Effects and Evaluation of the Impact Sound of Wooden Floors

© Photo LIGNUM

The so-calles "Japanese rubber ball" proved to be a representative noise source for subjectively perceived walking noise.

© Photo LIGNUM

Living in good neighbourly relations is very pleasant. However, these good relations are in danger if the desired level of silence cannot be achieved when closing the entrance door of your dwelling. One of the main reasons for this is the transmission of noises from the apartment above. Especially if the impact sound insulation is implemented inadequately, walking noise caused by neighbours is inevitable. This low-frequency and impulsive noise is perceived as annoying booming noises. Some protection against walking noise is provided, for example, by floating floors being used in multi-storey buildings and increasingly also in single-family houses. The efficiency of the ceiling construction depends both on the materials used and the quality of the implemantation. The acoustic yuality is represented by the normalized impact sound pressure level, which is measured by a standardized tapping machine.

Impact sound is of high relevance especially in buildings of lightweight construction, for example buildings with a wooden support structure. Even if approved floor systems were used and the building code requirements were fulfilled, a high rate of inhabitant complaints occurred in some of the newly build multi-storey houses of lightweight construction. Therefore, acousticians and psychologists participating in the European research project ACUWOOD particularly aimed to investigate the evaluation of the impact sound in detail. The subjective rating of the impact sound noises by test persons in the laboratory and by inhabitants in their real living environment serve as basis for the research. By comparing the various technical evaluation methods with the subjective human perception of walking noise on the same floors, results showed significant differences. Especially for the standardized evaluation method, the study revealed that the frequency range of 100 up to 3150 Hz needs to be extended to lower frequencies, at least down to 50 Hz, to achieve an evaluation corresponding to the users’ requirements. Furthermore, evaluation methods were identified providing a better prediction quality compared to the normalized impact sound pressure level.

On this basis, requirement values for the different evaluation methods were defined. They are deduced from subjective evaluations and represent the percentage of persons feeling annoyed by a specific impact sound pressure level.

The transformation of dB values into a comprehensible scale for non-acousticians presents a significant step forward in the field of building acoustics. On the basis of the percentage of annoyed persons, planers and building contractors will be able to define exactly the level of impact sound insulation required by the individual user. If there are, in addition, inexpensive and acoustically efficient ceiling systems available, good neighbourhood relations can be ensured for the future.