Editing Golden Gate Bridge (section)

==== Wind safety retrofit introduces wind "songs" ====
[[File:Bridge Whistle.wav|thumb|A recording of the noise produced by the Golden Gate Bridge taken in the Presidio of San Francisco on Sunday March 2, 2025.]]
In June 2020 residents across [[San Francisco County|San Francisco]] and [[Marin County, California|Marin]] Counties began to notice a humming noise. The noise has been described as "eerie", "a shrill screeching sound", and for some evokes a feeling that "something bad is about to happen."<ref>{{Cite news |last=Bartlett |first=Amanda |title=SF officials say an end is coming to the Golden Gate Bridge's eerie song |url=https://www.sfgate.com/local/article/golden-gate-bridge-song-san-francisco-19952341.php |archive-url=https://web.archive.org/web/20241208020646/https://www.sfgate.com/local/article/golden-gate-bridge-song-san-francisco-19952341.php |archive-date=December 8, 2024 |access-date=2025-03-02 |work=SFGATE |language=en |url-status=live }}</ref><ref>{{Cite news |last=Swan |first=Rachel |title=San Francisco Golden Gate Bridge's infamous 'singing' will finally go away |url=https://www.sfchronicle.com/sf/article/golden-gate-bridge-singing-noise-fix-19934862.php |archive-url=https://web.archive.org/web/20250222072456/https://www.sfchronicle.com/sf/article/golden-gate-bridge-singing-noise-fix-19934862.php |archive-date=February 22, 2025 |access-date=2025-03-02 |work=San Francisco Chronicle |language=en |url-status=live }}</ref><ref name=":2">{{Cite web |date=2023-01-12 |title=Why the Golden Gate Bridge Sounds Like It's Screaming Bloody Murder Right Now |url=https://www.popularmechanics.com/science/a42476120/why-golden-gate-bridge-is-screaming/ |access-date=2025-03-02 |website=Popular Mechanics |language=en-US}}</ref> The [[Golden Gate Bridge, Highway and Transportation District|Golden Gate Bridge Highway and Transportation District]] determined that the "unsettling" whistle is produced by new railing slats when a strong [[West wind|zephyr]] blows.<ref name="bridge harmonic resonance issues">{{cite news |first=Eric |last=Ting |url=https://www.sfgate.com/bayarea/article/Golden-Gate-Bridge-noise-humming-why-wind-sound-15321767.php |title=Why the Golden Gate Bridge made strange noises with the wind Friday |newspaper=San Francisco Chronicle |date=June 6, 2020 |access-date=June 6, 2020 |archive-date=July 5, 2020 |archive-url=https://web.archive.org/web/20200705073455/https://www.sfgate.com/bayarea/article/Golden-Gate-Bridge-noise-humming-why-wind-sound-15321767.php }}</ref>

The new slats were installed starting in 2019 on the west side of the bridge; they are more flexible than their predecessors and were selected to improve the bridge's aerodynamic tolerance of high wind to {{convert|100|mph|km/h|0|abbr=on}}. The sound had been predicted from [[wind tunnel]] tests,<ref name="Chron-sing" /> but not included in the environmental impact report.<ref>{{cite news |last=Chamings |first=Andrew |date=July 1, 2020 |title=Golden Gate Bridge officials look to fix 'screeching that sounds like torture' |url=https://www.sfgate.com/living-in-sf/article/San-Francisco-Golden-Gate-Bridge-singing-fix-15379759.php |newspaper=San Francisco Chronicle}}</ref>

The Bridge District determined that, in fact, there are two sounds that the bridge produces. When the wind passing through the slats reaches {{Convert|22|mph|km/h|abbr=on}}, "a low-pitched, low-frequency tone—between 280 and 700 [[hertz]]" is produced.<ref name=":2" /> When the wind passes through the slats at an angle and reaches {{Convert|27|mph|km/h|abbr=on}}, the slats produce "higher pitch and frequency (1.1 [[kHz]])."<ref name=":3">{{Cite web |title=Bridge Sounds During High Wind Events - Suicide Deterrent Net {{!}} Golden Gate |url=https://www.goldengate.org/district/district-projects/suicide-deterrent-net/bridge-sounds-during-high-wind-events/ |access-date=2025-03-02 |website=www.goldengate.org}}</ref>

On December 16, 2021, the Bridge District approved a fix for the noise; 12,000 '''∪'''-shaped clips with rubber dampers are to be installed between the slats at a cost of $450,000.<ref>{{Cite web |date=December 16, 2021 |title=APPROVE ACTIONS RELATIVE TO REDUCING WIND INDUCED SOUND EMANATED BY THE GOLDEN GATE SUSPENSION BRIDGE WEST RAILING |url=https://www.goldengate.org/assets/1/25/2021-1216-bocomm-no3-appractreducingwindretrofit.pdf?7522 |website=goldengate.org}}</ref> Testing suggests that this fix will reduce the noise by 75%; however, even with the fix, the bridge is expected to emit the high frequency tone an average of 70 hours per year; the low frequency tone is expected 18 hours per year. The Bridge District expects instillation to be "completed in 2025."<ref name=":3" />

An independent engineering analysis of a 2020 sound recording of the tones concludes that the singing noise comprises a variety of [[Physics of whistles#Aeolian tone|Aeolian tone]]s (the sound produced by air flowing past a sharp edge), arising in this case from the ambient wind blowing across metal slats of the newly installed sidewalk railings.<ref>{{cite web|url=https://vibrationdata.wordpress.com/2020/07/13/golden-gate-bridge-singing/|title=Golden Gate Bridge Singing|website=Vibrationdata: Shock & Vibration Software & Tutorials|author=Tom Irvine|date=July 13, 2020|access-date=December 1, 2021}}</ref> The tones observed were frequencies of 354, 398, 439 and 481&nbsp;Hz, corresponding to the [[musical note]]s F<sub>4</sub>, G<sub>4</sub>, A<sub>4</sub>, and B<sub>4</sub>; these notes form an F Lydian Tetrachord.