Noise surveys and noise assessments: when you need one

Updated 24 October 2026

Modeled estimates for general information only — not measurements, not a guarantee, and not for legal, medical or real-estate decisions.

A noise survey measures sound at a place with calibrated instruments. A noise assessment judges existing or expected noise against a rule or standard, usually in a report by an acoustical consultant. In California, CEQA’s checklist asks about noise, so a project under environmental review may need one. Quiet LA is a model, not a survey.

Official pages and directories linked below were checked on 23 October 2026. Quiet LA does not endorse, rate or rank any consultant, firm or directory.

What is a noise survey?

A noise survey is a set of sound measurements taken at chosen places and times. Caltrans’ Technical Noise Supplement, written for highway projects, lists the reasons to measure: to find ambient and background levels, to validate or calibrate a prediction model, to record construction noise, to check how well a noise barrier performs, and for special studies. It also covers where to place the microphone, when to measure, how long, how many times, which instruments to use and which weather rules to follow.

What a survey tells you is what the instruments recorded at that site, in that period, in those conditions. That is its strength and its limit: it does not tell you about the next street or a different season.

What is a noise assessment?

A noise assessment, sometimes called a noise study or noise impact assessment, is an analysis. It states the existing noise, predicts the noise a project or a source would add, and compares the result with the criteria that apply, such as a local noise ordinance or a general plan. It may rest on a survey, on a model or on both, and it is written up for the agency that asked for it. Caltrans publishes its own procedure for these studies on highway projects, the Traffic Noise Analysis Protocol.

How do environmental and construction noise assessments work in California?

The California Environmental Quality Act (CEQA) reviews the environmental effects of projects. Its Appendix G checklist, a sample form for an initial study, has a Noise section with three questions. They ask whether a project would generate a substantial temporary or permanent increase in ambient noise levels in excess of standards in the local general plan or noise ordinance or of other agencies; whether it would generate excessive groundborne vibration or noise; and, near an airport or airstrip, whether it would expose people to excessive noise. The form says its questions are meant to encourage thoughtful assessment and do not necessarily represent thresholds of significance, so each agency decides what counts.

Outside the United States the same idea is often called an environmental impact assessment (EIA). In California the review is CEQA, and the noise part of it is usually the environmental noise assessment a consultant prepares. The City of Los Angeles has published a paper on how it assesses construction noise under CEQA, in which it notes that its municipal code limits construction hours and, within 500 feet of a residential zone, construction machinery to 75 dBA at 50 feet. The hours and rules are on our noise ordinance and construction hours page.

General plans have a noise element too. The state’s General Plan Guidelines say noise elements use either CNEL or Ldn; see what CNEL means.

What about industrial and residential noise surveys?

An industrial noise survey or assessment looks at noise from a facility, such as equipment, trucks and processes, at its property line or at nearby homes. Quiet LA does not model factories and rail yards as sources of their own, so it has nothing to say about them. A residential noise survey is a measurement at a home or a lot, taken to document the sound there. In both cases the evidence is the measurement, and the map cannot stand in for it.

How is a noise survey different from a modeled noise map?

At a single address the map is typically about 6 dB off, higher or lower. See Limits and How it’s made.

When do you need a professional noise survey?

• When the agency reviewing a project, permit or complaint asks for a noise study. The agency decides what it needs; ask it for its requirements before hiring anyone.
• When you need a measured level at a particular place and time, such as a site next to a business or a freeway.
• When the result will be used for a legal, medical or real-estate purpose. Quiet LA is not for those, and nothing here is legal or medical advice.

A map can help before a survey. Look up the address to see which modeled sources are near it, such as a freeway, a rail line or an airport, and note the data release date. That is background to bring to a consultant, not evidence.

Look up an address on the map

Where can I find official guidance and consultants?

Official guidance: the CEQA Guidelines and Appendix G, the state’s General Plan Guidelines on noise elements, Caltrans’ Technical Noise Supplement and Traffic Noise Analysis Protocol, and your city or county planning department for the rules that apply to your site. They are linked under Sources.

Directories: two professional bodies keep public directories, the National Council of Acoustical Consultants (NCAC) and the Institute of Noise Control Engineering (INCE-USA, board-certified members). They are listed as places to search. Quiet LA has no relationship with them or with any consultant and does not recommend one.

Need a noise report for a property or a project? Quiet LA does not offer one today. If you would use one, email hello@quietlamap.com and tell us what you need.