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Let Freedom Ring…Loudly


It’s a calm July evening in New England, and you’ve just finished setting up an outdoor picnic with family and friends. There is probably some light conversation, minimal music being played, and maybe some distant sounds of a highway or wind through the trees. It’s a weeknight, but it’s calm and restful enough to feel fine staying out a little later than usual. All of a sudden:


Sound interrupts all conversation and demands everyone’s attention in the immediate area. Anyone dozing off is now firmly awake. You can feel the rumble in your body, and it is impossible to ignore. Any common noise control ordinance in the United States has just been violated. However, you’re probably not rushing to the phone to call your local noise complaint hotline or investigating the source of the sound. It’s Independence Day, and you likely know exactly where the sound is coming from, and you’re likely starting to applaud and smile.


If you’re like me, you probably have a great time at the fireworks, but the same sounds in your home or office would probably be an immediate and severe source of annoyance. Even if you weren’t trying to focus or converse, the same sounds over time would likely cause a major nuisance and source of stress in your life. So the question becomes, why are loud sounds so obtrusive at some times, and so enjoyed at others? For an answer, it’s interesting to turn to the natural sounds of the outdoors.

The National Park Services conduct acoustical surveys at various national parks in the United States attempting to define and quantify a measure of serenity at these parks. Serenity is defined as “the state of being calm, peaceful, and untroubled”. A fantastic feeling, to be sure, but the circumstances that inspire such a state are complicated and have a lot do with all of our senses, especially our auditory senses.

A consistent finding of such studies is that the measurement of a sound level alone is a poor indicator of the serenity of a place, even in a protected natural environment. The Grand Canyon in Arizona has some of the quietest outdoor sound levels in the United States, sometimes reaching levels below the human threshold of hearing. However, patrons surveyed did not always consider it as serene as possible. Despite the incredibly quiet sounds, barely audible helicopters in the distance break the spell and snapped visitors out of the immersive majesty of the landscape.

In contrast, a clearing at the base of a large waterfall in Yellowstone National Park was surveyed to be one of the most serene places in the entire country. However, sound levels here are loud enough such that prolonged exposure would cause hearing damage, and significantly exceeded levels nearby to some of the most populated highways and airports in the United States. Despite the incredible din, you will likely find hikers, swimmers, and meditators nearby.

It is our opinion that feelings of serenity don’t have much do to directly with the level or character of noise at all. But serenity has a lot to do with what people are expecting to hear. When you’re in the desert with nothing living around you as far as you can see, the barely audible sound of a helicopter can hurt the solitude. When you approach a gigantic waterfall and can hear the roar steadily increasing for miles, the serenity upon reaching it can take the breath away.


Similarly, you wouldn’t be entirely surprised to experience the earth shaking, low boom of an explosion when you’re at a fireworks show, and you’re probably fine with some momentary interruptions in speech and sleep. However, loud unexpected sound levels, whether from fireworks, the roar of a generator or rooftop HVAC unit, or the hum of an electrical transformer, probably don’t contribute positively to your personal serenity while trying to sleep at night with your windows open.

As acoustical consultants, we design our projects to meet the design goals and criteria defined by federal, state, and local codes and statutes which apply to many of our projects. However, we look at these published criteria in many cases as the bare minimum design goal. It is our hope that we are able to consult our clients to design systems which go much further than that.

Acentech’s Noise and Vibration Group is currently working with a long-standing client to install an electrical utility transformer at an existing substation in a densely populated residential area. The project is designed to meet criteria which are specified by the local municipality and state agencies which oversee the project. However, as our colleague Mike Bahtiarian discussed in his recent blog post, those criteria alone may not represent accurately all of the acoustical elements of a project such as for a transformer, which produces some predictably tonal (and annoying) sounds. We are utilizing research on these machines, started by Bolt Beranek & Newman (from which Acentech was founded) in 1977 and continually improved until the present day, to ensure that the sounds of this project are not obtrusive to the quiet existing nighttime sounds. Our goal for this project is not just to design a project that is legally permitted, but rather one that improves the quality of life for residents, without harming the serenity of others where they live and work.

From a design perspective, we are in a constant state of balancing the feasibility and cost-effectiveness of a project design for our clients with the acoustical environments and expectations of all those that live nearby. In many cases, this means that we are designing buildings, products, and mechanical systems to produce characteristics of sound that are congruent with the expectations of the listener to the best of our ability, and we plan to continue our reputation in that respect.

From everyone at Acentech, we hope you have a safe and happy holiday weekend this July. And most importantly, that you hear some of the loudest fireworks around, and find that despite the noise, you are in a state of serenity.