UNIVERSIDAD POLITÉCNICA DE MADRID
Máster Universitario en Ingeniería Acústica
MASTERS DISSERTATION
“ACOUSTIC CHARACTERISTICS OF TWO
PORTUGUESE CHURCHES BUILT AT THE END OF THE 1960’S”
ADÁN IGLESIAS BARROS
SEPTEMBER / 2021
Trabajo Fin de Máster
Título
Acoustic characteristics of two portuguese churches built at the end of the 1960’s
Autor Adán Iglesias Barros
Firma
Tutor / Co-Tutor Juan José Gómez Alfageme Firma
Director Externo Rui Miguel De Sousa Lima E Sá Ribeiro Firma
Tribunal Examinador Presidente/
Secretario/
Vocal
Fecha
Calificación
Secretario
UNIVERSIDAD POLITÉCNICA DE MADRID
Máster Universitario en Ingeniería Acústica
MASTERS DISSERTATION
“ACOUSTIC CHARACTERISTICS OF TWO
PORTUGUESE CHURCHES BUILT AT THE END OF THE 1960’S”
ADÁN IGLESIAS BARROS
SEPTEMBER / 2021
Resumen
El presente proyecto pretende determinar los parámetros acústicos para evaluar la calidad acústica de dos iglesias construidas a finales de los 60. El principal objetivo es analizar la distribución temporal y espacial de la energía en las iglesias a partir de los parámetros acústicos obtenidos de las medidas de la respuesta al impulso en las mismas. Estos parámetros se contrastarán con el actual estado del arte al respecto.
Las iglesias medidas son:
Igreja Matriz Nossa Senhora do Rosário (Marinha Grande).
Igreja Paroquial de Rio Maior (Rio Maior).
Además, una tercera iglesia, Igreja de Santa Clara (Oporto), la cual es barroca, será utilizada como referente en los indicadores acústicos a conseguir en nuestras soluciones.
Abstract
This project aims to determine the acoustic parameters to evaluate the acoustic quality of two distinct churches built at the end of the 1960’s. The main objective is to analyze the temporal and spatial distribution of energy in churches based on the acoustic parameters obtained from the measurements of the impulse response in these builds. These parameters will be contrasted with the current state of the art in this regard.
The measured churches are:
Igreja Matriz Nossa Senhora do Rosário (Marinha Grande).
Igreja Paroquial de Rio Maior (Rio Maior).
A third church, Igreja de Santa Clara (Oporto), which is baroque, was used as a benchmark to provide reference values for speech and music design goals.
Index
1 Introduction and Objectives ... 1
Introduction ... 2
1.1. Objectives ... 2
1.2. 2 State of art ... 5
Standard methodology and equipment ... 6
2.1. Reference acoustic parameters ... 9
2.2. 2.2.1. Decay range ... 9
2.2.2. Reverberation Time Estimated T20 and T30 ... 9
2.2.3. Early Decay Time, EDT ... 12
2.2.4. Clarity of Music, C80 ... 13
2.2.5. Speech Definition, D50 ... 14
2.2.6. Central Time, TS ... 15
2.2.7. Early Lateral Energy fraction, LF and LFC ... 15
2.2.8. Speech Transmission Index, STI male and STI female ... 17
2.2.9. Articulation loss of Consonants, ALCONS male and female ... 21
3 Measurements and data analysis ... 23
Benchmark, Igreja de Santa Clara (Oporto) ... 24
3.1. 3.1.1. Location and conditions... 24
3.1.2. Acoustic parameters ... 25
Igreja Matriz Nossa Senhora do Rosario (Marinha Grande) ... 29
3.2. 3.2.1. Location and conditions... 29
3.2.2. Acoustic parameters ... 31
Igreja Paroquial de Rio Maior (Rio Maior) ... 35
3.3. 3.3.1. Location and conditions... 35
3.3.2. Acoustic parameters ... 37
4 3D Modelling ... 43
Computer Aided Designs (CAE) ... 44
4.1. Drawing with SketchUp ... 45
4.2. 4.2.1. Software description ... 45
4.2.2. Plans ... 46
4.2.2.1. Igreja Nossa Senhora do Rosario (Marinha Grande) ... 48
4.2.2.2. Igreja Paroquial de Rio Maior ... 50
Export to CATT-Acoustic ... 52
4.3. Simulation with CATT-Acoustic ... 55
4.4. 4.4.1. Software Description ... 55
4.4.2. Completing the geometry properties... 55
4.4.3. Introducing sources and receivers ... 57
4.4.4. Model´s validation ... 58
4.4.4.1. Igreja Nossa Senhora do Rosario ... 58
4.4.4.2. Igreja Paroquial de Rio Maior ... 62
4.4.5. Acoustic parameters in full occupied condition ... 66
4.4.5.1. Igreja Nossa Senhora do Rosario (Marinha Grande) ... 67
4.4.5.2. Igreja Paroquial do Rio Maior ... 70
5 Setting Design Criteria ... 73
Igreja Nossa Senhora do Rosario (Marinha Grande) ... 74
5.1. 5.1.1. Room drawbacks and design goals ... 74
5.1.2. Proposed solutions ... 78
5.1.3. Target´s fulfillment ... 80
5.1.4. Estimated results after the reform for the occupied condition ... 84
Igreja Paroquial de Rio Maior ... 85
5.2. 5.2.1. Room drawbacks and design goals ... 85
5.2.2. Proposed solutions ... 89
5.2.3. Target´s fulfillment ... 90
5.2.4. Estimated results after the reform in full occupied condition ... 95
6 Theoretical analysis ... 97
Theoretical Acoustic parameters ... 98
6.1. 6.1.1. Reverberation Time ... 98
6.1.2. Direct and reflected sound energy ... 99
6.1.3. Clarity (C80) ... 100
6.1.4. Early Decay Time (EDT) ... 100
6.1.5. Definition (D50) ... 101
6.1.6. Speech Transmission Index (STI) ... 101
6.1.7. Articulation Loss of Consonants (ALCONS) ... 101
Igreja Nossa Senhora do Rosario (Marinha Grande) ... 102
6.2. Igreja Paroquial de Rio Maior ... 103 6.3.
7 Conclusions ... 105 8 Bibliography ... 107
Figure´s Index
Figure 2. 1. Brüel and Kjaer OmniPower 4296 (2) ... 6
Figure 2. 2. Directivity OmniPower 4296 and limit of Standard ISO 3382-1 (left), max level in each octave band OmniPower 4296 (right) (2) ... 6
Figure 2. 3. Core Sound Tetramic 1st order by Ambisonic (3) ... 7
Figure 2. 4. MOTU 4pre USB audio (4) ... 8
Figure 2. 5. Dynamic range of register (4) ... 8
Figure 2. 6. RT recommended by Michael Barron (5) ... 11
Figure 2. 7. Acoustic seating area simplified in models. (5) ... 11
Figure 2. 8. MTF by Houtgast and Steeneken (7) ... 18
Figure 2. 9. MTF by Schröeder (8) ... 18
Figure 3. 1. Location of Igreja Santa Clara (Oporto) (12) ... 24
Figure 3. 2. Igreja de Santa Clara (12)... 24
Figure 3. 3. RT measured in Igreja Santa Clara ... 25
Figure 3. 4. Location of Igreja Matriz Nossa Senhora do Rosario (12) ... 29
Figure 3. 5. Igreja Matriz Nossa Senhora do Rosario (12) ... 30
Figure 3. 6. Igreja Matriz Nossa Senhora do Rosario´s interior ... 30
Figure 3. 7. Igreja Matriz Nossa Senhora do Rosario´s plane with measurements points ... 31
Figure 3. 8. RT measured in Igreja Matriz Nossa Senhora do Rosario ... 32
Figure 3. 9. Location of Igreja Paroquial do Rio Maior (12) ... 35
Figure 3. 10. Igreja Paroquial do Rio Maior (12) ... 36
Figure 3. 11. Measurements points in Igreja Paroquial do Rio Maior ... 37
Figure 3. 12. RT measured in Igreja Paroquial do Rio Maior ... 38
Figure 4. 1. Modelling in Sketchup ... 45
Figure 4. 2. Hiding faces in Sketchup to view the interior of the models... 46
Figure 4. 3. Empty models ... 46
Figure 4. 4. Models in full occupied condition ... 47
Figure 4. 5. Igreja Marinha Grande model ... 49
Figure 4. 6. Igreja Rio Maior model ... 51
Figure 4. 7. Fixed faces ... 53
Figure 4. 8. First paragraph. GEO ... 54
Figure 4. 9. Vertices statement in CATT files ... 54
Figure 4. 10. Faces statement in CATT files ... 54
Figure 4. 11. Material statement structure in .GEO files (18) ... 55
Figure 4. 12. Material statement example ... 56
Figure 4. 13. Scattering correction (18) ... 56
Figure 4. 14. Receiver file structure in CATT ... 57
Figure 4. 15. Source file structure in CATT ... 58
Figure 4. 16. Material properties in Igreja of Nossa Senhora do Rosario ... 58
Figure 4. 17. CATT model of Igreja of Nossa Senhora do Rosario ... 60
Figure 4. 18. Material properties in Igreja Paroquial do Rio Maior ... 63
Figure 4. 19. Acoustic model of Igreja Paroquial do Rio Maior ... 64
Figure 4. 20. Occupied audience area in church pews (14) ... 67
Figure 4. 21. Material properties in Igreja Nossa Senhora do Rosario in full occupied condition ... 68
Figure 4. 22. Material properties in Igreja Paroquial do Rio Maior in full occupied condition ... 70
Figure 5. 1. Late and destructive reflection with empty church ... 74
Figure 5. 2. Late and destructive reflection with church in full occupied condition ... 75
Figure 5. 3. Reflections capted from IRIS and imported in Sketchup models ... 77
Figure 5. 4. Energy decay in Igreja Nossa Senhora do Rosario ... 84
Figure 5. 5. Late and destructive reflections with empty church ... 86
Figure 5. 6. Late and destructive reflections with the church in full occupied condition ... 86
Figure 5. 7. Reflections measured from IRIS and imported in Sketchup model 88
Figure 5. 8. Energy decay after reform ... 94
Table´s Index
Table 2. 1. Maximum deviation permited by Standard 3382-1 (1) ... 7
Table 2. 2. Male and female modulation for Speech transmission (10) ... 19
Table 2. 3. Evaluation thresholds by the IEC 60268-16 standard (12) ... 20
Table 2. 4. IEC 60268-16 standard evaluation table (12) ... 21
Table 3. 1. Acoustic parameters in Igreja Santa Clara ... 26
Table 3. 2. Decay Range in Igreja Santa Clara ... 26
Table 3. 3. Objective assessments in Igreja Santa Clara ... 27
Table 3. 4. Assessment of STI by Standard IEC 60268-16 (12) ... 28
Table 3. 5. Difference between points of EDT measurements in Igreja Santa Clara ... 28
Table 3. 6. Acoustic paramaters in Igreja Matriz Nossa Senhora do Rosario ... 32
Table 3. 7. Decay Range in Igreja Matriz Nossa Senhora do Rosario ... 33
Table 3. 8. Objective assessments of acoustic parameters in Igreja Matriz Nossa Senhora do Rosario ... 34
Table 3. 9. Assessment of STI in Igreja Matriz Nossa Senhora do Rosario by IEC 60268-16 (12). ... 35
Table 3. 10. Acoustic parameters in Igreja Paroquial do Rio Maior ... 39
Table 3. 11. Decay Range in Igreja Paroquial do Rio Maior ... 40
Table 3. 12. Objective assessments of acoustic parameters in Igreja Paroquial do Rio Maior ... 41
Table 3. 13. Assessment of STI in Igreja Paroquial do Rio Maior by Standard IEC 60268-16 (12) ... 41
Table 4. 1. Validating the model of Igreja of Nossa Senhora do Rosario ... 62
Table 4. 2. Validating the model of Igreja Paroquial do Rio Maior ... 66
Table 4. 3. Acoustic parameters exported from CATT in Igreja Nossa Senhora do Rosario in full occupied condition ... 69
Table 4. 4. Acoustic parameters exported from CATT in Igreja Paroquial do Rio Maior ... 71
Table 5. 1. Reference product acoustic properties (Sonacoustic) (15) ... 79
Table 5. 2. Recomendations and details ... 80
Table 5. 3. Acoustic parameters estimated from CATT after reform in Igreja Nossa Senhora do Rosario ... 81
Table 5. 4. Improvement of acoustic quality after the reform ... 83
Table 5. 5. Acoustic parameters estimated from CATT in Igreja Nossa Senhora do Rosario after reform and in full occupied condition ... 85
Table 5. 6. Reference product acoustic properties (MUTE) (16) ... 89
Table 5. 7. Recomendation and details... 90
Table 5. 8. Acoustic parameters estimated from CATT after reform ... 92
Table 5. 9. Improvement of acoustic quality after the reform ... 94
Table 5. 10. Acoustic parameters in Igreja Paroquial do Rio Maior after reform and in full occupied conditions ... 95
Table 6. 1. Comparative between theoretical calculation and model simulation estimate in full occupied conditions ... 102
Table 6. 2. Comparative between theoretical calculation and model simulation estimate in full occupied conditions ... 104
Equation´s Index
Equation 2. 1. Energy equation by Schröeder (1) ... 9
Equation 2. 2. RT max for concert halls (6) ... 11
Equation 2. 3. RT min for concert halls (6) ... 12
Equation 2. 4. RT max for polyvalent rooms (6) ... 12
Equation 2. 5. RT min for polyvalent room (6) ... 12
Equation 2. 6. RT max for speech transmission (6) ... 12
Equation 2. 7. RT min for speech transmission (6) ... 12
Equation 2. 8. C80 equation (1) ... 13
Equation 2. 9. D50 equation (1) ... 14
Equation 2. 10. Ts equation (1)... 15
Equation 2. 11. LF equation (1) ... 16
Equation 2. 12. LFC equation (1) ... 16
Equation 2. 13. MTF equation by Houtgast and Steeneken (7) ... 17
Equation 2. 14. MTF equation by Schröeder (8) ... 17
Equation 2. 15. Signal to noise ratio in each fm (9) ... 18
Equation 2. 16. Signal to noise ratio average in each band (9) ... 19
Equation 2. 17. Signal to noise ratio max in each fm (9) ... 19
Equation 2. 18. Signal to noise ratio min in each fm (9) ... 19
Equation 2. 19. Signal to noise ratio global (9) ... 19
Equation 2. 20. STI equation from signal to noise (9) ... 20
Equation 2. 21. ALCONS percentage equation (10) ... 22
Equation 6. 1. Statistical RT estimation (17) ... 98
Equation 6. 2. Relationship between absortion coheficient by Sabine and Eyring (17) ... 99
Equation 6. 3. Direct energy (5) ... 99
Equation 6. 4. Early sound energy within 50 or 80 ms (5) ... 99
Equation 6. 5. Late sound energy after than 50 or 80ms (5) ... 99
Equation 6. 6. Theoretical C80 (5) ... 100
Equation 6. 7. C80 theoretical correction (5) ... 100
Equation 6. 8. Theoretical EDT (5) ... 100
Equation 6. 9. Theoretical C50 (5) ... 101
Equation 6. 10. C50 theoretical correction (5) ... 101
Equation 6. 11. Theoretical D50 (18) ... 101
1 Introduction
and Objectives
2
Introduction 1.1.
This project aims to establish an efficient working method to solve real problems of acoustic conditioning in rooms where the speech transmission and intelligibility is essential or in rooms destined for music concerts, as well as following the ISO 3382 parameters. In this case, two churches from Portugal, built at the end of the 60´s, were analysed.
During the development of the project, many issues were arising which could be solved by reading from different sources and being advised by experienced professionals. This led to its structure in temporal order by presenting the issues that happen followed by the action taken, aiming to illustrate to someone else that may have similar issues in other projects in this field.
The present project will contain the standard´s summary of the Standard 3382- 1, the location and conditions in the churches, starting complain from the priests, acoustic measurement sessions, modelling and estimation of the acoustic parameters, design targets and design solutions and compare them with the original measurements.
In addition to solving these problems with CAE, CATT Acoustic, which is a technology less than 20 years old, there is also the inclusion of theoretical estimates as a tribute to acousticians such as Beranek, M. Barron, H. Arau, Sabine or Schroeder, since the simulation technology was not always available and there are not enough resources in the hands of all acousticians.
Objectives 1.2.
The main specific objectives to be achieved are:
• Determine and analyze the main acoustics parameters as RT, C80, D50, EDT, LF… and compare them to analytical formulation (ex.: “revised Theory” by Michael Barron).
• Recommend and design room acoustic solutions in order to improve speech intelligibility and musical clarity based on measurements and estimated model results
3
• Evaluate costs vs benefit approaches and recommend correction solution for the two churches testing efficiency on models.
4
2 State of art
6
Standard methodology and equipment 2.1.
The present project follows the standard methodology of measurements Standard ISO 3382-1: “Acoustics. Measurements of room acoustic parameters. Part 1:
Performance spaces (1).” Therefore, the following specifications of the standard have been taken into account for the selection of the equipment.
The dodecahedron source OmniPower 4296, shown in the Figure 2. 1, meets the requirements specified of directivity in the standard ISO 3382-1 Table 2. 1, shown in the Figure 2. 2. The dodecahedron source has sufficient sound power level to perform correct measurements in the required bands, shown in the Figure 2. 2.
Figure 2. 1. Brüel and Kjaer OmniPower 4296 (2)
Figure 2. 2. Directivity OmniPower 4296 and limit of Standard ISO 3382-1 (left), max level in each octave band OmniPower 4296 (right) (2)
7
Frequency, Hz 125 250 500 1000 2000 4000
Maximum deviation, dB ±1 ±1 ±1 ±3 ±5 ±6
Table 2. 1. Maximum deviation permited by Standard 3382-1 (1)
The tetrahedral microphone class 1 has four diaphragms with less than 13mm of diameter. Core Sound Tetramic 1st order Ambisonic contains 4 diaphragms of 12mm diameter, which is specialized in diffuse field measurements.
Figure 2. 3. Core Sound Tetramic 1st order by Ambisonic (3)
The digital register presents a uniform frequency response with a tolerance below ±3dB between 125Hz-4KHz.
The digital register was never oversaturated, and the dynamic range is greater than 50dB.
The MOTU 4pre USB audio interface contains 4 XLR inputs with phantom. For the IRIS application, 44.1 or 48KHz sampling frequencies must be chosen, with a dynamic range, as seen in the Figure 2. 5, of 60 dB for each microphone, and 96dB in the sum of the four at the output. Finally, this sound card requires the computer to have a processor of more than 1GHz and a RAM with more than 2GB.
8
Figure 2. 4. MOTU 4pre USB audio (4)
Figure 2. 5. Dynamic range of register (4)
The source was located at a height of 1.8 meters, where priests, speakers or musicians are usually located.
The points of measurements chosen have a height of 1.2 meters spaced at least 2 meters apart (340 [m/s] / (63*2) [Hz]). They were located where the audience should be seated and evenly distributed throughout the room. It can also be considered that all the rooms measured have only one acoustic zone in empty conditions and with furniture.
The measurements were taken with one of the integrated impulsive response methods, in this case, the sine sweep, covering the octave bands required by the standard 3382 in the engineer method, this is from 125 to 4000 Hz octave bands. The sweep sine also allows to perform only a single source-receiver measurements with an uncertainty 10 times lower than using the interrupted noise method.
9
Reference acoustic parameters 2.2.
In the three churches measured, the parameters follow the Standard 3382-1 from the backwards energetic decay curve calculated by means of Schroeder backwards time integral, as shown in the Equation 2. 1.
𝐸(𝑡) = ∫ 𝑝2(ῖ)𝑑ῖ =
∞
𝑡
∫ 𝑝2(ῖ)𝑑(−ῖ) =
𝑡
∞
∫ 𝑝2(ῖ)𝑑ῖ − ∫ 𝑝2(ῖ)𝑑ῖ
𝑡
0
∞
0
Equation 2. 1. Energy equation by Schröeder (1)
In the parameters some of values described are advanced to do not repeat in each church.
2.2.1. Decay range
This parameter is defined as the sound power level that the sound level decreases during the integration time of the excited impulse. This parameter is not valued as an objective or subjective aspect of the listener, but it is a parameter that needs to be considered in order to consolidate the reliability of the measurements in each band.
In general, the measurements can be considered reliable if the decay range exceeds 45dB, less than that it would be necessary to analyze the results in the conflicting bands to know if they are consistent in the average value or if some measurement points have a large deviation from average, and this is related to an incorrect measurement at some point.
2.2.2. Reverberation Time Estimated T20 and T30
This parameter is defined as the time in which the power sound level decreases 60dB. The noise often makes impossible to have an energy decay of 60dB. The parameters T20 and T30 are used to predict the reverberation time in the room from the decay curve by backwards integration (Schroeder), calculating the regression line
10
where the curve falls between -5dB and -25dB for T20 and -5dB and -35dB for T30.
For example, in these parameters, the decay range needed for T30 is at least 45dB for a reliable prediction, while for T20 only 35dB is needed.
In this project, an attempt has been made to establish an algorithm using Excel to objectively assess the acoustic quality indicators, attending to different specialists in the field, specifically Michael Barron, Higini Arau Puchades and Leo L. Beranek.
Regarding reverberation times, various acoustic thresholds have been placed in the Excel formulas with the help of conditional functions to automate the calculations and display the results.
- The first threshold was established according to various acoustic indicators. It is acceptable for churches to have between 2 and 3 seconds of reverberation, thus, the first threshold was set at 3.2 seconds, above which the reverberation time is considered "BAD". It is not considered the volume to calculate this parameter and if the reverberation time is below this first threshold and above the second threshold, the cell message will be "ACCEPTABLE FOR CHURCHES".
- The second threshold was placed according to the graph proposed by Michael Barron, who related the volume of a room with the audience area, as shown in the Figure 2. 6, in which a line is shown to indicate the reverberation time according to the factor V / area of audience. In the evaluation tables, volume and audience area are placed as if the church was empty. It should be added that for an audience area, Beranek recommends adding 0.5 meters to the perimeter of the real audience surface, as marked by the Figure 2. 7, to compensate the absorption of the edges of each block. Therefore, if the reverberation time is between this and the third threshold, the message will be "ACCEPTABLE FOR THIS VOLUME AND AUDIENCE AREA".
11
Figure 2. 6. RT recommended by Michael Barron (5)
Figure 2. 7. Acoustic seating area simplified in models. (5)
- The following thresholds delimit the range of optimum values for music and speech in relation with the volume, and are calculated with the formulas proposed by Higini Arau. In the Equation 2. 2 and Equation 2. 3 for music performance, the message will be “NICE FOR MUSIC”; In the Equation 2. 4 and Equation 2. 5 for music and speech performance, the message will be “ACCEPTABLE FOR MUSIC AND SPEECH”; In the Equation 2. 6 and Equation 2. 7 for speech performance, the message will be “NICE FOR SPEECH”. Lastly, the value may be below the minimum value for the transmission of the word, whose displayed message will be "ACCEPTABLE FOR SPEECH".
𝑇𝑚𝑖𝑑 𝑜𝑝𝑡𝑖𝑚𝑢𝑚 𝑚𝑎𝑥 = 0.6 ∗ 𝑉0.1325
Equation 2. 2. RT max for concert halls (6)
12
𝑇𝑚𝑖𝑑 𝑜𝑝𝑡𝑖𝑚𝑢𝑚 𝑚𝑖𝑛 = 0.5125 ∗ 𝑉0.1328
Equation 2. 3. RT min for concert halls (6)
𝑇𝑚𝑖𝑑 𝑜𝑝𝑡𝑖𝑚𝑢𝑚 𝑚𝑎𝑥 = 0.509 ∗ 𝑉0.1325
Equation 2. 4. RT max for polyvalent rooms (6)
𝑇𝑚𝑖𝑑 𝑜𝑝𝑡𝑖𝑚𝑢𝑚 𝑚𝑖𝑛 = 0.396 ∗ 𝑉0.1273
Equation 2. 5. RT min for polyvalent room (6)
𝑇𝑚𝑖𝑑 𝑜𝑝𝑡𝑖𝑚𝑢𝑚 𝑚𝑎𝑥 = 0.368 ∗ 𝑉0.1505
Equation 2. 6. RT max for speech transmission (6)
𝑇𝑚𝑖𝑑 𝑜𝑝𝑡𝑖𝑚𝑢𝑚 𝑚𝑖𝑛 = 0.264 ∗ 𝑉0.1394
Equation 2. 7. RT min for speech transmission (6)
To complete this parameter, it is important to describe the listener's sensitivity to changes "JND", since it will define the tolerance allowed between the different measurement points of the solutions and the validation of the models. This sensitivity is defined in the Standard (2) for almost all the indicators in table A.1 (1), in which it is viewed that T20 and T30 1JND correspond to 5% of the average T20 and T30.
2.2.3. Early Decay Time, EDT
EDT is used to predict the sensation of the listener's reverberation time and it is calculated in the same way as previously stated, but between the instants 0dB and - 10dB. According to Higini Arau (6), a room with an EDT lower than RT will sound duller for the music and more intelligible for the speech, and he also proposes some thresholds that are used in this project.
13
- The first threshold of EDT is set at 3.2 seconds independent of the volume, above which it will be considered "BAD".
- The second threshold is placed between 0.9 and 1.5 of the value of T20, which is considered "NICE FOR MUSIC".
- The third threshold is set between 0.75 and 0.9 of T20, which is considered “ACCEPTABLE FOR MUSIC AND SPEECH”.
- The fourth threshold is placed between 0.6 and 0.75 of T20, which is considered “NICE FOR SPEECH”.
- The fifth one is between 0.5 and 0.6 of T20, which is considered “ACCEPTABLE FOR SPEECH”.
- And finally, if the value of EDT is below 0.5 of T20, it is considered “BAD”.
According to Standard 3382 (1) the minimum difference perceptible by the listener is considered the same as T20 and T30, 5% of the average EDT.
2.2.4. Clarity of Music, C80
This parameter was defined as the logarithm of the fraction between the energy of the first 80ms and the energy after the 80ms, or also called “EARLY TO LATE SOUND INDEX”, and it is expressed mathematically in the following Equation 2. 8.
𝐶80= 10 ∗ log10(∫080𝑚𝑠𝑝2(𝑡)𝑑𝑡
∫80𝑚𝑠∞ 𝑝2(𝑡)𝑑𝑡) , 𝑑𝐵
Equation 2. 8. C80 equation (1)
A high C80 is associated with a small EDT related to RT. This usually occurs in places with a relatively low ceiling above the listeners or where the ceiling does not have much sound dispersion.
In this project the thresholds were established based on the studies of H. ARAU (6), M. Barron (5) and W. Reichardt (5).
- The first threshold is placed at -3dB, below which is considered "VERY LOW".
14
- The second threshold is placed between -3dB and -2dB, which is considered "LOW".
- The third threshold is between -2dB and 4dB, which is considered
"ACCEPTABLE".
- The next threshold is set between 4dB and 5dB, which is considered
"ACCEPTABLE HIGH".
- The last threshold is between 5dB and 6dB, which is considered "HIGH". If the threshold of 6dB is exceeded, it is considered "VERY HIGH".
To complete this indicator, 1dB is considered as the minimum perceptible difference by the listener, or "JND" for the C80.
2.2.5. Speech Definition, D50
This indicator is defined as the fraction of immediate energy in the first 50ms with the total energy of the impulse response. As the denominator is the total energy (Equation 2. 9) this parameter has a range of values from 0 to 1, if it is correctly calculated. In this project it will be expressed as a percentage that is multiplied by 100.
𝐷50=∫050𝑚𝑠𝑝2(𝑡)𝑑𝑡
∫ 𝑝0∞ 2(𝑡)𝑑𝑡
Equation 2. 9. D50 equation (1)
A low-definition index is usually due to excessive reverb, which gives the feeling of a not very intimate environment for the speech, but it could be nice for musical performances. That is why the thresholds are established in percentages, according to H. ARAU (6).
- The first threshold is established between 0 to 30%, in which it will be considered "BAD".
- The second threshold is set between 30 to 45%, which will be considered
"GOOD FOR MUSIC".
- The next threshold is placed between 45 and 65, and will be considered
"INTERMEDIATE MUSIC AND SPEECH".
15
- Above 65% it will be considered "GOOD FOR SPEECH".
Finally, and following the standard 3382, 5% will be considered as the minimum difference perceptible by the listener in absolutely terms.
2.2.6. Central Time, TS
This parameter is defined as the instant in which the area below the energy decay curve is divided into equal parts and mathematically is expressed in the Equation 2. 10. This parameter gives an idea of how the energy is distributed along the decay curve and is expressed in milliseconds.
𝑇𝑠 =∫ 𝑡 ∗ 𝑝0∞ 2(𝑡)𝑑𝑡
∫ 𝑝0∞ 2(𝑡)𝑑𝑡
Equation 2. 10. Ts equation (1)
According to the Standard 3382-1, the typical ranges in medium frequencies for this parameter are between 60 and 260ms, according to H. Arau (6), values from 110ms to 150ms are optimal for music. However, in the absence of information on this parameter and given that it is directly influenced by the reverberation time, there will be values that will decrease with frequency, so the range of values from 50ms to 260ms are considered "ACCEPTABLE", and everything far from it is considered as "NOT ACCEPTABLE".
Finally, the Standard 3382-1 establishes as the minimum difference perceptible by the listener (1 JND) 10ms.
2.2.7. Early Lateral Energy fraction, LF and LFC
This parameter is defined according to M. Barron (5) and Marshall (7) as the fraction of energy of the first 80ms measured with a microphone with a directivity in the shape of an 8, with its null point directed to the sound source between the total energy
16
measured with an omnidirectional microphone at the same measured thanks to the orthogonality of the 4 heads of the tetrahedral microphone used. The function is defined mathematically as follows in the Equation 2. 11:
𝐿𝐹 =∫5𝑚𝑠80𝑚𝑠𝑃𝐿2(𝑡)𝑑𝑡
∫080𝑚𝑠𝑝2(𝑡)𝑑𝑡
Equation 2. 11. LF equation (1)
The directivity in 8 of the microphones varies in the form of a cosine, and in the formula, it is seen that the power of this microphone is squared so that the energy varies as the square of a cosine. This often causes an imprecision in the measures of this indicator, which is fixed by making the contributions vary only as a function of the cosine of the LFC angle, mathematically expressed in the Equation 2. 12.
𝐿𝐹𝐶 =∫5𝑚𝑠80𝑚𝑠|𝑃𝐿2(𝑡) ∗ 𝑝(𝑡)|𝑑𝑡
∫080𝑚𝑠𝑝2(𝑡)𝑑𝑡
Equation 2. 12. LFC equation (1)
As for the D50, by dividing a small part of energy by the total energy, a dimensionless number range from 0 to 1 is obtained, which can also be expressed as a percentage if multiplied by 100. When this spatial parameter is within the range from 5% to 35%, the listener can get an idea of the spatial location of the musicians on stage. Therefore, in this project it will be considered "ACCEPTABLE" for this range and
"NOT ACCEPTABLE" for lower or higher ranges.
According to the Standard 3382-1, the minimum difference perceptible by the listener (1JND) is 5% of difference of the average LF or LFC in absolutely terms.
17
2.2.8. Speech Transmission Index, STI male and STI female
STI is a measure of speech transmission quality. This parameter with a single value in all bands is a good predictor of how the room will affect the speech transmission. Below, it is described how this parameter is calculated.
Based on earlier studies by Houtgast and Steeneken, shown in the Equation 2.
13, in which δ is the relative amplitude between source and receiver and ῖ is the single echo of the delay time, Schroeder proposed an MTF modulation matrix dependent on the reverberation time in each band measured in the room, shown in the Equation 2.
14, called Rapid STI or RASTI. The two previous matrixes are used to predict the signal-to-noise ratio in each band that will be in a room depending on its reverberation time. Understanding as noise is the destructive reflections that make it difficult for speech transmission and is generated by the source itself within the room. This matrix follows the equation shown in the figure. In which w=2*π*fm, where fm is the modulation frequency that is in the range of 0.4 to 18Hz.
𝑚(𝑓𝑚) =√1 + 2𝛿 ∗ cos (2𝜋𝑓𝑚ῖ + 𝛿2) 1 + 𝛿
Equation 2. 13. MTF equation by Houtgast and Steeneken (7)
𝑚(𝑓𝑚) = 1
√1 + (2𝜋𝑓𝑚𝑇 13.8 )
2
Equation 2. 14. MTF equation by Schröeder (8)
Taking into account that T is the reverberation time in each band, as previously stated, the MTF graph that presents three examples of T is the one shown in the Figure 2. 9. The continuous line being the function for T = 0.1s, the dashed line T = 1s and the dotted line T = 10s. In this example, 18 precision frequencies have been taken in the range 0.4Hz to 18Hz to draw the lines from the second Equation 2. 14. Regarding the first equation and assuming ῖ=0.038 with different relative amplitudes, the figure portrays an example with 17 points of resolution.
18
Figure 2. 8. MTF by Houtgast and Steeneken (7)
Figure 2. 9. MTF by Schröeder (8)
The S / N at each point of the matrix is calculated according to the Equation 2.
15. Then, the arithmetic mean of the 18 points is carried out, in this case in the Equation 2. 16, taking into account the conditions of the Equation 2. 17 and in the Equation 2. 18 in each S/N.
(𝑆 𝑁)
𝑖
= 10 ∗ log10( 𝑚 (1 − 𝑚))
Equation 2. 15. Signal to noise ratio in each fm (9)
19 (𝑆
𝑁)
𝑒𝑎𝑐ℎ 𝑏𝑎𝑛𝑑
= 1
18∗ ∑ (𝑆 𝑁)
𝑖 18 0.4
Equation 2. 16. Signal to noise ratio average in each band (9)
(𝑆 𝑁)
𝑖
≥ 15𝑑𝐵 ⇒ (𝑆 𝑁)
𝑖
= 15
Equation 2. 17. Signal to noise ratio max in each fm (9)
(𝑆 𝑁)
𝑖
≤ −15𝑑𝐵 ⇒ (𝑆 𝑁)
𝑖
= −15
Equation 2. 18. Signal to noise ratio min in each fm (9)
In order to calculate the Rapid STI, the S / N that resulted from each band can be averaged and, in the present project, how the STI male and female are calculated, the S / N results for each band must be weighted according to the Table 2. 2 where it can be seen that for the STI female the 125 HZ band is not taken into account.
Table 2. 2. Male and female modulation for Speech transmission (10)
Finally, the global RASTI is calculated according to the Equation 2. 20 with the global S/N, calculated in the Equation 2. 19:
(𝑆 𝑁)
𝑔𝑙𝑜𝑏𝑎𝑙
= ∑ (𝑆
𝑁)
𝑒𝑎𝑐ℎ 𝑏𝑎𝑛𝑑 8000𝐻𝑧
125𝐻𝑧
Equation 2. 19. Signal to noise ratio global (9)
20 𝑆𝑇𝐼 =
(𝑆
𝑁)𝑔𝑙𝑜𝑏𝑎𝑙+ 15 30
Equation 2. 20. STI equation from signal to noise (9)
This dimensionless acoustic indicator has a range of values from 0 to 1, which multiplied by 100 can be represented as percentages. According to the Standard IEC 60268-16 (12), the thresholds that will be used in this project to objectively evaluate the exported results will be as the Table 2. 3 shows. In addition, the same standard provides a table with appropriate values for each type of enclosure in the Table 2. 4.
Table 2. 3. Evaluation thresholds by the IEC 60268-16 standard (12)
21
Table 2. 4. IEC 60268-16 standard evaluation table (12)
Finally, the minimum perceptible difference (1JND) is set at 0.03 or 3% in absolutely terms and, although in some of the tables in the following sections, only the 125 to 4KHz bands are performed, the 8KHz band has been taken into account, although it does not contribute much to the global result.
2.2.9. Articulation loss of Consonants, ALCONS male and female
ALCONS is defined as an indication of the loss of speech intelligibility that occurs in difficult acoustic environments. This parameter is the only one that is not exported from the IRIS collection and calculation program. It is predicted directly from the STI male and female, since the relationship between the two indicators is empirically demonstrated by many acousticians.
22
𝐴𝐿𝐶𝑂𝑁𝑆 (%) = −170.5405 ∗ 𝑒−5.419∗𝑆𝑇𝐼
Equation 2. 21. ALCONS percentage equation (10)
In this equation, STI range have values from 0 to 1 without being multiplied by 100, and the result is between 0-1 too, which can also be expressed as a percentage.
Like the STI, the Alcons has the following thresholds for its objective assessment:
- Between 0 and 3%, the ALCONS is considered "EXCELLENT".
- Between 3 to 7%, the ALCONS is considered “GOOD”.
- Between 7 to 15%, the ALCONS is considered “FAIR”.
- Between 15 to 33%, the ALCONS is considered “POOR”.
- Lastly, if the value of ALCONS is above 33%, it is considered “BAD”.
The minimum difference perceptible by the listener (1JND) is considered 2% in absolutely terms.
3 Measurements
and data analysis
24
Benchmark, Igreja de Santa Clara 3.1.
(Oporto)
3.1.1. Location and conditions
The Church of Santa Clara is a Catholic church located in the Freguesia da Sé, in the city of Porto, Portugal (13).
Figure 3. 1. Location of Igreja Santa Clara (Oporto) (12)
In its interior we can find one of the best examples of the gilded woodcarving art of the Baroque Joanino. The Church of Santa Clara was completed in 1457 (13).
Figure 3. 2. Igreja de Santa Clara (12)
25
There is no additional information on the volume and audience area, in addition, the church was in a middle of reform without furniture and with a scaffold in the hall.
3.1.2. Acoustic parameters
When entering the church, its small volume suggests that only 6 receiver positions are needed. With respect to the source, only one position is needed due to the small box.
Even in an empty church, the acoustic sensation is pleasant in terms of word transmission and the decay is uniform, and no echoes are perceived. It is possible to notice that the excess of decoration and the characteristics of the materials cause an adequate absorption and dispersion for performances, which is verified once the indicators shown in the following table have been calculated.
After some initial tests, the reverberation times were measured between 1 and 1.2 seconds, as shown in the Figure 3. 3, so the integration time for the sine sweep was adjusted to those seconds as indicated in the Standard 3382-1.
Figure 3. 3. RT measured in Igreja Santa Clara 0,00
0,20 0,40 0,60 0,80 1,00 1,20 1,40 1,60 1,80
63 125 250 500 1000 2000 4000 8000
T30 T20 EDT
26
Finally, the results calculated with the IRIS application are exported to excel, in which the arithmetic averaging is performed, as it appears in the Standard 3382-1. The standard deviation of the measurement points is also calculated in order to see the uniformity with which the sound is distributed throughout the room and performed in JNDs. The results can be seen in the Table 3. 1.
Table 3. 1. Acoustic parameters in Igreja Santa Clara
Before interpreting the results, it is also necessary to look at the decay ranges in the measurements to know if the observed results are reliable. The decay ranges are presented in the Table 3. 2.
Table 3. 2. Decay Range in Igreja Santa Clara
27
According to this standard and the IRIS manual, the calculated parameters are not entirely reliable if the decay range is less than 45dB, so looking at the Table 3. 2, all bands are reliable, because the standard demands the bands between 125Hz to 4KHz, so the objective assessment is shown in the Table 3. 3.
OBJECTIVE ASSESSMENT OF THE ACOUSTIC PARAMETERS
freq 125 250 500 1000 2000 4000
T20 NICE FOR SPEECH
ACCEPTABLE FOR MUSIC AND SPEECH
ACCEPTABLE FOR MUSIC AND
SPEECH
NICE FOR MUSIC
ACCEPTABLE FOR MUSIC AND
SPEECH
ACCEPTABLE FOR MUSIC AND SPEECH
T30 NICE FOR SPEECH
ACCEPTABLE FOR MUSIC AND SPEECH
ACCEPTABLE FOR MUSIC AND
SPEECH
NICE FOR MUSIC
ACCEPTABLE FOR MUSIC AND
SPEECH
ACCEPTABLE FOR MUSIC AND SPEECH
EDT NICE FOR SPEECH
ACCEPTABLE FOR
MUSIC AND SPEECH NICE FOR MUSIC NICE FOR MUSIC
ACCEPTABLE FOR MUSIC AND
SPEECH
ACCEPTABLE FOR MUSIC AND SPEECH C80 ACCEPTABLE
HIGH ACCEPTABLE ACCEPTABLE ACCEPTA
BLE ACCEPTABLE ACCEPTABLE D50
INTERMEDIAT E MUSIC AND
SPEECH
GOOD FOR MUSIC GOOD FOR MUSIC
GOOD FOR MUSIC
GOOD FOR MUSIC GOOD FOR MUSIC
Ts ACCEPTABLE ACCEPTABLE ACCEPTABLE ACCEPTA
BLE ACCEPTABLE ACCEPTABLE LF ACCEPTABLE ACCEPTABLE ACCEPTABLE ACCEPTA
BLE ACCEPTABLE ACCEPTABLE LFC ACCEPTABLE ACCEPTABLE ACCEPTABLE ACCEPTA
BLE ACCEPTABLE ACCEPTABLE
STI mal FAIR
STI fem FAIR
ALCONS
male FAIR
ALCONS
female FAIR
Table 3. 3. Objective assessments in Igreja Santa Clara
In the previous Table 3. 3, the objective assessments of the averages of the acoustic parameters are shown. The parameters are good in terms of averages, it can be said that the room has good acoustics. More specifically, it can be stated that the room more prepared for music than for speech due to the low D50 of 35% in mid frequencies and STI of 50%. According to the IEC standard (12), the empty church would be classified between F and G (Table 3. 4), but with a PA system it can be perfectly equipped to be a room dedicated to the transmission of speech.
28
Table 3. 4. Assessment of STI by Standard IEC 60268-16 (12)
Considering the other parameters, the averages look good, as previously mentioned. The only observation is that the deviation in JNDs of the EDT parameter is too high for the 125Hz band, Table 3. 1. The following Table 3. 5 shows the values for the six measurement points in which the points that differ most from the average are marked, highlighting the “P5” receiver point that when in octave band of 125Hz it drops to 0.66s and the “P6” receiver point reaches 1.5s when in octave band of 125Hz. It is possible that such measurements are due to the random nature of the sine sweep signal, since the RT estimated from T20 and further from T30 converges towards the average value.
Table 3. 5. Difference between points of EDT measurements in Igreja Santa Clara
Finally, all the measures are within what is acceptable, and this room can be considered good for music concerts and acceptable for concerts in which the transmission of speech is important. In addition, it is expected that with the occupation of the room the indicators would improve even more, with the increase in the absorption area of the audience and the decrease in the volume of air inside the room.
29
Igreja Matriz Nossa Senhora do Rosario 3.2.
(Marinha Grande)
3.2.1. Location and conditions
The Church Matriz Nossa Senhora do Rosario is a Catholic church located in the district of Leiria, in the city of Marinha Grande, Portugal (15).
Figure 3. 4. Location of Igreja Matriz Nossa Senhora do Rosario (12)
This church was launched in 1971, after the previous one was demolished, in 1969, as it became too small due to the increase in city’s population (15).
30
Figure 3. 5. Igreja Matriz Nossa Senhora do Rosario (12)
This church has an estimated volume of 4331m3 when it is empty, and it is prepared for an estimated capacity of 451 people. The large volume of the church in front of a small number of seats is due to a considerably high ceiling in the central audience area, which can result in different acoustic zones. Despite the absence of physical barriers, the central zone has a ceiling height of up to 11.7 meters and the lateral areas of 4.23 meters. The heights can be observed in the Figure 3. 6. Due to this, the microphone was placed at 10 different positions, and two positions for the fountain where the priest normally performs the liturgy. The following Figure 3. 7 shows the positions for the source and receiver where the nomenclature in later tables is respected.
Figure 3. 6. Igreja Matriz Nossa Senhora do Rosario´s interior
31
Figure 3. 7. Igreja Matriz Nossa Senhora do Rosario´s plane with measurements points
3.2.2. Acoustic parameters
After some initial tests, the reverberation times were measured between 5 and 6 seconds, as shown in the Figure 3. 8, so the integration time for the sine sweep was adjusted to the seconds indicated in the Standard 3382-1.
32
Figure 3. 8. RT measured in Igreja Matriz Nossa Senhora do Rosario
Finally, the results calculated with the IRIS application were exported to Excel, where the arithmetic averaging is performed as it appears in the Standard 3382-1. The standard deviation of the measurement points is also calculated to see the uniformity with which the sound is distributed throughout the room and performed in terms of JNDs. The results can be seen in the Table 3. 6.
Table 3. 6. Acoustic paramaters in Igreja Matriz Nossa Senhora do Rosario 0,00
1,00 2,00 3,00 4,00 5,00 6,00
63 125 250 500 1k 2k 4k 8k
T20 T30 EDT
33
Before interpreting the results, it is also necessary to look at the decay ranges in the measurements to know whether the results observed are reliable. The decay ranges are shown in the Table 3. 7.
Table 3. 7. Decay Range in Igreja Matriz Nossa Senhora do Rosario
According to the Standard 3382-1 and the IRIS manual (16), the calculated parameters are not entirely reliable if the decay range is less than 45dB. So, looking at the Table 3. 6, the 63Hz and 125Hz bands may not be entirely reliable. There is a problem with the 125Hz octave band, because it has to be considered by the standard that requires it, even though it is not entirely reliable. Therefore, the objective assessment is shown in the Table 3. 8.
34
OBJECTIVE ASSESSMENT OF THE ACOUSTIC PARAMETERS
frequency 125 250 500 1000 2000 4000
T20 BAD BAD BAD BAD BAD ACCEPTABLE FOR
CHURCHES
T30 BAD BAD BAD BAD BAD ACCEPTABLE FOR
CHURCHES
EDT BAD BAD BAD BAD BAD NICE FOR MUSIC
C80 VERY LOW VERY LOW VERY LOW VERY LOW VERY LOW LOW
D50 BAD BAD BAD BAD BAD BAD
Ts NOT
ACCEPTABLE
NOT ACCEPTABLE
NOT ACCEPTABLE
NOT ACCEPTABLE
NOT
ACCEPTABLE ACCEPTABLE
LF NOT
ACCEPTABLE ACCEPTABLE ACCEPTABLE ACCEPTABLE ACCEPTABLE ACCEPTABLE
LFC NOT
ACCEPTABLE ACCEPTABLE ACCEPTABLE ACCEPTABLE ACCEPTABLE ACCEPTABLE
STI male POOR
STI female POOR
ALCONS
male POOR
ALCONS
female POOR
Table 3. 8. Objective assessments of acoustic parameters in Igreja Matriz Nossa Senhora do Rosario
Firstly, the averages of all the parameters for the mid and low frequencies, essential for music and speech, are not appropriate, this is due to high reverberation times, between 4 and 5 seconds between the bands of 125Hz to 2000Hz, already observed in the Table 3. 6.
The next thing that can be seen is that for the 125Hz frequency, in which the decay range was between 40 and 51dB, and the measurements have limit reliability, neverless, the temporal and energetic parameters in this frequency follow the expected trend and are hence included in the analysis.
According to the Standard IEC 60268-16, with 0.34 and 0.35 STI values, the empty church would be classified as U, and even if amplification systems are placed, understanding speech would be very difficult (12).
35
Table 3. 9. Assessment of STI in Igreja Matriz Nossa Senhora do Rosario by IEC 60268-16 (12).
Finally, in the following sections, solutions will be proposed and described to adjust the church to the requirements of the priest, which is a church prepared for musical performances, including an organ, and acceptable for speech transmission for liturgies.
Igreja Paroquial de Rio Maior (Rio 3.3.
Maior)
3.3.1. Location and conditions
The parish church is a Catholic church located in the district of Santarém, in the city of Rio Maior, Portugal (17).
Figure 3. 9. Location of Igreja Paroquial do Rio Maior (12)
36
This church began to be built in 1961 and was launched in 1968 (17).
Figure 3. 10. Igreja Paroquial do Rio Maior (12)
This church presents irregular geometry and an estimated volume of 4661m3, planned for a capacity of up to 1,355 people. It is characterized by widely spaced walls and a minimalist atmosphere due to the lack of ornamentation, which usually characterizes other churches or cathedrals. Following the Standard 3382-1, for this capacity it is recommended 10 microphone points placed uniformly throughout the room (2), and for the sound source, two significant points are chosen within the church, where the priest performs the liturgies. The positions of these points are shown in the Figure 3. 11, in which the point 3 of the receiver is slightly changed in the two source positions, since for F2 it remains behind the column.
37
Figure 3. 11. Measurements points in Igreja Paroquial do Rio Maior
When entering the hall, a noisy environment can be perceived, where each acoustic excitation lasts too long. Late reflections are heard with great clarity due to the distance from the walls and the amount of polished and reflective surface in the room.
3.3.2. Acoustic parameters
After the first measurements of the reverberation times, exorbitant values are between 10 and 11 seconds in low frequencies are obtained, as shown in the Figure 3.
12.
38
Figure 3. 12. RT measured in Igreja Paroquial do Rio Maior
The integration time of the signal is adjusted following the Standard 3382-1 and the IRIS manual (16), exporting the results to Excel, with the help of the application, where the average values and also the deviations performed in terms of JNDs are shown below in the Table 3. 10, in order to see the uniformity which the room behaves.
0,00 2,00 4,00 6,00 8,00 10,00 12,00
63 125 250 500 1k 2k 4k 8k
T20 T30 EDT
39
Table 3. 10. Acoustic parameters in Igreja Paroquial do Rio Maior
Before interpreting the results, it is also necessary to look at the decay ranges in the measurements to know to what extent the observed results are reliable. The decay ranges are shown in the Table 3. 11.
40
Table 3. 11. Decay Range in Igreja Paroquial do Rio Maior
According to the Standard and the IRIS manual (16), the calculated parameters are not entirely reliable if the decay range is less than 45dB. So, looking at the table, the 63Hz band may not be entirely reliable, but it is not a problem, because the Standard demands bands between 125Hz to 4KHz. It also seems that there is a problem with receiver points 4 and 5, since in almost all bands it does not reach the minimum required, and there can be problems with these points. Later, it will be verified if it really affects the measurements to make the deviations very high with respect to the average in the previous Table 3. 10. Therefore, the objective assessment is shown in the Table 3. 12.
41
OBJECTIVE ASSESSMENT OF THE ACOUSTIC PARAMETERS
frequency 125 250 500 1000 2000 4000
T20 BAD BAD BAD BAD BAD BAD
T30 BAD BAD BAD BAD BAD BAD
EDT BAD BAD BAD BAD BAD BAD
C80 VERY LOW VERY LOW VERY LOW VERY LOW VERY LOW VERY LOW
D50 BAD BAD BAD BAD BAD BAD
Ts NOT
ACCEPTABLE
NOT ACCEPTABLE
NOT ACCEPTABLE
NOT ACCEPTABLE
NOT
ACCEPTABLE ACCEPTABLE LF ACCEPTABLE ACCEPTABLE ACCEPTABLE ACCEPTABLE ACCEPTABLE ACCEPTABLE LFC ACCEPTABLE ACCEPTABLE ACCEPTABLE ACCEPTABLE ACCEPTABLE ACCEPTABLE
STI male POOR
STI female POOR
ALCONS male POOR
ALCONS
female POOR
Table 3. 12. Objective assessments of acoustic parameters in Igreja Paroquial do Rio Maior
In the Table 3. 12, taking into account the averages, the problem of having such high reverberation times is seen, having all the acoustic parameters in unacceptable values for a show room. Only LF and LFC are saved since the room is completely reflective. Considering the deviations of the temporal and energetic parameters, in Table 3. 10, there are not big differences between the measurement points, which is normal since with a reverberation of 10 seconds 1 JND corresponds to a difference of half a second.
According to the IEC standard (12), with 0.31 and 0.32 STI values, the empty church would be classified as U, and even if amplification systems are placed, understanding speech would be very difficult.
Table 3. 13. Assessment of STI in Igreja Paroquial do Rio Maior by Standard IEC 60268-16 (12)
42
This church has a serious limitation at low frequencies creating a condition to allows missed noise (mainly from the vowels) impining speech intelligibility. In addition the consonants (whose spectrum shows high energetic values at high frequencies) lose energy very quickly. The Figure 3. 12 with the reverberation time at the frequency spectrum illustrates this effect.
4 3D Modelling
44
Computer Aided Designs (CAE) 4.1.
After analyzing the results from the previous section, it is evident that two of the churches have an acoustic problem that has to be fixed, and it is one of the objectives of this project. Currently, there are complex simulation tools called Computer Aided Design (CAE) based on finite element mathematical methods (FEM) through which it is possible to test acoustic solutions from a computer by designing the naves of the churches themselves, in which case it is possible to get:
Simulation of behavior before remodeling.
High success rate.
No need for tests in the church itself.
Productivity increase.
All of the above translate into more economical and satisfactory solutions for the client.
In this project, the simulation software used is called Catt-Acoustics (18), with which the models of the churches are validated in order to see if the behavior corresponds to reality. Thus, it is verified how the churches behave in a state of occupancy, and then acoustic solutions are tested until a satisfactory one is found, thanks to the calculations of the acoustic indicators simulated by the program following the Standard 3382-1.
Without delving into deep explanation, the operation of this program is to generate rays that simulate acoustic signals coming from a source placed by coordinates in a text file, and then it calculates how those rays arrive at the microphone points, also placed by coordinates in another file later to bounce around the limits of the room, also defined by coordinates in a third text file, where the dispersion and absorption coefficients of what would be the construction and cladding materials of the churches are also defined. This method of operation, by coordinates in text files, forces the carrying out of a previous step through another program in which the geometry of the churches is visually designed and then, thanks to a plug-in, exported to the coordinate language that CATT Acoustics use.
45
Drawing with SketchUp 4.2.
4.2.1. Software description
SketchUp (formerly known as Google SketchUp) is a face-based three- dimensional (3D) modeling and graphic design program. It is used for modeling urban planning, architecture, civil engineering, industrial design, scenic design, GIS, video games or movies. It is a program developed by Last Software, a company acquired by Google in 2006 and later sold to Trimble in 2012 (19).
SketchUp publishes the language in which it is written, Ruby, so that users can write program segments to change functionality. These small or large programs are called plug-ins. There is a great variety of these with particular applications such as automated roof drawing, zoom tools etc. From the 21st century on, it is being widely used because its functions are very useful for architects and acousticians.
In this program, apart from designing the geometry for later calculations, it is possible to assign colors and labels to the different faces to later facilitate the import work in CATT, as shown in the Figure 4. 1.
Figure 4. 1. Modelling in Sketchup
This program also has an infinite number of tools to rotate, enlarge and decrease the views, make different geometry shapes etc. In order to be able to work on interior faces, it is also possible to hide the exterior faces and access the interior of the enclosures, as shown in the Figure 4. 2.
