Source: https://jmrplens.github.io/phonometry/materials/absorbers/suspended-ceilings/ # Suspended ceilings: the EN 16487 test code EN ISO 354 measures the sound absorption of a specimen in a reverberation room and leaves a good deal to the laboratory: how large the specimen is, how it is mounted, how much air is behind it. For most materials those choices move the answer by less than the measurement uncertainty. For a suspended ceiling they do not: a tile absorbs partly by itself and partly through the plenum behind it, so a laboratory that hangs it 400 mm below the ceiling has measured a different product from one that hangs it at 150 mm. EN 16487 is a test code; it adds no measurement of its own and fixes the arrangement so the one EN ISO 354 describes gives the same answer everywhere. ## The specimen is a fixed size, and the mounting is the product 4.1.1.1.1 asks for a specimen as close to 10,80 m2 as the product allows, built from test objects of 0,6 m by 0,6 m butted together with no seal in the joints, the exposed face level with the top of the mounting fixture and the edges at 10 degrees or more to the nearest room wall. For the type E mounting a ceiling actually uses, 4.1.1.2.3.1 fixes the overall depth of construction at 200 mm and says that this is the depth the data for CE marking is compiled at. ```python from phonometry import materials check = materials.check_ceiling_specimen(area_m2=10.8, mounting="E", depth_mm=200.0) print(check.satisfied) # True print(check.ce_marking_depth) # True print(materials.mounting_type("E")) # suspended from a hard surface with an air space behind it ``` The area is a target and not a tolerance, so the check reports the difference and leaves the judgement to the laboratory. A type E depth other than 200 mm passes too, with a warning that says only that the result is not the CE marking data. What the verdict judges is every limit of clause 4 that a dimension of the arrangement can be held to: a substructure no more than 30 mm wide and 50 mm deep, support units no larger than 50 mm by 50 mm at centre distances of at least 1,2 m, a mounting fixture of at least 20 kg/m2, a deflection of no more than 5 mm and, when `relative_humidity_percent` gives one value per measurement, the 50 % of 4.2.2 in every one of them. Leaving one makes `satisfied` false and raises a `SuspendedCeilingWarning` that says which. The 0,6 m test object, the 10 degree edge angle and the substructure pitch of about 0,6 m are targets the clause asks to be aimed at, published as constants to build to and not judged. ```python dry = materials.check_ceiling_specimen( area_m2=10.8, mounting="E", depth_mm=200.0, support_width_mm=40.0, support_height_mm=40.0, support_centre_distance_m=1.2, relative_humidity_percent=[41.0, 44.0], ) print(dry.supports_ok, dry.humidity_ok, dry.satisfied) # True False False ``` ## How the measurement goes Four views of one test arrangement. Top left, the floor of a reverberation room in plan: a specimen of ten point eight square metres made of thirty test objects of sixty by sixty centimetres, five by six, butted together with the joints unsealed and no grid over them, framed by a mounting fixture that covers its perimeter, the whole turned at least ten degrees off the walls and kept at least seventy-five centimetres from every room edge, one metre where possible. Top right, the two runs the absorption is a difference of: the empty room with the fixture taken out, giving T1 and A1, and the room with the specimen in its fixture, giving T2 and A2, with the temperature and the humidity checked for each, over notes asking for a relative humidity of at least fifty per cent with the humidifier off while measuring, the empty room measured at least once a day in stable conditions and again the same day if the air correction passes zero point zero five, and no microphone plane parallel to a room surface. Bottom left, a section through the type E mounting standing face up on the floor, not sunk into it, as CE marking requires: a solid fixture of at least twenty kilograms per square metre sealed to the floor, the exposed face flush with its top and the joint taped, two hundred millimetres of overall depth from the floor to the face, substructure profiles no more than thirty millimetres wide and fifty high at about sixty centimetre centres on support units no larger than fifty by fifty millimetres, a closed air space with no partitions, and a deflection of no more than five millimetres at any point, under a note that the face up arrangement is only for a ceiling whose absorption gravity does not change, a loosely laid porous backing being held to the tile by a wire grid of wire no thicker than two millimetres with a mesh of about one hundred millimetres. Bottom right, the substructure seen from below, the profiles running one way about sixty centimetres apart and their supports at least one metre twenty apart. A box at the foot carries the absorption coefficient as A2 minus A1 over S, with S taken over the test objects, and the air-absorption correction, four V times m2 minus m1 over S, whose magnitude is capped at zero point zero five in every band, with the note that the uncertainty of Table 1 holds for this mounting alone Build the specimen to 10,80 m2 out of whole test objects, butted together, with the joints unsealed and the perimeter covered by the mounting fixture. Mount it at 200 mm overall depth if the result is to support CE marking, on a substructure inside the 30 mm by 50 mm section carried by supports inside 50 mm by 50 mm and at least 1,2 m apart, and check the deflection at the worst point. Set the specimen edges at an angle to the room walls. Measure the empty room and then the room with the specimen in it as EN ISO 354 prescribes, holding temperature and humidity steady between the two runs and the humidity at 50 % or more in each: the correction below is the difference between them, and it is a difference of days rather than of ceilings. ## The air in the room is part of the answer The absorption coefficient comes from two reverberation times measured on two occasions, so a change of temperature or humidity between them shows up as absorption the specimen never had. 4.2.1 caps the whole effect: the correction `4V(m_2 - m_1)/S` shall not exceed 0,05 at any frequency, and 4.2.2 asks for at least 50 % relative humidity. ```python correction = materials.air_absorption_correction( volume_m3=200.0, specimen_area_m2=10.8, attenuation_with=[0.0011, 0.0013, 0.0018, 0.0028, 0.0055, 0.0170], attenuation_empty=[0.0010, 0.0012, 0.0016, 0.0025, 0.0050, 0.0160], ) print(correction.round(3)) # [0.007 0.007 0.015 0.022 0.037 0.074] ``` That last band is over the cap and the library says so rather than returning it quietly: the answer is a second measurement of the empty room, which is what 5.2 asks for. ## What the whole thing buys Table 1 is the point of the exercise: the reproducibility between European laboratories from the round robin of Annex A. ```python print(materials.reproducibility_uncertainty().round(2)) # [0.23 0.23 0.11 0.1 0.1 0.13] print(materials.WEIGHTED_UNCERTAINTY) # 0.08 print(materials.EN16487_COVERAGE_FACTOR) # 2.8 ``` Two things are worth reading twice. The figures are an expanded uncertainty, with the note under the table multiplying the ISO 5725-6 reproducibility standard deviation by 2,8 rather than by the usual 2. And 6.2 says plainly that they hold for a plane absorber with the type E mounting at 200 mm and that nothing has been investigated for any other absorber or mounting, which leaves a baffle, a raft or a free-hanging unit outside them. ## What this page does not cover The measurement itself, which is EN ISO 354; discrete absorbers, baffles and rafts measured as objects rather than as a plane; and the product requirements of EN 13964 beyond the definitions and the CE marking depth this code refers to. ## See also - [Measuring sound absorption](https://jmrplens.github.io/phonometry/materials/absorbers/absorption-measurement/): the reverberation-room method this code constrains, with the Sabine coefficient and its rating. - [Spatial sound decay in workrooms](https://jmrplens.github.io/phonometry/buildings/rooms/workroom-sound-decay/): what an absorbing ceiling is bought for, measured in the finished hall. - [Room-noise criteria](https://jmrplens.github.io/phonometry/buildings/rooms/room-noise/): the target the absorption is chosen against. - API reference: [`materials.absorbers.suspended_ceilings`](https://jmrplens.github.io/phonometry/reference/api/materials/suspended-ceilings/).