Receive direction from City Council regarding sound level regulations at special events.

Through the Future Agenda Item Request process, Council requested to review the sound level regulations for special events,  including the maximum decibel level, a discussion on the bass level, and consideration of possible changes to these sound limits.  MD Acoustics was hired to perform a sound study during a permitted special event in Wheeler Park on June 2, 2018.

Events at Wheeler Park generate more sound complaints than events held at other parks.  Although categorized as a neighborhood park, Wheeler Park remains one of Flagstaff’s most desirable event venues each year due to its shade trees and downtown location.  

All frequencies across the audible spectrum, 20hz to 20khz, were reviewed and sound was primarily evaluated in dBA and dBZ. “A” weighting (dBA) is the most common weighting used in noise measurement. Like the human ear, this effectively cuts off the lower and higher frequencies that the average person cannot hear. Although the “A” weighted response is used for most applications, “C” weighting (dBC) is also available on many sound level meters. “C” weighting is used in some entertainment noise measurements, where the transmission of bass noise can be a problem. “Z” weighting is a flat frequency response between 10Hz and 20kHz ±1.5dB.

The current special event rules and regulations state that decibel levels read from 100 feet of the speaker locations must not exceed 90 decibels, “A” weighted.  Prior to the June 2 event, baseline readings were conducted at 204 W. Birch Avenue (American Legion), 410 N. Leroux Street, 54 N. Sitgreaves Street, and 402 W. Birch Avenue. The baseline noise level ranged between 52.9 to 73.4 dBA.

Some results from the sound study on June 2 are as follows:

• At 410 N. Leroux St. the sound of crowd cheering was audible and when music was played the noise level increased from 47 to 49 dBA.
• At 54 N. Sitgreaves St. the low frequency data (<125 Hz) was the dominant sound from the festival.
• At 402 W. Birch Ave. the ambient condition with no music ranged between 43 and 45 dBA; when music was playing the noise level ranged between 46 and 49 dBA. The study found that the festival caused an increase in noise level of 3 to 6 dBA.

The average noise level at the mixing board, located 45-feet from the center of the stage, measured 84.9 dBA. During the event on June 2, 2018, no noise complaints were filed with the Office of Community Events or the Flagstaff Police Department. The noise level read from 100 feet of each speaker location never exceeded 90 decibels.
 
MD Acoustics recommends the following options:

1. Make no changes to the noise limit.
2. Change the noise limit to state the following: “Decibel levels read from 100 feet of the speaker locations must not exceed 100 decibels, "C" weighted.” This would better incorporate low frequency sound pressure levels with overall sound levels.

It should be noted that Option 2 is a stricter limit because it incorporates the low frequency (< 125 Hz) sound pressure levels with the overall sound levels, whereas A-weighted filters de-emphasize the lower frequency data significantly, thereby not effectively accounting for the sound levels at these lower frequencies.