Wednesday, April 24, 2013

Sound Level Limits in Live Mixing

It's been a while since I've had to go toe-to-toe with someone over the loudness of a show but SPL levels are still on my mind. At the church where I work I'm in a 1400 seat aud with SPL limits of 92 for evening services and 94 for Sunday mornings. That's C-weighted, slow response, at the mix position. As long as I hold to that, nobody squawks. Almost...

A lot of the problem with volume levels is perception. A well balanced mix that's a little heavier on the bottom can go to 96 on the peaks in that room and nobody will bat an eyelash. But throw a harsh vocalist or guitar in the mix and I'll get complaints from a service where the meter read 90. Dynamics have a lot to do with it as well. A song that builds slowly and peaks at 96 for eight bars at the end is a completely different story from one that starts and stays at 94 before it does that same ending.

It doesn't help that a lot of people in our industry, let alone the general public understand how decibels work and how the different weightings affect the readings. Many a time have I been approached at an outdoor event by some municipal official waving the same Radio Shack SPL meter that I have with it set to A/fast. Well of course they're pissed that I'm at 115! Click, click. "Oh, you're at 103. Well the neighbors are complaining so how about you make it half as loud. Yeah. Shoot for 50."

Don't even get me started about cell phone apps. What a nightmare. It's becoming more and more common to be approached by people who have some slight knowledge of OSHA regulations from their place of employment. They'll come up and demand that I turn down a service because their phone was reading above 85 at some points. I'll grab my meter with the proper settings dialed in, show them the number, tell them it's well within established limits and that there's no way that the mic on their phone will ever take an accurate reading. 

One more thing about OSHA regulations. The actionable limit for noise in the workplace (from Standard No. 1910.95) is 85 dBA, slow. That means that you have to be exposed to that level of continuous noise for the full length of a working day before it's considered dangerous enough for your employer to have to offer you earplugs. The exposure limit for 95 dBA, slow is four hours. Which in my case means that if we were paying our congregation to sit through services they could sit through three and a half of them and we wouldn't be required to offer protection.

Now that's exposure for continuous noise like engines or fans. Things that are more dynamic can be more dangerous. The long term average on a rifle range isn't that high because there's a lot of silence in between shots, but a single gunshot close to your ear can ruin you for life. So while averages are good to look at the peaks need to be taken into account as well. In my 70 minute services the music is about 45 to 48 minutes. Add in a bunch of speaking and the average level is pretty low. For someone sitting close to the drums though that big fill at the end of a song can be pretty loud. Setting the meter to take max readings and taking a look now and then isn't a bad idea.

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