Standard Guide for Field Measurements of Airborne Sound Attenuation of Building Facades and Facade Elements
5.1 The best uses of this guide are to measure the OINR and the AOITL(θ) or OITL(θ) at specific angles of incidence. By measuring the AOITL(θ) or OITL(θ) at several loudspeaker sound incidence angles, by energy-averaging the receiving room sound levels before computing results, an approximation of the diffuse field results measured with Test Methods E90 and E336 may be obtained.
5.2 The traffic noise method is to be used only for OINR measurements and is most suitable for situations where the OINR of a specimen at a specific location is exposed to an existing traffic noise source.
5.3 The OINR, AOITL(θ), and OITL(θ) produced by the methods described will not correspond to the transmission loss and noise reduction measured by Test Methods E90 and E336 because of the different incident sound fields that exist in the outdoors (1)4. All of these results are a function of the angle of incidence of the sound for two reasons.
5.3.1 The transmission loss is strongly influenced by the coincidence effect where the frequency and projected wavelength of sound incident at angle, θ, coincides with the wavelength of a bending wave of the same frequency in the panel (2, 3, 4, 5). This frequency and the angle of least transmission loss (greatest transparency) both depend on specimen panel stiffness, damping and area mass. In diffuse-field testing as in the laboratory, the effect is a weakness at the diffuse field average coincidence frequency that is dependent on material and thickness, often seen around the frequency of 2500 Hz for drywall and glass specimens. Thick wood panels, such as doors, and masonry wall exhibit lower coincident frequencies while thinner sheet steel exhibits higher coincidence frequencies. For free field sound coming from one direction only, the coincidence frequency varies with incidence angle and will differ from the diffuse-field value (5). Near or at grazing (θ close to 90°) it will be much lower in frequency than the diffuse field (E90 and E336) value, and will increase with reducing θ to be considerably above the diffuse-field frequency when θ is 30° or less.
5.3.2 The OINR is influenced by the angle of incidence of free field sound coming from a specific angle as compared to a diffuse field. This is because the intensity of free field sound incident across the specimen surface S is reduced by cos(θ) when the sound is not incident normal to the surface. Additionally, when the sound of level L arrives as a free-field from one direction only, and that is normal to the surface, the resulting sound intensity in this direction is 4 times that due to diffuse-field sound of the same level, L. These factors are reflected by the cos(θ) and 6 dB terms in Eq 6.
5.3.3 The methods in this guide should not be used as a substitute for laboratory testing in accordance with Test Method E90.
5.4 Of the three methods cited for measuring the outdoor sound field from a loudspeaker, the calibrated loudspeaker and flush methods are most repeatable. The near method is used only when neither the calibrated speaker nor the flush method are feasible.
5.5 Flanking transmission or unusual field conditions could render the determination of OITL(θ) difficult or meaningless. Where the auxiliary tests described in Annex A1 cannot be satisfied, only the OINR and the AOITL(θ) are valid.
5.6 When a room has multiple surfaces exposed to outdoor sound, testing with just one surface exposed to test sound will result in a greater OINR than when all surfaces are exposed to test sound. The difference is negligible when the OITC of the unexposed surface is at least 10 greater than the OITC of the exposed surface.
1.1 This guide may be used to determine the outdoor-indoor noise reduction (OINR), which is the difference in sound pressure level between the free-field level outdoors in the absence of the structure and the resulting sound pressure level in a room. Either a loudspeaker or existing traffic noise or aircraft noise can be used as the source. The outdoor sound field geometry must be described and calculations must account for the way the outdoor level is measured. These results are used with Classification E1332 to calculate the single number rating outdoor-indoor noise isolation class, OINIC. Both OINR and OINIC can vary with outdoor sound incidence angle.
1.2 Under controlled circumstances where a single façade is exposed to the outdoor sound, or a façade element such as a door or window has much lower transmission loss than the rest of the façade, an outdoor-indoor transmission loss, OITL(θ), or apparent outdoor-indoor transmission loss, AOITL(θ), may be measured using a loudspeaker source. These results are a function of the angle of incidence of the sound field. By measuring with sound incident at many angles, an approximation to the diffuse field transmission loss as measured between two rooms can be obtained. The results may be used to predict interior sound levels in installations similar to that tested when exposed to an outdoor sound field similar to that used during the measurement. The single number ratings of apparent outdoor-indoor transmission class, AOITC(θ), using AOITL(θ) and field outdoor-indoor transmission class, FOITC(θ), using OITL(θ) may be calculated using Classification E1332. These ratings also may be calculated with the data obtained from receiving room sound pressure measurements performed at several incidence angles as discussed in 8.6.
1.3 To cope with the variety of outdoor incident sound field geometries that are encountered in the field, six testing techniques are presented. These techniques and their general applicability are summarized in Table 1 and Figs. 1-6. The room, façade, or façade element declared to be under test is referred to as the specimen.
FIG. 1 Geometry—Calibrated Source Method
FIG. 2 Geometry—Nearby Average Method
FIG. 3 Geometry—Flush Method
FIG. 4 Geometry—Equivalent Distance Method
FIG. 5 Geometry—2 m (79 in.) Position Method
FIG. 6 Geometry and Formulas—Line Source Flush Method
1.4 The text of this standard references notes and footnotes which provide explanatory material. These notes and footnotes (excluding those in tables and figures) shall not be considered as requirements of the standard.
1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
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