The sound insulation coefficient of a partition (e.g., windows, walls, etc.) is expressed in dB (decibel) and determines the value of noise reduction, the source of which is outside the partition.

The bigger the value of the coefficient, the better the acoustic insulation of the partition. Considering the fact that the acoustic parameters are defined based on the logarythmic scale, it is accepted that reducing the noise by 10 decibels means it was realistically reduced by around 50%. 

How to declare the acoustic properties of windows?

According to the EN 14351-1 norm, acoustic properties should be declared, using the following values:

• R_w – weighted sound reduction index,
• C_tr – spectral adaptation index for low and medium frequency sounds,
• C – spectral adaptation index for medium and high frequency sounds.

What the correct notation should look like: R_w ( C ; C_tr )

Specific acoustic insolation index - RA1 and RA2

If the sources of the noise are:

• residential noise (conversation, music, radio, television),
• children playing,
• trains riding at a medium or high speed,
• cars running on the expressway > 80 km/h,
• jets flying in a near location,
• industrial plants emitting mainly medium or high frequency noise

the requirments refer to the index RA₁ = R_W + C.

If the sources of the noise are:

• city traffic,
• trains riding at a low speed,
• helicopters,
• jets flying in a remote location,
• club music,
• industrial plants emitting mainly low and high frequency noise

the requirements refer to the index RA₂ = R_W + C_tr.

The values of the indexes C and C_tr are negative (C =  -1 -3 dB, C_tr = -4 -8 depending on the construction of the window), therefore RA₁ and RA₂ are always lower than R_w. 

 

Methods of determining acoustic insolation of windows

Izolacyjność akustyczną R_w ( C ; C_tr ) (wg EN 14351-1, zał. B, pkt. B.1) okien należy określić za pomocą:

• Method 1: tabulated values in accordance with Annex B of EN 14351-1+A1

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• Method 2: tests

Method 1: Determining the acoustic insolation of windows with insulated glass units IGU using tabulated values

The general requirements for determining the Rw(C;Ctr) for a window based on the IGU data: Fixed and opening single-frame windows and air permeability min. class 3.

Diagram of the procedure for determining sound insulation using Method 1 on the example of a window with the following characteristics:

• single-wing,
• measurements: 1600 x 1700mm,
• fitted with 2 seals,
• air permeability in class 4,
• insulated glass unit IGU with the acoustic insolation value equal to Rw(C;Ctr)=30(-1;-4)dB.

Step 1: Using the R_w=30dB value for the glass, we can read the Rw value for a window, and it equals R_w=33dB.
Step 2: Using the insolation value of the glass, we can calculate the value of the RA2 index, and it equals RA₂ = R_W + C_tr = 30 + (-4) = 26dB.
Step 3: Using the RA2=26dB value for the glass, we can read the RA2 value for the window, which is RA2=28dB.
Step 4: the value of the C index for the window is assumed to be -1dB.
Step 5: Using the Rw=33dB and RA2=28dB that you can read from the tables, we can calculate the value of Ctr = RA2 - Rw = 28 - 33 = -5dB.
Step 6: We can calculate the area of the window F = 1.6 x 1.7 = 2.72m2.
Step 7: From Table B.3, for the calculated window area F = 2.72m2, we can read the correction value, which is -1dB.
Step 8: Then we have to adjust the value of Rw=33dB from step 1 by -1dB. Rw = 33 - 1 = 32dB.
Step 9: the value of sound insulation of the window according to the requirements of the standard is: Rw ( C ; Ctr ) = 32 ( -1 ; -5 )

This method can be used for acoustic insolation of windows that equals:

R_w ≤ 38 dB or RA₂ = R_w + C_tr ≤ 34 dB!

Method 2: Determining the acoustic insolation of windows using tests

This method can be used for all values of Rw and RA2, but must be used for values of Rw > 38 dB or RA2 = Rw + Ctr > 34 dB. The unquestionable advantage of the test method is that better values of window sound insulation are obtained compared to the table method.

Example:

• single-wing window, 
• measurements 1230 x 1480mm, F = 1,82m²
• aluplast's IDEAL 4000 system – 2 seals,
• air permeability class 4,
• glass 6/16/6 – R_w ( C ; C_tr ) = 31 ( -1 ; -3 )

According to the tabular method, such window is characterized by a sound insulation value of Rw (C;Ctr) = 33 (-1;-4), while from the tests the result was Rw (C;Ctr) = 37 (-2;-4). The tests were conducted on reference windows, i.e. windows with an area of less than 2.7m2. The transfer of test results to windows of other sizes is carried out according to the rules in Table B.3.

Observing the process, using set example:

• Acoustic insolation requirements of windows not lower than Rw (C;Ctr) = 42 (-1;-5).
• 2200x2300mm windows made using the Ideal 4000 system.
• Window area equals 5,06m2 so more than 4,6m2,
• According to the table B.3 the acoustic insolation of the tested window has to be lowered by 3 dB. 
• To meet the requirements the window had to achieve Rw (C;Ctr) = 45 (-1;-5) in tests.
• This level of acoustic insolation was achieved when testing a window made using Ideal 4000 system with 13VSGSi/19/9VSGSi glass unit. 

Conclusions:

• The sound insulation of windows with Rw ≤ 38 dB or RA2 = Rw + Ctr ≤ 34 dB can be determined by tabulated values or tests,
• The sound insulation of windows with a value of Rw > 38 dB or RA2 = Rw + Ctr > 34 dB must be determined by tests,
• Often, the sound insulation values obtained in tests are better than those determined using the tabular method.

Aluplast's Technical Department has developed a tool that enables the selection of windows with specific sound insulation based on both tabular data and a wide range of tested window constructions in different aluplast systems with different glazing packages.