Mean third- octave levels were louder in the 125-Hz band (annual mean level of 96.0dB re 1μPa) than in the 63-Hz band (92.6dB re 1 μPa). Underwater sound was recorded for 30min h(-1) over the period June 2012 to November 2013 for a total of 435days. These levels are described for Falmouth Bay, UK, an active port at the entrance to the English Channel. This indicator is the yearly average sound level in third- octave bands with centre frequencies at 63Hz and 125Hz. The EU's Marine Strategy Framework Directive (MSFD) includes a specific indicator focused on this noise. Garrett, J K Blondel, Ph Godley, B J Pikesley, S K Witt, M J Johanning, LĬhronic low-frequency anthropogenic sound, such as shipping noise, may be negatively affecting marine life. Long-term underwater sound measurements in the shipping noise indicator bands 63Hz and 125Hz from the port of Falmouth Bay, UK. An ANOVA revealed significant effects (threshold range: -19 to -35 dB re 60 dB SRL). The independent variables were octave-band-filtering (bypassed, 0.25 - 2.0 kHz Fc) and reverberation time (0.2- 1.1 sec). The reverberation was produced and manipulated by 3-D audio modeling based on an actual room. (Technical Monitor)Īuditory thresholds for 10 subjects were obtained for speech stimuli reverberation. Octave-Band Thresholds for Modeled Reverberant Fieldsīegault, Durand R. These results indicate that noise of moderate intensity and duration is sufficient to induce TTS under water in these pinniped species. Control sessions in which the subjects completed a simulated noise exposure produced shifts that were significantly smaller than those observed following noise exposure. Recovery to baseline threshold levels was observed in test sessions conducted within 24 h of noise exposure. Following exposure, three of the subjects showed threshold shifts averaging 4.8 dB (Phoca), 4.9 dB (Zalophus), and 4.6 dB (Mirounga). Each subject was trained to dive into a noise field and remain stationed underwater during a noise-exposure period that lasted a total of 20-22 min. Test frequencies ranged from 100 Hz to 2000 Hz and octave-band exposure levels were approximately 60-75 dB SL (sensation level at center frequency). Additional thresholds were obtained following a 24-h recovery period. Pure-tone sound detection thresholds were obtained in water for one harbor seal (Phoca vitulina), two California sea lions (Zalophus californianus), and one northern elephant seal (Mirounga angustirostris) before and immediately following exposure to octave-band noise. Kastak, D Schusterman, R J Southall, B L Reichmuth, C J Underwater temporary threshold shift induced by octave-band noise in three species of pinniped. In the region of overlap (between 50 Hz and 200 Hz) the agreement was good. These curves were compared with the contours of equal noisiness of Kryter and Pearsons. Four contours of equal noisiness were developed for one-third octave bands, extending down to 25 Hz and ranging in intensity from approximately 58 db SPL to 86 db SPL. The thirty-two subjects used a method-of-adjustment technique, producing comparison- band intensities as noisy as standard bands centered at 100 Hz and 200 Hz with intensities of 60 db SPL and 72 db SPL. This study examined the relative noisiness of low frequency one-third octave bands of noise bounded by the bands centered at 25 Hz and 200 Hz, with intensities ranging from 50 db sound pressure level (SPL) to 95 db SPL. The Noisiness of Low-Frequency One-Third Octave Bands of Noise. A recommended prediction procedure is described for 1/3 octave band absorption coefficients. However, for many cases, the absorption for a finite band was nearly equal to the pure tone absorption at the center frequency of the band. For some of the cases considered, comparison with the extrapolation of ARP-866A showed a difference as large as a factor of 2. The results depended on spectrum shape, on filter type, and nonlinearly on propagation distance. Absorption of bands of noise was numerically computed by using the pure tone results. The resulting absorption was compared with that from a proposed procedure for computing sound absorption in still air. The absorption was measured by varying the transmitter receiver separation from 1 to 4 m and observing the decay of multiple reflections or change in amplitude of the first received burst. Special solid-dielectric capacitance transducers, one to generate bursts of sound waves and one to terminate the sound path and detect the tone bursts, were constructed to fit inside the tube. Pure tone sound absorption coefficients were measured at 1/12 octave intervals from 4 to 100 KHz at 5.5K temperature intervals between 255.4 and 310.9 K and at 10 percent relative humidity increments between 0 percent and saturation in a large cylindrical tube (i.d., 25.4 cm length, 4.8 m). Atmospheric absorption of high frequency noise and application to fractional- octave bands
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |