Written in English
|The Physical Object|
|Number of Pages||228|
Nowadays, the two-microphone method is accepted as the standard as specified in ASTM E for measuring in-duct acoustic properties. However, research results on using the least square method with multiple measurement points and broadband excitation have been reported for enhancing the frequency response of the two-microphone by: Using the two‐microphone method, acoustic properties in ducts, as, for example, reflection coefficient and acoustic impedance, can be calculated from a transfer function measurement between two microphones. In this paper, a systematic investigation of the various measurement errors that can occur and their effect on the calculated quantities is made. The input data for the calculations are Cited by: Nowadays, the two-microphone method is accepted as the standard as specified in ASTM E for measuring in-duct acoustic properties. However, research results on using the least square method with multiple measurement points and broadband excitation have been reported for enhancing the frequency response of the two-microphone method. In this paper, the effects of varying the relative Cited by: F.J. FAHYRapid method for the measurement of sample acoustic impedance in standing wave tube Journal of Sound and Vibration, 97 (), pp. Google Scholar.
This test method is intended to provide a much faster measurement technique than that of Test Method C 5. Signiﬁcance and Use This test method can be applied to measure sound absorption coefficients of absorptive materials at normal inci-dence, that is, 0°. It also can be used to determine speciﬁc impedance and admittance ratios. Tt has been customary to measure acollstic impedance indirectly by measuring the standing wave ratio and the distances from the termination to sllt'cessive minima in a standing wave tube in which the absorber acts as the termination. From the two sets of readings the acoustic impedance . (STLs) and acoustic properties (characteristic impedances, propagation wavenumbers, effective densities, bulk moduli) of acoustic materials in normal incidence condition, an impedance tube is commonly used. For measuring specific impedances and SACs, the two microphone transfer function method using an impedance tube is shown in Figure 1. This. An alternative technique, ASTM E , the “Standard test method for impedance and absorption of acoustical materials using a tube, two microphones and a digital frequency analysis system” is preferable because measurements can be made over a range of frequencies simultaneously.
An investigation was conducted to explore potential improvements provided by alternate implementations of two impedance-measurement methods, known as the two-microphone and multipoint methods. This investigation is part of a continuing technology development to find more efficient and convenient methods for impedance measurements in harsh. A special investigation has been undertaken for measuring impedance or reflectance in an acoustic-measuring tube, in which the sound pressure was measured at several fixed measuring points. The measurements for determining the acoustic properties of new materials were based on a two-microphone transfer-function method according to ISO , which is characteristic for horizontally mounted orientation-sensitive materials. To determine the acoustic absorption coefficient, 14 tests were accomplished. It is also shown that the neglect of attenuation between the microphones leads to a low frequency limit for the applicability of the two microphone method. A new technique for measuring the Mach.