Towards the establishment of traceability in sound power in airborne sound, the present study focuses on the dissemination procedure. Aerodynamic reference sound sources were studied as potential transfer standards. Initially, the sources were examined in the up-to-present requirements. The core of the study is the correction required for the transition from calibration to in situ conditions. The influence of atmospheric pressure, ambient temperature and fan rotation speed was investigated and the corresponding correction was determined. A comparison to an existing correction was also performed. Near field effects were another part of the study. The related uncertainty was estimated in a transparent approach. The dependency of the uncertainty on the in situ and calibration condition values is also presented.

Reference sound sources used in sound power measurements are currently calibrated according to well-documented techniques. Low frequency limitations and solely broadband analysis restrict the applicability of these methods. The concept of traceability is introduced to overcome these deficiencies. This study presents the calibration of reference sound sources through a measurement chain, which is based on the substitution method. The applicability of the substitution method extends to sound intensity measurements and narrowband frequency analysis. A specially designed apparatus allows the detection of the sound field over a fully scanned hemisphere. The results of the apparatus are comparable to the results of the existing methods. The substitution method reduces the required corrections, which are presented. The sound power levels are supplemented by a transparent uncertainty budget, which allows the estimation of each uncertainty component individually. The comparison between the methods is also given in terms of a confidence interval.

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The dynamic stiffness of underlays is a required quantity to predict the reduction of impact and airborne noise transmitted through floating floors. The measurement of the dynamic stiffness is standardized in ISO 9052–1 using a floating floor section of 200 mm edge length. If open pore insulating materials are used for the underlay, the air flow and its flow resistivity have a significant impact on the dynamic stiffness. The standard ISO 9052–1 therefore calculates the dynamic stiffness based on three distinct intervals of the flow resistivity. This contribution analyses and discusses the mathematical origin and practical consequences of these three standardized intervals and proposes an improvement for a revision of the standard. The current physical model is expanded to examine if the results, that are gained from the geometrically reduced systems of the standard, can be transferred to room sized systems.

ISO 9614 describes the determination of sound power levels by the two microphone intensity technique. Despite some physical advantages the method is relatively seldom used. To improve this situation, theoretical and experimental investigations were performed, which focused mainly on the adequacy of the currently standardized indicators and criteria. This paper summarizes these results and develops first ideas for a revision of ISO 9614. One main proposal is to perform measurements generally in the one-third octave bands between 50 Hz and 10 kHz with a 12 mm spacer and to apply appropriate corrections in the highest three one-third octave bands. Furthermore, it is proposed to require additional measurements with a larger spacer at lower frequencies, if the dynamic capability of the instrument is insufficient. The A-weighted sound power level is calculated from the one-third octave band levels, which may have different grades of accuracy. Calculating different A-weighted sound power levels from different sets of frequency bands fulfilling criteria for different grades of accuracy then allows for designating a grade of accuracy to the A-weighted sound power level. This is considered to be a major improvement since the A-weighted sound power level is the main descriptor for the sound emission of sources.