Prediction of sound transmission loss through multilayered panels by using Gaussian distribution of directional incident energy

Most acoustic measurements are based on an assumption of ideal conditions. One such ideal condition is a diffuse and reverberant field. In practice, a perfectly diffuse sound field cannot be achieved in a reverberation chamber. Uneven incident energy density under measurement conditions can cause discrepancies between the measured value and the theoretical random incidence absorption coefficient. Therefore the angular distribution of the incident acoustic energy onto an absorber sample should be taken into account. The angular distribution of the incident energy density was simulated using the beam tracing method for various room shapes and source positions. The averaged angular distribution is found to be similar to a Gaussian distribution. As a result, an angle-weighted absorption coefficient was proposed by considering the angular energy distribution to improve the agreement between the theoretical absorption coefficient and the reverberation room measurement. The angle-weighted absorption coefficient, together with the size correction, agrees satisfactorily with the measured absorption data by the reverberation chamber method. At high frequencies and for large samples, the averaged weighting corresponds well with the measurement, whereas at low frequencies and for small panels, the relatively flat distribution agrees better.

Section: A Rectangular Roommentioning

confidence: 99%

A correction of random incidence absorption coefficients for the angular distribution of acoustic energy under measurement conditions

Jeong

2009

“…2,14,26,27,[34][35][36] The problem of modeling cavity absorption was already mentioned by Hongisto. 17 The most problematic situation that none of the models investigated by Hongisto can deal with is very thin and empty cavities (d < 30 mm).…”

Section: Cavity Absorptionmentioning

confidence: 99%

“…TMM simulation for infinite structures and diffuse sound field excitation shows a large underestimation of STL in a broad frequency band between the mass-spring-massresonance of the structure around 200 Hz and the coincidence frequencies around 2000 Hz. Even after applying correction terms for the diffraction effects by spatially windowing the results, 28 or a Gaussian distribution of incident energy, 27 the discrepancy remains. The agreement between simulation and measurement result is good over a broad frequency range.…”

Section: Vibro-acoustic Couplingmentioning

confidence: 99%

“…The discrepancy between measurement results and infinite layer simulations in the frequency range between the mass-springmass-resonance dip and the coincidence dip can be explained by the finite dimensions. In literature, 14,27,[34][35][36] one often introduces cavity damping or cavity absorption when modeling double walls with empty cavities. However, sound absorption coefficients which are higher than the physical sound absorption coefficients have to be assumed for infinite models.…”

Section: Cavity Absorptionmentioning

confidence: 99%

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Sound transmission through finite lightweight multilayered structures with thin air layers

Dijckmans

Vermeir

Lauriks

2010

The sound transmission loss (STL) of finite lightweight multilayered structures with thin air layers is studied in this paper. Two types of models are used to describe the vibro-acoustic behavior of these structures. Standard transfer matrix method assumes infinite layers and represents the plane wave propagation in the layers. A wave based model describes the direct sound transmission through a rectangular structure placed between two reverberant rooms. Full vibro-acoustic coupling between rooms, plates, and air cavities is taken into account. Comparison with double glazing measurements shows that this effect of vibro-acoustic coupling is important in lightweight double walls. For infinite structures, structural damping has no significant influence on STL below the coincidence frequency. In this frequency region, the non-resonant transmission or so-called mass-law behavior dominates sound transmission. Modal simulations suggest a large influence of structural damping on STL. This is confirmed by experiments with double fiberboard partitions and sandwich structures. The results show that for thin air layers, the damping induced by friction and viscous effects at the air gap surfaces can largely influence and improve the sound transmission characteristics.

“…19 Furthermore, better agreement was found using smoothly varying angular distributions of incident energy rather than using a sharp truncation at 78°by Kang and co-workers. 20 Makita and Hidaka 21 discussed possible variations of absorption coefficients in non-uniform energy field. Recently, Jeong 17 investigated incident energy density distributions for a rectangular and an irregular room using a beam tracing technique.…”

Section: ͑1͒mentioning

confidence: 99%

Non-uniform sound intensity distributions when measuring absorption coefficients in reverberation chambers using a phased beam tracing

Jeong

2010

Measured absorption coefficients in reverberation chambers often differ from theoretical random incidence absorption coefficients, because ideal assumptions for the theoretical random incidence absorption coefficient are not fulfilled during measurements in actual reverberation chambers. Therefore sound intensity distributions on absorber under measurement conditions have been simulated using a phased beam tracing, and used as correction functions for reducing discrepancies between the measured and theoretical absorption coefficients. Two reverberation rooms were investigated by assuming that a test specimen was attached to a vertical surface and the floor. The frequency-dependent sound intensity distributions on absorbers were found to be affected by the reverberation chamber geometry and dimensions, the absorption capability of the specimen, and the placement of the specimen. High frequency intensity distributions above 1 kHz were similar for all studied cases, but some variations in low frequency intensity distributions were observed. If the non-uniform intensity distribution and a finite size effect are taken into account for correcting the theoretical absorption coefficients, a good agreement is found between corrected and measured statistical absorption coefficients. The non-uniform sound intensity can account for the discrepancy at high frequencies.