Get guidance on how to monitor amplified sound

The approved outdoor sound limit is listed as a condition on the approved entertainment permit. 

To learn more about Smartphone app decibel meters and other types of decibel meters, see "What are suggested devices for sound monitoring?" in the FAQs below. 
 

Measuring Temporary Outdoor Event Sound

•    If the permit states not to exceed a prescribed decibel limit (dBA/dBC), go to the designated spot check location listed on the permit and take a sound measurement using either your Smartphone app or handheld decibel reader. 

•    If the permit instead states not to exceed ambient sound at an “approved distance,” follow the instructions listed below for measuring sound at a temporary event. 

          o    For all temporary event permits with an “approved distance” sound condition, go to the approved distance (number of feet) from the event’s property plane in the direction of where the sound is traveling. 
                    - The “property plane” is the property line which determines the property boundary, like the approved street closure footprint, edge of the parklet, or patio.  

          o    From the approved distance, listen to the sound coming from your event taking note of other ambient sounds in the area.  
                    - Stand at the approved distance for 3-5 minutes and listen to the event sound to ensure both busy moments and lulls in ambient sounds are being considered.

                    - The sound is compliant if it is significantly drowned out by normal traffic and other ambient sounds when standing at the approved distance from the event’s property plane.

                    - The sound is non-compliant and needs to be turned down if it can clearly be heard over sounds such as city buses or general automobile and foot traffic in the area when standing at the approved distance from the event’s property plane.

Measuring Brick and Mortar Outdoor Sound

•    If the permit states not to exceed ambient sound at an “approved distance,” follow the instructions listed above for measuring sound at a temporary event. 

•    If the permit states not to exceed a prescribed decibel limit (dBA/dBC), go to the designated spot check location listed on the permit and take a sound measurement using either your Smartphone app or handheld decibel reader. 

•    To learn more about Smartphone app decibel meters and other types of decibel meters, see "What are suggested devices for sound monitoring?" in the FAQs below.

If you have questions about how to comply with your permit’s sound limit, contact the Entertainment Commission Enforcement Team at entertainment.enforcement@sfgov.org. 

Decibel readings for amplified sound are typically done with two different measurements: dBA and dBC. These are also called A-weighted (dBA) and C-weighted (dBC) decibels. They both measure sound pressure level, but in order for decibel measurements to correspond to perceived loudness, different frequency weights are used (ex. dBA and dBC). Using different weights accounts for the high and low frequencies that the human ear is less sensitive to.

Oftentimes, sound pressure level is measured using A-weighted decibel limits. In theory, this is supposed to be a realistic representation of human hearing since our ears are more sensitive to midrange frequencies. This is why it is often used as a standard.

However, A-weighted decibel readings only work when sound is at lower volumes and do not consider the loud low-end frequencies (bass) that occur during performances with amplified sound. C-weighted measurements include a wider range of frequencies. When experiencing louder volumes, this is actually a closer representation of human hearing. 

To ensure sound limits are appropriate for each unique space, both A-weighted frequencies and C-weighted frequencies may be listed in the required sound limits in the entertainment permit. 

Ambient sound can be defined as background noise of any given outdoor environment. Ambient sound measurements are used as a point of reference when studying a separate intrusive sound source. The Entertainment Commission uses a 10-minute decibel measurement to determine an average value of the consistent background noises in the immediate area. These ambient noises often include, but are not limited to, traffic sounds, people, and ventilation systems. 

Sample Handheld Decibel Meters

• Tadeto SL720
• Protmex PT6708 Sound Level Meter
• Grainger EXTECH, General Purpose Sound Level Meter

Sample Smartphone App Decibel Meters
 

• For iPhone (iOS): 
  
  NIOSH Sound Level Meter.  Free app. It is capable of measuring both A and C weighted frequencies. Includes live readouts and logging of dBA and dBC. iOS only.
   
• For Android and iPhone (iOS):
  
  Decibel X. Paid subscription required. Measures all weights needed. Has a camera-based logging function which is useful for proof of monitoring. This app has the most features after in-app purchases and can be calibrated with EC meters.