Helping Our Peninsula's Environment


Maximum Noise vs Average Noise (CNEL)

Copyright 2004 David Dilworth & HOPE

HOPE - Helping Our Peninsula's Environment

Box 1495, Carmel, CA 93921 [email protected]

831/ 624-6500

Sarah Hardgrave

Monterey County General Plan Update

Salinas, CA May 2, 2003


Hearing Damage and Noise Pollution - Maximum Noise vs CNEL

For the County General Plan Update


Dear Sarah,

We appreciate the amount of work you and your staff have put into our General Plan Update, This responds to a Mestre Greve, Associates letter to the County of Sept 11, 2002 favoring average noise levels (Community Noise Equivalent Levels or "CNEL" and Level Day/Night or "Ldn") and completely ignoring our reasonable request to consider and incorporate peak or maximum noise levels (Lmax) in our General Plan.

We realize you have an overwhelming task with this Update, but we must respond as this is a very important health and quality of life issue.



The renowned humorist and riverboat pilot Mark Twain once observed --


"I never cross a river when I only know its average depth is six inches."


Twain's comment vividly illustrates how the use of a bald average can drown you.



  • People do not often complain about noise at CNEL or Ldn levels as measured and mapped for General Plans.


  • People specifically complain about the loudest or "peak" noises -- those which significantly exceed CNEL and Ldn levels.


  • Why? Because CNEL and Ldn are average noise levels - not peak levels.


An analogy using traffic flow goes like this - The "CNEL or Ldn" of traffic on Highway 1 past Carmel is about 20,000 cars per day. What is missing from this is that in late night only 5 to 10 cars travel this road per hour, while rush hour traffic is 200 to 400 times as busy and includes a proportional increase in air pollution.

This is why Traffic engineers use Peak Traffic Volumes to determine thresholds of traffic impact significance. Peak traffic volume is analogous to peak or maximum noise levels.



Hearing Damage

Noise is now recognized as a "serious health hazard" - not merely a nuisance (World Health Organization Feb 2001).


  • It is the loudest noises, the maximum noise levels, which do the most irreversible hearing damage.


Maximum Noise (Lmax)

Instead of measuring averages, Maximum Noise Level (Lmax) measures maximum noise levels - the noise levels that people do complain about and which cause the most hearing damage.


Single Event Noise Exposure Levels (SENEL)

Instead of measuring day-long noise averages, Single Event Noise Exposure Levels (SENEL) measures the average noise level of a single aircraft overflight.


Extraordinary Claims

Your Consultant wrote "...[that] Ldn ignore noise levels is simply wrong."

It is rather astounding to have a so-called expert call a valid point wrong by using a false assertion and a misleading and faulty analysis.

We never claimed Ldn ignores anything. You will not find the word "ignore" in our comments. What we assert is that Ldn and CNEL cannot distinguish between two otherwise similar neighborhoods where one endures short term loud ("impulse") noises such as dog barking, gunfire or car horns. This can also be due to using CNEL or Ldn instruments (i.e. analog) which cannot respond rapidly enough to detect short term noises.

We further assert that CNEL and Ldn will not adequately recognize harmful and disturbing regular, predictable leaf blower, lawnmower or chainsaw noise - because those noises will most often occur when there is no CNEL or Ldn monitoring.


Consultant Qualifications Lacking

You should only use noise consultants who are members of the professional organization that deals specifically with problems in noise - INCE the Institute of Noise Control Engineering. Membership in INCE is gained by passing the written examination and submitting evidence of education and experience in the field. Just like you and I - your consultants are not members.

Membership is important because your consultants would not receive copies of the international publication "Noise Control Engineering Journal" which contains current information about the field.

Unlike your consultant, I do not make my living purely as a noise consultant, but in the course of compiling and editing for publication the world's largest database of quantified environmental impacts, I have access to, understand and can apply the best available science studies and world experts in many fields - specifically including noise.

The points you force us to raise here are simply standard noise science, with which any member of Institute of Noise Control Engineering would be comfortably familiar.



The Consultant's analysis and calculations are appallingly misleading because of their mistaken assumptions.

First, one never calculates a CNEL or Ldn (as your consultant does) except for theory. CNEL and Ldn are cumulative measurements of the real world, which cannot be calculated - only measured.

Next, the noise from a rifle shot does not last for "one second" as your "expert" asserts, nor is it a constant noise level. Gunshot noise resembles a spike reaching an instantaneous peak - not a square wave. This peak reaches some 140 to 160 dBA and lasts for perhaps tens of milliseconds - not 1,000 milliseconds (one second).

This means the calculations they offered are at least grossly, probably three times, too high on the sound power of a gunshot alone. This correction then significantly reduces the Ldn they calculated, making their defense of Ldn at best invalid, at worst weak to meaningless.


Ldn -- not CNEL !?!

Your consultant claims "Ldn was used because ... it correlates best with people's perception and sensitivity to the noise environment."

This is in sharp contrast to how California is well respected worldwide for using CNEL as a big improvement over Ldn in recognizing noise annoyance and complaints.

Why in the world would we use anything less - such as the weaker Ldn? This consultant appears unfamiliar with standard noise science. Don't we deserve at least the same minimum quality noise protection of the rest of California?

Further, Ldn and even CNEL have been widely recognized as flawed in articles for at least the past 20 years.



State General Plan Guidelines do require "Noise contours shall be shown for all of these sources and stated in terms of community noise equivalent level (CNEL) or day-night average level (Ldn)."

The legislature intended this to require some minimal recognition of noise problems. They did not need to anticipate recognition of an array of noise impact facets (i.e. maximum-noise or noise spectrum) because that is covered by CEQA and responsible professionals.

Contrary to your consultant's implication, the legislature did not intend that other methods of noise impacts should be ignored.




CEQA mandates the recognition of all noise problems most particularly those which generate complaints. Your consultant should have informed you of the litigation risk you raise by not addressing maximum noise problems. A recent court case found CNEL "inappropriately excluded consideration of [noise] impacts."


In Berkeley Keep Jets Over the Bay Committee v. Board of Port Commissioners of the City of Oakland, 91 Cal.App.4th 1344 (2001), the First District Court of Appeal invalidated the Port of Oakland's certification of an EIR for the Airport Development Plan.


"The court found that the EIR had failed to adequately address the noise impacts from nighttime air cargo operations. Specifically, the court made clear that the EIR's reliance on the CNEL metric as the sole criterion to evaluate the significance of the project's noise impacts inappropriately excluded consideration of the potential sleep disturbance impacts on area residents resulting from nighttime flights. In reaching this conclusion, the court acknowledged the expert opinion that supported the need for this noise analysis, public concern about nighttime noise impacts, and the CEQA standards of significance, which recognize a site-sensitive threshold for evaluating noise impacts."


Perhaps you may legally ignore maximum noise problems in the General Plan, but the CEQA document for the General Plan may not ignore maximum noise problems. Having expert advice showing the significant difference between the two noise contours should impel you as a professional to add the better method in the General Plan.


INCLUDE Lmax Contour Maps along with CNEL

We respectfully request you include noise contour maps of Lmax exceeding 45 dBA in the General Plan (along with CNEL maps) so the EIR tail does not have to wag the General Plan dog.


INCLUDE SENEL Contour Maps along with Lmax Contour Maps and CNEL

We respectfully request you include noise contour maps of Single Event Noise Exposure Levels (SENEL) exceeding 45 dBA in the General Plan (along with Lmax and CNEL maps) so the EIR tail does not have to wag the General Plan dog.


Why ignore the World's Best advice - especially when it is free?

However qualified your noise consultant may or may not be, and whatever you are paying them - you have been offered and neglected the free services of one of the world's most highly qualified acousticians, Dr. Herman Medwin Ph.D.

Dr. Medwin, is a Fellow, a Gold Medalist, and Past President of the Acoustical Society of America. He is also a co-author of two graduate textbooks on acoustics, one of which sold over 10,000 copies. As a retired Professor of the Naval Postgraduate School, Medwin continues to run a successful business as a world-renowned consultant in acoustics. He is a resident of Pebble Beach who has assisted the Monterey County Planning Department and other government agencies of the Monterey Peninsula, Pro-Bono, for the past 30 years.

Unlike Dr. Medwin, your consultants are not members of the Institute of Noise Control Engineering, INCE, the world-wide professional organization with head offices in the USA, whose members deal specifically with noise problems. Membership in INCE is awarded only after passing a professional test, and after submitting evidence of competence and experience in noise control.


Yet Dr. Medwin's free offer of world class expertise has been ignored.


I most respectfully urge you to contact Dr. Medwin.



David Dilworth


Copies sent to: Supervisor David Potter

Assemblyman John Laird

Senator Bruce McPherson

Monterey County Herald

Institute of Noise Control Engineering

International Association of Environmental Professionals


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831 / 624-6500 P.O. Box 1495, Carmel, CA 93921

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This Page Last Updated February 5, 2004

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