PROCEEDINGS of the
23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

Sound insulation of fenestration systems: a comprehensive webbased simulation program and validation
Tejav DeGanyar 1; Fangliang Chen 1, 2; Yihe Huang 1
1

Virtual Construction Lab of Schuco, New York, NY
2

Columbia University, New York, NY

ABSTRACT
Aluminum framed fenestration systems are becoming a leading choice for modern buildings. They provide
a superior aesthetic appearance, a higher degree of weathering reliability, and quicker installation. At thesame time, they offer more transparency and environmental efficiency. However, because of the complexityof the framing systems, the estimation of sound insulation of such systems for preliminary design or analysis
becomes time-consuming and difficult. Currently, there is no efficient tool available for convenient andreliable estimation of the sound insulation performance of fenestration systems. To this end, the engineering
team led by the authors conducted extensive studies on various fenestration systems consisting of different
glazing and aluminum frames. Based on our research outcomes, a comprehensive web-based simulation
program, the so-called Digital Acoustic Lab (DAL), has been developed recently. This program can provide
a quick analysis and accurate prediction of sound insulation of window, door, and façade systems consist ofvarious aluminum frames and glazing infills. A series of laboratory tests were conducted to validate thepredictions by the DAL. The goal of this program is to provide designers, engineers, and architects aneffective and economical tool to facilitate the design.
Keywords: Sound, Transmission Loss, Framed Window, Façade, STC, OITC, Acoustic Simulation

1. INTRODUCTION

The need for acoustical enhancements of exterior envelops while maintaining cost efficiency is an
ongoing topic of research. This need has become more prevalent with the advent of highly intricate
thermally-isolated and light-weight aluminum framing systems, which are the norm for most of themodern commercial and multi-unit residential constructions of today.
Even though aluminum framing has a smaller exposed area; it is made of various cavities andoften contains orifices for drainage and air circulation. These features can alter the acousticalcharacteristics of glazing elements. Also, aluminum extrusions thicknesses are frequently optimized
to archive a higher degree of economy, while mechanical interlocking systems are employed to reduce
field labor costs. All these factors can contribute to the degradation of acoustical performance of theoverall system.
In the past few decades, the main metric for evaluation and comparison of facade products has
been the use of a single number rating (Rw in Europe and STC/OITC in the USA). These numbers arecalculated based on “Sound Transmission Loss (STL)” measurements conducted at certified
laboratories (1-3).
The municipalities or the building design team usually dictate the acceptable range of the soundtransmission classification or the acceptable noise criteria. The numerical value of the classification
is mainly a measure of comparison, and not necessarily the true indicator of the acoustic behavior. On
occasion, the required ratings are augmented by a set of STL’s at the octave or one-third octave band
frequencies.
1

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TDeGanyar@schuco-usa.com

These ratings are either published by manufacturers or conducted at the request of building owners
or developers for custom projects. This practice, however, has its drawbacks. Although the cost andthe duration associated with the testing are in general reasonable, the overall process requires the needfor the fabrication and assembly of the final product, which require weeks or sometimes months ofpreparation. Seldom these amounts of lead time are afforded in construction schedules. Furthermore,in the event of unsatisfactory results, the possibility of any modification or redesign is severelycompromised.
This article addresses the need for a computational tool to estimate the acoustic performance offenestration elements in buildings. We will examine the current estimation practices and will present“Digital Acoustic Lab” a cloud-based software tool, for the estimation of sound transmission loss offramed glazing systems.

2. SINGLE NUMBER RATINGThe single number rating to measure the acoustic performance of architectural demising walls andinterspatial spaces has been the norm for the building industry for the past half-century. The practicestarted in 1970, with the introduction into ASTM standards, and although the testing and measurement
procedures have gone through several revisions, the fundamental concept behind the methodology hasremained the same.
The original metric “Sound Transmission Class (STC)” was designed to calculate a weighted
average of the sound transmission loss through interior partitions. It is based on the amount of soundattenuation required to reduce each octave-based level of a somewhat arbitrary “standard household
noise” spectrum (a composite of live speech, radio and television music and speech, vacuum cleaner
noise and air conditioning noise) to match the NC-25 curve. NC or “noise criteria” curves are a set of
curves established by the American Society of Heating Refrigeration and Air-Conditioning Engineers(ASHRAE), to classify the various levels of background noise for the design of building facilities.
Even though STC (and its ISO approximate equivalent Rw) is not strictly appropriate to evaluate
the sound transmission through exterior envelopes, it has been widely adopted as a means of
performance measurements for windows. In 1990 a new metric OITC (Outside-Inside -Transmission
Class) was introduced. The OITC rating system (and its ISO equivalent Rw+ Ctr) is designed tomeasure the transmission of urban sounds (such as car horns, sirens, construction, and low-flying
airplanes) through exterior walls, windows and façade elements. Urban noise tends to be more
dominated by lower frequencies, so the OITC rating system tends to emphasize this range more in its
calculations. The test procedure for both these metrics is the same.
Although the OITC rating is a more reliable means of evaluation of façade elements than STC, it
is still abstract and lacks enough information needed to evaluate a robust performance of the exterior
barriers. Also, there are two distinct drawbacks with the use of this approach.
First, the loss of resolution by eliminating the frequency dependent nature of sound in the
STC/OITC metric can create inconsistencies in the noise response predictions. For example, elementswith similar acoustical behavior can have different ratings, or in reverse, products with similar ratings
can have different characteristics. The graph in Figure-1 demonstrates the laboratory tested STL of
three different glass compositions. The deviation of STL’s at different frequencies are shown in thebar diagram. As it can be seen the overwhelming majority of the deviations are within a 3dB range
which is indistinguishable by human ears, while the OITC rating differs up to five points and STC
differs up to two points. One can argue that OITC predicted this anomaly. However, a more in-depth
analysis might eliminate the significance of one particular frequency, in favor of either a more
economical solution or a more realistic design.
The second concern with single number rating is the differences in laboratory test results. All
testing facilities have some level of voluntary government sanction accreditations. The facilities are
required to follow stringent procedures and quality equipment to guarantee as much uniformity as
possible. However, no two facilities are identical. This observation is especially true for the size ofchambers, location, and application of diffusers, as well as the positioning of the speakers andmicrophones. So, there is some level of flexibility as to the variations allowed on the results. In general,these tolerances have always resulted in fairly uniform ratings for the tested products, especially whenit comes to STC ratings. However, the popularity of high performing glass and glazing products, aswell as the greater need to consider the low-frequency range of STL response, make the laboratory

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attributes a more important factor. This aspect can be seen in the test results of a very high performing
triple layer insulated laminated glass, tested in three different laboratories. These results are presented
in Figure 2 and are summarized in Table 1. As can be seen, there can be a discrepancy of three to five
points in the value of the OITC. It is important to note that the specimen with the highest rating also
was the one with the smallest area, which is another factor that is lost in the single number rating of
windows and facades. The discrepancies in results happen mostly in lower frequencies, where there
may be more of an interaction between room acoustic modes and the test specimen. The testing labs
in this experiment all met the size requirements of the ASTM-E90, but all were of different dimensions.
Also, the lower frequency response is more susceptible to mounting technique and positioning of thespecimen in the chamber’s demising wall that is less standardized among the different testinglaboratories.
70
STC = 41, OITC = 35

Sound Transmission Loss(dB)

60

STC = 43, OITC = 36
STC = 40, OITC = 30

50
40
30
20
10
0

6 (dB)
3 (dB)

50

63

80

100 125 160 200 250 315 400 500 630 800

1k 1.25k 1.6k

2k

2.5k 3.15k 4k

5kFrequency(Hz)Figure 1 – Comparison of the laboratory STL of three glass compositions. Green – 6.37 mm outer
glass / 12.7 mm airspace / 4.76 mm+1.52mm PVB + 4.76 mm inner glass, Gray– 6.37 mm outer
glass / 12.7 mm airspace / 6.37 mm+1.52mm PVB + 6.37 mm inner glass, Blue– 6.37 mm outer
glass / 12.7 mm airspace / 6.37 mm+1.52mm PVB + 3.17 mm inner glass.
All these factors highlight the need for a more detailed criteria to be used for evaluation of theacoustic performance. Especially in cases that the cost implication is significant, such as commercial
or residential high-rise buildings, or cases where human health and comfort are more critical, such as
hospitals, and educational facilities. These criteria also need to be used in the design process as wellas the certification. To this end a more accurate and practical computational tool is needed for rapid
evaluation and assessment of acoustical characteristics of windows and facades. More importantly thecomputational approach will need to address the frequency dependent nature of façade acoustics andnot rely on single number ratings only.
Table 1 – Test results for triple layer laminated glass

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Glass Area

Glass Density

Temperature

Relative(m2)(kN/m2)C˚

Humidity

36

3.33

0.75

24

51%

45

38

2.02

0.74

22

51%

46

33

3.33

0.75

24

51%

Laboratory

STC

OITC

E

45

C
W

80
Laboratory E

70

Laboratory C
Laboratory W

Sound Transmission Loss (dB)

60
50
40
30
20
10
0

50

63

80

100 125 160 200 250 315 400 500 630 800

1k 1.25k 1.6k

2k

2.5k 3.15k 4k

5kFrequency(Hz)Figure 2 – Comparison of the sound transmission loss frequency response of identical glass
composition at three different testing laboratories.

3. SIMULATION METHODS

Without a doubt, the laboratory testing of windows and curtainwalls are the most accurate meansof evaluating the acoustical performance of the building envelopes. However, as mentioned before,
analytical or empirical means for preliminary and comparative evaluation of these building component
is of significant pragmatic value. The design and manufacture of façade components could takemonths, which severely hinder the opportunity for corrective measures as well as fine-tuning andoptimization of the final design.
Several mathematical, closed formed solutions are derived for the solution of multilayer soundbarriers with cavities (4,8). However, none corroborate favorability with the test results for bounded
and sealed, and laminated glass.
The current practice heavenly depends on results of tests from existing or similar products. The inhouse testing facility is highly desirable, but not within reach of many designers and engineers. Thereis some commercial software (6,7) that can provide quick analysis for designers, but there arelimitations when it comes to multilayer glazing components with framing surrounds.
The use of general propose multi-physics Finite Element Analysis (FEA) software packages canhelp with modeling of complex material geometries, especially the ones encountered in window
framing. These packages (8,9) can efficiently model both air-borne, structure-borne, and the linked
fluid-structure interaction behavior of window frames and glazing. The user can model both thechambers and specimen with great accuracy. FEA methods, however, are more accurate in the lowfrequency range where the mesh counts are reasonable, and solution times are practical. Also, thecreation of a true defused sound filed require some level of expertise and fine-tuning of the models.
The newer versions of FEA packages have attempted to solve this problem. The vibro-acoustic
behavior of the simulation can also be modeled using FEA tools. This factor is important for theunderstanding of the realistic behavior of attachment mechanisms and the interaction between glassand the framing systems.
Another approach is the use of Statistical Energy Analysis (SEA) technique (5). SEA has been themethod of choice among automotive and aircraft industries, and some attempts have been made toextend this approach in architectural acoustics. The main concept in SEA is that a structure (i.e., awindow or a curtain wall system) is partitioned into coupled “subsystems” and the stored andexchanged energies are then analyzed. The original theory is based on the study of the interactions
between, and relative behaviors of, the various subsystems. While this concept is clever from amathematical point of view, it is not very practical for quick insight into the acoustic behavior of agiven system.
The most important step in SEA is to segment the structure to be analyzed into rational subsystems.
This is often a challenge, as the underlying theoretical assumptions must be satisfied while at the same3515

time, several practical considerations must be accounted for. Moreover, for any given structural
system, there may be several possible model constructs, each potentially yielding different behavior
characteristics of the various subsystems. The challenge is to develop a model that most accuratelyreflects the true behavior of the tested system. On the other hand, the SEA is very efficient for thecomputation of sound transmission loss in the high-frequency range.
To remedy this limitation of SEA, one might consider a hybrid approach (11). Here, the primaryconcept is to determine parametric properties of the various components of the window by FEA or
perhaps experimental means. Then the appropriate relationship can be established between thecomponents using SEA modeling. Once the parametric model is established, the assembly of thesubsystems can be used to predict the response of the overall structure to various input conditions.
In essence, rather than subdividing the field equations (models, boundaries) into elements (theapproach used by FEA method), the system is subdivided into a series of sub-systems with interacting
properties. The authors have performed simulation analysis utilizing this technique with some mixed
results.
Figure 3 presents a comparison of laboratory test results for a triple layer insulated glass, with FEA
and SEA approach. Although some promising trends can be established at the two ends of thefrequency spectrum, it is very hard to establish a substantiating argument in the appropriateness ofthe technique. The other shortcoming of this approach is the tedious nature of the modeling work as
well as the need for the utilization of multiple platforms to obtain the solution.

80
SEA

70

Laboratory Test
FEASound Transmission Loss (dB)

60
50
40
30
20
10
0

50

63

80

100 125 160 200 250 315 400 500 630 800

1k 1.25k 1.6k

2k

2.5k 3.15k 4k

5kFrequency(Hz)Figure 3 – Comparison of the sound transmission loss frequency response of a triple layer glass
using SEA and FEA simulation analysis. The glass was made form 10 mm outer layer 19 mm argongap, 10 mm laminate middle pane, 19 mm argon gap, and 10 mm laminated inner pane.
The limitations discussed above is the motivation behind the development of the Digital Acoustic
Lab (DAL) program. The primary objective of this software is to create an easy platform for theestimation of the sound transmission loss of fenestration products. It combines sound theoreticalmethodology with the myriad of laboratory test results to create an accurate and reliable computational
approach for the evaluation of the acoustic properties.

4. DIGITAL ACOUSTIC LAB (DAL)

The purpose of the developed Digital Acoustic Lab (DAL) program is to provide a platform forusers, such as architects, building owners, and other stakeholders, to design, analyze and report a
project-specific configured window, door or curtain wall façade system. It consists of three basic
components, which are system designing module, theoretical analyzing module, and output/reporting
module. The “Design Module” provides a simple and user-friendly interface for users to perform
acoustical analysis of Schüco products. The “Analysis Module” integrates the accurate theoretical3516

models to quickly evaluate the sound transmission loss of various glass panels, aluminum frames, andtheir coupling effect between them. The “Output Module” offers a smooth way to post-processing theresults, builds an interface to visualize the processed data, and automatically generates an informative
product report.
4.1 Design Module
In the design module, users can design a window, door or curtain wall with any customized design
by inputting the dimension of the glazing panels, the size of the frame and possible split pane as shownin Figure 4 (a window system illustrates the usage). After the overall size of the window is defined,available window frames and various glazing panels such as single or multiple monolithic, insulatingor laminated. For multiple laminated glazing panels, as shown in Figure 5, combinations of individualglass, interlayer, and cavity gap of most common practices are provided for users selection. The
combination of the farming system, geometry, and glass composition will complete data preparation.

Figure 4 –Design Module: System definition

Figure 5 –Design Module: System configuration

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4.2 Analysis Module
The configuration of the designed window, door, or curtain wall assembled in the design module
will be transferred to the back end of the analyzing module and analyzed by clicking the computebutton shown in Figure 5. The recently developed theoretical formulation by the authors (12-14) isthe basis of the analysis module. The application first computes the sound transmission loss of theglazing system. The applied theoretical models provide an accurate and reliable evaluation of theacoustic performance of single or multiple laminated glazing panels. The overall STL spectra and thesingle number ratings is computed with the incorporating the aluminum framing contributions byusing the area-weighted logarithmic average.
4.3 Output Module
The output/reporting module post-processes the results computed in the analyzing module andprovides an interface for users to visualize the processed data. As illustrated in Figure 6, the soundtransmission loss of a configured system is shown in 1/3 Octave band from 50 Hz to 5000 Hz, fromwhich the STC/OITC/Rw (C, C tr ) classifications are obtained for the designed system. Also, theprogram provides comparisons of different window configurations, which offers the user a convenient
approach to specify the configuration that performs the best at any interested frequency regions.

Figure 6 – Output/reporting module
Also, DAL provides an audio track to help user perceive the acoustic performance of the designed
window with realistic soundtracks. The program has several preload environmental noise types (traffic
noise, airplane takeoff noise, fire siren noise). Users can change the window opening percentages
through a sliding bar, and the program will calculate the window sound transmission loss result at
each opening percentage and process the original audio track accordingly. The audio simulation isbased on one third octave band graphic equalizer in the range of 50 Hz to 5000 Hz. Comparing fully
opened position with closed window position, the user will hear a clear difference due to the sound.

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REFERENCES
1. ASTM E90-09. Standard Test Method for Laboratory Measurement of Airborne Sound
Transmission Loss of Building Partitions and Elements 2009.
2. ASTM E1332 - 16 . Standard Classification for Rating Outdoor-Indoor Sound Attenuation
2016.
3. ISO 12354-1:2017(E). Building acoustics -- Estimation of the acoustic performance ofbuildings from the performance of elements -- Part 1: Airborne sound insulation between
rooms.
4. Frank Fahy, Foundations of Engineering Acoustics Academic Press, 200
5. Craik Robert J.M,. Sound Transmission Through Buildings Using Statistical Energy
Analysis, Aldershot, Hampshire, England ; Brookfield, Vt. : Gower, c1996
6. INSUL-08 - Predicting Sound Insulation: A quick & accurate tool for predicting the soundinsulation in walls, floors, and ceilings, Marshall Day Acoustics.
7. WinFlag, Version 2.1, Tor Erik Vigran, Trondheim
8. Vigran TE. Building acoustics. CRC Press; 2014.
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10. ANSYS www.ansys.com. ANSYS Inc., Canonsburg, PA USA.
11. VA-One , www.esi-group.com, ESI group, Paris, France.
12. Huang Y, Chen F, DeGanyar T. Sound insulation of a single finite panel—Comparison,validation, and parametric studies. The Journal of the Acoustical Society of America. 2018
Sep 1;144(3).
13. Chen F, Huang Y, DeGanyar T. Sound Insulation of Monolithic or Laminated Single- andDouble-Glazing Panels. In: Prediction methods for sound insulations. Aachen; 2019.
14. Huang Y, Chen F, DeGanyar T, Boehm A, Grotemeyer-Bagnall TR. Sound Transmission
through Aluminum Framings of Window, Door and Façade Systems. In: Prediction methods
for sound insulations. 2019.

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