Application Notes

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The Application Note verifies the new Symmetrical Pinnae for Head and Torso Simulator (HATS) Type 4128-C, by comparing measurements obtained using the original pinnae to those obtained using the new symmetrical pinnae.

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DIRAC PC software is used for measuring a wide range of room acoustical parameters. Based on the measurement and analysis of impulse responses, DIRAC supports a variety of measurement configurations. For accurate measurements according to the ISO 3382 standard, you can use the internally generated MLS or sweep signals through a loudspeaker sound source. Survey measurements are easily carried out using a small impulsive sound source, such as a blank pistol or even a balloon. Speech measurements can be carried out in compliance with the IEC 60268-16 standard, for male and female voices, through an artificial mouth-directional loudspeaker sound source or through direct injection into a sound system, taking into account the impact of background noise. DIRAC is not only a valuable tool for field and laboratory acoustics engineers, but also for researchers and educational institutions.

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The aim of this application note is to give a brief overview of the mobility measurement based modal analysis methods and give some practical explanations and hints for use of the different techniques. This includes multi-reference and Multiple-Input Multiple-Output measurement techniques.

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Non-stationary Spatial Transformation of Sound Fields (NS-STSF) is a revolutionary technique for mapping noise in 3D-space and time. NS-STSF in effect allows you to film the noise emanating from a test object as a sequence of snapshots of instantaneous sound pressure using a microphone array. You can then map the noise distribution in time and space by transforming the measured sound-field to other planes, parallel to the measurement plane. All common soundfield descriptors such as SPL, intensity and spectral content are available from a single measurement. This system is the only truly transient implementation of the Acoustic Holography technique.

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The Multi-analyzer System PULSE™ includes Envelope Analysis Type 7773. This application note briefly describes the ideas behind Envelope Analysis of local bearing faults, how Envelope Analysis is implemented in PULSE™, practical considerations, and two case studies.

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This application note presents a case and explains the concepts and features of tone assessment in Sound Level Analyzer Type 2260 H. The description is based on the JNM2 method, since this is the de facto standard and the one specified in most detail. For computer-based tone assessment, the JNM2 method includes guidelines which are implemented in Type 2260 H.

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Operational Modal Analysis, also called Ambient Modal or Output-only Modal, is a technique where modal parameters are estimated from response data without knowing the input loading force. The method has, for over a decade, been used for parameter estimation on civil structures such as bridges and towers where artificial excitation and determination of forces present a problem.

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Until now it has been fairly difficult to measure accurately automobile aerodynamic noise in a wind flow using a microphone, because of disturbances such as the microphone self-generated wind noise and background noise in a wind tunnel.
This Application Note presents the results of checking the validity of the Spatial Transformation of Sound Fields (STSF) technique for noise measurements in a wind flow.

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The modal parameters of simple structures can be easily established by the use of PULSE™, the Multianalyzer System Type 3560. This application note describes how to measure the modal frequencies by inspection of frequency response functions, how to determine the modal damping with the aid of the frequency weighting function included in the analyzer, and how to establish the mode shapes by examining the value of the imaginary part of the frequency response function.