WI #16-125
MEMORANDUM
9 February 2022
To: Reena Brilliot, Leah Ruch, Andrew Crabtree
Community Development Department, City of Santa Clara
Fr: Sarah Kaddatz, Derek Watry
Re: Levi’s Stadium Noise Level Monitoring Project
San Francisco 49ers 2021 Sunday Game-Day Noise Levels (Cheeney & Lenox)
This memorandum presents an analysis of game-day noise levels put in the context of non-game- day noise levels and noise level estimates taken from the stadium’s environmental impact report (EIR) documents. Data is being collected continuously in the neighborhoods around the stadium using Seti-Media noise monitoring stations installed expressly for this purpose. Measurements are being made at four locations around the stadium (see Figure 1), but this memo only reports data from the monitor at Cheeney and Lenox.
The Cheeney and Lenox monitor characterizes noise in the neighborhood south of the stadium which was the focus of the stadium’s EIR noise analysis. It is about the same distance from the stadium as the Hughes Elementary School monitor, and is lined up with the open southern end of the stadium. The Hughes location is shielded from stadium noise to a large extent by the bleacher seats on the eastern side. At the City’s request, data from the Hughes and the other monitors could be added to this report.
Game-Days Analyzed The football game-day data analyzed to date are for the following San Francisco 49ers game days, all Sundays:1
1 Analysis of data from other days (Saturdays, Monday) could be done if desired. Data from Sunday 10/24/21 (Colts) are not analyzed because the noise monitoring station at Cheeney & Lenox was not functioning properly on that day due to rainfall.
Levi’s Stadium Noise Level Monitoring
Noise Levels of 2021 49ers Sunday Games
2 Event Date Event Start Time End Time
8/29/2021 49ers vs. Raiders 1:05 p.m. 3:56 p.m.
9/26/2021 49ers vs. Packers 5:22 p.m. 8:30 p.m.
10/3/2021 49ers vs. Seahawks 1:05 p.m. 4:14 p.m.
11/7/2021 49ers vs. Cardinals 1:25 p.m. 4:25 p.m.
11/28/2021 49ers vs. Vikings 1:25 p.m. 4:33 p.m.
Explanation of Sound Level Metrics Sound (noise) levels vary continuously, so the acoustics community has developed a number of metrics to characterize this variability. This section explains the two used in this memo.
Average or Equivalent Level (Leq) The equivalent level, abbreviated “Leq” is the steady sound level that contains the same amount of acoustical energy during the measurement period as the actual, time-varying sound level did. For all intents and purposes, it is the average level and shall be referred to as such in this memo.
L1 Statistical Noise Levels (“Maximum”) The L1 is the noise level exceeded 1% of the time during a measurement period. For a one -hour measurement period (3,600 seconds), the noise level is higher than the L1 for 36 seconds and lower for the other 59 minutes and 24 seconds. It more fairly represents the “maximum” noise level during the hour for a source like Levi’s stadium, and it is used in this report as a proxy for the maximum noise level.2
Data Analysis & Presentation
• The data analysis uses data collected in 1-hour intervals. • The noise monitoring system is able to filter out most jet noise based on the typical characteristics of jet noise .3 When it detects a jet, the system disregards the 30 seconds during which the jet flies over. Data with and without the inclusion of jet noise are presented in this report.
• For context, the data from the 46 Sundays in 2021 when there was not an NFL game (non - game days) were analyzed to ascertain the average for non-game days.
2 The true maximum noise level during the hour is the single loudest second. 3 If the jet is not particularly loud or there is another, constant noise source such as a lawnmower at the time, the filter may not identify the jet. The filter excludes the noise from about 85% of all jets.
Levi’s Stadium Noise Level Monitoring
Noise Levels of 2021 49ers Sunday Games
3 • Also for context, the stadium noise level estimates in the project EIR are presented. From the Environmental Noise Assessment done for the project:4
Hourly average noise levels generat ed during the game are calculated to range from 61 to 66 dBA Leq at the nearest residential receivers to the south . . . Game-related hourly- average noise levels would exceed typical Sunday afternoon average noise levels by about 4 dBA Leq . . .
Maximum instantaneous noise levels generated by v arious sources associated with a n NFL game (e.g., PA System, music, crowd cheering) would typically range from about 55 to 68 dBA at the nearest residential receivers . . .
The EIR predictions are for the residences closest to the stadium whereas the Cheen ey & Lenox sound monitoring station is more deeply embedded in the community, about 50% farther away. To account for the extra attenuation with distance, 4 dB have been subtracted from the EIR-predicted levels.5
• The 2021 Sunday game -day noise levels are plotted a gainst the contextual backdrop of average non-game Sunday noise levels and the EIR-predicted noise levels. The approximate timeframe of the football game is indicated on each data plot. • The hourly average (Leq) data for each of the five games along with commentary are presented in Figure 2 8-29-21 (Raiders) – Hourly-Average Noise Levels to Figure 6 11-28- 21 (Vikings) – .
• The “maximum” (L1) data for all five games are presented in Figure 7.
* * * * *
4 Illingworth & Rodkin, 49ers Stadium Project Environmental Noise Assessment, Santa Clara, California, I&R Job No. 08-046, 24 February 2009, p 14.
5 Technical note: Noise attenuates with distance for the same reason that the height of circular waves resulting from a rock thrown in a still lake get smaller as the travel away from the source: the energy in the wavefront is spread over a larger and larger area which reduces the wave’s amplitude. This is called “attenuation due to geometric spreading”. Noise that is fairly far from the source – even a large source such as Levi’s Stadium – spreads at a rate of 6 dB per doubling of distance. The distance from the center of the stadium (which is the effective location of the noise source) to the homes where the EIR predicted noise levels is about 1,200 feet, whereas the distance from the center of the stadium to the Cheeney and Lenox monitor is about 1,800 feet , a 50% increase. Given the logarithmic mathematics of decibels, one may calculate that the expected attenuation for a 50% increase in distance is 3.5 dB using the equation 20 log 10 (distance1/distance2).
Levi’s Stadium Noise Level Monitoring
Noise Levels of 2021 49ers Sunday Games
4 Figure 1 Area Map with Noise Monitoring Locations
(Distances are measured from the center of the stadium)
#4
Ave de Lago &
Ave de los Arboles
Stadium: 2,700 ft
#3
Hughes Elementary
Stadium: 1,800 ft
#1
Cheeney & Lenox
Stadium: 1,850 ft
#2
4624 Cheeney
Stadium: 2,460 ft
Stadium
Levi’s Stadium Noise Level Monitoring
Noise Levels of 2021 49ers Sunday Games
5 Figure 2 8-29-21 (Raiders) – Hourly-Average Noise Levels 49ers 34 Raiders 10
It is reasonable to atrribute the game-day noise levels without jet noise (solid blue line) that exceed the average non-game-day noise levels without jet noise (solid black line) to activities at Levi’s stadium. Over the 6-hour period centered on the game time, game-day levels were 2 to 6 dB higher than non-game-day levels.
The stadium noise levels (represented by the solid blue line) are generally below the range predicted for the EIR.
Approx. Game Time
Levi’s Stadium Noise Level Monitoring
Noise Levels of 2021 49ers Sunday Games
6 Figure 3 9-26-21 (Packers) – Hourly-Average Noise Levels 49ers 28 Packers 30
Over the 6-hour period centered on the game time, game-day levels were 3 to 6 dB higher than non- game-day levels (solid blue compared to solid black).
The stadium noise levels (represented by the solid blue line) are generally below the range predicted for the EIR.
Approx. Game Time
Levi’s Stadium Noise Level Monitoring
Noise Levels of 2021 49ers Sunday Games
7 Figure 4 10-3-21 (Seahawks) – Hourly-Average Noise Levels 49ers 21 Seahawks 28
Over the 6-hour period centered on the game time, game-day levels were 1 to 4 dB higher than non- game-day levels (solid blue compared to solid black).
The stadium noise levels (represented by the solid blue line) are below the range predicted for the EIR.
Approx. Game Time
Levi’s Stadium Noise Level Monitoring
Noise Levels of 2021 49ers Sunday Games
8 Figure 5 11-7-21 (Cardinals) – Hourly-Average Noise Levels 49ers 17 Cardinals 31
Over the 6-hour period centered on the game time, game-day levels were 3 to 5 dB higher than non- game-day levels (solid blue compared to solid black).
The stadium noise levels (represented by the solid blue line) are below the range predicted for the EIR.
The high noise level in the game-day data including jet noise (dashed blue line) appears to have been caused by jets flying low over the stadium just before game time. Although not confirmed, this may have been part of the NFL and 49ers’ salute to veterans given the proximity to Veteran’s Day.
Approx. Game Time
Levi’s Stadium Noise Level Monitoring
Noise Levels of 2021 49ers Sunday Games
9 Figure 6 11-28-21 (Vikings) – Hourly-Average Noise Levels 49ers 34 Vikings 26
Over the 6-hour period centered on the game time, game-day levels were 2 to 5 dB higher than non- game-day levels (solid blue compared to solid black).
The stadium noise levels (represented by the solid blue line) are below the range predicted for the EIR.
Approx. Game Time
Levi’s Stadium Noise Level Monitoring
Noise Levels of 2021 49ers Sunday Games
10 Figure 7 “Maximum” (L1) Noise Levels on Sunday Game Days (without Jet Noise)
In contrast to the hourly-average noise levels, the measured “maximum” noise levels on NFL game days is at the higher end of or above the range predicted for the EIR on most game days. Jet noise has been filtered out of these data, so they set an upper bound on noise from Levi’s Stadium, but they may not all be attributable to Levi’s..
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W ILSON IHRIGACOUSTICS, NOISE &VIBRATION CALIFORNIA
W ASHINGTON
NEW YORK
W I #16-125
MEMORANDUM
4 March 2022
To: Reena Brilliot, Leah Ruch, Andrew Crabtree
Community Development Department, City of Santa Clara
Fr: Sarah Kaddatz, Derek Watry
Re: Levi's Stadium Noise Level Monitoring Project
San Francisco 49ers 2021 Sunday Game-Day Noise Levels (Cheeney &Lenox) This memorandum presents NFL game-day noise levels ,compares them to the community noise level target set in the Stadium's Development Permit, and puts them in the context of average non- game-day noise levels and noise level estimates taken from the Stadium's environmental impact report (EIR).
Data is being collected continuously in the neighborhoods around the Stadium using Seti-Media noise monitoring stations installed expressly for this purpose. Measurements are being made at four locations around the Stadium (see Figure 1), but this memo only reports data from the monitor at Cheeney and Lenox. The Cheeney and Lenox monitor characterizes noise in the neighborhood south of the Stadium which was the focus of the Stadium's EIR noise analysis. It is about the same distance from the Stadium as the Hughes Elementary School monitor and is lined up with the open, southern end of the Stadium. The Hughes location is shielded from Stadium noise to a some extent by the bleacher seats on the eastern side. At the City's request, data from the Hughes and the other monitors could be analyzed and added to this report.
Game-Days Analyzed The football game-day data analyzed to date are for the following San Francisco 49ers game days, all Sundays:l
1 Analysis of data from other game days (Saturdays, Monday) could be done if desired. Data from Sunday 10/24/21(Colts) are not analyzed because the noise monitoring station at Cheeney &Lenox was not functioning properly on that day due to rainfall.
5900 HOLLIS STREET, SUITE TI EMERYVILLE, CA 94608 (510) 658-6719 WWW.WILSONIHRIG.COM ~V~el~ ti\~N~~ ~ M,~~C~ ~~ ~! ~,
WILSON IHRIGACOUSTICS, NOISE &VIBRATION
Levi's Stadium Noise Level Monitoring
Noise Levels of 202149ers Sunday Games
Event Date Event Start Time End Time
8/29/2021 49ers vs. Raiders 1:05 p.m. 3:56 p.m.
9/26/2021 49ers vs. Packers 5:22 p.m. 8:30 p.m.
10/3/2021 49ers vs. Seahawks 1:05 p.m. 4:14 p.m.
11/7/2021 49ers vs. Cardinals 1:25 p.m. 4:25 p.m.
11/28/2021 49ers vs. Vikings 1:25 p.m. 4:33 p.m.
Explanation of Sound Level Metrics Sound (noise) levels vary continuously, so the acoustical engineers and scientists have developed a number of metrics to characterize this variability. This section explains the two used in this memo.
Average or Equivalent Level (Leq) The equivalent level, abbreviated "Leq" is the steady sound level that contains the same amount of acoustical energy during the measurement period as the actual, time-varying sound level did. For all intents and purposes, it is the average level and shall be referred to as such in this memo.
L1 Statistical Noise Levels ("Maximum") The L1 is the noise level exceeded 1% of the time during a measurement period. For cone-hour measurement period (3,600 seconds), the noise level is higher than the L1 for 36 seconds and lower for the other 59 minutes and 24 seconds. It more fairly represents the "maximum" noise level during the hour for a source like Levi's Stadium, and it is used in this report as a proxy for the maximum noise level.z Data Analysis &Presentation
• The data analysis uses data collected in 1-hour intervals. • The noise monitoring system can filter out most jet noise based on the typical characteristics of jet noise.3 When it detects a jet, the system disregards the 30 seconds during which the jet flies over. Data with and without the inclusion of jet noise are presented in this report. The levels without jet noise include Stadium noise and all other non-jet sources. • The Stadium's Development Permit includes the following condition regarding noise:
In order to control noise, the stadium loudspeakers systems (permanent and temporary) shall be oriented in a manner consistent with Community Noise Analysis prepared by WJHW, dated May 27, 2010 for the proposed 49ers Stadium, Z The true maximum noise level during the hour is the single loudest second. 3 If the jet is not particularly loud or there is another, constant noise source such as a lawnmower at the time, the filter may not identify the jet. The filter excludes the noise from about 85% of all jets.
WILSON IHRIG Levi's Stadium Noise Level Monitoring
ncousrics,NOISE&VIBRATION Noise Levels of 2021 49ers Sunday Games in order to control noise impacts to adjacent residential neighborhoods. In accordance with Section 9.10.070(c) of the Santa Clara City Code, and the recommendations of this noise analysis, sound system levels shall be limited to 100 dBA for NFL games and other uses of the permanent speaker system, and not mote than 105 dBA for temporary concert speaker systems as presented in the analysis. For sound system installations and modifications within the stadium site, the target for maximum sound level exposure in residential areas to the east and south shall be 60 dBA, in order to minimize noise impacts to sensitive receptors 4 The game day noise levels are compared to the 60 dBA target. As established in the WJHW report, this decibel level target is intended for the 1-hour Leq ("average") level. • For context, the data from the 46 Sundays in 2021 when there was not an NFL game (non- game days) were arithmetically averaged to ascertain representative levels for non-game days.
• Also for context, the Stadium noise level estimates in the project EIR are presented. From the Environmental Noise Assessment done for the projects
Hourly average noise levels generated during the game are calculated to range from 61 to 66 dBA Leq at the nearest residential receivers to the south ... Game-related hourly-average noise levels would exceed typical Sunday afternoon average noise levels by about 4 dBA Leq .. .
Maximum instantaneous noise levels generated by various sources associated with an NFL game (e.g., PA System, music, crowd cheering) would typically range from about 55 to 68 dBA at the nearest residential receivers .. .
The EIR predictions are for the residences closest to the Stadium whereas the Cheeney & Lenox sound monitoring station is more deeply embedded in the community, about 50% farther away. To account for the extra attenuation with distance, 4 dB have been subtracted from the levels predicted in the EIR.6
4 Development Permit PLN2008-06947, 11/30/2010, Condition P23 5 Illingworth & Rodkin, 49ers Stadium Project Environmental Noise Assessment, Santa Clara, California, I&R Job No. 08-046, 24 February 2009, p 14.
6 Technical note: Noise attenuates with distance for the same reason that the height of circular waves resulting from a rock thrown in a still lake get smaller as they travel away from the source location: the energy in the wavefront is spread over a larger and larger area which reduces the wave's amplitude. This is called "attenuation due to geometric spreading". Noise that is fairly far from the source — even a large source such as Levi's Stadium — spreads at a rate of 6 dB per doubling of distance. The distance from the center of the stadium (which is the effective location of the noise source) to the homes where the EIR predicted noise levels is about 1,200 feet, whereas the distance from the center of the stadium to the Cheeney and Lenox monitor is about 1,800 feet, a 50% increase. Given the logarithmic mathematics of decibels, one may calculate that the expected attenuation for a 50% increase in distance is about 4 dB using the equation 20 login (distances/distancez). 3 WILSON IHRIGACOUSTICS, NOISE &VIBRATION
Levi's Stadium Noise Level Monitoring
Noise Levels of 2021 49ers Sunday Games
The 2021 Sunday game-day hourly average levels (Leq) are plotted along with the 60 dBA target from the Development Permit and the contextual backdrop of average non-game Sunday noise levels and the EIR-predicted noise levels. The approximate timeframe of the football game is indicated on each data plot. The data for each of the five games along with commentary are presented in Figure 2 8-29-21 (Raiders) —Hourly-Average Noise Levels to Figure 6.
• The "maximum" (Ls) data for all five game days with jet noise removed are presented in Figure 7. Also shown in Figure 7, for context, is the range of maximum Stadium noise levels predicted in the EIR. The L1 data for non-game days with the jet noise removed has not yet been analyzed for comparison, but could be.
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----~ 8-29-2021 49ers vs Raiders with Jet Noise
8-29-2021 49ers vs Raiders without Jet Noise
EIR Predicted Range
Figure 2 8-29-21 (Raiders) -Hourly-Average Noise Levels 49ers 34 Raiders 10
6 9 12
60 dBA target set in
Development Permit
It is reasonable to atrribute the game-day noise levels without jet noise (solid blue line) that exceed the average non-game-day noise levels without jet noise (solid black line) to activities at Levi's Stadium.
Over the 6-hour period centered on the game time, game-day levels did not reach or exceed 60 dBA.
They were 2 to 6 dB higher than average non-game-day levels, but were generally below the range predicted for the EIR.
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WILSON IHRIGACOUSTICS, NOISE &VIBRATION
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----• 9-26-2021 49ers vs Packers with Jet Noise
9-26-2021 49ers vs Packers without Jet Noise
EIR Predicted Range
Figure 3 9-26-21 (Packers) -Hourly-Average Noise Levels 49ers 28 Packers 30
6 9 12
60 dBA target set in
Development Permit
Over the 6-hour period centered on the game time, game-day levels did not reach or exceed 60 dBA.
They were 3 to 6 dB higher than average non-game-day levels, but were generally below the range predicted for the EIR.
7 WILSON IHRIGACOUSTICS, NOISE &VIBRATION
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----~ 10-3-2021 49ers vs Seahawks with Jet Noise
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EIR Predicted Range
Figure 4 10-3-21 (Seahawks) -Hourly-Average Noise Levels 49ers 21 Seahawks 28
6 9 12
60 dBA target set in
Development Permit
Over the 6-hour period centered on the game time, game-day levels did not reach or exceed 60 dBA.
They were 1 to 4 dB higher than average non-game-day levels, but were generally below the range predicted for- the EIR.
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----• Non-Game Sundays 2021 with Jet Noise 60 dBA target set in Non-Game Sundays 2021 without Jet Noise Development Permit ----~ 11-7-2021 49ers vs Cardinals with Jet Noise
11-7-2021 49ers vs Cardinals without Jet Noise
EIR Predicted Range
Figure 5 11-7-21 (Cardinals) -Hourly-Average Noise Levels 49ers 17 Cardinals 31
Over the 6-hour period centered on the game time, game-day levels did not reach or exceed 60 dBA.
They were 3 to 5 dB higher than average non-game-day levels, but were generally below the range predicted for the EIR.
The high noise level in the game-day data including jet noise (dashed blue line) appears to have been caused by jets flying low over the Stadium just before game time. Although not confirmed, this may have been part of the NFL and 49ers' salute to veterans given the proximity to Veteran's Day.
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- ---~ Non-Game Sundays 2021 with Jet Noise
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- ---~ 11-28-2021 49ers vs Vikings with Jet Noise
11-28-2021 49ers vs Vikings without Jet Noise
EIR Predicted Range
Figure 6 11-28-21 (Vikings) -Hourly-Average Noise Levels 4 9ers 34 Vikings 26
6 9 12
60 dBA target set in
Development Permit
Over the 6-hour period centered on the game time, game -day levels did not reach or exceed 60 dBA.
They were 2 to 5 dB higher than average non -game -day levels, but were generally below the range predicted for the EIR.
10 WILSON IHRIGACOUSTICS, NOISE &VIBRATION
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11-28-2021 (49ers vs Vikings)
EIR Predicted Range
Figure 7 "Maximum" (L1) Noise Levels on Sunday Game Days (without Jet Noise) In contrast to the hourly-average noise levels, the measured "maximum" noise levels on most NFL game days were at the higher end of or above the range predicted for the EIR. Jet noise has been filtered out of these data, so they set an upper bound on noise from Levi's Stadium, but they may not all be attributable to Levi's Stadium noise.
Levi's Stadium Noise Level Monitoring
Noise Levels of 2021 49ers Sunday Games
11