ASA 158th Meeting - Hot Topics in Noise

Hot Topics in Noise

Nancy S. Timmerman, P.E. - nancy.timmerman@alum.mit.edu

Consultant in Acoustics and Noise Control

25 Upton Street
Boston, MA 02118-1609

Popular version of paper 3pID3
Presented Wednesday afternoon, October 28, 2009
158th ASA Meeting, San Antonio, TX

Once in a while, scientists talk about the newest things that they are doing so that others know what's going on. In this talk, the subject is noise, a term which, for most people, needs no translation. There are seven topics presented here. They will be discussed one at a time.

Community Noise and Vibration from Transportation:

Noise from transportation affects nearly everyone (Figures 1 - 4). The amount of noise which can be produced is regulated by (Federal) law. This noise can be reduced by home improvements (reducing the amount that gets in).

The Federal Aviation Administration (FAA) oversees airport noise studies. Their NextGEN program is working on making quieter aircraft. Aircraft noise exposure is still computed using the Integrated Noise Model (INM), and revision 7.0b was just released (this month). They are working toward having one modelling program to cover both air quality and noise (AEDT), to be available in 2010.

For highways, the state highway departments and turnpike authorities are responsible for addressing the community noise. Two ways to reduce this noise source are to put up barriers along the road (which, usually, blocks the view as well) and to use porous pavements (in warm climates). A recent medical study in Sweden has related high blood pressure with highway noise.

Sustainable Energy - Wind Turbines:

Sustainable energy is all the rage in all levels of the U.S. government. What is usually meant is not coal, oil, or natural gas (fossil fuels). Unfortunately, energy produced from solar panels and wind turbines is more expensive. Therefore, governments have "subsidized" them to encourage their development. Solar panels and wind turbines are thought to be "environmentally friendly".

It has been known for some time that neighbors of wind turbines sometimes complain about the noise (Figure 5). This is particularly true when they are in rural areas. Background sound levels it these areas are low, and nighttime levels of 35 dBA have caused complaints. The turbines produce a "swishing" sound which is very annoying. In order to avoid these problems, about a mile of buffer is needed around the turbines.

National Parks:

The National Park Service (NPS) has been working on the problem of maintaining the character of wilderness areas and their sounds since the early 1990's. The first studies came as a result of air tour operations in the Grand Canyon. It was found that the ability to hear the aircraft was key. This is at odds with the typical noise exposure criterion in use by the Federal Aviation Administration (FAA) for people around airports. A new standards effort has just been started (S3-SC1-WG4) on this topic under the direction of two scientists at the NPS.

Soundscapes:

The term "soundscape" is just like "landscape", but for sounds (Figures 6 - 9). It is used as a more positive alternative to the word "noise" to describe sounds an area, usually in a city. Recent work in this area have found that the absolute sound level is often less important than the viewpoint of the listener. The influences of the norms of society also play a role.

In addition to the "sound walks" which have occurred in recent years, a new workshop series has started to bring acoustics into the planning processes in cities. The first such workshop occurred in Portland, and another is possible in Baltimore.

"Green building" codes and standards:

For the first time since the LEED (U.S. Green Building) standards were introduced, credit can now be taken for acoustical design of schools and hospitals. The classroom standards currently allow for one credit for design similar to that in the national standard on classroom acoustics. (Figue 10)

The credit for hospitals is in the current revision of the green building document for hospitals (Figure 11). A national standard is in the works to go with it. Two credits are possible: one for speech privacy and one for ambient levels. The speech privacy criterion supports the idea that conversations between doctors and patients should not be easily overheard. The ambient level criterion is meant to provide a hospital interior that is quiet enough to be restful, which is not the case in many current designs.

Energy savings from noise control:

The sealing of sound leaks in an outside wall uses the same materials as strategies used for energy conservation, namely caulking and weatherstripping. In both cases, the best improvement is to use a solid material intervening between the inside and outside. Ratings of both acoustical performance (using the STC, sound transmission class) and infiltration (the amount of air which came in through the cracks) are available for doors with different degrees of treatment. Cost savings were determined for Boston, using fuel oil for heating (boiler efficiency of 80 percent) at $2.50 per gallon.

For each untreated door with an STC of 21 dB, the annual fuel usage for infiltration is $756. Reducing the crack sizes by half would increase the STC to 24 dB and reduce the fuel use to $378. For two types of treated doors, the STC improved to 42 dB, with a fuel usage of $23.30, and 44 dB, with fuel usage of $2.66 per year. Thus, depending on the initial condition of the door, cost savings range from $378 per year to $753 per year per door.

Hearing loss from personal music devices:

Over time, the listening of music has moved from portable "boom boxes" to Sony Walkmen to iPods and mp3 players today. While this has been good from the point of view of the people who listen to music which was not theirs, it has brought a new potential problem to light.

Several years ago, a medical doctor noticed that some teenage patients of his had developed the kind of hearing loss associated with working in factories all day. Careful research showed that the levels developed in the ear were 74 to 110 dBA (loud shouting to ear-splitting). This result has been repeated again and again in current research. The European Commission is studying whether to make a rule of requiring automatic volume control. The fact that people are subjecting themselves to this kind of sound when they are not working has made it harder to attribute hearing loss strictly to places of work.