SR 05:028 - Laserfiche WebLink

Acoustical Analysis The purpose of this memorandum is twofold. First we describe the characteristics of acoustics related to outdoor performances at a proposed amphitheatre that is sited within the Cultural Arts Center (CAC) complex. Second, we analyze the differences in sound impacts at two locations being considered for the amphitheatre and CAC. Both potential sites am located within the Central Area of the Bernal Property and may be considered in the Phase II Specific Plan and EIR. The two locations being considered are a southern location, south of Valley Avenue and adjacent to the existing wetland. MD Fothefingham, the design competition winner has proposed this location for the CAC and amphitheatre. The second location is a northern site approximately 600 feet south of Bernal Avenue and west of the 50-acm Bernal Community Park sports fields. Both sites are approximately 25 acres in size. The type of amphitheatre envisioned is one that could facilitate amplified sound and lighting systems for ticketed events. A permanently covered stage and chair seating are considered optional improvements. The sloping lawn area and stage, both recessed below existing grade, could serve a number of different formal and informal functions and gatherings. The impacts of noise are lessened if the amphitheatre becomes a multi- functional outdoor public place without built-in facilities for amplified sound. The Specific Plan could consider a range of amphitheatre types for future consideration. Primer on Sound Wave Patterns Sound travels in straight lines and the transmission of sound generates outward in a 3-dimensional cone, similar to a cone of light generated by a flashlight. The actual waveforms of various frequencies are a consideration, but that aspect of sound goes beyond the basics of this discussion. How the ever-widening cone of sound is directed, or intercepted, has everything to do with how sound is best heard or not heard. Also, as distance from a sound source increases, the level of sound is reduced. The nature of the sound changes from 'direct' to 'ambient' in relation to the distance from the sound source. It is much easier to block direct sound when closer to the sound source. In addition, at a critical distance from the sound source, both direct and ambient sound is perceived. Beyond the critical distance, ambient sound is predominant. The loudness or decibel level is a measurement of the sound impact, measured at a horizontal distance from the sound source, and is mapped as a noise contour. Generally, exterior parks and open spaces are not impacted by sound levels at 65 decibels or lower. Noise Generated by Off-site Sources The quality of a performance in an outdoor amphitheatre can be diminished by noises from sources surrounding the facility. The primary noise factor at the Bemal Property is traffic noise. Three sources of traffic noise have been identified: 1-680 Freeway, Bernal Avenue and the Union Pacific Railroad line. The Draft Environmental page 1 I M.D. FOTHERINGHAM, Landscape Archirecrs Inc. 323 Geary Street, Suite '107 San Francisco, CA 94102 415~34-82~2