Red RocksWhen the topic of noise comes up, the adage that “One man’s floor is another man’s ceiling” becomes palpably relevant, especially if you’re the one in the downstairs apartment. That’s how many of the residents of Morrison, Colorado, felt about the growing number of electronic dance music (EDM) and other amplified music concerts being booked at the Red Rocks Amphitheater, an open-air, acoustically natural venue used for live performances for over a century. Red Rocks Amphitheater is owned and operated by the city of Denver, 15 miles to the east, but Morrison, a western suburb of the city, is barely a mile from the venue.

The issue came to a head in 2013, when residents voiced their concerns at town meetings, focusing on the increased volume of bass sound being emitted during EDM shows, as that genre grew in popularity during the decade. The venue enacted new rules, setting a limit of 105 dBA after midnight on weekdays and an hour later on weekends. Exceeding those limits could result in fines of up to $10,000 per occurrence.

This improved the situation, but it wasn’t enough. 

“Music is a tough one,” observes Rich Zwiebel, founding principal of K2, the Boulder, CO, acoustical consulting firm the city of Denver retained to analyze the problem and look for solutions. “What’s music to one person’s ears is noise to another’s.”

Zwiebel, working with the firm’s acoustician and senior consultant, Ted Pyper, undertook what would become a nearly four-year project. The first order of business was to measure and document the sound levels coming from the venue. It wasn’t a simple task. Unlike a typical concert venue, Red Rocks is as organic as it gets, and given the propagation characteristics of low-frequency energy (LFE), even structure-borne sound energy through the bedrock slab could not be discounted initially.

A system was used to measure sound levels for two seasons, but the initial findings revealed they would need a more granular measurement protocol to provide better and faster reporting. In 2016, they brought in a QSC Q-SYS sonic analysis system. Studio Six Digital and Bruel & Kjaer sound-capture platforms were positioned outside the venue. (Zwiebel is also an executive at QSC.)

The Q-SYS platform is often deployed as part of the design process for spaces such as music venues, but it is more typically used to provide the signal processing for the audio program material. However, it offers users the flexibility to create custom capabilities via programming and script writing. K2 created a measurement protocol that displays SPL (sound pressure level) and Leq measurements on screens at various locations including front of house (FOH). This system provides a way to derive hard data from the measurements, which would be as detailed as one reading per second. Data logs are created and kept of every event.

“The reason we went to the Q-SYS system was that no off-the-shelf product offered multiple inputs and real-time reporting that also focused in on the very specific frequencies we were targeting,” says Pyper. “We could program the Q-SYS core for that. This was a very unique project and we had to come up with unique ways to approach it.”

Using a bass-heavy PA rig that they managed to get an incoming show to set up one day early, the original mockup system measured SPL from eight ground-stacked 4 x 21-inch subwoofers, another 16 flown-rigged subs plus another 16 flown, full-range speaker cabinets — what might have seemed like a virtually militarized sonic arsenal or, for the more rabid EDM fan, a typical weekend show. For subsequent surveys, in addition to measuring sound levels at three locations, K2’s technicians also appraised weather conditions — wind direction and speed, as well humidity levels, all playing a part in sound propagation. Measurements have taken place over the course of the concert season, from April through October, for three years.

Sound measurements were divided into two categories, dBA and, to focus on LFE, in the range between 25 and 80 Hz — just above what’s known as the infrasonic range, where sound is more felt than heard. Analysis of the data determined that the cause of concern was mostly in the 40-63 Hz range, with a 12-to-18-dB “bump” in that range.

The data was further broken down by music genre, with hip-hop somewhat less bass heavy, with a 6-to-9-dB bump in the 63-Hz to 100-Hz bands; rock music measuring as “flat” — no particular frequency bumps; and some country music actually showing a dip below 100 Hz; heavy metal music produced lots of midrange intensity but not enough to warrant further scrutiny. Thus, EDM was the main source of complaints, and with the added complication that the sound was made more noticeable by the fact that Morrison itself was a pretty quiet place, with a measured community noise floor in the 45-to-50-dBA range.

The data gathered was translated into an abatement strategy: Music performances would be monitored by sound-measurement devices, with a limit of 105 dBA after a certain time of night. The prevalence of complaints related to LFE warranted the creation of a custom category, what K2 referred to as “dB1,” with a limit of 125 dB in the 25-to-80-Hz range after a specific time of night. Each subsequent year, the protocol was modified based on data.

Everything was monitored by a system that was permanently installed at the Red Rocks FOH sound-mixing position, keeping continuous track of critical dBA and dB1 frequency bands. The system sent emails to K2 personnel and Red Rocks Amphitheater management, alerting them whenever any of the monitored frequencies were exceeded. If it happened three times, it would automatically trigger a fine to the event promoter.

The strategy worked. After the dB thresholds were tweaked a year later, the number of complaints dropped substantially. Refinements to the protocols were also made in each subsequent year.

Data Produced a Positive Outcome

Zwiebel says the data provided a basis for a set of protocols that accomplished real noise reduction in the identified frequency ranges. It also established the perception that the city and the venue were genuinely responsive to community concerns. Tad Bowman, venue director at Red Rocks (and the Denver Coliseum, both under the auspices of the Denver Arts & Venues agency), says the data collected and parsed over the past three years at Red Rocks led to a “balanced” outcome. It’s one that left most affected stakeholders at least mollified, although he acknowledged it’s impossible to please everyone when it comes to what’s proven to be a contentious issue in many municipalities.

“I want the experience of patrons and performers to be a high priority,” said Bowman, “but not at the expense of the venue’s neighbors.” Thus, a series of testing and data analysis led to the establishment and refinement of a set of protocols that established clear loudness and time-of-night (curfew) guidelines, as well as the methodology that continues to ensure and monitor those guidelines, and put some teeth into them, in the form of the possible fines. (Bowman says no fines have been assessed so far.)

While complaints haven’t been eliminated completely, the numbers have declined. That may also have been helped by the fact that some EDM artists have avoided the venue since the new guidelines were implemented. But Bowman is clear that he feels the effort expended on problem measurement, assessment and analysis, from which workable guidelines were drawn, was the foundation for the solution.

Zwiebel says a similar measurement approach was deployed for the city of Telluride’s annual music festival last summer. As the music festival sector continues to grow — in 2014, there were more than 800 music festivals in the U.S. alone attended by 32 million people, according to Nielsen Music — more of them may turn to this type of data-based analysis to address noise complaints. “Without data,” says Zwiebel, “you’re just guessing.”