IGF-Nr.: 20926 N

Forschungsvereinigung für Luft- und Trocknungstechnik (FLT)

Funding period: 01.11.2019 – 31.02.2024

Summary:

In a prior project L247 (IGF No.: 18919 N), an algorithm for a more perceptually appropriate description of fan noise based on the specific loudness was developed and a prediction of the acoustic quality of fan noise was made possible. In the present research project L264 (IGF No.: 20926 N), the scope of this model was significantly extended with regard to the sound pressure level range and tonal signatures.

The acoustic quality is indirectly defined here as the level of a fan noise compared to a reference noise for which it is equally preferred (Preference PSE). The level difference between the fan noise, at the PSE, and the reference noise can thus be interpreted as a level adjustment (penalty or bonus) on a dB scale, similar to those used in various DIN standards ([DIN45681, DIN45645-1, DIN45645-2]). The existing prediction model from the previous project used the spectral envelope form of the specific loudness curve to calculate an index (single-number value) and, together with results from listening tests, predict the level adjustment at a sound pressure level of 60 dB(A). Together with the A-weighted sound pressure level, this level supplement can be used to predict a fan-specific rating level, which includes the effect of the sound character on the (un-)pleasantness of the noise. As part of the current research project, the existing prediction model was significantly extended through extensive listening tests with regard to its range of application to lower and higher sound pressure levels and now covers a dynamic range of 45 dB(A) to 75 dB(A).

In addition, the influence of prominent tonal signatures, which often occur with fan noises, was investigated and converted into a dedicated tone index. Using the tone index, the prediction of level adjustments was extended so that a distinction can be made between purely noise-like sounds and sounds containing tonal signatures and the greater unpleasantness of tonal sounds, as assessed in further listening tests, is better represented. It turned out that a characterization of the effect of tonal signatures with several harmonics via a ratio of the loudness of all tonal components and the overall loudness of a sound is advisable. Existing and standardized tonality models are often only based on the most prominent tonal component and do not take higher harmonics into account.

The extended prediction model was implemented into a demonstrator software, which enables a simple calculation of the developed indices and output of the level adjustment or ventilator rating sound level. As part of the project, correlations of the preference PSEs with existing psychoacoustic parameters were also considered in parallel to the specially developed indices, so that a prediction of the level adjustments is also possible on their basis, in general. The usage of the developed prediction models can enable the development of acoustically better fan products that sound better and are perceived more pleasantly by people beyond their compliance with limit values.

The final report can be obtained from Forschungskuratorium Maschinenbau (FKM) e. V. (Adress: Lyoner Str. 18, 60528 Frankfurt am Main, E-Mail: info@fkm-net.de, Tel.: +49 69 6603 1352).

Link to the IGF-Projektsteckbrief