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

Sound Transmission through Aluminum Framings of Window, Doorand Façade Systems
Yihe Huang 1; Fangliang Chen 1; Tejav DeGanyar 1; Anselm Boehm2 and Tjorven Rebeccah
Grotemeyer-Bagnall2
1

Virtual Construction Lab of Schuco, New York, NY
2

Schuco International KG, Bielefeld, Germany

ABSTRACT
Recent environmental regulations bring up higher standards on acoustic comfort. Mitigating the noisetransmission from façade exterior to interior is rising as an important issue in building envelop designs.
Modern façade systems consist of aluminum frames and multiple high-performance layers of insulating or
laminated glass. Thus, the overall sound insulation of such systems depends not merely on glasses but mightmore on frames and the coupling between them. Particularly when the STC of glass reaches 40 or higher, thesound path through the framing elements becomes more critical. However, this crucial issue has not received
enough investigation, and no satisfactory approach has been developed in the literature yet. This issue isaddressed by studying the coupling between aluminum frames and glazing infill, and an extended model has
been accordingly developed. A series of laboratory tests with different frames were conducted to validate thepredictions. As an application of this research, a design-orientated simulating platform has been developed
to provide quick estimations of the sound insulation performance of window and façade systems.
Keywords: Sound, Insulation, Transmission Loss, Aluminum Frame, Window, Facade

1. INTRODUCTION

Aluminum-framed window has become a prevailingly popular choice for commercial andresidential high-rise buildings. Due to the high strength of the aluminum material, it offers a large
daylight opening to frame ratio at a relatively low purchase cost. The narrow frame width is ofparticular importance for modern curtain wall designs.
Meanwhile, Aluminum has material that has high durability and longevity properties that performs
well under harsh weather conditions. Also, with the high-quality thermal broken design, high energy
efficiency window and façade systems have been evolved tremendously over the past few years, which
offers exceptional performance through thermal insulation and water – air tightness. Compared to theefforts dedicated to improving the thermal performance, much less attention has been paid to theacoustic performance of Aluminum-framed window systems so far. With the rapid urbanization over
the world, environmental noise pollution has become a bigger concern, especially for residential
construction in noisy areas. However, there is not a satisfactory approach developed yet to address
this critical issue up to date systemically.
The overall sound insulation of an Aluminum-framed window depends not merely on glasses but
might more on frames and the coupling between them. It is common practice for window
manufacturers and fabricators to obtain acoustic performance of a window system by conducting
laboratory “sound transmission loss” experiments. Laboratory test does provide a straightforward way
to access the sound transmission characteristics. However, numerous evidence showed that poor
repeatability among different laboratories exhibits. Also, it suffers from time and expense cost to1

Yhuang@schuco-usa.com

203conduct a series of tests. Moreover, each window system has its profile details and glazing selections,making it far expensive to target a series of test of a complete system.
Because of the high complexities of airborne interactions and sound transmission paths cross the
Aluminum-framed window system, it is increasingly challenging to evaluate the overall acoustic
performance of a framed window system. For this reason, very limited theoretical models can be foundin the literature so far.
The effort of this study is to tentatively characterize the overall sound transmission of thealuminum-framed window system. The coupling between aluminum frames and glazing infill will becarefully studied, a series of laboratory tests with different glazing options are conducted and analyzed,
through which a feasible method will be proposed to predict the aluminum window transmission loss
in 1/3 octave bands frequency. As an application of this research, a design-orientated simulating
platform has been developed to provide quick estimations of the sound insulation performance of
window and façade systems.

2. METHODOLOGY
The approach used in this paper to estimate the overall window acoustic performance is thefollowing. Firstly, the daylight opening area in the window frame is shielded of high sound insulation
masking panel from the sound field. Heavy panels are attached to the vision area to block the soundpath and the masked window setup is tested. Then, the acoustic performance of the composite mask
is measured by adjusting the opening size of the filler wall and installing the mask without a frame.
The frame sound transmission coefficient can be reverse calculated using the following equation:
1∑𝑁𝑁
𝑅𝑅𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡 = −10 𝑙𝑙𝑙𝑙𝑔𝑔10( ∑𝑁𝑁
𝑛𝑛=1 𝑆𝑆𝑛𝑛 𝜏𝜏𝑛𝑛 ), where 𝑅𝑅𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡 is the framed mask transmission loss. 𝑆𝑆𝑛𝑛 is the𝑛𝑛=1 𝑆𝑆𝑛𝑛

individual component surface area. 𝜏𝜏𝑛𝑛 is the individual component sound transmission coefficient.
With the frame transmission loss calculated based on experimental data and the glass performance
calculated by theoretical model, the overall window element transmission loss is easy to obtain byusing the area-weighted logarithmic average of individual components.
The measurements were divided into two categories: one in which only the unframed infills were
tested, and the other one has the same kind of infills tested inside an inward opening Aluminum
window frame.

2.1 Test Environment
The experiments in this paper were performed by Riverbank Acoustical Laboratories™ (RAL) by
ASTM E90 – 09(2016) “Standard Test Method for Laboratory Measurement of Airborne Sound
Transmission Loss of Building Partitions and Elements.” There are three testing chambers in RAL
that can be used as either source room or receiving room. The volume of chamber1, chamber2, andchamber3 were 177 m3 , 178.3 m3 and 131.3m3, respectively. An air gap structurally and vibrationallyisolated each of the two adjacent rooms. In the tests, all specimens were placed at the edge of thereceiving chamber. Rotating microphones obtained space and time-averaged sound pressure levels,and these values were measured to calculate the transmission loss(TL) in 1/3 Octave bands from 50
Hz to 5000 Hz.
2.2 Type of Test Samples
The unframed infills tests used Chamber 2 as the source room and Chamber 3 as the receivingroom. Chamber 3 has a dimension of 6.11m x 4.27m x 5.04m. The filler wall between two chambers
was built with solid cast concrete. The tested opening for unframed infill was 1045mm x 1294mm.
Three different glass and one composite mask were tested in this group. Table 1 shows the measured
composition of each infill type. The glass specimen tested for this study were all manufactured by
Viracon.
For the frame performance study, one kind of typical Aluminum window frame was used for all
framed infill tests. The tests in this category used Chamber 1 as the source room and Chamber 2 as
the receiving room. Chamber 2 has a dimension of 7.14m x 5.18m x 4.56m. The filler wall wasconstructed using multi-layered gypsum board with a measured STC value of 61. The tested opening
for framed infill is 1230mm x 1480mm.

204Table 1 – Composition detail of the unframed infills
No.

Glass Details

STC1

13.1mm Glass(1.52mm PVB), 19.1mm Air space, 7.4mm Glass (0.76mm PVB)

4229.5mm Glass, 18.4mm Air space, 3.9mm Glass

39

3

5.7mm Glass, 13.7mm Argon, 5.8mm Glass

33

4

Composite Mask

52

2.3 Mask Composite
In testing aluminum profiles it is crucial to have a setup that can ensure the only significant soundtransmission path was through the tested aluminum frame. There are some criteria that was follow
when designing the masking technique. Firstly, the surface of the mask panel needs to be aligned withthe surface of the frame to avoid grazing incidence on the mask edge. Secondly, for geometry reasons,only a limited frame depth is available to hold the mask panels, the mask composition needs to choose
the material with high density and ideally good damping capability.
Table 2 – Composite mask construction detail from source room to receive room
Composition

Thickness(mm)Weight(kg)Steel plate

3.10

32.32

Mass Loaded Vinyl sheet

3.18

7.49

Glass No. 1

39.69

64.18

Gypsum board

15.88

13.27

Mass Loaded Vinyl sheet

6.63

13.38

Steel plate

3.10

32.32

Gypsum board

15.88

13.27

In the setup, the mask panel consists of two layers of 3.1mm thick steel plate to guarantee higharea mass. In between these steel layers, two layers of the mass loaded vinyl sheet is included to
improve damping effect, and the remaining space are filled with gypsum board. The construction
sequence of the composite mask is explained in Table 2. The area density of the composite maskreached a high number of 130kg/m2 . Figure 1 shows the photo of mask setup and 3D rending for the
exploded view of the composite mask design. The drawing details is presented in Figure 2. The
masking panels constructed have the exact size of the window frame’s daylight opening size, and thepanels are fastening into the frame through a friction fit. The edges of the mask are well-sealed withacoustic caulk and duct tape.

Figure 1 - (left) A Photograph of the masked window (right) Exploded view of the masked window

205

Figure 2 - Drawing detail of the masked window

3. RESULTS and DISCUSSIONS
3.1 Framed Glass vs. Unframed Glass
Figure 3 - 5 compares the unframed glass and the framed glass for three different test cases. The
glazing composition for glass No.1 - 3 is shown in Table 1. Their sound transmission behavior differs
in different frequency ranges; the resonance frequency and coincidence frequency for each glass
sample are marked in the chart.
In the frequency range below 100Hz, the measurements do not follow a clear pattern as the datacollected is greatly affected by the testing environment. In the frequency range above 100Hz, the test
data is reliable. The main reason is that the Chamber 2 and Chamber 3 are relatively large as receiving
chambers, and thus they all give very low fundamental frequencies. The eigenfrequencies of the test
chambers can be calculated by𝑐𝑐
𝑛𝑛2 𝑚𝑚3 𝑝𝑝2(1)∙� 2 + 2 + 2
𝐿𝐿
𝐵𝐵
𝐻𝐻
2
where L, B, and H are length, width and height of the room, c is the sound speed in air and n, m andp represent the order of room modes corresponding to L, B, and H, respectively. The analyticallysolved first eigenfrequencies for the receiving chambers are below 40Hz. As a result, the test chamber
effect is negligible in a higher frequency range. Also, the 95% confidence interval of the experimental
results at a frequency higher than 100Hz is less than ±1dB, which suggests a stable testing result withthis frequency range.
For frequency range between100Hz and the double layer glass resonance frequency, the inclusionof the Aluminum frame decreased the glass TL by 0dB ~ 4dB. The reduction was expected, as thealuminum frame vibration may deliver the sound power to the glass panels through the glass edges.
At higher frequencies, the double panel glass model can be simplified to a model of two limp mass
coupled by a spring(1). The mass-air-mass frequency is derived assuming the only normal incidence
excites the partition, the equation obtained is:
𝑓𝑓𝑛𝑛𝑛𝑛𝑛𝑛 =𝑓𝑓𝑟𝑟 =

𝜌𝜌0
𝑐𝑐
1
1∙� ∙� +
�𝑑𝑑 𝑚𝑚1 𝑚𝑚2
2𝜋𝜋

(2)

where 𝑚𝑚1 and 𝑚𝑚2 are the surface densities, 𝜌𝜌0 is the air density, d is the spacing between two panels.
In Figure 3 and 4, it is noticeable that for the two double insulating glass specimens of glass No.2 andglass No.3, the framed glass and unframed glass both have a dip in the calculated glass resonancefrequency. However, for the double laminated glass No.1, the same dip at the glass resonancefrequency did not occur. Figure 5 presents the glass No.1 transmission loss curve comparison between
the published data from the manufacture and the measurements taken in this study. The manufacture
specimen size was 2.1336m x 0.9144m. The data from the manufacture shows a clear dip in resonancefrequency. As the specimen in RAL was held in the test opening by dense mastic around the perimeter,
the extra damping at the specimen edges reduces the resonance amplitude and is likely responsible
for the missing dip.
Above the resonance frequency, the framed glass shows close performance to the unframed glassfor double insulating glass; in this region, the sound behavior is mainly based upon the total mass of206

the sample. In the higher frequency range, the two panels act individually. For every single plate, thecoincidence frequency is given by:
𝑐𝑐 2
𝑚𝑚
(3)
𝑓𝑓𝑐𝑐 =∙�
2𝜋𝜋𝐵𝐵
where B is the bending stiffness, m is the surface density of the calculated plate. Again, framed glass
TL curve shows a dip at the same frequency of the unframed glass critical frequency. A larger
difference between unframed glass and framed glass TL are found at frequencies above the criticalfrequency.
In all three tests, the single number ratings of the framed glass closely reached the unframed glass
ratings, the same holds for the high sound insulation glass with a measured STC value of 42dB. The
STC of framed glass No.3 and the OITC value of framed glass No. 1 are even 1dB higher than thoseof the unframed glass tests. The observation is in line with previous studies on Aluminum window
frame(2, 3). Hence, it can be concluded that, with proper design and sealant, even though Aluminum
frame was full of cavities and extruded in thin wall thickness, it can achieve high sound reduction forthe overall window systems together with good performance glass.
60
Glass No. 3

Sound Transmission Loss(dB)

50

Frame + Glass No.3
fc

40

30

f0

20

10

0

50

63

80

100 125 160 200 250 315 400 500 630 800
Frequency(Hz)1k 1.25k 1.6k

2k

2.5k 3.15k 4k

5k

Figure 3 - STL of unframed and framed double insulating glass No. 3
60
Glass No. 2

Sound Transmission Loss(dB)

50

fc2

fc1

Frame + Glass No.2

40

f0

30

20

10

0

50

63

80

100 125 160 200 250 315 400 500 630 800
Frequency(Hz)1k 1.25k 1.6k

2k

2.5k 3.15k 4k

5k

Figure 4 - STL of unframed and framed double insulating glass No. 2

207

70
Glass No. 1 (RAL)

Sound Transmission Loss(dB)60

Glass No. 1 (Viracon)
Frame + Glass No.1

50
40

fc1

fc2

f0

30
20
10
0

50

63

80

100 125 160 200 250 315 400 500 630 800
Frequency(Hz)1k 1.25k 1.6k

2k

2.5k 3.15k 4k

5k

Figure 5 - STL of unframed and framed double laminated glass No. 1

3.2 Masking Procedure
The fundamental idea of the masking procedure design is built up a heavy mass shield to block theincident airborne sound power path in the window vision area, only leave the frame area as the primarypath for sound energy transmission. Using the result of the mask only test and framed mask test, theacoustic properties of the frame can be extracted using Eq (4).
As the window and façade element consists of frame components and infill component, thelogarithmic average equation becomes:
1
𝑅𝑅𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡 = −10 𝑙𝑙𝑙𝑙𝑙𝑙10 �× (𝑆𝑆𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓 𝜏𝜏𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓 + 𝑆𝑆𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖 𝜏𝜏𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖 )�
𝑆𝑆𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓 + 𝑆𝑆𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖(4)

where 𝑅𝑅𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡 is the framed mask transmission loss, 𝑆𝑆𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓 is the frame surface area, 𝑆𝑆𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖 is theinfill surface area, 𝜏𝜏𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓 is the frame sound transmission coefficient and 𝜏𝜏𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖 is the frame soundtransmission coefficient.
The calculated Aluminum frame transmission loss using masking procedure can be found in Figure
6. Comparing the tested mask TL and calculated frame TL, the sound power transmitted through themask composite is more than 10dB in all frequencies range except at 100Hz, 125Hz, and 160Hz. It
can be further observed that the TL of the composite mask shows an increasing linear trend above
200Hz, which indicates a mass-controlled behavior and no flanking transmission concern around thesample perimeter. Thus, it is reasonable to assume that, in a framed mask test, most of the soundenergy passes through the aluminum frame.
The STC/OITC value of the composite mask is 52/44dB. In the condition that the masking
procedure is difficult to conduct, a high sound insulation glass can be used as the masking shield if
the single number rating of the glass is close to the composite mask. Using high-performance glass as
the shield, it ensures a more comparable boundary behavior and sealing condition. As in most designs,
the frame and glass connection mechanism is consistent for the same aluminum frame product line,
and the glass is likely to be installed to the Aluminum frame through a gasket made of EPDM or
structural silicone.

208

70
Measured (Frame + Mask)

Sound Transmission Loss(dB)60

Measured Mask
Calculated Frame

50
40
30
20
10
0

100

125

160

200

250

315

400

500 630 800
Frequency(Hz)1k

1.25k 1.6k

2k

2.5k 3.15k

4k

5k

Figure 6 - STL of measured framed mask system, unframed mask composite, and calculated frame results

3.3 Validation
Figure 7 presents four validation cases for the masking procedure; A good agreement can be seen
for the general trend between the measured and predicted window element performance. The
prediction method also gives a good estimation of the single number rating within ±1dB (see Table 3).
60

Diff
Measured40

Sound Transmission Loss(dB)Sound Transmission Loss(dB)60

Calculated

20
0

100

1000

-20

Diff
Measured40

Calculated

20
0

100

-20

Frequency(Hz)Frequency(Hz)(a) Glass No.3(b) Glass No.2

60

40

Diff
Measured20

Calculated
100

1000

-20
Frequency(Hz)(c) Glass No.1

Sound Transmission Loss(dB)Sound Transmission Loss(dB)

60

0

1000

40

Diff
Measured200Calculated
100

1000

-20
Frequency(Hz)(d) Glass No.4 - 8mm/20mm/6mm

Figure 7 - STL comparison of measured and predicted window results of four different glass options

209

Table 3. Single number rating comparison of measured and predicted results
Glass No.1

Glass No.2

Glass No.3

Glass No.4

STC

OITC

STC

OITC

STC

OITC

STC

OITC

Measured unframed glass

42

33

39

31

33

28

43

33

Measured framed glass

41

34

38

31

34

28

42

34

Predicted framed glass

41

35

39

32

34

29

42

34

It is worth mentioning that the comparison data in Figure 7(d) were gathered from the ift
Rosenheim testing lab at various times over all the years, but still achieved a good comparison trend.
The glass composition is 8mm clear glass with 0.76mm acoustic PVB interlayer, 20mm argon space,and 6mm clear glass.
Although the prediction method shows good agreement with the experiment results, this method
shall not be treated as a replacement to the laboratory test; it could serve as a quick and relatively
accurate sound performance analysis method in building pre-construction phase.

4. CONCLUSIONSThis study focused on the sound behavior of the Aluminum frame in window systems. A series ofunframed and framed glass tests were conducted to study the acoustical effect of inclusion of
Aluminum frame as the window perimeter.
Also, a masking procedure to obtain the frame sound performance is proposed. The frame
performance can then be combined with the glass TL estimation to get the entire window or façade
STL. Once the frame STL is obtained, and the glass STL estimated through experiments or theoreticalmodel, the window element sound properties can be calculated using Eq(5). An accurate glass
estimation method for double insulating glass and double laminated glass has been proposed in anotherwork from the second co-author of this paper(4).
As a conclusion, the idea of the masking method would be an effective and economical approach
to identify the aluminum window and façade element sound characteristics.

REFERENCES
1.

Hassan OAB. Building Acoustics and Vibration: Theory and Practice. World Scientific Publishing
Company; 2009. 970 p.

2.

Tadeu AJB, Mateus DMR. Sound transmission through single, double, and triple glazing.
Experimental evaluation. Applied Acoustics. 2001 Mar 1;62(3):307–25.

3.

Bielefeld H.W, DeGanyar T. Acoustical Performance of Aluminum Framed Façade Systems.
Conference Proceedings. 2018;8.

4. Chen F, Huang Y, DeGanyar T. Sound Insulation of Monolithic or Laminated Single- and DoubleGlazing Panels. In: Prediction methods for sound insulations. Aachen; 2019.

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