Audio, AV Police Squad

Setting Mic Levels To Combat The ‘Yelling Crawler’

I had the privilege of watching an IT guy setting microphone levels the other day. It was a difficult room that was notorious for having poor audio, so I had asked the client’s operators to set it up as they normally would for a meeting. Since AV is “technology,” operation of the room fell to IT. They opened their laptops, connected to the mixer and then explained that they check the mic levels on every mic at the mixer because of the problems they’ve had in the past. I was impressed up to this point at their thoroughness. One operator manned the laptop and the other “tested” the microphones. The test included crawling on the table, getting right up next to the microphone and yelling “CAN YOU HEAR ME ON THIS MIC?!” into each element. The reason for the room’s poor audio performance became clear.

In the after action meeting, they asked if they could do anything better. I simply asked how many of their users crawl up on the table and yell into the microphones during their meetings. Apparently, it happened one time at a late night company party…but that was the only time. (Author’s Note: That person (aka: “the yelling crawler”) was ultimately let go, and never heard from again.)

I often see blanket performance specifications in design packages detailing how loud a source should be at the microphone element to properly set levels. I’ve seen 72dBA, 80dBA and even 94dBA at the microphone element. However, I think that designer who recorded 94dBA got confused with signals used while calibrating a microphone, bless his heart. To make matters worse, these same designers use the same nominal levels regardless of microphone type and/or placement.

It may be perfectly reasonable to expect 72dBA at the element of a gooseneck positioned 10” away from the talker’s mouth. This makes sense. The IEC 60268-16 standard specifies a sound pressure level for a standard talker to be 60dBA measured at a distance of 1 meter. Every time we halve the distance, sound pressure increases 6dB by the inverse square law. So, if a standard talker is 60dBA at 1m, it’ll be 66dBA at 0.5m, and then 72dBA at 0.25m (or about 10”). So, if someone’s mouth is going to be roughly 10” away from a microphone, setting levels with a 72dBA source at the element makes total sense.

However, specifying that integrators should set systems up with a 72dBA source measured at the element for table microphones positioned 6 feet away from the talker doesn’t make any sense. Using the same logic as above, any time we double the distance, sound pressure will drop 6dB by the inverse square law. So, if a standard talker is 60dBA at 1m, it’ll be 54dBA at 2m (or about 6’). Using a 72dBA source to set up table microphones is setting their nominal level to be 18dB above standard talker levels. It’s very difficult to raise your voice 18dB above standard levels. It’s even more difficult to sustain this screaming level throughout an entire conference without being carted off by the police. This method makes no sense.

A more elegant solution is to simply use the IEC 60268-16 standard talker level in your performance specification. Instead of specifying a level at the microphone element, just specify the level coming out of the mouth of a standard talker. Then, set up the microphones using a standard talker anywhere a mouth would be. Easy-peasy. In fact, a remarkable company makes a device whose only function is to act like a standard talker. That, combined with a tripod to position it where a mouth would be, makes setting up audio systems quick, simple and painless. Added bonus: You also don’t have to continually ask it to count to ten…again…and again…one more time.

My point is: Be wary of people who crawl on tables to set microphone levels. Also, be wary of blanket levels used to set microphones that disregard microphone placement with respect to users’ mouths. Both will get you in a lot of trouble. However, one is way more fun to watch.

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