Volume 104, Issue 3, September 1998
Index of content:
- ACOUSTICAL MEASUREMENTS AND INSTRUMENTATION 
104(1998); http://dx.doi.org/10.1121/1.424360View Description Hide Description
In order to discuss acoustical quality of sound fields in a forest, measurements were carried out obtaining four orthogonal factors [Y. Ando, J. Acoust. Soc. Am. 74, 873–887 (1983)]. Results were compared with those in a concert hall. In the forest, for example, the subsequent reverberation time, was 1.66 s (500 Hz), and the interaural cross correlation (IACC) was 0.44 (1 kHz) at a point 40 m from the source. Such an outdoor space has specific acoustic properties being blended for certain sound sources involving the middle and higher frequency ranges. It was found that the value of the width of the interaural cross-correlation function, which is related to the apparent source width (ASW) of sound fields in the forest, was smaller than that in the concert hall.
A new transducer holder mechanism for efficient generation and reception of Lamb modes in large plates104(1998); http://dx.doi.org/10.1121/1.424361View Description Hide Description
A new transducer holder mechanism is described in this paper. This mechanism is very useful for inspecting large plates by Lamb waves. The new mechanism allows water coupling between the ultrasonic transducers and the specimen but requires neither a water jet nor a big water tank for immersing the specimen into it. This mechanism allows the transducers to rotate for changing the angle of strike of the incident beam and avoids undesirable multiply-reflected signals between the transducer and the specimen. An aluminum plate with fabricated internal defects has been inspected by the Lamb wave technique using the new transducer holder mechanism. The experimental results clearly show the superiority of the new design when compared with the conventional designs available today.
Investigation of the near field of a loudspeaker using tomographic reconstruction from TV-holography measurements104(1998); http://dx.doi.org/10.1121/1.424362View Description Hide Description
It has previously been shown that a three-dimensional mapping of an acoustic field’s amplitude and phase may be calculated from a set of TV-holography measurements by use of tomographic techniques. In this paper a thorough mathematical description of this measuring technique is given. An increased number of measured projections improves the tomographic reconstructions significantly. Techniques for obtaining quantitative data for the pressure amplitude of the acoustic field are implemented. The technique is demonstrated by measurements of the near field of a loudspeaker and these measurements are shown to agree well with measurements obtained with a microphone.