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Flexural Vibration of Plates and Shells
Published in Dhanesh N. Manik, Vibro-Acoustics, 2017
Barrier materials are used to separate two spaces from any acoustic interaction and they prevent noise from moving from one space to another. For example, noise transmission between two rooms or from outside to inside is generally controlled by the material in between these spaces. Therefore, barrier materials are used as part of doors, windows, walls, roofs, and so on. We can say that sound absorbing materials (discussed in Chapter 8) are defined within a given space, and barrier materials are defined for sound transmission across two spaces. The capability of a barrier material to prevent sound transmission across two spaces can be defined by transmission loss.
Introduction
Published in Qiu Xiaojun, An Introduction to Virtual Sound Barriers, 2019
In general, the transmission loss through a porous layer depends upon the angle of incidence and is a function of material density, thickness, flow resistivity, and frequency. In the low-frequency range, the transmission loss of common porous layers is usually less than 20 dB, but can be greater than 20 dB in the high-frequency range. The transmission loss usually increases with the material density, thickness, flow resistivity, and frequency. Passive sound barriers usually use woods, steel sheets, bricks, or concrete blocks, whose transmission loss is generally greater than 20 dB.
Mathematical modelling of sound transmission loss (STL) in metallic and graphite based coatings
Published in Transactions of the IMF, 2022
G. E. Yalcin, H. Ergin Esen, M. Yagimli, E. Arca
Sound transmission loss (STL) level of the coatings was measured by a method called amplitude modulation,24 where the intensity of the laser beam is altered with the sound signal.25 Laser beams (ThorLabs CPS450, CPS532, CPS670F, CPS980, Dachau, Germany) were modulated with a UNI-T UTG 9010C function generator creating sinusoidal signals with an amplitude of 80 dB (dB(A)) at 10, 20, 50, 100, 300, 500, 1000, 4000, 10,000, 16,000 and 20,000 Hertz (Hz) frequencies. The aim is to identify the effect of the wavelength on the sound transmission loss. The mean of the measured STL percentage was used for determining the sound transmission loss and the error was estimated with the eleven different frequencies. Each signal was sent through the coated surfaces and the transmitted signal was measured with a photodetector in which sound wave and the laser beam were separated with an in-house designed electric circuit. For each case, sound wave was then sent to a speaker with a decibel meter (Cem DT-8850) measuring the corresponding sound transmission loss. A photographic image of the experimental equipment is depicted in Figure 5.