strategies to avoid boomy screeds

Transcription

1 strategies to avoid boomy screeds Christian Burkhart 1 ; Michael Wolf 2 1 Akustikbüro Schwartzenberger und Burkhart, 2 Akustikbüro Schwartzenberger und Burkhart, ABSTRACT Residents of dwellings often complain a low-frequency boomy noise coming from walking on the screeds in adjacent dwellings. Only a few publications about the reasons and physical context could be found and the problem seems unsolved. The presentation will show some new measurements from buildings and actual knowledge about the problem and some ideas to improvements. Keywords: impact-sound, walking-noise, low-frequency noise, I-INCE Classification of Subjects Number: INTRODUCTION Residents of dwellings often complain a low-frequency boomy noise caused from walking on the screeds in adjacent dwellings. Often the results of measurements of the impact-sound insulation shows, that all legal requirements and also the increased requirements are fulfilled. The spectral view of the impact-sound shows that a low-frequency transmission at 100 Hz or less is the reason for the complaint. Also we can see that the actual measured variable impact-sound-insulation would not be the right value to describe the problem and the boomy hearing of the residents. Figure 1: result of a measurements of ceiling between dwellings with increased impact-sound at low frequencies Only a few publications about the reasons and physical context could be found and the problem seems still unsolved. The located literature gives different ideas about the technical reasons and the methods for avoiding the physical effect. 1 cb@akustikbuero.com 2 mw@akustikbuero.com 3798

2 2. EXAMPLES The following example shows the actual technical knowledge and measurements. The results are given from measurements about the impact-sound-insulation between the 2nd and the 1st floor of a building (see ground plot in figure 2). The colored rooms in figure 2 are the receiving rooms at the 1st floor. Figure 2: ground plot: example, room 1 red marked, room 2 blue marked The ceiling construction is a 250 mm thick reinforced concrete with a light-weight concrete (50 mm thick) on it. The floating screed (65 mm thick) is for heating and fits on an high-quality insulation matting (17 mm thick) made of polyurethane with a dynamic stiffness of s' < 12 MN/m³. The impact-sound-insulation of these construction gives a result of L' n,w = 33 db for room 1 (see figure 4). This gives a very good result and clear compliance of the legal requirements and also the increased requirements. All this we can afford with only one layer of insulation matting. From the measured results a dynamic stiffness of s' < 5 MN/m³ could supposed instead of the technical sheet of the manufacturer. In addition to the impact-sound-insulation we get some measurements in room 1 about real walking with three different types of stimulation. Table 1: analysis of walking, different types of walking type type of stimulation Sound-level in room 1, L(t) 1. walking without shoes, walking over the heels up to 40 db(a) (intensive stimulation) 2. walking with shoes, up to 30 db(a) walking over the heels (normal stimulation) 3. walking with shoes, normal walking up to 25 db(a) A spectral comparison of the equivalent sound-levels shows different levels in the frequency range below Hz. As expected we see the highest A-weighted sound-levels with the stimulation of walking without shoes. 3799

3 Figure 3: spectral comparison of different types of stimulation, equivalent sound-level in room 1 In the frequency-range below 80 Hz the tapping machine and the walking without shoes will give nearly the same stimulation. So we can concentrate our discussion on the impact sound to the frequency-range below 100 Hz and we are allowed to use the tapping machine as a stimulation for the measurements. In the example we also did some measurements in the room 2 (see figure 2, blue colored). The ceiling construction and the flanking constructions are the same as room 1, only the geometrical form and volume are different. The spectral view to the impact-sound is quiet similar (see figure 4), but we can see differences on lower frequency. Since the construction is equal, the reason could be the different volume. L' n,w (C I, ) = 29 (8) db L' n,w (C I, ) = 33 (12) db Figure 4: example, impact-sound-insulation, room 1 red, room 2 blue 3. THEORETICAL ANALYSIS In (2) a computing model is shown for calculating filter-functions using geometrical modes as far as structural modes of the participating constructions. With a weighted summation of these fil- 3800

4 ter-functions and the theoretical spectrum of ceiling construction together with the floating screed we can calculate the estimated spectrum of the impact-sound-insulation. The weighting of the filter-functions is optimized over a growing number of examples we ve calculated and measured. figure 5: example of prediction A, right side summation of weighted spectra (red = geometrical modes, blue = floating screed, green = ceiling construction, black = summation), left side: prediction of the impact-sound-insulation and measured spectrum Figure 6: example of prediction B, right side: summation of weighted spectra, left side: prediction of the impact-sound-insulation and measured spectrum The calculation model shows a good compliance at lower frequencies even without the use of structural modes. It is assumed that higher values of the impact-sound often follow a compliance of geometrical modes and frequency of the floating screed. We can see this in figure 5 and 6 with the examples A and B, it should be validated through further measurements. With the results of the computing model we can expect, that the higher impact-sound-levels are produced from an overlay of geometrical modes and the resonance frequency from the floor construction. This is shown in figure 5 and 6 with the examples A and B and should confirmed through further measurements in other buildings. Also in the rooms 1 and 2 (see figure 7 and 8) we can see a good compliance of measured and theoretical impact-sound insulation. In the larger room 1 the geometrical modes and the resonance frequency from the floor construction are nearby and a higher impact-sound results. In the smaller room 2 the geometrical modes and the resonance frequency didn t match and lower impact-sound results. 3801

5 Figure 7: example of prediction room 1, right side: summation of weighted spectras, left side: prediction of the impact-sound-insulation and mesured spectrum Figure 8: example of prediction room 2, right side: summation of weighted spectra, left side: prediction of the impact-sound-insulation and measured spectrum 4. RESULTS For a reduction of low-frequency-walking noise floating screeds should be planned with a resonance frequency nearby the threshold of audibility. Unfortunately, the influence of geometrical modes could not be changed for architectural reasons. From figure 3 we can see, that a resonance frequency of 40 Hz or less is important. Therefor we need materials with a stiffness of s' 7 10 MN/m³ and screeds with a thickness of 8 cm and a mass of r = 2600 kg/m³ for example. REFERENCES 1. Kühn, B., Blickle, R.: Untersuchungen zum Sonderfall des dröhnenden Unterlagsbodens, wksb, Heft 32, Burkhart, C: Tieffrequenter Trittschall Messergebnisse, Mögliche Ursachen, DAGA Burkhart, C: Tieffrequenter Trittschall Messergebnisse, Beurteilung, DAGA Siebel, A.: Guter Trittschallschutz mit voller Dröhnung zwischen Norm und Realität, Lärmbekämpfung, Bd. 3 Nr. 4, Langner, N., Fischer, H.-M., Schneider, M.: Ursachen und Verbesserungspotential des Phänomens der tieffrequenten Trittschallgeräusche bei klassischen schwimmenden Estrichen auf Stahlbetondecken im Wohnungsbau, Forschungsarbeit, Wolf, M., Burkhart, C: Vermeidungsstrategien und Ansätze einer Vermeidung des Estrichdröhnens, DAGA