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Acoustical Performance Testing



Q:

What is difference between the STC & OITC ratings?

A:

The STC rating is calculated in accordance with ASTM E413 (Originally published in 1970). It was created to provide a single number rating for interior building partitions that are subjected to noises from speech, television, radio, office equipment and other mid to high frequency noise sources. The higher the number, the better the noise isolation. The STC rating is calculated over the frequency range of 125 to 4000 hertz. The rating is calculated by comparing the measured sound transmission loss to a reference contour curve. The STC rating must only be assigned to specimens tested in a laboratory.

The OITC rating is calculated in accordance with ASTM E1332 (Originally published in 1990). It was created to provide a single number rating for facades (exterior walls) and facade elements (windows and doors) that are subjected to transportation noises (aircraft, trains, automobiles, and other low to mid frequency noise sources). The higher the number, the better the noise isolation. The OITC is calculated over the frequency range of 80 to 4000 hertz. The OITC is calculated by subtracting the logarithmic summation of the transmission loss values from the logarithmic summation of the A-weighted transportation noise reference spectrum. An Apparent OITC rating can be assigned to specimens tested in the field and in the laboratory.

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Q:

Are the STC and OITC ratings determined by the same test?

A:

The sound transmission loss values from the ASTM E90 test are used to calculate the STC and OITC ratings in accordance with ASTM E413 and ASTM E1332 respectively.

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Q:

What is the ASTM E1425 / AAMA 1801 test procedure?

A:

The ASTM E1425 / AAMA 1801 test procedure is only for windows, doors and glazed wall sections.

These procedures were developed by ASTM and AAMA to ensure that all acoustical fenestration products were being tested in a fully operable condition. Since air leakage has a major impact on sound transmission loss, the air leakage must be also measured and reported. The AAMA 1801 test procedure specifies the use of ASTM E1425, which requires operating force or latching force, air leakage and sound transmission loss measurements on the test specimen. ASTM E1425 specifies using ASTM E2068 for the operating force test, AAMA/WDMA/CSA 101/I.S. 2/A440 for the latching force test, ASTM E283 for the air leakage test, and ASTM E90 test method for the sound transmission loss test. The operating force test is only performed on specimens with operable sash or panels. The size of the test specimen shall be in accordance with ASTM E1425. The pass/fail requirements for the operating force and air leakage tests are listed in the AAMA/WDMA/CSA 101/I.S. 2/A440 document.

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Q:

What type of glazing would I need to use in my product to achieve an OITC rating of 30 or an STC rating of 40?

A:

Based on our experience at the Architectural Testing Acoustical Laboratory, an OITC rating of 32 or STC rating of 40 is very difficult to achieve on a window with conventional 1" insulating glass. To achieve these ratings and above, a dual window configuration with two sets of sash or a prime window with an exterior or interior storm panel is generally required. The table below outlines the typical range of ratings of different glazing options. These ratings may be lower if the window has significant air leakage or if there are flanking problems between the primary and secondary sash. There are many other factors that may affect the overall rating of a window (e.g. materials used, daylight opening size, etc.). If you require a different rating or have any questions about the table below, please contact us for more information.

Prime Window IG Glazing Prime Window IG Glazing Prime to Secondary Air Space OITC Rating STC Rating
1/8" anneal, 1/2" air, 1/8" anneal N/A None 23-24 27-28
1/4" anneal, 1/2" air, 1/4" anneal N/A None 25-26 31-32
1/4" anneal, 1/2" air, 1/4" lami N/A None 27-28 34-35
*1/4" lami, 1/2" air, *1/4" lami N/A None 28-29 37-38
1/8" anneal, 1/2" air, 1/8" anneal 2" 1/8" anneal 28-30 39-41
1/4" anneal, 1/2" air, 1/8" anneal 2" 1/4" anneal 32-35 42-44
*1/4" lami, 1/2" air, 1/8" anneal 2" 1/4" anneal 34-36 43-45
*1/4" lami, 1/2" air, 1/8" anneal 2" 1/4" anneal 35-37 44-46
*1/4" Lami consists of two layers of 0.12" thick glass with a 0.030" interlayer material.

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Q:

Do I need to place a wood buck around my window for the sound transmission loss test?

A:

No. Our test openings are specifically designed to accommodate most standard window sizes for the ASTM E90 and ASTM E1425 / AAMA 1801 sound transmission loss tests. The test openings are designed to minimize air leakage and sound transmission around the test specimen.

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Q:

Do I test my window with or without the nailing fin?

A:

We normally test the window without the nailing fin because we are evaluating the performance of the window and not the installation. Appendix D of the AAMA Laboratory Accreditation Program Operations Manual provides window installation details for sound transmission loss tests. We can however test the window and the installation, if we are only conducting an ASTM E90 test. The specific details of the installation would need to be recorded in the test report.

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Q:

How do laboratory and field sound transmission loss test results vary?

A:

For the laboratory testing, the products are tested in a closely controlled environment. The temperature and humidity conditions are controlled and very nearly the same on both sides on the test specimen. The test rooms are designed to provide a very uniform diffuse sound field on both sides on the sample. The rooms and filler walls are designed to minimize any exterior noises and to minimize any sound that might bypass (flank) the test specimen. The sound absorption of the receiving room is very low and it can be accurately determined.

For testing in the field, however, most of these conditions can not be controlled. The temperature and humidity conditions are monitored, recorded and used in the calculations but they can not be closely controlled. Room sizes and absorption characteristics vary substantially from one project to the next and rarely do you find good diffuse sound field conditions. Exterior and interior noise sources can affect the test results if they are not eliminated or minimized. When performing a sound transmission loss test on a facade element such as a window or door, sometimes the surrounding walls might have lower transmission loss than the element being tested, or there could be flanking problems through other parts of the building. Tests can be performed to determine if there is a flanking problem but if there is one, the sound transmission loss can not be accurately determined. Poor construction practices can also affect the test results.

It is generally accepted that field sound transmission loss measurements will be 3 to 5 dB lower than laboratory sound transmission loss measurements on the same test specimen.

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Q:

What is the difference between NRC and SAA?

A:

The Noise Reduction Coefficient (NRC) and Sound Absorption Average (SAA) values are both single number ratings that indicate the level of sound absorption provided by the product being tested. The NRC value is the average of the sound absorption coefficients at four 1/3 octave frequencies (250, 500, 1000 and 2000 hertz). The SAA value is the average of the sound absorption coefficients at twelve 1/3 octave frequencies ranging from 200 to 2500 hertz. The NRC value is rounded off the nearest 0.05 increment. The SAA value is rounded off the nearest 0.01 increment. The NRC and SAA values normally range from 0.00 to 1.00, with 1.00 indicating 100% sound absorption per square foot of material. These values can exceed 1.00 when thick specimens or specimens with large air spaces are being tested.

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Q:

What affects the sound absorption of an acoustical product?

A:

There are many physical characteristics that will affect the sound absorption of a product. The primary factors are product thickness, density, and fiber diameter. How a product is installed can affect its absorptive properties. If the product is installed with an air space behind it, it will have higher sound absorption. If the product has a facing material, the sound absorption can decrease or increase at certain frequencies depending on the porosity of the facing material and the product thickness.

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