Airborne Sound Transmission Loss Research Articles

Prediction to Reality, Leveraging modeling to speed solution development

When developing a noise control solution, it is beneficial to provide modeling of the system to optimize the resulting solution limiting testing to relevant solutions meeting the various constraint requirements of cost, performance, manufacturing, and shipping. A recent study on predicting sound transmission through vehicle panels to eliminate the multiplicity of testing needed to identify the best solution. This paper will present a study to identify a solution to improvement of the sound transmission of a vehicle panel leveraging modeling and comparing the model results to the actual test results. by comparing model predictions to test results from ASTM E90 - Standard Test Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions and Elements1. Vehicle panels featuring distinct absorbing configurations identified through modeling were installed within a composite plug wall and subjected to standardized acoustic excitation. The agreement between model predictions and experimental data will demonstrate effectiveness of models in predicting panel performance.

A hybrid test method for measurement of airborne sound transmission loss of building partitions and elements

Single-number ratings, such as sound transmission class (STC), outdoor to indoor transmission class (OITC), and weighted sound reduction index (Rw), have been widely used to indicate the sound transmission properties of the building elements. The required transmission loss values over the frequency spectrum can be obtained from the two reverberation rooms test method (ASTM E90, ISO 10140), field measurement method (ASTM E966), or intensity method (ISO 15186). The limitations of the number of testing facilities that can provide the diffused field, minimum cut-off frequency, and other standard laboratory requirements, made the sound transmission loss measurement a costly and time-consuming procedure. In this study, alternative methods to measure the sound pressure and intensity have been investigated. The main objective of this research was to eliminate the complicated requirements of the diffused field and the room absorption measurement by averaging the direct sound amplitude at several angle of incidents and using the intensity probe to measure the sound intensity. In conclusion, the sound transmission loss, STC, and OITC values of double-glazed windows obtained from the hybrid method have been compared with predictions from the existing theory and the ASTM E90 standard test results.

Improvement of the low-frequency sound insulation performance of hollow double-leaf panels by inserting a bending panel

Air-borne sound transmission loss of building materials generally follows the mass law. Transmission loss decreases at lower frequencies and is minimal at the fundamental natural frequency f0. On the other hand, transmission loss increases below f0, and is controlled by stiffness. Moreover, the stiffer the materials, the higher the f0. In the other words, even without increasing the mass, increasing the stiffness can improve low-frequency transmission loss. We focus on the fact that flexible lightweight panels are easily stiffened by bending deformation. We conduct a basic study on the effect of inserting a bending panel into hollow double-leaf panels. Experimental results on single panels showed a correspondence between the increase of f0 by bending deformation and the improvement of low-frequency sound insulation performance. In the case of the double-leaf panels with the lightweight bending panel inserted inside, the stronger the bending, the more low-frequency sound insulation performance tended to be improved.

Airborne sound transmission loss of ship bulkheads: A new methodological approach for in-laboratory assessment by including low frequencies

Current standard laboratory measurements of sound transmission loss properties of ship bulkheads at low frequencies, below 100 Hz, are not accurate enough due to the non-diffuse acoustic field of typical laboratory volumes. However, what has been recently observed in non-diffuse field conditions is the transmission of source modes into the receiving room through the partition. On the basis of this, in this paper, a novel procedure to determine the laboratory airborne sound transmission loss properties of ship bulkheads at low frequencies through the airborne modal sound transmission loss is investigated. It is defined as the difference between the average sound pressure levels of source room modes peaks that occur in both source and receiving rooms. A correction method is proposed to suppress the influence of natural receiving room modes. Normalization terms related to receiving room volume and modal damping are introduced, and an envelope method is applied to extend the results in third octave bands. Measurements on five different ship bulkheads show that the standard transmission loss in the low frequency range provides unlikely results, whereas the proposed descriptor follows the expected theoretical curve. This evidence confirms the validity of the proposed method, at least for comparison purposes in marine applications.

Empirical investigation of interzonal air leakage and airborne sound transmission correlation in multi-unit residential buildings

In the context of suite compartmentalization in multi-unit residential buildings, knowing the airtightness of individual pressure boundaries (e.g. floor, corridor wall, suite wall, etc.) is imperative for the diagnosis and remediation of issues such as regulating ventilation air delivery and managing pollutant transfer. However, conventional quantification methods, such as the pressure neutralization method, are cumbersome to complete. The feasibility of an acoustic testing approach, which leverages the relationship between increased air leakage rate and decreased airborne sound transmission loss was examined. Limited studies have explored this relationship in building enclosure elements, and no attempts were made to assess the correlation in interior partitions. In-situ measurements were conducted across twelve suite partition walls from three multi-unit residential buildings to obtain experimental correlations between the two parameters. The area-normalized air leakage rate at 50 Pa (q50) varied among specimens of the same composition, demonstrating the importance of air-sealing details for the overall partition airtightness. The variation in q50 was best reflected by the area-normalized sound transmission loss at 630 Hz; a non-linear model and the inclusion of air pressure differential information also improved the models’ accuracy. While the root-mean-square error of 0.56 L/s/m2 in q50 prediction suggests this acoustic approach needs further refinement to verify compliance with increasingly stringent compartmentalization targets, the current study demonstrates the application and potential benefits of the acoustic approach in a real-world context. Further data could improve the model so that it could be suitable for screening partitions with similar construction and in pre- and post-retrofit comparisons.

Acoustical performance of horizontal-sliding-panel operable partition walls

Field measurements of airborne sound transmission loss were made on several operable partitions of the horizontal-sliding-panel type between conference rooms. Apparent Sound Transmission Class (ASTC) and Noise Isolation Class (NIC) ratings were computed. Very significant deviation of field-measured sound transmission ratings and manufacturers' Sound Transmission Class (STC) ratings were found. Clients were not satisfied by actual sound isolating performance. Transmission of voice was clearly audible. Some deficiencies of field conditions were found. Some deficiencies of partition installation were found. Modifications were made; acoustical performance did not change significantly.

Case Study: Floating Jack-Up Slabs for Multi-Story Cinema in Manhattan

A review of a uniquely designed floated jack-up concrete slab to isolate fourteen movie theaters on multiple floors within a multi-use building. The jack-up boxes were engineered and custom tailored to increase airborne sound transmission loss performance while achieving a very high vibration isolation efficiency specified. Field test results were obtained to validate the floating jack-up concrete's acoustical performance.

Test and rating method comparison between Japan and the U.S. for airborne sound insulation in buildings

The Japanese test methods for laboratory measurement of airborne sound transmission loss for building partitions are basically the same as the American test methods. However, the two countries’ field test methods for airborne sound insulation in buildings differ. The octave band sound pressure level difference between two rooms is the most significant value for the field evaluation of sound insulation in Japan, whereas the apparent transmission loss for a partition installed in a building is the most popular value for the field evaluation of sound insulation in the US. Why is the octave band sound pressure level difference popular in Japan? It is the basic way of thinking in Japan that an acoustical engineer should take responsibility for the total spatial sound insulation performance, including sound absorption and flanking transmission from the design stage to completion and the field test and evaluation method as the completion inspection should be simple. If the insulation performance does not meet th...

Acoustic contributions of a sound absorbing blanket placed in a double panel structure: Absorption versus transmission

The objective of this paper is to propose a simple tool to estimate the absorption vs. transmission loss contributions of a multilayered blanket unbounded in a double panel structure and thus guide its optimization. The normal incidence airborne sound transmission loss of the double panel structure, without structure-borne connections, is written in terms of three main contributions; (i) sound transmission loss of the panels, (ii) sound transmission loss of the blanket and (iii) sound absorption due to multiple reflections inside the cavity. The method is applied to four different blankets frequently used in automotive and aeronautic applications: a non-symmetric multilayer made of a screen in sandwich between two porous layers and three symmetric porous layers having different pore geometries. It is shown that the absorption behavior of the blanket controls the acoustic behavior of the treatment at low and medium frequencies and its transmission loss at high frequencies. Acoustic treatment having poor sound absorption behavior can affect the performance of the double panel structure.

A method for increasing the damping properties of fiber reinforced composite structures

The passive material damping concept discussed in this paper is a sandwich construction of continuous fiber reinforced composite layers separated by a constrained visco-elastic material (VEM) layer. The fiber orientations in the composite layers are spatially oriented to produce systematic stiffness variations. It has been shown that three independent shear components may be developed in the VEM for simple applied loads using this spatially varying stiffness (SVS) approach, which is a distinct improvement over other traditional constrained layer treatments. To demonstrate predicted high-damping levels, modal loss factor data are presented for simple tubular and beam bending elements. Results of airborne sound transmission loss measurements on 1-m square SVS panels of various areal densities are described. Random vibration levels for an equipment mounting plate constructed using the SVS material are also presented and compared to results for a metallic base plate.

About the sound insulation of windows

The results of statistical research and measurements of the airborne sound transmission loss of windows of any kind of frame material (aluminium, wood, PVC,...), glass types, and window dimensions are reported to revise the well-known table 40 in the German standards DIN 4109, Beiblatt 1 (issue 1989). A new table will be presented with a strong connection of the sound reduction index R of both the glass and the frame material and of the frame-to-pane-ratio, or, better to say, the dependence of the sound reduction from the dimensions of the window resp. the glass pane. Proposals are given as to correction terms to respect these substantial influences for the predictional work in practice. [Work supported by DIBt and Bundesverband Fenster & Fassade.]

Sound Bridging By Wall Ties in Cavity Brick Walls: Theory and Experiment

In cavity brick wall construction, wall ties are frequently used to provide resistance to water penetration and to transfer lateral forces, thereby increasing the load-carrying capacity of the wall. The presence of such ties, however, introduces an additional path through which sound and vibration transmission can take place. As a consequence, the sound insulation performance of cavity walls with ties may be lower than those of identical walls with no ties. In this paper, sound transmission loss results obtained from laboratory measurements on a common cavity wall system with two different types of wall ties are reported. The statistical energy analysis (SEA) method is used to construct a model representing a cavity wall system with or without ties, and predicted airborne sound transmission loss values are compared with experimental results. By considering the wall ties as rigid point bridges that excite the second leaf, which in turn radiates the transmitted sound power, expressions are developed that allow the calculation of the reduction in transmission loss at different frequencies. Reasonable agreement between theory and experimental results has been found by using both methods.

Measurement of normal incidence airborne sound transmission loss for open-plan office panels

A new laboratory test procedure is developed that evaluates the normal incidence sound transmission loss characteristics of a partial height panel. A comprehensive comparison of test data and the resulting single number ratings are made between the proposed and the existing barrier/sound transmission loss test procedures. Experimental attenuation measurements for various open-plan office configurations were in close agreement with calculated theoretical predictions using the geometrical theory of diffraction and normal incidence sound transmission loss test data. Measurements were conducted in a semi-anechoic room using a one-third octave band real time analyzer and pink noise as the test signal. The new test procedure provides one-third octave band data for complete acoustical analysis and a single number rating, called Weighted Articulation Index Average, for partial height panel comparisons.

Intercomparisons of laboratory determinations of airborne sound transmission loss

An analysis of transmission loss (TL) data from seven north american laboratories was organized by ASTM Subcommittee E33.05 to study ASTM E 90 accuracy performance for single- and double-panel partitions. Several mass law expressions are reviewed and compared with TL data from seven laboratories for four different limp-mass panel materials. It is noted that the laboratory TL data are not as linear with frequency as generally assumed, and examples are found where TL variation from mass law exceeds that suggested by E 90 precision requirements. In addition, an interlaboratory difference of 2 dB was found for some laboratories. For double-panel walls, TL data from two laboratories for similar constructions (STC ≳50) showed unexpectedly large variation in TL (up to eight points) and in STC (six points). Using double-panel theory, these TL differences are explained on the basis of interlaboratory differences in mass law and flanking (perhaps due to the test frame liners). A TL performance test series is illustrated with recent data from two laboratories and suggested as a basis for improving laboratory TL accuracy.

Effect of sound-absorptive facings on partition airborne sound-transmission loss

Laboratory measurements of the effect of sound-absorptive facings on partition airborne sound-transmission loss are presented. For a double-leaf partition of 1/2-in. gypsum board on 2×4 in. studs, the application of sound-absorptive facings has led to improvements in transmission loss of as much as 10 dB or more in the 1/3-octave bands above 1 kHz. Corresponding, but smaller, improvements have been measured at lower frequencies. A preliminary theoretical analysis is presented.

Effect of Diffuseness of Incident Sound Field on the Measurement of Airborne Sound Transmission Loss

Much of the literature on airborne sound transmission loss (TL) indicates that TL of a panel at a given frequency is dependent on distribution of sound intensity with angle of incidence in the incident sound field. Observed TL in most laboratory tests employing a “diffuse” sound field yields data which may be described as lying between that to be anticipated if the energy in the sound field were concentrated at normal incidence, and that expected if the sound field were uniformly distributed over all angles of incidence (Random Incidence). An ad hoc approach to dealing with this phenomenon has involved the postulation of a “field incidence” sound field, which assumes that the distribution of incident intensity is uniform up to a limiting angle of 75° to 80° from the normal to the panel. This approach provides a means for calculating TL which agrees with measurements, but no satisfactory analytical model has evolved which provides justification for this approach. Some careful experimental evaluations involving convolution of the cross correlation of the incident pressure field with an analytic model of panel response have shown that the fundamental approach is reasonable, but still provides no basis for explaining this phenomenon. In this paper, the recent published and unpublished data of a number of authors are reviewed, which imply that TL is more sensitive to local perturbations from a diffuse incidence sound field than from gross perturbations in the source room. One hypothesis which seems to correlate with these observations is that the aperture in which a panel is tested should be viewed as a spatial filter which limits the incident sound field in addition to the effects of “diffusivity” present in the source room. It is postulated that the limitations produced by the aperture are more significant than those provided by the room for a “reasonably reverberant” source room.

Measurement of Room Absorption by Steady-State and Decay-Rate Methods

Steady-state and decay-rate methods of measuring A2, the total sound absorption in the receiving room of a transmission-loss experiment, were compared to determine how well they agreed. The results of a series of experiments under controlled laboratory conditions showed a very close agreement between the two methods, with differences averaging less than half a decibel ia measurements of 10 log10 A2. These results indicate that a steady-state method may be substituted for the reverberation-time method in measuring A2 without sacrificing the accuracy of laboratory measurements of airborne sound transmission loss of building partitions.

American Standard Recommended Practice for Laboratory Measurement of Air-Borne Sound Transmission Loss of Building Floors and Walls

The American Standards Association recently issued the standard which is reproduced below, complete and unabridged, with their permission. This new standard can be regarded as an up-to-date revision of the ASTM Tentative Recommended Practice for the same measurement (ASTM E 90-50T, later ASTM E 90-55), which was printed in this Journal [23, 686, (1951)]; in 1955 the “Tentative” was deleted from the title, the text remaining unchanged. Some other countries, including Britain and Germany, have standards on this topic (British Standard 2750:1956, and German Standard DIN 52210, both obtainable from the American Standards Association), and a draft exists for an international standard; the latter includes provisions for field measurements as well as laboratory measurements, and for measurements of impact as well as air-borne sounds. At present ASTM Committee E-6 is working to prepare a new Recommended Practice for the measurement of the sound transmission loss of building structures, and will consider the inclusion of field and impact measurements.

New Airborne Sound Transmission Loss Measuring Facility at Riverbank

A new sound transmission loss measuring facility has been in use at Riverbank Acoustical Laboratories for more than a year now. This paper describes the two reverberation rooms, installation of the test panel, instrumentation, and measurement technique. The several checks made for measurement accuracy and repeatability are discussed. Test results are given comparing the old method of test with the new, and results are also given for a folding door measured at four testing laboratories in the United States and Canada.