Amplified music rules in San Mateo County, CA — also called sound permit, PA system, or live music ordinances — set decibel limits, time-of-day restrictions, and when permits are required.
Amplified music in unincorporated San Mateo County is regulated by County Code Chapter 4.88 Noise Control, which caps exterior noise at 55-75 dBA daytime and 50-70 dBA nighttime at neighboring residential property lines. Outdoor events with amplified sound require a Special Events Permit from the Sheriff and/or Planning Department, and operators must comply with CEQA noise analysis for new entertainment venues.
County Code §4.88.330 prohibits any person from creating exterior noise exceeding the cumulative-duration limits in Table I at any single-family or multi-family residence, school, hospital, church, or public library. During daytime (7 AM-10 PM) limits are 55 dBA for 30+ minutes/hour rising to 75 dBA for 1 minute/hour; nighttime (10 PM-7 AM) drops 5 dBA across the board. §4.88.350 also prohibits any unreasonably loud, unnecessary, or unusual noise regardless of measured level. §4.88.360 exempts authorized public events and permitted activities. Large outdoor events and amplified gatherings on private property in unincorporated areas typically require a Special Events Permit; coastal-zone events may also need a Coastal Development Permit. Live entertainment at commercial venues is controlled through conditional use permit (CUP) conditions, which include decibel caps and sound-system orientation requirements. CEQA review applies to new entertainment uses.
§4.88.330 dBA exceedance: infraction $100/$200/$500 per §4.88.390. §4.88.350 disturbing the peace: misdemeanor possible under Penal Code §415. Unpermitted event amplification: permit revocation, stop-event order, daily fines.
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