Meanwhile, Red Rocks is dealing with noise complaints from residents from the nearby town of Morrison. The residents say that concerts featuring the increasingly popular bass-heavy electronic dance music known as EDM causes the windows in their houses to rattle. Are the two phenomena -- falling rocks and rumbling homes -- related? It's a subject we explore in the sidebar to our cover story, which is reprinted in its entirety below.
Anyone who's been stuck in traffic next to a car with booming speakers knows that loud music -- especially music with deep bass frequencies -- can make things shake, rattle and roll. But would you expect to feel the same type of vibrations at your house?
As the Red Rocks concert season gets under way this year, some residents of the town of Morrison, which is located at the foot of the iconic music venue, are renewing their complaints about the window-rattling tremors caused by bass-heavy electronic dance music, or EDM. Red Rocks hosts several EDM shows each year, including the multi-day Global Dance Festival.Last year, Denver hired sound engineers to measure the low-frequency noise from EDM concerts that causes vibrations. The engineers took measurements at two Morrison homes, and although they found that the vibrations didn't exceed ambient levels, they recommended further study. Those engineers also helped Red Rocks develop its own noise limits and curfews, which were implemented on January 1 of this year in an attempt to appease the town's residents.
For the 2014 concert season, which began last month, performers who continue past 12:30 a.m. on weekdays or 1:30 a.m. on weekends will be fined $5,000 per half hour. In addition, the limits state that noise levels should not exceed 125 decibels, which is somewhere between the volume of a saw and that of a jet engine, at the frequency of 25 to 80 hertz -- about the range in which sound can be felt as well as heard -- for more than a minute. Performers who violate that limit five times in a day will be fined $10,000.
But since Red Rocks is owned by the City of Denver and located in Jefferson County, Morrison can't actually do anything to enforce the new rules. And town clerk Kara Zabilansky says it's too early to know whether the limits will make a difference.
She also points out that some residents have questioned whether the vibrations are causing damage to the rocks. "I have heard people in public meetings express concerns about low-frequency noise from concerts: 'Could it affect the rocks?'"Good question. Could vibrations from the music cause rocks to fall?
That's not an allegation being made by the lawyers representing the four people who were hit by rocks at a Sound Tribe Sector 9 concert in September 2011. (STS9 isn't considered an EDM act, though their music appeals to some EDM fans.)
And three local sound engineers, who are not involved in the case, say it's highly unlikely.
"Realistically, I would say that while it may be possible, it's doubtful," says Walter Beamer, a professor of civil engineering who researches acoustics at the University of Colorado at Boulder. The amphitheater isn't an enclosed space that would trap the vibrations, he adds.
David Adams, of D.L. Adams acoustical consultants in Denver, agrees. "Freezing, thawing, freezing and thawing is more likely to cause the rocks to fall," he says.
Jim Borzym of Borzym Acoustics in Boulder says one way to think about it is to remember the old Memorex commercial in which Ella Fitzgerald shatters a wine glass with her voice. Rocks, he says, are much harder than glass. "Yes, sound can move things," Borzym adds, "but it takes a tremendous amount of sound."
For more on the concertgoers' lawsuit against Red Rocks, read this week's cover story, "Rocks and Roll."