound pressure levels (SPL) are measured in decibels.
I know most of you have a decibel meter in your house of worship, so you just look at the number. If it is too high, you attempt to turn down the volume. Many houses have a limit as to how many decibels they want their music and voices amplified to.
Let me give you some decibel milestones. 40dB is a soft whisper at six feet, 65dB is an average conversation at three feet, heavy traffic at five feet is about 90dB, a loud orchestra at 10 feet is 100dB, 120dB represents a loud rock band at 10 feet and 130dB is the pain threshold for the average person. These references are good to understand and remember, but sound waves and decibels do not travel and increase in a perfectly linear fashion.
"What in the hell (or heaven) does this have to do with my congregation," you may ask. The point is (finally) that individuals react differently to sound pressure levels, and those levels can vary lot in a house of worship.
Opening a Dialogue
Since our job as sound techs is to amplify worship music and the spoken word, we must be sensitive to the needs of our congregation. I decided to interview various church members to get a better idea of what they are hearing.
I have changed the names of these people in the interest of privacy. My first questions were posed to an elderly woman named Anna. She told me that at times the music from the worship band would vibrate the fillings in her teeth, and that, at times, it was painful. I was amazed by this claim, but I did my research and found that this is indeed possible. This phenomenon is caused more by frequency than decibel level. In other words, your worship music can be playing along at 95dB, but a guitar solo at 96dB with its presence emanating at 1000 Hertz can rattle Anna's head.
Did I just jump to Hertz? Hertz are a measurement of cycles per second. The higher the cycles per second (or Hertz), the higher the frequency. Hertz were named for 19th century physicist Heinrich Hertz. Scientist and inventors always name stuff after themselves. But I digress, back to Anna. She said that if she sits further back from the main speakers, the effect disappears, or is reduced. I also interviewed a variety of people who are sensitive to bass frequencies. This group seems to be able to feel bass more than others. To some this is uncomfortable and to others it is just part of the worship music experience.
One of the people I spoke with, a middle-age man named Paul, said that, at times, he was really bothered by his pastor's voice. It seems that Paul's pastor's voice had a definite bite to it at around 2 kHz, or 2000 cycles per second. Paul would become actually irritated by his pastor's voice and had even considered leaving the church and looking for another place of worship.
A Skewed Sample
Now to be fair, I purposely looked for people who were having problems with what they were hearing in their worship houses. I regularly work at four different churches, and most of the people I talked to were very satisfied with their worship experience. Almost all of those who had issues with the sound grew up or came from churches that did not have sound systems. The fact of the matter is that we now have a generation of people who only have an experience of amplified music and speech. But (as you know) my job is to serve the congregation, and part of that job description is to satisfy as many people as possible.
By being able to recognize the needs of your congregation and having the ability to correct flaws in your sound system, you can really do a great service for your people.
I can't address your individual needs, but I can tell you that by training your ears to identify frequencies accurately and quickly, you will be able to EQ your house system and individual microphones more effectively. And we know that equalization is our best tool for defining music and speech.
I realize that mixing live sound is a constantly moving target. What may sound brilliant one day may sound like mud the next. Sound will change with the temperature of your worship space. It will change if the room is packed with bodies or mostly empty. But your job requires that you learn the sound characteristics of you worship room as best you can. And I suggest you talk to as many folks in your congregation and ask what they think of the sound.
