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The Ups and Downs of SPL Restrictions

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If you want to keep working, you have to learn how to play nicely with others in the sandbox. Part of those skills may require that at some point or another (for whatever reason), you’ll have to work within an SPL limit. It’s a difficult task, especially with a full band on stage, so let’s take a look at why SPL limitations exist and what you can do to make the best of a quiet situation.

 

How Come I Gotta Turn It Down?

Sound pressure level restrictions exist for several reasons. An issue that crops up during the summer tour season is that concerts at outdoor venues spill sound to the neighbors. Oddly enough, not everyone likes Slayer, so often venues enforce a curfew specifying no noise past a certain time, and often set a maximum SPL of “X” dB (we’ll get to that in a moment). Sometimes, there may be a monetary fine if an artist plays past a certain time, or louder than a certain SPL. In severe cases, you may be shut down if you exceed the SPL limit for an extended period.

Other venues have different types of “neighbors.” Casino showrooms, for example, may want an SPL limit so that people outside the showroom aren’t disturbed from their gambling activities. And let’s face it: I don’t care what artist you work for, but a casino books that artist to get people onsite to lose their money on the floor and buy a hotel room, not because they love the latest album. The Wolf Den at Mohegan Sun (CT) is an example of a venue that is open to part of the casino. You’ll often find people standing around the perimeter of the venue, watching the show after the seats are filled. In such a case, it’s very easy to piss off people who are not interested in your show because high SPLs easily leak sound on the casino floor. If you want that date on the calendar again next year, it’d be smart to play by the rules.

Festivals in Europe (not so much here in the U.S.) enforce SPL restrictions to avoid damage to patrons’ hearing, which is probably a smart idea given the fact that there’s always some ambulance-chasing lawyer whose client didn’t think that a rave or hip-hop concert would be loud. The SPL limit at such festivals may also exist because there are multiple stages operating simultaneously, and it would be nice if the audience (and band) at one stage did not hear the performance from another stage.

Those of us who work the state/county fair circuit sometimes find that SPL limits are in place to protect animals that live on the premises. These limits might be temporary if (for example) you are performing after a horse race and need to wait until the horses are moved from the track (where the stage is located) to their stables, where the noise won’t scare them.

Some engineers completely disregard SPL limits in the above scenarios because it puts a cramp in their artistic creativity. Maybe it’s acceptable in the world of other engineers and artists, but in my world, I want the venue to book the band again next year, so I’ll play by their rules. A date on my calendar means I’m getting paid.

My favorite SPL limitation (not) is when you are playing in support of a headliner who can’t bear the thought of your act being louder than them. Three years ago, I mixed a support act in front of a major headliner who basically turned off two-thirds of the P.A. system before our set. Really? Bush league.

Who’s Hiding the Meter?

To play by the rules, you need to know the rules. Duh. It’s amazing how many times I have run into situations where the SPL rules were not laid out clearly. You need to know where that SPL will be measured, for how long, and what weighting is being used. Venues that are smart will measure SPL at the mix position so that the engineer can be aware of how loud they are running. It also avoids the issue of “I dunno how loud it is at the last row.”

You have every right to expect that there will be a meter at the measurement position, not some clown who arbitrarily decides ‘it’s too loud.” Some venues will want you to heed a long-term average that does not creep past a certain point. This allows you to achieve peaks occasionally, maintaining the act’s dynamics. The last time I mixed at Sweden Rock (no sound check), one of my crew announced the band, and I had his mic way louder than it should have been. Red lights started blinking, TV screens were flashing, and a police helicopter came down to arrest me (Okay, I’m kidding about the last part). I briefly hit a peak of 120 dB (yikes), but the systems engineer smiled and told me it was okay, as long as I came back down for the show SPL average, which I believe was around 105 at FOH.

You also need to know what weighting will be used for the measurement. A- and C-weighted SPL measurements are two very different animals, so if someone tells you the limit is 97 dB, your perception of the volume level will differ based on weighting. A-weighted measurements filter out the bottom-end compared to C-weighting, so an SPL restriction of 97 dB A-weighted at FOH is actually a fairly workable number, given the fact that the SPL meter won’t care too much about the bottom end.

The Other Side of the Stage

A vital part of the equation is the willingness of the band to reduce their stage volume. If the band is running 105 dB on stage, it will be very difficult to honor a 95 dB limit at front of house in a small casino showroom. Guitar and bass amps are typically the main offenders. If you can get those players to turn down, that will help. Other solutions that I’ve tried include facing guitar cabinets upstage, moving the cabinets off stage into closets or dressing rooms, and eliminating amps on stage altogether. A plexi screen in front of the drumkit reduces the volume of the drums quite a bit, but make sure that the band sound checks with the baffle in place. It can be very disarming for a drummer to play behind a barrier for the first time, and they’ll need the chance to properly dial in their monitors. Speaking of monitors, using IEMs instead of stage wedges is another way to reduce control stage volume and will also make for cleaner monitor and front of house mixes.

Steve “Woody” La Cerra is the tour manager and Front of House engineer for Blue Öyster Cult.

 

SPL RestrictionsOSHA Audio Guidelines: It’s the Law

The U. S. government’s Occupational Health & Safety Administration (OSHA) has long established guides on the job for sound exposure, which seem well suited to assembly line manufacturing and noisy trades such as airport workers. Although sound reinforcement would fall under these same guidelines, exactly how they would apply to our industry is a bit murky as the noise level (meaning music, but with some artists, “noise” may be more accurate) in many cases is controlled by the employees — (i.e., the FOH or monitor engineer).

OSHA regulations within the 29 CFR Occupational Safety and Health Standards (subpart G, #1910) spells out permissible daily exposure levels, as shown here.

Permissible Noise Level Exposures

Daily Duration       A-Weighted SPL

8 Hours                90 dBA

6 Hours                92 dBA

4 Hours                95 dBA

3 Hours                97 dBA

2 Hours                100 dBA

1.5 Hours              102 dBA

1 Hour                  105 dBA

30 Minutes            110 dBA

15 Minutes            115 dBA

It also states that “The employer shall administer a continuing, effective hearing conservation program… whenever employee noise exposures equal or exceed an 8-hour time-weighted average sound level (TWA) of 85 dB measured on the A scale (slow response) or, equivalently, a dose of 50 percent.”

Less obvious (and outside of OSHA’s jurisdiction) is sound exposure to the audience and to the surrounding environs. The audience part may be tougher for the FOH engineer to control, especially when attendees are free to wander the venue and may be in the close-in mosh pit areas and standing in front of subwoofer or ground-stacked speaker all night. The audio level might be at a comfortable 100 dB at the FOH position, but you can bet it’s a bit louder when you’re three feet in front of the P.A.

The out-of-venue levels — sound spill — is often regulated by local codes, mostly to make peace with neighboring businesses or residents and can drastically change from venue to venue. In extreme cases, this may require a real-time sound logging system that stores and records the system SPL history, typically measured from the boundary of the facility.

One interesting recent approach to SPL monitoring is the Sound Level Predictor from NTI (nti-audio.com), a free PC-based app that works in conjunction with the company’s XL2 audio analyzer and gives the FOH engineer a prediction of sound levels over the next 10 minutes based on past history.

—George Petersen