Consultancy Report Ref: 9383-R01

Transcription

1 Consultancy Report Ref: 9383-R01 Submitted to: Prepared by: Mr Tim Simmons The Woolley Shepherd Secret Meadow Weekmoor Milverton Taunton TA4 1QE John Fithyan Laboratory Manager Approved for issue by: Andy Varley (MIOA) Senior Consultant Sound absorption tests on a range of sheep s wool based materials February R01 ISVR Consulting, University of Southampton, Highfield Campus, Southampton SO17 1BJ, United Kingdom Tel: +44 (0) Fax: +44 (0) consultancy@isvr.co.uk Web:

2 Contents 1. Introduction Measurement Method Results Ambient Conditions Test results 6 Tables 1 to 6: Sound Absorption Coefficients Figures 1 to 3: Photographs of the test samples inside the reverberation chamber Appendix 1 Appendix 2 Instrumentation and Calibration Acoustic Environment ISVR Consulting Report 9383-R01 / February 2015 Contents

3 1. Introduction ISVR Consulting were engaged by The Woolley Shepherd, to undertake measurements on a range of products to establish their sound absorption coefficient (a S ) or equivalent sound absorption area (A obj m 2 ) depending on the product being tested. The sound absorption measurements were performed in the Reverberant Suite of the Rayleigh Laboratories of the ISVR, University of Southampton. The tests were carried out on the 10 th February The measurements were carried out in accordance with BS EN ISO 354: 2003 Acoustics Measurement of sound absorption in a reverberation room. When a sound source operates in an enclosed space, the level to which reverberant sound builds up, and the subsequent decay of reverberant sound when the source is stopped, are governed by the sound-absorbing characteristics of the boundary surfaces, the air filling the space, and objects within the space. In general, the fraction of the incident sound power absorbed at a surface depends upon the angle of incidence. In order to relate the reverberation time of an auditorium, office, workshop, etc, to the noise reduction that would be effected by an absorbing treatment, knowledge of the sound-absorbing characteristics of the surfaces, usually in the form of a suitable average over all angles of incidence, is required. Since the distribution of sound waves in typical enclosures includes a wide and largely unpredictable range of angles, a uniform distribution is taken as the basic condition for the purposes of standardization. If, in addition, the sound intensity is independent of the location within the space, the sound distribution is called a diffuse sound field, and the sounds reaching a room surface are said to be at random incidence. The sound field in a properly designed reverberation room closely approximates a diffuse field. Hence, sound absorption measured in a reverberation room closely approximates the sound absorption that would be measured under the basic conditions assumed for standardization. ISVR Consulting Report 9383-R01 / February 2015 Page 3 of 20

4 BS EN ISO 354: 2003 Acoustics Measurement of sound absorption in a reverberation room specifies a method of measuring the sound absorption coefficient of acoustical materials used as wall or ceiling treatments, or the equivalent sound absorption area of objects, such as furniture, persons or space absorbers, in a reverberation room. The materials tested were described as follows: Standard wall panel Limpets Clouds The standard wall panels are rectangular panels designed to be mounted onto walls. They can be used individually or combined to cover larger areas of wall. The limpets are a bit like a scalloped rectangle and are designed to be fitted flush onto ceilings. They would normally be installed individually but one ceiling might have multiple limpets fitted. The clouds are similar to the limpets but they are designed to hang from ceilings. The materials were tested as either individual (discrete) absorbers or as plane absorbers depending on their application. The results obtained can be used for comparison purposes and for design calculation with respect to room acoustics and noise control. ISVR Consulting Report 9383-R01 / February 2015 Page 4 of 20

5 2. Measurement Method The averaged reverberation rimes (RT 60 ) in 1/3 octave bands were determined for the empty chamber in the frequency range 100 Hz to 5000 Hz, as described in the standard, using an interrupted broad band noise. Thirty two decays were measured, (eight microphone combinations at each of four sound source locations). The sample of absorbent material was introduced into the chamber and either laid out on the floor or hung from the ceiling in accordance with the guidelines given in the standard. The test arrangement was chosen depending on whether the sample was a discrete absorber or a plane absorber. In the case of the plane absorbers the edges of the sample were covered with metal plate to prevent the edges from absorbing any of the sound waves. Once the sample was positioned in the chamber, the averaged reverberation time spectrum was determined as before. The absorption in the chamber was calculated for the sample and the increase in absorption due to the absorbent material relative to the empty chamber, was found. For the plane absorbers the coefficient of absorption (a S ) in each 1/3 octave band was calculated. The results are shown as a value between 0 and 1 where 1 signifies total absorption and 0 signifies no absorption. NB. In practice the test method can give values greater than 1 which can be confusing. Where a value of greater than 1 is given for a plane absorber it has been caused by edge effects of the test sample. For the discrete absorbers the equivalent sound absorption area (A obj m 2 ) in each 1/3 octave band was calculated. The sound absorption property of discrete objects is quantified by the equivalent sound absorption area expressed as m 2 per object. This is the area of a 100% fictive absorbing surface which would absorb the same amount of sound as the object in question. ISVR Consulting Report 9383-R01 / February 2015 Page 5 of 20

6 3. Results 3.1 Ambient Conditions Barometric pressure kpa Temperature 15.0 C Relative Humidity 44 % 3.2 Test results The results in the tables below are given as either the coefficient of absorption (a S ) or as the equivalent sound absorption area (A obj m 2 ) depending on the type of sample being tested. In the case of the plane absorbers where the results are given as the coefficient of absorption (a S ), BS EN ISO can be used to express the spectrum of results as a sound absorption class. The classes range from A to E where A is the top class. The standard is not applicable to single items, such as the limpets and clouds measured during these tests. NB. There are other standards, namely ASTM C a that can be used to express the sound absorption test spectrum as a single number. ASTM C423 uses the term Noise Reduction Coefficient (NRC) although this is being replaced by Sound Absorption Average (SAA). Both the NRC and SAA terms have values between 0 and 1 where 1 indicates total absorption. ASTM C423 test procedures should be used when calculating the NRC or SAA value. In this report we have used BS EN ISO 354 to determine the sound absorption coefficient. The methods in the two standards differ slightly. However for indication purposes I have used the BS EN ISO 354 values to calculate an NRC and SAA value for the materials we tested. Table 1 shows the results with 20 individual wall panels butted together to form a large rectangle. The outer edges of the rectangle were covered to prevent them absorbing more sound. ISVR Consulting Report 9383-R01 / February 2015 Page 6 of 20

7 Table 2 shows the results with 20 individual wall panels butted together to form a large rectangle. The outer edges of the rectangle were left uncovered and therefore absorbed more sound. Table 3 shows the results when the 20 wall panels were tested as discrete absorbers. The results are given as the equivalent sound absorption area (A obj m 2 ). Table 4 shows the results with 25 individual limpets butted together to form a large sample. The outer edges of the sample were left uncovered and therefore absorbed more sound. Table 5 shows the results when the 25 limpets were tested as discrete absorbers. The results are given as the equivalent sound absorption area (A obj m 2 ). Table 6 shows the results when the 8 clouds were tested as discrete absorbers. The results are given as the equivalent sound absorption area (A obj m 2 ). Figures 1 to 3 show photographs of the samples under test. ISVR Consulting Report 9383-R01 / February 2015 Page 7 of 20

8 Airborne sound absorption measured in a reverberation chamber. BS EN ISO 354:2003 Customer: Woolly Shepherd Construction tested Standard Wall Panel All sample panels butted together. Edges covered Frequency Absorption Hz a s Sound Absorption Coefficient a s Sound absorption coefficient BS EN ISO Sound absorption class = A Frequency, Hz Test Standard: BS EN ISO 354 Project No: 9383 University of Southampton Tested by: J.Fithyan Highfield, Southampton Test date: 27/01/2015 Using the ISO 354 test data above to calculate the ASTM C a descriptors, which is not strictly correct, you would get these values: NRC 0.95 SAA 0.93 Table 1: Standard wall panels butted together with outer edges covered ISVR Consulting Report 9383-R01 / February 2015 Page 8 of 20

9 Airborne sound absorption measured in a reverberation chamber. BS EN ISO 354:2003 Customer: Woolly Shepherd Construction tested Standard Wall Panel All sample panels butted together. Edges left uncovered Frequency Absorption Hz a s Sound Absorption Coefficient a s Sound absorption coefficient BS EN ISO Sound absorption class = A Frequency, Hz Test Standard: BS EN ISO 354 Project No: 9383 University of Southampton Tested by: J.Fithyan Highfield, Southampton Test date: 27/01/2015 Using the ISO 354 test data above to calculate the ASTM C a descriptors, which is not strictly correct, you would get these values: NRC 0.95 SAA 0.97 Table 2: Standard wall panels butted together with outer edges left uncovered ISVR Consulting Report 9383-R01 / February 2015 Page 9 of 20

10 Airborne sound absorption measured in a reverberation chamber. BS EN ISO 354:2003 Customer: Woolly Shepherd Construction tested Standard Wall Panel All sample panels moved apart. Edges left uncovered Frequency Absorption Hz A obj m Equivalent sound absorption per wall panel A obj m 2 Sound absorption coefficient Frequency, Hz Test Standard: BS EN ISO 354 Project No: 9383 University of Southampton Tested by: J.Fithyan Highfield, Southampton Test date: 27/01/2015 Table 3: Twenty individual standard wall panels tested as discrete absorbers ISVR Consulting Report 9383-R01 / February 2015 Page 10 of 20

11 Airborne sound absorption measured in a reverberation chamber. BS EN ISO 354:2003 Customer: Woolly Shepherd Construction tested Limpets All samples butted together. Edges left uncovered Frequency Absorption Hz a s Sound Absorption Coefficient a s Sound absorption coefficient BS EN ISO Sound absorption class = A Frequency, Hz Test Standard: BS EN ISO 354 Project No: 9383 University of Southampton Tested by: J.Fithyan Highfield, Southampton Test date: 27/01/2015 Using the ISO 354 test data above to calculate the ASTM C a descriptors, which is not strictly correct, you would get these values: NRC 1.00 SAA 1.00 Table 4: Limpets butted together with outer edges left uncovered ISVR Consulting Report 9383-R01 / February 2015 Page 11 of 20

12 Airborne sound absorption measured in a reverberation chamber. BS EN ISO 354:2003 Customer: Woolly Shepherd Construction tested Limpets All samples moved apart. Edges left uncovered Frequency Absorption Hz A obj m Equivalent sound absorption per limpet A obj m 2 Sound absorption coefficient Frequency, Hz Test Standard: BS EN ISO 354 Project No: 9383 University of Southampton Tested by: J.Fithyan Highfield, Southampton Test date: 27/01/2015 Table 5: Twenty-five individual limpets tested as discrete absorbers ISVR Consulting Report 9383-R01 / February 2015 Page 12 of 20

13 Airborne sound absorption measured in a reverberation chamber. BS EN ISO 354:2003 Customer: Woolly Shepherd Construction tested Clouds Frequency Absorption Hz A obj m Equivalent sound absorption per cloud A obj m 2 Sound absorption coefficient Frequency, Hz Test Standard: BS EN ISO 354 Project No: 9383 University of Southampton Tested by: J.Fithyan Highfield, Southampton Test date: 27/01/2015 Table 6: Eight individual clouds tested as discrete absorbers ISVR Consulting Report 9383-R01 / February 2015 Page 13 of 20

14 Figure 1: Standard wall panels ISVR Consulting Report 9383-R01 / February 2015 Page 14 of 20

15 Figure 2: Limpets ISVR Consulting Report 9383-R01 / February 2015 Page 15 of 20

16 Figure 3: Clouds ISVR Consulting Report 9383-R01 / February 2015 Page 16 of 20

17 Appendix 1: Instrumentation and Calibration 1.1 Measuring Equipment Noise Generation Instrument Manufacturer Type Ser No Cal Due Amplifier Cambridge Audio A1 V Not required Loudspeaker Not required Noise Measurement Instrument Manufacturer Type Ser No Cal Due Microphone Brüel & Kjær August 15 Microphone Brüel & Kjær August 15 Microphone Brüel & Kjær August 15 Microphone Brüel & Kjær August 15 Microphone Brüel & Kjær August 15 Microphone Brüel & Kjær August 15 Pre-amplifier Brüel & Kjær September 15 Pre-amplifier Brüel & Kjær September 15 Pre-amplifier Brüel & Kjær September 15 Pre-amplifier Brüel & Kjær September 15 Pre-amplifier Brüel & Kjær September 15 Pre-amplifier Brüel & Kjær September 15 Freq Analyser Brüel & Kjær 3560C October 15 Freq Analyser Brüel & Kjær 3560B October 15 Mic Calibrator Brüel & Kjær September System Calibration The noise measuring system was calibrated by applying the microphone calibrator (type 4231) to the transducer and adjusting the analyzer to the reference level at the beginning of the measurement session. The level was also checked at the end of the session to ensure that no drift or fault had occurred. The above equipment is calibrated against the transfer standards below. ISVR Consulting Report 9383-R01 / February 2015 Page 17 of 20

18 1.3 Traceability Microphones and Calibrators Microphones and Calibrators ISVR Consulting hold two transfer standard Microphones, type 4145, serial numbers and The most recent calibration was carried out by Campbell Associates. This is fully documented in Certificates and 17841, dated 22 nd January A transfer standard Pistonphone, type 4220, serial number and a transfer standard calibrator, type 4231, serial number are also held. These were calibrated by Campbell Associates and are documented in certificate numbers and 17842, dated 22 nd January Additional Instrumentation A Digital Voltmeter (Fluke type 8050A) and a Frequency Counter (Marconi type 2430A) are used with these Transfer Standards to calibrate the above equipment. Both instruments were calibrated by Southern Calibration Laboratories and carry certificates numbered and respectively and both are dated 25th November The instrumentation complies with the requirements for a type 1 instrument, as specified in BS EN 61672:2003, BS EN 60942:2003 and BS EN IEC 61260:1996. The Standards are traceable to the National Physical Laboratory, Teddington, England. ISVR Consulting Report 9383-R01 / February 2015 Page 18 of 20

19 Appendix 2: Acoustic Environment 2.1 Large Reverberation Chamber Construction The chamber is constructed of reinforced concrete and is separated from the foundations and neighbouring walls by rubber vibration isolators. It is designed with an inclined ceiling and non-parallel walls to ensure a uniform distribution (with frequency) of the normal acoustic modes of the room Dimensions Mean edge lengths 9.15 m 6.25 m 6.10 m - height Volume 348 m 3 Surface Area 302 m Walls and Ceiling All inside surfaces of the chamber are finished with a hard gloss paint to give a high reflection coefficient. The walls are 305 mm thick, and the ceiling, which is 460 mm thick, includes two removable sections (1.75 m x 0.86 m) which provide access for a chain hoist capable of carrying loads up to 2000 Kg, and an entry for a 4000 Watt siren driven horn. Connections to the equipment in the chamber may be made via any of five cable ports in the walls. A glazed window (305 mm x 305 mm) permits visual observation from the control area Diffusers Ten diffusers are hug from the ceiling of the chamber. These diffusing elements are plywood sheets painted with gloss paint so that they have a low sound absorption. The diffusers, which are of varying sizes are orientated at random and positioned at different heights within the chamber. The total surface area of the diffusers is 43.2 m 2. ISVR Consulting Report 9383-R01 / February 2015 Page 19 of 20

20 2.1.5 Floor Area The floor is 305 mm thick and has a steel vibration isolated pad (2.1 m x 3.6 m) set into it. This pad may be used for mounting test rigs or vibrators without structural vibrations being transmitted to the chamber Doors One set of double doors connects the chamber and the corridor, another set opens into the small reverberation chamber and incorporates removable panels (1.07 m x 1.07 m) for transmission loss measurements. The doorway (2.4 m x 2.0 m) may be used for testing larger panels. The doors (2.56 m x 2.26 m x 130 mm thick) are a sandwich construction of wood wool, wood and steel, and have an average transmission loss in excess of 50 db Ventilation and Lighting At each corner of the floor there is an air inlet vent, and there are four outlet vents situated high up on one wall. With all vents open the air is changed at a rate of 100 m 3 per minute. When not required the vents are covered by steel plates and these have diagonal stiffeners to reduce panel vibrations. The chamber is lit by six sodium discharge lights mounted on the wall at 3 m above the floor. ISVR Consulting Report 9383-R01 / February 2015 Page 20 of 20