Volume 104, Issue 5, November 1998
Index of content:
- ACOUSTICAL MEASUREMENTS AND INSTRUMENTATION 
104(1998); http://dx.doi.org/10.1121/1.423873View Description Hide Description
Nonintrusive devices are needed to measure sound pressure levels in the mid- to high-frequency range. This need arises due to the small acoustic wavelengths which are present at these frequencies, and the interference caused by conventional microphones which are typically of relatively large diameter. Smaller microphones are less sensitive, and may not be small enough to be useful at very high frequencies or when physical size constraints are limiting. Simple probe attachments have been developed by others to address these problems; however, generally the transfer functions of these devices have possessed undesirable peaks due to the presence of standing waves within the transducers. In this paper, several possible options for making a microphone attachment that will convert a standard -in.-diam microphone into a probe-tube are discussed. Recommendations are made with regard to the particular use and ease of construction of the attachment. The new concepts eliminate standing waves, within certain frequency bands that are controlled by the geometry of the attachment, without the addition of damping material in the sound path.
104(1998); http://dx.doi.org/10.1121/1.423874View Description Hide Description
Current standards have defined the methods to verify the rms (root-mean-square) detectorcharacteristic of sound level meters. When using these methods, there will be a systematic error in the measuring results. The results then cannot accurately express the error in the rms detectorcharacteristic of a sound level meter. The reason for this is that the effect of the difference between the frequency-weighting characteristics of the sound level meter to be inspected and that of the standard system is ignored. So, an erroneous judgment may be made. Aiming at this problem, this paper contains some theoretical analysis and quantitative calculation in detail. An improved verifying method is put forward.