Thus, the damping structure without binding part would be more desirable to reduce the magnetic shield vibration. Both structures were effective, however the structure with binding part changed the eigen modes of the magnetic shield and the frequency properties of SEM image noise. As countermeasures, the damping structures with and without binding part were applied. With changing the acceleration voltage of the electron beam, it was shown that the vibration of the magnetic shield affected magnetically to the electron beam path. corresponded to those natural frequencies. We investigated the eigen mode shapes of the magnetic shield experimentally, and found out the frequency of the image noise measured with “Spot-beam analysis”.
The vibration of the electron beam path also causes SEM image noise. Not only the mechanical vibration but also electro-magnetic field influences the quality of SEM image. This paper addresses Scanning Electron Microscope (SEM). The measured intelligibility correlated quite well with a figure obtained by adding the value of background noise in decibels A‐scale to the NR expressed as STC. A simple but accurate speech‐intelligibility test was conducted at each site to relate speech privacy to background levels and NR's. Background‐noise levels from 34 to 46 dbA were measured, these being due almost entirely to air‐conditioning noise. NR's were strongly influenced by the type and location of return‐air plenum openings and ducted connections between rooms. NR values ranging from 24 to 48 STC were observed, the latter value being obtained with a ceiling of acoustical tile adhered to gypsum board. used to determine one‐number ratings of the measured NR curves. Measurements of NR and background noise were made in octave bands. The tests were made to determine typical noise‐reduction (NR) values between offices as found in present‐day construction.
Sound‐transmissionmeasurements were made in 15 pairs of occupied offices with suspended acoustical ceilings and continuous plenum in high‐rise buildings in several areas of the USA. It was evident that structural flanking was controlling the remaining sound reaching the offices. The resulting average level of four flushes was less than 40 dB in all offices though some individual flushes were slightly greater than 40 dB. The remaining walls were then modified similarly. A wall on one floor was modified by adding a layer of damped gypsum with successful results. Sound levels within the rest rooms were greater than 80 dB, and within the toilet stall of the loudest toilet?96 dB. Results were mostly in the range of 40 to 50. The building owner made changes including an improved wall on one of the seven affected floors and asked the author to repeat the measurements. A study by others documented some maximum A?weighted slow sound levels greater than 60 dB with most greater than 50 dB and recommended a limit of 40 dB. The toilets were a 1.2 gallon per flush model. An office building was experiencing loud toilet flushing noise in offices adjacent to the toilets.
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