In part one (CPM October 2007), we talked about how volume affects worship, and how hard it can sometimes be to keep it pulled back, even when it’s the right thing to do. In this edition, we’ll talk a bit more about the meters, the numbers, hearing, good volumes, and our responsibilities as sound engineers.
Meters
Shortly after moving into the new Willow Creek Community Church nearly four years ago, we self-imposed a 95 db(C)-SPL-peak-fast limit. If you don’t know what any of that means, go to Radio Shack and pick up an analog SPL meter for less than $50. We have been measuring on several meters and software programs to learn their subtle differences. Your SPL meter will have a “weight” or filter switch, typically offering “A” and “C” as options. These are EQ filters that color the way the meter’s mic responds to sound. To oversimplify, (A) passes mostly midrange, and (C) is closer to flat.
Most of the research for noise exposure and hearing conservation has been done using the (A) scale, which has a slightly heightened sensitivity to the ear’s most sensitive range of frequencies. Using (A) to measure music to protect hearing has proven consistently suc-cessful and (A) has been adopted by several governments as a standard of measurement for hearing protection and conservation. Therefore, set your meter to (A)-slow for documenting your services (yes, your church should be documenting, as you’ll soon read). Meters are our friends, not techno-geek weapons aimed against the artists. It’s OK for that number to be over to the side where others can see it. Things feel very different between a PM service and a 5:30 am. conference rehearsal. Glancing at a meter when your head is still numb is sometimes the only way to know if you are in the ballpark in an empty room.
OSHA and A/C Weighting
OSHA (Occupational Safety and Health Association of the USA) is a government organization that places regulations on noise exposure in the work place. Its specifications for time exposure limits use the (A) Weighting filter. Observe Fig. 1. For all the reasons above, Willow made the change from (C) to (A). dB SPL(A) reads lower than dB SPL(C) because dB SPL(A) is looking at the midrange. Our studies reveal that for our services and the kinds of music, and the quality of the PA (four years ago), dB SPL(A) can read between 4 and 11 dB lower than dB SPL(C). The average for music seems to be 5 dB lower. If you have deep sub bass and bright highs, the difference for music between (A) and (C) might be closer to 11 dB. So as we migrated from (C) to (A), we were keeping under 90 dB SPL(A) Slow-response, (approximately equivalent to the 95 dB SPL(C) fast peak ceiling we had been operating under). By switching to slow, we were finally paying a little less attention to instantaneous peaks, and more to the mix.
Keep in mind that this is a full range 90, with sub support down to 32 Hz. The amount of lows and highs still make a difference on a meter reading (A), just not as dramatic as if it were on (C). A reading of 90 out of a quality PA is quieter and more musical than 90 out of a mid-rangy, “honky” system, which would seem much louder, more annoying, and less musical to our mid-range-sensitive ears.
Leq Matters
In addition to watching peak/average, fast/slow volume levels, recording total exposure is very important. Leq (Level Equivalent) is a number that represents exposure over time as a value equivalent to a constant sound for that same duration. Some sounds are dangerous instantaneously. Most can be dangerous with exposure over time. Every ear is different and every environment is different. Ears respond differently on any given day with regards to health, tension, humidity, temperature, and even caffeine and sugar consumption as variables.
Mental preparedness can even affect the muscles in the ear and make you more or less prepared for exposure to sound. The ear has many miraculously engineered subsystems. One of them is a built-in attenuator that clamps down and restricts the eardrum movement, a response called TTS (Temporary Threshold Shift). This natural attenuator can engage up to 15 dB of attenuation upon detecting a loud transient. It can feel like your ears are plugged. It’s temporary, and will naturally disengage typically within a day. One might experience this if hitting two pieces of pipe together (not recommended). The first bang is loud, you feel your head kind of “pressurize.” The second bang sounds quieter and muffled, missing the mid-highs. This is automatic hearing-protection in effect. This is an awesome mechanism, but take it as your personal built-in warning that you were exposed to something too loud for continuous or repeated exposure without protection.
A Service Leq is Low
A one-hour service with peaks of 92 dB-SPL(A)-Fast might have an Leq(1) of 76 dB-SPL(A). This means that a constant noise of 76 dB(A)-slow for an hour would be the same exposure as attending the one-hour service. This is because there is music at varying levels, speech at varying levels, and sometimes silence. This number can be compared to the OSHA noise exposure limits. With Leq in these ranges, it’s clear that the service itself poses no safety concerns, as it doesn’t even register on the chart which starts at 85dB SPL (A) slow. Keep in mind that we are comparing music and speech exposures to a noise scale. Music is not noise (if everyone has done their job, and depending on the personal preference of who’s listening) and could benefit from unique weighting and measuring standards someday. For now, we’ll use the currently available and historically-proven (A) weighting, where all the research has been done to assure safety, and to better understand the hearing experience.
Measure/Log/Be Safe
It’s one thing to think you are running safe levels, and another to know it. Even if you are obviously safe, every church has the responsibility to measure and log. It’s the only way to definitively answer any questions concerning volume. Even if you are super safe, OSHA requires that any employer log exposure if staff are exposed to 85 dB during their work day, even if it is for one minute a year. Yes, it’s that important. And required even if you are just “dusting off the rig” with your favorite song now and then.
Protecting your own hearing is also obviously on the list. Our engineers have their own custom-molded in-ear monitors (IEMs), attenuators, plugs, and have all recently undergone formal hearing tests by audiologists. These are minimum requirements for us engineers. If you learn the facts, are educated, know yourself, and love music, you can relax and truly enjoy and mix a wide variety of volumes. It’s comforting to know that my engineers are exposed to 200%-500% more exposure than anyone walking in the doors (with rehearsals, sound checks, run-throughs). Measured, experienced, and unprotected, we are a very safe place yet with good energy.
It is any organization’s responsibility to professionally deliver a safe presentation, and measure and log it to ensure that safety But it is an individual’s responsibility to take hearing protection and conservation in their own hands, or ears … whatever. I can only give Willow my best if I protect my hearing at concerts and events that I know are a little (or a lot) too loud for me, even if they are within OSHA guidelines. Protection at other events sometimes means discreetly slipping in my attenuators, or paying close attention to the sensation in my ears, or sometimes discreetly leaving that location and finding a quieter one (typically off axis or farther back). Notice the repeated use of the word “discreet.” Protection does not mean to stand there with my fingers in my ears, totally distracting and detracting from the experience of those nearby. When you can feel the tension in your skull, you should have protection in or relocate. This is normal. Even in totally safe environments, it’s OK to find your comfort zones. It’s wise and responsible.
Unhappy Minority
Some will still disagree with the levels we run at in church; some still complain, and some even leave. And every one of them makes me sad. However, there are more people now saying that they love the sound than there are those who don’t-0.03% can’t govern the ex-perience of 99.97%. Some municipalities consider noise (like trains and factories) to be a problem when 17% of the community complains. If we see a concern trend even among 1/10th of 1%, we’ll check it out. For some, we’ll simply be too loud, but we have many wonderful, quieter seating options available to offer.
We have identified quieter seating so that ushers can suggest more comfortable, quieter seating for those concerned or uncomfortable. I also assembled some data and information on how we manage volume and the system, and to express how much we care. The right vo-lume will always be too quiet for some, too loud for others. The challenge is to seek out those that think it’s too quiet. They just don’t seem to flock the booth after a great service.
Our SPL - Proportional
Because of all these factors, there is no common volume we can all share. I can tell you for your referencing pleasure, in our room, with our congregation, our band, through our system, with our engineers driving, for a cookin’ worship song with an engaged congregation, 86 dB-SPL(A)-slow might seem wimpy and 96 dB-SPL(A)-slow might seem hot. Somewhere in there is a changing “pocket” where the congregation still has an acoustic sense of community (a personal mixing value that totally depends on a great system in a great acoustic work space). This proportional relationship obviously changes dramatically between when there are 2,000 in the room, and a packed out closing session of a conference of 7,200.
The PA and the FOH engineer are best supporting the experience when they are not noticed, but when the congregation is being boldly led by the stage, with sound mixing support that is proportional to the energy being expressed by the leader and band. This is when the awesome sound of a congregation worshipping and the acoustics of the room are being professionally considered as elements of a total mix. There’s a goal to not be wimpy, as well as to not steamroll over the room. But instead, to hear everything you see on stage, in its proper place in the mix.
Sometimes silence whispers to some, and sometimes being washed in powerful full-spectrum sound “whispers” to others. I respect being a slave to these laws of physics, and I absolutely love this art.
Chris Gille is also known as “Papa Audio,” or audio & systems director in the production department of Willow Creek Community Church.
