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Two recent trends in the development and use of magnetic resonance imaging (MRI) equipment have created challenges for acoustical engineers: (1) the trend toward more powerful MRI machines with greater magnetic field strengths, and (2) the tendency of health care facilities to locate these machines, which were previously located in basements or on grade, on upper floors adjacent to (and in some cases above) other critical use areas. For newer, 3-T MRI machines, sound levels well over 100 dBA in the examination room are common. Along with these trends, some equipment manufacturers are now providing design recommendations to address the issues of airborne and structure-borne noise within hospitals and clinics. In addition, MRI manufacturers sometimes have strict requirements for acceptable levels of building vibration from other sources, to prevent potential image quality problems. This paper discusses experience gained during the course of addressing MRI-generated noise on several projects. Data for airborne sound levels measured inside MRI rooms and adjacent rooms and vibration levels measured below MRI units will be presented.

In 1993, the Tri-County Metropolitan Transportation District of Oregon (Tri-Met) began construction of the Westside Light Rail project in Portland, OR. The project included the construction of a 3-mile-long twin tunnel through the hillside west of downtown. The original plan called for the tunnels to be excavated from the east using a tunnel boring machine that was supposed to be quick and quiet. However, soon after excavation began, the composition of rock along the tunnel path began to cause problems for the boring machine. Excavation fell behind schedule. Tri-Mets contractor decided that a second excavation team needed to move from the west end of the tunnels toward the boring machine to ensure the project would stay on schedule. Tri-Met requested permission to allow the contractor to conduct 24-h blasting in the vicinity of residences to help catch up in the excavation phase. Daly-Standlee & Associates, Inc. (DSA) assisted in defining noise criteria that could be used to ensure blasting noise would be acceptable at residences and, once blasting began, DSA assisted in developing mitigation measures that could ensure the criteria were met. This paper presents the experience gained by the firm during the tunnel boring project.

This paper presents the results of tests conducted to determine the subjective response of human test subjects to vibration directed into the hand by means of a small diameter vibrating handle. For these tests individuals were exposed to a reference vibration level at 100 Hz and then were asked to adjust the vibration levels at other test frequencies until the same sensation as was perceived due to the reference vibration was produced. This resulted in equal sensation curves for the reference frequency and levels that were used. The effects of the selection of reference frequency, of the area of the hand into which the vibration was directed, and of the manner in which the vibrating handle was clasped upon the resulting equal sensation curves were discussed. A possible explanation of the physiological characteristics of the sensory receptors in the hand and arm and how they interact to produce the measured equal sensation curves is presented.

In early 2009, the Acoustical Society of America funded the development of materials that could be used to introduce urban planners and decision makers to the concept of using soundscaping as a tool in land-use planning. After several months of discussion among interested persons, a symposium outline was generated and speakers were solicited to develop materials that would address specific topics considered important in training urban planners. The materials were developed and first used at a symposium co-sponsored by the ASA and the City of Portland during the ASA May, 2009 meeting in Portland, Oregon. The materials were again presented at a symposium co-sponsored by the ASA and the City of Baltimore during the ASA April, 2010 meeting in Baltimore, Maryland and finally at a symposium co-sponsored by the ASA and the City of Seattle during the ASA May, 2011 meeting in Seattle, Washington. This paper presents a summary of the materials used at the three symposiums and discusses how the material can continue to be used as an ASA outreach event at future meetings around the country.