Posts Tagged ‘noise’

A Book About Noise

Tuesday, October 26th, 2010

by Nick Miller

In early 2007, I received an invite to the Noise Pollution Clearing House 10th Anniversary celebration.  Well, ok, no marketing possibility there, but Les Blomberg has been nice enough to me to keep me apprised of his latest projects, and send interesting people my way; plus, I noted that the celebration was to be held in Bill Moyer’s New York apartment.  Sign me up.  A real New York experience!

Arriving there via Acela through Penn Station and a cab uptown, the doorman directed me to the elevator and the operator who took me to the Moyers’ apartment.  Les led me through two crowed rooms and introduced me to a gentleman named Garret Keizer.  Garret told me he was writing a book about noise, and started asking me questions about what I do, while scribbling notes on a little pad.  That meeting translated into many phone calls, many emails, a visit to HMMH to interview a half dozen of us who have been in the noise business for many years, and dinner at my house with me, my wife Andrea, Doug Barrett and Diana Duffy. Garret’s book came out last spring and late this summer, Noise Control Engineering published a review I had written of the book:

  • The Unwanted Sound of Everything we Want, A Book about Noise
  • Garret Keizer
  • Public Affairs, Perseus Books Group, New York, 400pp, 27.95 USD – Hardcover, ISBN 978-1586485528

Garret Keizer’s first sentence gave me confidence that I was starting a book that would not be a straight polemic about the evils of noise and the wonders of quiet: “Noise is not the most important problem in the world.”  And so it is not, but with Garret’s relentless research into history, countless interviews with the makers, receivers and analyzers of noise, and synthesis of all, noise provides a window on culture, politics, power and weakness.  He goes on that noise is a “weak” issue in that it affects the weak, and if you complain about it, you’re often considered weak – a “complainer” who can’t deal with the way the world works.  But, he warns, “…be wary of drawing pat moral analogies between noise and evil, quiet and good.”  Ted Bundy was a “quiet and helpful tenant.”

Well, that last is a bit extreme, perhaps, but Garret throws out zingers from time to time and made me think – a lot.  In considering America’s influence on other cultures, has it ever occurred to you that a “…culture attempting to imitate America rarely grows quieter?”  And every few pages, I found myself stopping to reflect on a linkage he’d just made.  But don’t pigeon-hole Garret; he admits he loves midtown Manhattan, his chain saw, and the Rolling Stones.

I suspect a lot of us are like Garret.  We love our appliances, but want to get away from them once in a while.  Which leads to a sad truth that he raises in many ways: the poor and disadvantaged of the modern (industrialized or industrializing) world can’t get away from the noise.  My wife and I lived briefly in a rather noisy suburban apartment complex, but we could get away on weekends to the pastoral quiet of York County, PA.  I can imagine there are many people living in tight quarters where the noise never stops, and there’s no going up the country for a quiet vacation.

Scale Modeling for Shut-ins

Thursday, April 1st, 2010

by Doug Barrett

Not so long ago (OK, I’m talking about the 1970s and 1980s, maybe that was a long time ago!) acousticians sometimes had to build real 3-D models. Computer models today can account for shielding provided by terrain and structures, reflections off of and diffraction over and around obstacles, and acoustical impedance of different ground types. But just a couple of decades ago, these calculations were beyond the reach of the best computer models, and acousticians sometimes resorted to constructing actual scale models. These scale models would include buildings and other objects all constructed to scale, much like an architect’s model, but also would include microphones at the receiver locations and artificial noise sources.

Acoustical Scale Model Study (1979)

Acoustical Scale Model Study (1979)

Building a scale model of a house or a street is one thing, but acousticians also had to deal with creating properly-scaled sound waves. For example, one may have been interested in modeling 500-Hz traffic noise which, in the real world, has a wavelength of about two feet. However, in a 1:24 scale model (one inch = two feet), one had to use an artificial noise source with a wavelength of about one inch to model 500-Hz sound. To have a one-inch wavelength, the artificial noise source would need to generate a frequency of about 12,000 Hz.

Acoustical Scale Model Study (1979)

Acoustical Scale Model Study (1979)

Now stick with me, because I promise this all ties-in, but a few weeks ago, I came down with pneumonia and spent a lot of time flat on my back. One day, while recuperating, I was resting on my living room couch. Every now and then I would cough, and each time – almost exactly concurrent with my cough – I heard a faint ringing sound, not unlike a gong sounding in a distant room. At first I attributed this either to my fever or too much cough medicine, but upon reflection, another explanation occurred to me.

To digress for a moment, individuals living close to airports, particularly in locations alongside a runway or behind the start-of-takeoff roll for departing aircraft, sometimes complain of rattling windows or other loose objects, such as pictures on walls or light objects on shelves. The rattling is caused when low-frequency noise (LFN) generated by departing jet aircraft excites, or shakes, the homes. Sometimes the LFN may be difficult to hear directly (our ears do not hear LFN as well as they do higher frequencies), but the wavelengths may be about the same length as major elements of a house. For example, at 50 Hz, the wavelength is approximately 20 feet. When this occurs, LFN can cause elements of the house to resonate, or vibrate, at that particular frequency. This, in turn, causes windows and other loose objects to rattle.

Mobile

Mobile

Getting back to my coughs and the mystery ringing noise — we happen to have a vaguely Calderesque mobile hanging in our living room directly above the couch where I was resting. The entire mobile spans a few feet and consists of nylon fabric panels stretched across wire frames. The largest panels, which are about six to eight inches across, would resonate at roughly 1,500 to 2,000 Hz. One possible explanation is that this also was the frequency range of my coughing. Now imagine that these six- to eight-inch panels represent walls of a 12- to 16-foot wide room built for a 1:24 scale model study. Keeping with the 1:24 scaling comparison, my coughs would scale down to about 60 to 80 Hz, not unlike LFN generated by a jet aircraft. So maybe it wasn’t too much cough medicine after all. Perhaps my coughing had created a low-budget scale model for LFN rattle effects!

That Crackly Sound

Friday, December 18th, 2009

by Doug Barrett

Four more days to go until the longest night of the year and it’s starting to get cold here in New England!  Last night’s low was around 14 degrees F. in Boston, and last weekend, up in New Hampshire, it was colder still.  My fabulous spouse and I live about five miles from Boston’s Logan International Airport, and depending on which way the wind is blowing, sometimes we are treated to a steady stream of departing aircraft.  The other day, after a particularly cold morning, she asked why the aircraft sound different in cold weather – both louder and “crackly” as she put it.

The short answer is that it’s complicated.  As for the long answer, I suspect that she’s noticing the dependence of atmospheric absorption of sound on temperature and relative humidity.  Leo Beranek said it better than I could: “energy is extracted from a sound wave by rotational and vibration relaxation of the oxygen molecules in the air.  The vapor content of the air determines the time constant of the vibration relaxation… In addition, this ‘molecular absorption’ depends in a major way on temperature.” (Leo L. Beranek, Noise and Vibration Control, McGraw Hill, 1971, P.170)

It’s especially interesting that at any particular relative humidity, molecular absorption peaks at a given temperature.  In other words, one can’t simply make a generalization that sound “travels” better when it’s cold outside.  Adding to the complexity, the effects of temperature and humidity vary dramatically depending upon the frequency of the sound.  In general, wider variations exist at higher frequencies.  Notice on the first figure below (reproduced from Beranek) that there is relatively little sensitivity to temperature or humidity at 500 Hz – only about 3 dB per 1,000 feet across a temperature range of 100 degrees F.  In contrast, at 8 kHZ, the second figure shows a whopping variation of up to 50 dB per 1,000 feet over the same temperature range.

Atmospheric Absorption for aircraft-to-ground propagation (500 Hz, 1,000 Hz, 2,000 Hz)

Atmospheric Absorption for aircraft-to-ground propagation (500 Hz, 1,000 Hz, 2,000 Hz)

Atmospheric Absorption for aircraft-to-ground propagation (8,000 Hz)

Atmospheric Absorption for aircraft-to-ground propagation (8,000 Hz)

Regarding the “crackly” sound, here are some molecular absorption values that I pulled from the figures: At 500 Hz to 1 kHZ (approximately speech frequencies), one expects molecular absorption at a rate of about 1 to 2 dB per 1,000 feet of propagation on either a pleasant summer morning (60 degrees F. and 50% RH) or on a nippy winter morning (10 degrees F. and 20% RH).  That is to say, at lower to mid-range frequencies, there’s not a big seasonal difference.  At 8 kHZ, however, one expects absorption at a rate of about 20 dB per 1,000 feet with the summer conditions, but only about 6 dB per 1,000 feet with the winter conditions.  Less high-frequency absorption with cold, dry weather equals more “crackly” sounding!

ACI-NA Rocks Austin!

Thursday, October 15th, 2009

by Mary Ellen Eagan

I’ve just returned from the ACI-NA Annual Conference in Austin, Texas, the Live Music Capital of the World, which offers me an opportunity to talk about temporary threshold shift.  TTS occurs when one is exposed to significant noise levels for a temporary period of time – listening to the Eggmen at Maggie Mae’s for several hours Monday night, for example.  A study in the 1980’s measured the temporary hearing loss of volunteer subjects exposed to a Bruce Springsteen concert.  The average sound exposure during the four-hour concert was 100 dBA.  The subjects’ hearing was tested 30 minutes and 16 hours after the end of the concert; immediately after the concert 5 of the 6 subjects experienced significant threshold shift (<50 dB) predominantly in the 4-8 KHz range; by 16 hours after the concert ended, hearing had returned to normal in all of the subjects.  I don’t know about the rest of you who were there on Monday, but my ears are still ringing.  However, I wouldn’t trade it for the world!

Other excitement at the conference included:

Look for the Environmental Affairs Seminar presentations to be posted soon on the ACI-NA website.

I’m looking forward to the next Environmental Affairs Committee Conference in San Antonio, April 13-16, 2010

Airport Noise Mitigation Discussed in Boca Raton, Florida

Friday, October 9th, 2009

by Gene Reindel

The Boca Raton Airport Authority hosted the ninth annual AAAE Airport Noise Mitigation Symposium (ANMS), which turned out to be one of the best nine years.  Kim Singer, Boca Raton Airport Authority Public Affairs and ANMS Chair for 2009, provided venue in Delray Beach that will be nearly impossible to beat, and scheduled a tour of their recently completed sound insulation program which highlighted the designs required to meet the recently updated codes in south Florida.

In between the fun, the ANMS provided attendees with applicable information for implementing a successful airport sound insulation or land acquisition program as part of their noise mitigation.  Topics ranged from shrinking noise contours to noise programs outside the 65 DNL on the noise side, to dealing with homeowners and green technologies on the implementation side, to implementing land acquisition programs and disposing of land acquired for noise purposes.  The most interesting session occurred when contractors and suppliers identified issues prevalent in sound insulation programs around the country and sought out solutions from the roundtable members and the audience.  This session was successful at keeping the audience engaged throughout the duration, much akin to the Merv Griffin Show – okay, now I am dating myself.

I feel compelled to recognize Eric Raboin from the Jones Payne Group in Boston for chairing the ANMS Agenda Committee and for delivering the successful and compelling agenda for the conference attendees.  Due to the economy at airports, the session moderators had a difficult time finding speakers, but through perseverance of the moderators and the unwavering support from Mr. Raboin, all the sessions were a success.  At the ANMS Planning Committee debrief after the Symposium concluded, the entire Committee in attendance thanked Mr. Raboin for his dedication and service with round of applause. 

For airports in the throws of implementing a sound insulation programs and/or a land acquisition program, or for those airports beginning or considering to implement such a program, the ANMS is a must attend event.  The social networking with peers in similar programs across the country is undeniably beyond compare.  You will get more information and tools to help ensure a successful program at your airport in two days at the ANMS than you would otherwise obtain in a year of planning.  And the connections you make at the ANMS will remain intact as you continue throughout the year in your programs.

I am already looking forward to the 10th annual ANMS, which will be hosted by San Francisco International Airport in early October, 2010.  Mark your calendars for October 3, 4, and 5, 1010.  I hope to see you in San Francisco.