A successful MRI installation requires careful coordination of design and construction disciplines to produce a noise isolation result satisfying the medical staff and their need for low distraction in the work environment. One of Seattle’s largest medical centers recently constructed a new facility designed to meet stringent requirements for its second floor location, chiefly that sound levels during MRI operation were required to be less than 34 dBA at any adjacent staff area. With separate clinics on the floors above and below the MRI, sound isolation details at perimeter beams, area partitioning, and resilient fastening methods were all important to achieving the noise goal. Design details will be presented, along with measurements of MRI noise reduction spectra collected after completion of the project, and comparison will be made with predicted performance of the architectural assemblies. Vibration isolation was important to the MRI operation. Vibration measurements will also be presented and discussed relative to the MRI manufacturer’s design criteria.
A model of the auditory process is proposed for performing singers, which incorporates the added signal from bone conduction, as well as the psychological distance for subjective preference of the performer from the acoustic sound field of the stage. The explanatory power of previous scientific studies of vocal stage acoustics has been limited by a lack of an underlying theory of performer preference. Ando’s theory, using the autocorrelation function (ACF) for parametrizing temporal factors, was applied to interpretation of singer sound field preference determined by the pair comparison method. Melisma style singing (no lyrics) was shown to increase the preferred delay time of reflections from a mean of 14 ms with lyrics to 23 ms without (p<0.05). The extent of the shift in preferred time delay was shown to be directly related to minima of the effective duration of the running ACF, (τe)min, calculated from each singer’s voice. Voice matching experiments for singers demonstrated a strong overestimate of the voice outside the head compared with the singer’s own voice (22.4 dB overestimate, p<0.01). Individual singer melisma singing delay preferences were compared for “ah” versus “hum” syllables, and the increased delay preference (41 ms) was shown to be correlated with (τe)min (r2<0.68, p<0.01). When the proposed bone conduction model was applied, using the measured overestimate of sound level of the singer’s own voice for each singer (9.9 dB mean overestimate difference between “ah” and “hum,” p<0.01), the relationship of singer preference to (τe)min was improved (r2=0.97, p<0.01).
Thesis advisor: Yoichi Ando
Copies of this thesis are available from the author by inquiry at BRC Acoustics, 1741 First Avenue South, Seattle, WA 98134 USA. E-mail address: dnoson@brcacoustics.com
A computational technique has been developed to calculate and display, in two dimensions, wave fronts from a point source reflected in rooms of variable shape. The reflections are generated in a series of time frames, generally at 10-ms intervals, for both a plan and section of the room. The technique calculates reflections from re-entrant surfaces such as balconies and suspended ceiling panels, and it includes variation in sound intensity and surface absorption. Rapid changes may be made in room shape and source location. Visual estimates can be quickly made of intensity distribution and arrival time of early reflections. The method has been used to examine some acoustical qualities of existing auditoriums, to evaluate the effects of remodeling room shapes, and to demonstrate acoustic defects.
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