Summer concert season is coming up fast and that, of course, means outdoor events. Already a challenge due to a host of obstacles such as weather, access to power, scheduling and playing nice with the neighbors, outdoor shows may also be subject to sound level limits, and engineers accustomed to mixing at very loud levels may find it difficult to comply with local noise ordinances. Where venues don’t post Sound Pressure Level (SPL) limitations, many engineers hit the gas pedal with a vengeance — until someone steps in and says it’s too loud. But that description doesn’t provide the information we really need to know. If we’re going to play by the rules, we need to know the rules.
Why Limit Sound Levels?
SPL limits can be mandated for a number of reasons: hearing protection for the public (this seems to be more of a concern in Europe than in the U.S.), minimizing noise spillage into neighboring communities, and sometimes as a means of protecting the structural integrity of an old, perhaps landmark building where subwoofers shaking the rafters could cause damage. Other reasons venues establish sound level limits include protecting their investment in the P.A. and avoiding equipment abuse by visiting engineers, or restricting noise until a certain time of day in an effort to accommodate neighbors operating nearby businesses. I’ve done shows at horse racing tracks where noise is prohibited until the horses have been brought to their stables, far enough from the infield that they won’t be frightened by the noise. And I’ve done shows in casinos where the house doesn’t want noise spilling onto the gaming floor for fear of interfering with their customers’ ability to lose money! The net result is the same: you may need to recalibrate your mixing skills to avoid an unpleasant encounter with the house crew or the police, or worse — being shut down entirely.
Forewarned is Forearmed
The first line of defense for SPL limits is knowing and understanding that there is in fact a limit. “You’re too loud” is not an acceptable criterion for a sound level limit. Asking about a sound level limit is usually part of my advance, not because I want to beat people over the head with volume but because I want to know what sort of volume level the venue expects. In addition to asking the specific dB level, you need to know what the weighting is, because — as we saw in the January FOH On the Digital Edge — 100 dBA is way different from 100 dBC. You also need to know exactly where this measurement will be taken; an SPL measurement taken at the FOH mix position is entirely different from an SPL measurement taken from the last row of the audience.
What’s in the Tool Box?
If there’s a noise ordinance at a venue, there’s usually (at the very least) an SPL meter at the house console, but it’s a good idea to carry one in your work box. A handheld SPL meter such as the Extech 407730 (Fig. 1) comes in handy, and — with a street price around a hundred bucks — certainly won’t break the bank.
A more accurate approach might be to run Rational Acoustics Smaart software with a calibrated microphone, which is probably a good idea anyway, so you can have a look at the system’s frequency response (Fig. 2).
I’ve been to more than a few outdoor festivals where there’s a large screen showing the current SPL with a warning indicator that flashes red when you hit the limit.
I don’t put too much stock in the accuracy of most SPL meter apps for smart devices, with one exception: SLM (Sound Level Meter) from NIOSH (National Institute for Occupational Safety and Health), shown in Fig. 3. Beside the fact that it’s free, one of the great features of SLM that makes it more useful than a lot of sound level meter apps is that it has a calibration mode enabling you to compare it with a dedicated (i.e., more expensive and more accurate) SPL meter and adjust the SLM readout to improve accuracy of measurements taken using your smartphone. Plus, it will measure A, C or unweighted, and can take LEQ measurements, which a lot of smartphone SPL meters won’t do.
How Fast for How Long?
“Top Speed” can be defined in different manners, depending upon the objective of the sound level limit: it could mean “don’t exceed 95 dBA ever” or it could be an LEQ (Equivalent Continuous Noise Level) measurement that allows a lot of leeway, because it’s a long-term average and brief peaks are basically ignored — so if you hit the limit briefly a few times during the course of a 90-minute show, you probably will be okay. A fair number of venues are more casual about SPL limits, leaving them to the discretion of the systems tech, which often means “as long as people aren’t complaining it’s too loud or running out the door, then we’re good.” This approach provides the systems tech with an opportunity to rein in an overzealous visiting engineer from causing damage to the system or chasing out the patrons, while allowing the artist to play loud enough for some impact.
One thing that helps in situations where there’s a sound level limit is getting the band to reduce their stage volume. This enhances an engineer’s ability to mix at a lower level while still overcoming the stage. I’ve seen engineers and bands take exception and throw hissy fits over SPL limits, but the fact of the matter is that ignoring them isn’t a good strategy. You might incur a fine from the local authorities, and it reduces the likelihood of being asked back to the venue.
Steve “Woody” La Cerra is the tour manager and front of house engineer for Blue Öyster Cult, and Jon Anderson & The Band Geeks. He can be reached via email at [email protected].
