02223cam a2200397Ia 4500011449629MiAaHDL20141009010000.0m d cr bn ---auauacr cnu||||||||910821s1973 dcua b f000 0 eng dsdr-uiuc6405732(OCoLC)24267142ABCABCAD#UIUUTL521.A3525 no. 7230NAS 1.14:D-7230NASA-TN-D-7230Norum, Thomas D.Measured and calculated transmission losses of sound waves through a helium layer[electronic resource] /by Thomas D. Norum.Washington, D.C. :National Aeronautics and Space Administration ;[Springfield, Va. :For sale by the National Technical Information Service],1973.23 p. :ill. ;27 cm.NASA technical note ;NASA TN D-7230Prepared at Langley Research Center.Cover title.Bibliography: p. 14.An experiment was performed to measure the transmission losses of sound waves traversing an impedance layer. The sound emanated from a point source and the impedance layer was created by a low-speed helium jet. The transmission losses measured were of the order of 12 db for frequencies of the source between 4 and 12 kHz. These losses are greater than those predicted from analysis when the observer angle is less than about 35 deg, but less than those predicted for larger observer angles. The experimental results indicate that appreciable noise reductions can be realized for an observer shielded by an impedance layer, irrespective of his position relative to the source of sound.Mode of access: Internet.System requirements: Adobe Acrobat Reader.Mode of access: World Wide Web.Jet nozzlesNoise.Helium.Acoustic impedanceMaterialsTesting.Sound-waves.United States.National Aeronautics and Space Administration.Langley Research Center.01144962920101111113645.020141009010000.020141112165512.02025-01-02T19:06:47Z2025-01-02T18:30:02ZSDR-UIUCUNKNOWNloader.pl-003-020BKsdr-uiuc6405732uiugSDRUIUCuiug.30112106748780UIU6405732UIUUIUC20250102googleuiug.301121067487801973pdbibUS fed doc--NTIS: pubdate < 2020