Measured effect of resilient edge joints on airborne sound insulation of heavyweight wall Jukka Keränen, Jarkko Hakala, and Valtteri Hongisto Turku University of Applied Sciences, Acoustics Laboratory Joukahaisenkatu 7, FI-20520 Turku, Finland

ABSTRACT It is common assumption that resilient joints around a heavyweight construction improve sound in- sulation between adjacent rooms. Effect of resilient joints on sound insulation has not been studied sufficiently. This study investigated how the joint resiliency around a heavyweight wall affected sound reduction index (SRI) measured directly through the construction. A calcium silicate block wall was built three times in a laboratory using three different joint types A−C between the wall and the build- ing frame: A) all four edge joints rigid, B) three resilient and one rigid joint, C) all four joints resil- ient. SRI was determined for A−C. Total loss factor (TLF) was determined for A−C by measuring structural reverberation time using hammer impact stimulus. SRI reduced, remarkably, with increas- ing level of joint resiliency. R w was 50 dB for joint type A while it was 45 dB for joint type B and 43 dB for joint type C. Correspondingly, TLF reduced with increasing level of resiliency. The effect of joint type was evident above the critical coincidence frequency 200 Hz of the wall. Resilient joints prevented the sound transmission to the building frame, which increased sound radiation to the re- ceiving room. Therefore, heavyweight wall should be mounted to surrounding heavy constructions using rigid joints if high sound insulation is desired above the coincidence frequency.

1. INTRODUCTION

Heavyweight constructions (e.g., concrete, clay, calcium silicate, sand lime) are often used to provide sound insulation against neighbor and environment noise [1]. Sound reduction index (SRI) of a sin- gle-leaf wall or intermediate floor construction depends on physical parameters, e.g., density, Young’s modulus, plate dimensions, and total loss factor (TLF). SRI and TLF are frequency depend- ent. TLF depends on internal losses, radiation losses, and coupling losses in the joints. The coupling losses have the strongest effect on TLF [2] and they depend on the joint types to the surrounding constructions and the properties of these constructions.

Resilient joints between constructions reduce vibration transmission from one element to another [3]. Thus, it has become a common assumption that resilient joints, in general, positively affect the sound insulation between adjacent rooms. Therefore, some masonry building instructions presume that the joints of the masonry wall against surrounding floor, ceiling, and walls, should be resilient when higher sound insulation is desired. Experimental evidence about the effect of resilient joints surrounding a heavyweight construction is very limited [4].

The purpose of the study was to investigate the effect of the joint type on the SRI of a single-leaf heavyweight wall. Three walls were tested using three different joint types between the perimeters of the wall and adjoining constructions. The SRI was measured using both sound intensity and sound

pressure methods to ensure reliable results at low frequencies. Another purpose was to see if the change in SRI could be explained by the difference between the measured TLFs.

2. MATERIALS AND METHODS

2.1 Laboratory The measurements were conducted in the FINAS accredited acoustics laboratory (Turku University of Applied Sciences, Turku, Finland). The wall was built into a test opening (10.2 m 2 ) between two test rooms (Figure 1). The installation frame is rigidly connected to the building, but the test rooms are vibration isolated. Therefore, the flanking transmission from the source room to the receiving room is minimized. The maximum measurable SRI between the test rooms is more than 15 dB higher than the results of the tested walls within the investigated 1/3-octave bands 50–5000 Hz.

2.2 Investigated constructions The heavyweight wall was built using calcium silicate masonry blocks (Saint-Gobain Finland Oy, Weber Kahi Runkopontti 300x130x198). The wall (3.61 x 2.77 m) was built three times into the test opening (Figure 1) using three different joint types A–C (Figure 2): • A. Four rigid joints . The seams were filled with mortar and the wall was mechanically tied to the test opening frame using a steel band every 500 mm on vertical sides. • B. Rigid floor joint, other joints resilient . Floor joint was filled with mortar. The other three joints were resilient (without steel bands), and the seams were filled manually with flexible solution. • C. Four resilient joints . The wall was built on top of a vibration isolation strip (resonance fre- quency of the mass-spring-system 14 Hz). The other three joints were similar as in B.

Each construction dried 4–7 days before the measurements. Each wall was built by the same ex- perienced person who was informed about the importance of careful workmanship. The materials are presented in more detail in Ref. [5].

2.3 Measurement methods The SRI was measured using sound pressure method ISO10140-2 [6]. The weighted SRI, R w , and spectrum adaptation terms C and C tr were determined according to ISO 717-1 [7].

The TLF was determined by measurements of structural reverberation time, T S , which was meas- ured using rubber hammer excitation, vibration accelerometer, and real-time analyzer. The decay of vibration level was measured instantly after the hammer impact and T S was determined according to ISO 3382-2 [8] based on 20 dB evaluation range. The TLF was determined using equation:

2.2

𝑓𝑇 S , (1)

𝜂 tot =

where f is the center frequency of the 1/3-octave band within 50–5000 Hz.

Figure 1: The wall installation between the source and receiving room.

Figure 2: The edge joint types A–C.

3. RESULTS

The single-number values are presented in Table 1. The measured SRI, R , with joint types A–C is presented in Figure 3a, and the measured TLF,  tot , with joint types A–C in Figure 3b. Table 1: The weigh ted SRIs according to ISO 717-1.

Joint type R w [dB] R w +C [dB] R w +C tr [dB]

A 50 48 46

B 45 44 41

C 43 42 39

4. DISCUSSION

Above the critical coincidence frequency (200 Hz), the SRI was reduced when the joint resiliency was increased. R w was 50 dB for joint type A while it was 45 dB for joint type B and 43 dB for joint type C. Correspondingly, TLF reduced with increasing level of resiliency. The effect of joint type was evident above the critical coincidence frequency. Resilient joints prevented the sound transmis- sion to the building frame, which increased sound radiation to the receiving room. On the other hand, the SRI improved within 63  80 Hz when the joint resiliency increased (joint types B and C). Resilient joints around heavyweight construction may be beneficial in situations where the

h a

reduction of low-frequency noise is of primary concern. This finding may be caused by the changes in the edge conditions and modal behavior of the construction. However, the finding did not concern all the 1/3-octave bands below 200 Hz. Therefore, we cannot recommend resilient joints as an undis- putable method to improve SRI below coincidence. Further research is needed in this respect. The reproducibility standard deviation of R w is 1.2 dB (between laboratories) according to ISO 12999- 1 [8]. Since the differences between the joint types A  C were larger than that, measured changes were most probably caused by the differences in joint types. The changes in TLF were clearly ob- served above 200 Hz. Although, the uncertainty of TLF measurements is not known, it is probable that the measured effect of the joint type on the TLF is reliable.

5. CONCLUSIONS

SRI reduced with increasing level of joint resiliency above the critical coincidence frequency of the wall. Heavyweight constructions should be mounted to surrounding heavy constructions using rigid joints if high sound insulation is desired above the coincidence frequency. 6. ACKNOWLEDGEMENTS

The work was funded by Saint-Gobain Finland Oy / Weber. 7. REFERENCES

1. Rasmussen, B., Machimbarrena, M., Fausti, P. COST Action TU0901: Building acoustics

throughout Europe. Vol. 2: Housing and construction types country by country . COST Office, e- ISBN 978-84-697-0159-1. 2. Rindel, J. H. Airborne sound transmission through single constructions. Sound Insulation in

Buildings, CRC Press, Taylor & Francis Group, 2018. 3. Crispin, C., Mertens, C., Blasco, M., Ingelaere, B., Van Damme, M., Wuyts, D. The vibration

reduction index K ij : laboratory measurements versus predictions EN 12354-1 (2000). Proceed- ings of Inter-noise 2004 . Prague, Czech Republic, 22-25 August 2004. 4. Meier, A., Schmitz, A. Application of total loss factor measurements for the determination of

sound insulation. Journal of Building Acoustics , 6(2) , 71-84 (1999). 5. Keränen, J., Hongisto, V., Effect of resilient joints on the airborne sound insulation of single-leaf

heavyweight constructions. Revised manuscript submitted for publication, March, 2022. 6. International Organization for Standardization (ISO), Acoustics. Laboratory measurement of

sound insulation of building elements. Part 2: Measurement of airborne sound insulation, ISO 10140-2:2010. 7. International Organization for Standardization (ISO), Acoustics. Rating of sound insulation in

buildings and of building elements. Part 1: Airborne sound insulation, ISO 717-1:2020. 8. International Organization for Standardization (ISO), Acoustics. Measurement of room acoustic

parameters. Part 2: Reverberation time in ordinary rooms, ISO 3382-2:2008. 9. International Organization for Standardization (ISO), Acoustics. Determination and application

of measurement uncertainties in building acoustics. Part 1: Sound insulation, ISO 12999-1:2020.

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b) Figure 3: a) The SRI of the wall using junction types A–C. The maximum measurable SRI, R max ,

is also presented. b) The TLF of the wall using junction types A–C. The minimum allowed TLF

for a building acoustic laboratory is also presented.