Acoustical Parameters - Teatro Argentino de La Plata and Teatro Margarita Xirgu

Acoustics Instruments and Measurements

June 2013, Caseros, Buenos Aires Province, Argentina

ACOUSTICAL PARAMETERS COMPARISON OF TWO HALLS: “TEATRO ARGENTINO DE LA PLATA” AND “TEATRO MARGARITA XIRGU” AGUSTÍN Y. ARIAS 1 1

Universidad Nacional de Tres de Febrero, Buenos Aires, Argentina. [email protected]

Abstract: This report describes the methods and results from several measurements performed in the hall s “ Teatro Argentino Teatro Argentino de La Plata” and “ Teatro Teatro Margarita Xirgu” to know the know the behavior of their main acoustical parameters. These parameters are evaluated in detail to classify each hall according to the degree of their acoustic comfort.

INTRODUCTION In the nineteenth century the acoustics becomes a science, with the discoveries of W. C. Sabine, who experimentally demonstrated the relationship between the physical properties of a room and its reverberation time. The reverberation time is sometimes considered the most important parameter to evaluate room acoustics. For a great acoustic comfort it is crucial that the reverberation time be the right-one according to the activity developed within the room (hall, concert hall, conference room, etc.). However, several researchers have shown that obtaining an adequate reverberation time is not enough to ensure good sound quality and then defined various acoustical parameters that serve as indicators of the acoustic performance of a room, which allows an “acoustical categorizing”. These acoustical parameters are indicators that reveal several properties of the behavior of sound waves in an enclosure and are perceived by listeners in the form of “sensations” (e.g., degree of liveliness of the room, apparent sound source size, clarity of voice and music, harmonious, degree of a correct speech comprehension, etc.). Thanks to the advancement of research and the rapid development of technology in the twentieth century, there have been able to define these “sensations” with measurable and quantifiable physical quantities described by acoustical parameters. These parameters have been the result of extensive research conducted by leading researchers of room acoustics. Today, the individual importance of each of these parameters generates several debates. For this reason there are different methods of evaluating them in order to quantify the degree of influence of each one to the contribution to the overall assessment of the room. For this reason various studies may judge the acoustic of a room in different ways, because many of them evaluated the importance of each parameter value with different criteria. Because of this, it still continues to investigate the importance that each parameter has when performing an acoustical evaluation of enclosures. This report describes the procedures used to carry out the measurements of the main acoustical parameters of the halls "Teatro Argentino de La P lata" and "Teatro Margarita Xirgu”. All results are analyzed, trying to justify the behavior of each individually and finally evaluating the degree of acoustic comfort of each room according to the type of activity (theatrical or musical).

1

ACOUSTICAL PARAMETERS COMPARISON OF TWO HALLS

PART I - Generalities

PART I GENERALITIES Before starting to develop the individual results obtained for eac h hall, it is important to define some generalities regarding the measurements and the parameters studied. To obtain the ac oustical parameters defined below, it was implemented the recommendations 1 and requirements specified in the Standard ISO 3382-2001 . The objective of the measurements process was to obtain the Impulse Response from both halls in each measurement position. The sound signal used was a Log-Sine sweep. To obtain the results of 2 each acoustical parameter the signals were recorded and post-processed with Aurora plugins in Adobe Audition 3.0. There were three different types of measurements according to the parameters studied: Monaural and Binaural Impulse Responses for the measurements performed in the audience areas and Monaural Impulse Response for the measurements performed on the stages. The equipment used was the follows: Dodecahedral loudspeaker + Subwoofer OUTLINE, used as omnidirectional sound source. Sound Level Meter Svantek 959 class one with its corresponding calibrator. Soundfield microphone to perform monaural im pulse response in the audience areas. Earthworks M50 microphone to perform monaural impulse response measurements on (“Teatro Argentino de La Plata” Plata” ). stages (“Teatro ). DPA 4060 microphone to perform monaural impulse response measurements on stages (“Teatro Margarita Xirgu” ). ). Dummy Head KEMAR to perform binaural-impulse response measurements in the audience areas. Notebooks. Audio interfaces. Aurora Plugins for Adobe Audition. The acoustical parameters evaluated in both halls are defined in the ISO 3382-2001 standard. The complete formulation that defines these parameters can be found in the Annex section of this report

Monaural Parameters: Reverberation time. Defined as the time (in seconds) that elapses between the sound source is stopped until the moment when the sound pressure level falls 30 dB relative to its initial value, interpolating the decay curve up to 60dB. Subjective impression: “Liveliness” of the room. o Parameter evaluated: RTmid. o Early decay time: Defined as six times the time elapsed since the radiated sound source stops until the sound pressure level drops 10dB. Subjective impression: “Liveliness” of the room (usually gives more reliable o results than the RT mid). Parameter evaluated: EDTmid. o 1

ISO-3382: “ Acoustics – Measurement – Measurement of the reverberation time of rooms with reference to other acoustical parameters”. parameters”. 2001. 2 Farina, Angelo: “Impulse Response Measurements by Exponential Sine Sweeps”. Parma, 18 October 2008.

2



Bass Ratio3: Relationship between the reverberation time values obtained at low and mid frequencies.

Subjective impression: Richness in bass sounds, mellow and soft music. Parameter evaluated: BR o Brightness3: Relationship between the reverberation time values obtained at high and o

mid frequencies.

Subjective impression: Richness in sharp sounds. Parameter evaluated: Br o Voice Clarity4: Relationship between the sound energy that reaches the listener during o

the first 50ms from the arrival of the direct sound and that comes after the first 50ms, calculated between the bands from 125 to 4000 Hz. Subjective impression: “Speech intelligibility degree. o Parameter evaluated: C50 (“speech average”). o Musical Clarity5: Relationship between the sound energy that reaches the listener during the first 80ms from the arrival of the direct sound and that comes after the first 80ms, calculated between the bands from 125 to 4000 Hz. Subjective impression: Degree of separation between the different individual o sounds members of a musical composition. Parameter evaluated: C80 (“music average”). o Definition: Relationship between the sound energy reaching the listener within the first 50ms since the arrival of the direct sound (including the direct sound and early reflections) and the total sound energy, measured between the octave bands of 125 to 4000 Hz. Subjective impression: Speech intelligibility degree. o Parameter evaluated: D50 o Strength Factor6: Difference between the total sound pressure level produced by an omnidirectional sound source at a given point of a room and the sound pressure level produced by the same source in a free field to ten meters away. Subjective impression: Degree of amplification caused by the room. o Parameter evaluated: Gmid o Center Time7: It is the time of the gravity center of the quadratic impulse response. Subjective impression: Degree of perceived definition, clarity, or the balance o between clarity and reverberation, in addition to speech intelligibility. Parameter evaluated: Ts (average from 125 up to 4000 Hz) o Lateral Efficiency8: Relationship between the sound energy reaching a listener laterally within the first 80ms since the arrival of the direct sound (excluded) and the received sound energy in all directions in that time interval. Subjective impression: Spatial impression of sound (apparent width of the o sound source). Parameter evaluated: LFE4 o

3

Beranek, L. L.: “Concert and Opera Hall s -How -How they Sound” . Acoustical Society of America, 1996. Ahnert, W. - Schmidt, W.: “ Acoustics in cultural buildings)” buildings) ” . Institut für Kulturbauten, Berlin 1980. 5 Abdel Alim, O.: “ Dependence Dependence of time and register definition of room acoustical parameters with music performances” performances” . Dissertation, TU Dresden 1973. 6 Lehmann, P.: “On the ascertainment of room acoustical criteria and correlation of the same with subjective assessments of the acoustic overall impression amkeit ” ” . Dissertation TU Berlin, 1976. 7 Kürer, R.: “A simple measuring procedure for determining the "center time" of room a coustical impulse impulse responses”. 7th Intern. Congress on Acoustics, Budapest 1971. 8 Barron, M.: “Auditorium Acoustics and Architectural Design”. Verlag E & FN SPON. London 1993. Kleiner, M.: “A New Way of Measuring Lateral Energy Fractions”. App. Acoust., Vol. 27, 321 ff (1989). 4

3



Binaural Parameter: Interaural Cross Correlation Coefficients 9: Cross correlation between the calculated impulse responses in both ears in the first 80ms. Indicative of the degree of similarity existing between the two signals. Subjective impression: Spatial impression of sound (apparent width of the o sound source). It was demonstrated that this parameter have much repeatability than the LF E4. Parameter evaluated: 1-IACCE3 o

Stage Parameter: Room Support 10: Parameter to evaluate the degree of acoustic comfort on stage and the orchestra pit. It is calculated as the ratio of the energy associated with early reflections (20 to 100ms) provided by the walls and ceiling of the stage, and the energy received after 20ms, both values obtained at one meter distance from the omnidirectional sound source located on stage. It is expressed on a logarithmic scale. Subjective impression: Musicians capacity to hear themselves and the rest of o the orchestra. Parameter evaluated: ST1mid o Each parameter has some recommended values that emerged after many years of room 11 12 13 acoustics investigations . Thanks to the contributions of Beranek , Barron and others experts in room acoustic, it is possible to compare the results obtained for a particular room and compare them with these recommended values, most of them derived from the greatest theaters and concert halls in the world in terms of acoustic comfort. They are listed in Table 1. Table 1. Recommend acoustical parameters values

ACOUSTICAL PARAMETER RTmid – occupied room EDTmid C50 (“speech average”) – occupied room Occupied room

RECOMMENDED VALUE

TYPE OF ACTIVITY

0,7< RTmid< 1,2s 1.8
Theater Concert Concert

C50 >2dB

Theater

-2
C80 (“music average”)

Concert Empty room

D50 – occupied room Gmid – Empty room LFCE4 – Empty room (1-IACCE3) – Empty room BR – Occupied room Br – Occupied room ST1mid

-450% 4
Theater Concert Concert Concert Concert Concert Concert

Note: in both halls the audience areas were unoccupied. 9

Beranek, L. L.: “Concert and Opera Halls -How they Sound ”. ”. Acoustical Society of America, 1996. Gade, A.C.: “Investigations of musicians' room-acoustic conditions in concert halls. Part I: Methods and laboratory experiments”. experiments”. Acustica 69, 1989. 11 Carrion Isbert, Antoni: “Diseño Acústico de Espacios Arquitectónicos”. 1º edition. UPC, July 1998. 12 Beranek, L. L.: “Concert and Opera Halls -How they Sound” . Acoustical Society of America, 1996. 13 Barron, M.: “Auditorium Acoustics and Architectural Design”. Verlag E & FN SPON, London 1993. 10

4



In addition, several background noise measurements were performed in order to compare the 14 results obtained with those recommend by the Argentinian Standard IRAM 4070 . These recommended values are listed in Table 2. The background noise descriptor chosen is the Noise Criteria profile. For both halls, the air conditioning systems were turned off. Table 2. Recommend background values according to IRAM 4070 standard.

BACKGROUND NOISE DESCRIPTOR

RECOMMENDED VALUE

TYPE OF ACTIVITY

NC (Noise Criteria)

NC-25 NC-20

Theater Concert Hall

MICROPHONES AND DUMMY HEAD CALIBRATION To calibrate the Soundfield and Earthworks M50 microphone and the Dummy head, they were located at 3m from the sound source and connecting each one to their respective Audio interface. The Sound Lever Meter was also located between them. Then, the sound source was turned on and reproducing Pink noise it was adjusted the signal level in order to measure a sound pressure level of 94dB. Once this value was reached, the audio interfaces gains were adjusted to obtain no levels difference diff erence between the microphones inputs.

STAGE MEASUREMENTS The microphone positions to perform the stage acoustical parameters measurements were located at 1 meter of the sound source (for both source position) covering a circular array at o o o o 0 , 90 , 180 and 270 around the geometrical center of the dodecahedron, as can be seen in Figure 1. 90 o

0

180

o

o

270

Sound Source

Figure 1. Microphone positions for the stage acoustical parameter (ST1mid) measurements.

14

IRAM 4070: “Ruidos – Procedimiento – Procedimiento para su evaluación utilizando los perfiles NC y RC” . 2008.

5


PART II – “Teatro – “Teatro Argentino de La Plata”

PART II ACOUSTICAL PARAMETERS OF THE “TEATRO ARGENTINO DE LA PLATA” ABOUT THE HALL: The project of the “Center for the Performing Arts ‘Teatro Argentino de La Plata ’” has been started as the result of a fire incident in the hall of the same name on August 18, 1977. After several discussions and controversies as it should be its reconstruction, the idea that prevailed was not only replace but add beside the lyric hall a series of additional and complementary rooms namely, a Prose, a Micro-Cinema multipurpose, rehearsal rooms for Scene and Orchestra where they could test the set-up with the decorated of each lyrical presentation, Choir rehearsal Halls, Auxiliary Halls, Ballet rehearsal Halls, Individual rehearsal Halls and many others. All of this putted together with restaurants, cafes, garages, TV and Radio Studio. Thus, 15 the hall constitutes a true cultural complex with a covered area of over 60,000 m2.

Figure 2. Stage view

ROOM GEOMETRY In Table 3 are listed the surface and volume data of the hall.

15

Sánchez Quintana, R.: “ Diseño Diseño de la sala de opera del Teatro Argentino de La Plata”. Plata ”. TecniAcústica Congress. Madrid, 2000.

6



Table 3. Surfaces and volumes.

Area

Total Surfaces

Audience

Seats

Covered area (m2)

Hallways

2200

1089

469

Pit

108

Stage

1365

Proscenium Arch

451

Stage Opening

198

Walls Walls Ceilings Sills Drapes 1114

1812

458

222

Volumes (m3) Stage

25200

Hall

15030 Table 4. Main dimensions.

Average Height

Average Width

Length

Maximum Distance

20,5m

27m

22m

37m

MEASUREMENTS POSITIONS Figures 3 to 5 show the sound source, microphones and dummy head positions to perform the IR measurements. For each measurement position the sound source was placed in two positions (Figure 3): A (stage) and B (sunken pit). As can be seen in Figure 2 there are three central balconies and six lateral balconies. The measurement positions showed in Figure 3 correspond to the ground floor, Figure 4 correspond to the first floor (1º central balcony and 1º lateral balcony) and to the second floor (2º central balcony and 3º lateral balcony) and Figure 5 correspond to third floor ( 3º central balcony and 5º lateral balcony).

A B 3

2

6

1

5

4

Figure 3. Ground floor. (●) Microphone positions ( ●) Source positions

7



7-9

8 - 10

Figure 4. First and Second floor measurement positions. Position 7: 1º Central balcony. Position 8: 1º Lateral balcony. Position 9: 2º Central balcony. Position 10: 3º Lateral balcony. (●) Microphone positions.

11

12

Figure 5. Third floor measurement positions. Position 11: 3º Central balcony. Position 12: 5º Lateral balcony. (●) Microphone positions

Figure 6. Left: Orchestra pit. Right: Stage

8



As it can be seen, a total number of twelve microphones and dummy head position and two sound source position were used to perform the measurements. The symmetry along the longitudinal axis of the hall allows locating the measurement positions on one side, estimating an invariance of the acoustical behavior for the other half of the hall. Figure 6 shows the Orchestra pit and the Stage.

MEASUREMENTS PROCEDURE Once the microphones and dummy head were calibrated, the Log-Sine sweep signal was recorded in each measurement position. This signal had the following characteristics: • Frequency range: • Length: • Fade-in: • Fade-out: • Number of repetitions:

20-20000 [Hz] 15 [s] 0.1 [s] 0.1 [s] 1

During the Log-Sine sweep signal recording process, ten background noise measurements were performed, each one in different areas (ground floor, first floor, second floor, third floor, boxes and stage). Then the average value was calculated to obtain the Noise Criteria profile of the hall.

RESULTS AND COMMENTS BACKGROUND NOISE RESULTS Figure 7 shows the spatial-average values in octave bands of the backg round noise. From these results, the corresponding NC profiled assigned to the hall is NC-35. This value is greater than the suggested, but there are some situations that could affected the measurements. Firstly, during the measurements, several stage-technicians were working in the back side of the stage, moving stage machinery (mobile platforms) and chatting to each other. In some situations, the backdoor of the stage (direct exit to the street) was opened. These activities affected directly the background no ise measurements, so they are not much reliable.

Figure 7. NC references curves and b ackground results

9



ACOUSTICAL PARAMETERS RESULTS The results obtained for each parameter were calculated with the Aurora plugins in Adobe Audition. In the following paragraphs the detailed observation of these parameters are described and discussed. All the acoustical parameters results for each microphone or dummy head and source positions are listed in Tables 6 to 10, except for the Reverberation Time (RTmid), Bass Ratio (BR) and Brightness (Br) parameters, which deserves a discussion regarding the spatial distribution:

Reverberation Time [RT mid] The T30 values in each octave frequency band can be represented as the space-average values from all the microphones and source positions. To justify this assumption, Table 5 shows the standard deviation between the results obtained in each frequency band for each microphone position. Table 5. T30 standard deviation

Source Position A B

T30 Standard Deviation [s] Frequency Band [Hz] 125 250 500 1000 2000

4000

0,26 0,22

0,04 0,05

0,14 0,07

0,09 0,05

0,10 0,08

0,18 0,09

Figure 8. Average T 30 and error bars.

As it can be seen, the major deviation occurs at 125 Hz for both sound source positions. The greater values of the T 30 at 125 Hz were found in the balconies positions (all of them) being approximately 2,5s. In the ground floor, this value is approximately 2s. For the other frequency bands, there are not considerable differences. For this reason, the spatial-average value of the T30 showed in Figure 8 represents the global value for the hall. According to Beranek, the RTmid value is obtained as the average T 30 in 500 and 1000 Hz octave bands. The result obtained was the following: RTmid = 1,79 s. Considering the acceptable invariance of the T 30 results, the Bass Ratio (BR) and Brightness (Br) parameters can be evaluated from the RT mid value: BR = 1,20 - Br = 0,82

10



The RTmid value obtained is slightly lower than the minimum value recommended, but it is important to remark that the references values defined in the Part I of this report were obtain for full audience occupancy, so it is necessary to consider people's absorption, which will reduce the T 30 (and therefore the RT mid) value, especially at mid-high frequencies. For this reason, the reverberation time of the hall is not optimal for concert presentations. The BR value is greater than the minimum recommended values, but the Br is not. So, these results suggest that the reverberation time of the hall should be longer at high frequencies, to get optimal RTmid and Br values for concert presentations. It will produce a flatter T 30 spectrum, which is highly recommended for concert halls. Below are listed the results obtained of the others acoustical parameters evaluated.

Ground floor results Table 6. Acoustical parameters results. Ground floor.

Source Position

A

B

Positio n

Acoustical Parameter EDTmid (s)

C50 (“Speech average”) (dB)

C80 (“Music average”) (dB)

D50 (%)

Gmid (dB)

Ts (ms)

LFCE4

IACCE3

1

1,77

-0,44

1,72

52,9

6,72

106,4

0,17

0,54

2

1,47

-3,58

0,28

34,6

3,59

111,2

0,24

0,49

3

0,74

0,93

5,43

54,8

0,33

82,7

0,34

0,40

4

1,72

1,70

3,53

61,8

5,96

87,3

0,29

0,47

5

1,39

0,28

3,01

50,8

3,38

97

0,37

0,35

6

1,01

0,02

3,98

49,7

-2,06

92,8

0,34

0,30

1

1,72

-4,51

-1,87

42,6

3,88

116,6

0,20

0,56

2

1,41

-11,51

-3,56

52,1

2,02

126,4

0,27

0,29

3

1,37

-5,78

-1,53

36,2

-6,85

116,5

0,39

0,25

4

1,56

-4,73

-0,69

53,5

3,73

116,3

0,34

0,30

5

1,19

-7,12

-2,35

34,6

3,69

113,9

0,38

0,28

6

1,41

-3,88

-0,92

70,5

-5,59

117,8

0,41

0,21

First floor results Table 7. Acoustical parameters results. First floor.

Source Position Position

A B




D50 (%)

Gmid (dB)

Ts (ms)

LFCE4

IACCE3

7

1,26

-1,91

3,11

42,6

3,45

93,9

0,26

0,34

8

1,42

1,22

2,81

52,1

0,77

82

0,26

0,49

7

1,06

-7,04

-0,35

14,7

4,22

116,5

0,34

0,35

8

1,55

0,02

2,01

42,2

1,62

93,6

0,28

0,42

11



Second floor results Table 8. Acoustical parameters results. Second floor.


A B




D50 (%)

9

1,00

-2,38

2,96

36,2

10

1,37

1,49

2,56

9

1,05

-3,22

10

1,41

-2,18

Gmid (dB)

Ts (ms)

LFCE4

IACCE3

1,83

88,9

0,29

0,28

53,5

-0,98

82,3

0,34

0,38

0,69

25,5

3,17

103,9

0,27

0,33

1,44

40,3

-1,21

105,6

0,39

0,33

Ts (ms)

LFCE4

IACCE3

Third floor results Table 9. Acoustical parameters results. Third floor.


A B




D50 (%)

Gmid (dB)

11

1,33

-2,41

2,65

34,6

1,03

97,1

0,39

0,32

12

1,06

3,49

5,40

70,5

4,12

78,5

0,45

0,58

11

0,99

-1,72

1,93

37,2

4,29

99,3

0,27

0,35

12

1,01

-0,20

2,93

49,5

3,88

85,9

0,38

0,60

Stage and Orchestra Pit Table 10. Acoustical parameters results. Stage and Orchestra pit.

Source Position

A (Stage) B (Orchestra Pit)

Acoustical Parameter ST1mid (dB) -20,2 -10,5

Early Decay Time [EDT mid] The EDT results are strongly related to the sound source and microphone positions, so it would not be correct to take an average value of this parameter. Figure 9 shows three EDT results for both sound source positions. The EDT mid values tend to decrease significantly in the measurement positions under the balconies in comparison with the other positions. Audience areas located under the balconies are isolated from a large number of reflections arriving from the top of the room. While lower the balconies, the greater the amount of reflection losses, especially in the areas close to the rear wall. This results in that for t hese areas, the room seems “drier”. It has been found also that the source position influence significantly the position 11 results.

12



Source Position: A

Source Position: B

Measurement position Nº2



Figure 9. EDT comparison between three measurements positions for the t wo sound source locations.

Speech Clarity [C 50 (“speech average”)]: The C50 (“speech average”) parameter results have interesting considerations. Firstly, the values measured in each position are greater for the sound source position “A”, especially for the ground floor measurements position. This is because direct energy from the source loc ated at position "B" is considerably reduced by the side surfaces of the orchestra pit. Secondly, in the audience areas located under the balconies it was perceived a slight increase in this parameter value due to the decreased late-energy caused by less reflections, as explained above.

Music Clarity [C 80 (“music average”)]: The results for the C 80 (“music average”) parameter have the same behavior that those for the C50 parameter regarding the sound source position and the audience areas under balconies. But it is remarkable that for the balconies position, especially for those in the Side balconies, the values increase significantly for both sound source positions. This suggests that the music played by the orchestra will be appreciated better in these positions.

Definition [D 50] Since this parameter is strongly related to the C 50, there is no appreciable difference between the results behavior in both cases. But, it is important to remark that only in the measurement position “12” the D 50 reaches the minimum suggested values. This reaffirms that the theatrical activities, where an optimal speech comprehension is required, do not have a high degree of acoustical comfort.

13



Center Time [T s]: 16

According to Hoffmeier , the higher the center time is, the more “spatial” is the acoustic impression at the listener's position. The maximum achievable center time T s is based on the optimum reverberation time. The results obtained lies on the recommend margin (between 70 and 150ms). It is interesting to note that the values obtained for each measurement position are slightly higher for the sound source position B.

Lateral Fraction [LFE4]: The LFE4 values in the listener positions near the longitudinal axis of the room (Ground floor) are lower than those located in the sides, as it can be expected. In the balconies there are subtle differences between the measurements positions because all of them were located near to a reflective surface (walls and balconies for positions “8” and “10”, walls and ceiling for positions “11” and “12” and balconies for positions “7” and “9”). Positions “1” and “2” are very distant from any reflective surface and for that reason the LF E4 values there are the lower ones and not reach the minimum value recommended. The Side balcony positions exceed the minimum recommended value of 0,19. It is important to remark that there are not considerable differences in the result according the sound source position. In the previous parameters [C 50 (“speech average”) and C 80 (“music average”)], the direct sound of the sound source placed in the position “B” (pit) affect significantly the results, especially in the audience area of the ground floor.

Interaural Cross Correlation Coefficients [1-IACC E3]: The first interesting results obtained for this parameter refers to the difference between the positions of the sound source for the audience area of the ground floor. As it was defined, the greater the 1-IACC E3 value, the greater the apparent sound source width. The results obtained for the sound source position “B” are more resemble to the suggested values than those obtained for the sound source position “A”. It indicate s an optimal sound amplification of the orchestra due to the pit location. The third floor side balcony (position “12”) showed the worst IACC E3 results for both sound source positions. It may be due to angle of incidence of the reflections. Ando demonstrated that the most important reflections that arrive to the listener are those between 35º and 75º angle of incidence (lateral reflections). For the three side balconies positions there are not near reflective surfaces to generate reflections in those directions. For this reason, in these positions the IACC E3 results were the worst.

Room Support [ST1 mid]: The ST1mid results suggest that the musician’s capacity to hear themselves and the rest of the orchestra is better in the Orchestra pit (position “B”), as it can be expected. However, the result obtained for this position is higher than the maximum recommended value indicating that there is a slightly excess of early reflections (those who reaches the musician’s positions between 20 and 100ms) which may produce a low perception of orchestral clarity. To improve this result it is necessary to add absorbing acoustical materials to the pit walls, or any other sound absorbing treatment in order to decrease the early reflections energy. The extremely low result obtained in the position "A" indicates a lack of early reflections due to the large distances between the sound so urce and the surfaces that make up the stage (side walls, back wall and ceiling). 16

Hoffmeier, J.: “Investigations on the influence of room timbres on speech definition” . Technical University of Denmark. Thesis for a degree at the TU Dresden, 1996.

14



GLOBAL ASSESSMENT OF THE HALL The main hall of the "Teatro Argentino de La Plata" is notable for its high degree of acoustic comfort for musical performances. But for theater activities, we have seen that the parameters related to speech intelligibility are not optimal, although the room can be used, by its dimensions, to accommodate a large number of audiences. For musical activities there are two failures: 1) Short reverberation time, which causes the room does not get the optimal degree of liveness. 2) High background noise, although we mentioned that the results were affected by human 15 activity itself within the room. In return, Quintana performed some measurements of background noise and obtained better results. Specifically, he ranked the room with the profile NC-20, which meets the requirements suggesting by the IRAM 4070 standard.

15


PART III – “Teatro – “Teatro Margarita Xirgu”

PART III ACOUSTICAL PARAMETERS OF THE “TEATRO MARGARITA XIRGU” ABOUT THE THEATER: Margarita Xirgu Cultural Complex, is located in the historic San Telmo neighborhood of Buenos Aires. Inside is the "Casal de Catalunya", a building built in the late nineteenth century was the center of various entities of the Catalan community in Buenos Aires. This building represents a true sample of the historical tradition of the Spanish architecture of this region. Since the sixties, the theater room of "Casal de Catalunya" is named Margarita Xirgu, in homage to the Catalan actress. With the advent of the new millennium, the theater became a true cultural complex, designed as a new space for creative meeting. Many operas have been brought to the stage of this theater during the last years. In addition to the plays presented in the main hall of the theater, it also offers workshops, seminars and permanent art exhibitions are organized. The incorporation of these proposals reflects the intention to strengthen ties with the community, bringing them closer workshops and courses offered by excellent professionals. The building was built by Luis Castells and Sivilla, in 1886. The library room, the restaurant, the grand staircase and the characteristic facade, dating back to 1909, when it was made the first major reforms, sought to respect the original architectural language derived from the Catalan Modernism. Further reforms took place between 1928 and 1936, but this time they adopt a neo-Gothic design in Barcelona version. Even today, the interiors show medieval and 17 modernist details in the woodwork, the capitals of the columns, in the windows and ceilings.

Figure 10. Stage view

17

Alternativa Teatral: http://www.alternativateatral.com/espacio68-teatro-margarita-xirgu-espacio-dearte

16



MEASUREMENTS POSITIONS Figures 11 and 12 show the sound source, microphones and dummy head positions to perform the impulse response recordings. For each measurement position the sound source was placed in two stage positions (“A” and “B”). As can be seen in Figure 10 there are two stories of the balcony seats.

A 1

3

B

2

4

Figure 11. Ground floor. (●) Microphone positions ( ●) Source positions.

Microphone position Nº4 is located in the side box.

5

6

Figure 12. First and second floor. Positions 5: First floor. Position 6: Second floor. (●) Microphone positions.

As it can be seen, a total number of six microphones and dummy head position and two sound source position were used to perform the measurements. The symmetry along the longitudinal axis of the hall allows locating the measurement positions on one side, estimating an invariance of the acoustical behavior for the other half of the hall. Figure 13 shows a first floor and a second floor audience views.

17



Figure 13. Top: Second floor view. Bottom: First floor view.

MEASUREMENTS PROCEDURE Once the microphones and dummy head were calibrated, the Log-Sine sweep signal was recorded in each measurement position. This signal had the following characteristics: • Frequency range: • Length: • Fade-in: • Fade-out: • Number of repetitions:

80-20000 [Hz] 30 [s] 0.1 [s] 0.1 [s] 1

During the Log-Sine sweep signal recording process, fourteen backg round noise measurements were performed, each one in different areas (ground floor, first floor, second floor, boxes and stage). Then the average value was calculated to obtain the Noise Criteria profile of the hall.

18



RESULTS AND COMMENTS BACKGROUND NOISE RESULTS Figure 14 shows the spatial-average values in octave bands of the background noise. From these results, the corresponding NC profiled assigned to the hall is NC-25. This value is the same than the suggested, so the hall can be considered quiet enough for theatrical presentations.

Figure 14. NC references curves and background results

ACOUSTICAL PARAMETERS RESULTS The results obtained for each parameter were calculated with the Aurora plugins in Adobe Audition. In the following paragraphs the detailed observation of these parameters are described and discussed. All the acoustical parameters results for each microphone or dummy head and source positions are listed in Tables 12 to 15, except for the Reverberation Time (RTmid), Bass Ratio (BR) and Brightness (Br) parameters, which deserves a discussion regarding the spatial distribution:

Reverberation Time [RT mid] The T30 values in each octave frequency band can be represented as the space-average values from all the microphones and source positions. To justify this assumption, Table 11 shows the variance between the results obtained in each f requency band for each microphone position. As it can be seen, the major deviation is 0,16 s and occurs at 125 Hz for the sound source position A. This difference is somewhat small to be taken into account. For the other frequency bands, the differences are also negligible. For this reason, the spatial-average value of the T 30 showed in Figure 15 represents the global value for the hall.

19


PART III – “Teatro – “Teatro Margarita Xirgu” Table 11. T30 standard deviation

Source Position A B

T30 Standard deviation [s] Frequency Band [Hz] 125 250 500 1000 2000

4000

0,16 0,11

0,03 0,05

0,04 0,09

0,07 0,06

0,04 0,10

0,05 0,11

Figure 15. Average T30 and error bars.

The RTmid value is obtained as the average T 30 in 500 Hz and 1000 Hz octave band. The result obtained was the following: RTmid = 1,12s. Considering the acceptable invariance of the T 30 results, the Bass Ratio (BR) and Brightness (Br) parameters can be evaluated from the RT mid value: BR = 1,21 Br = 0,83 The RTmid value is within the recommended values, but it is important to remark that the references values defined in the Part I of this report were obtain for full audience occupancy, so it is necessary to consider people's absorption, which will reduce the T 30 (and therefore the RTmid) value, especially at mid-high frequencies. Considering the audience areas sizes, it can be estimated that the RT mid value for full audience occupancy will still remain between the recommended values margins. For this reason, the reverberation time of the hall is optimal for theatrical presentations. The BR and Br value suggests that the reverberation time of the hall at low frequencies is acceptable for theatrical presentations, although generally it is recommended a “flat” T 30 spectrum to avoid possible speech intelligibility failures. This allows that the hall may be used for small concert presentations with a reasonable reverberation field behavior. Below are listed the results obtained of the others acoustical parameters evaluated.

20



Ground floor results Table 12. Acoustical parameters results. Ground floor.

Acoustical Parameter


A B

EDTmid (s)



D50 (%)

Gmid (dB)

Ts (ms)

LFCE4

IACCE3

1

1,17

1,07

2,81

57,7

14,59

77

0,18

0,44

2

1,04

2,25

4,59

61,8

12,67

70,5

0,25

0,34

3

0,75

4,38

6,28

71,2

16,01

61,4

0,32

0,21

4

1,05

2,33

4,26

58,9

11,84

67,1

0,30

0,28

1

1,48

2,64

3,36

63,0

9,79

73,8

0,13

0,60

2

1,28

0,95

2,98

52,8

8,42

76,7

0,21

0,51

3

1,03

2,01

4,07

58,5

8,95

73,4

0,27

0,30

4

1,23

0,07

1,78

47,4

7,83

78,5

0,21

0,42

First Floor results Table 13. Acoustical parameters results. First floor.


A B




D50 (%)

Gmid (dB)

Ts (ms)

LFCE4

IACCE3

5

0,81

4,78

7,23

69,6

16,04

54

0,31

0,26

5

0,66

5,43

7,71

75,4

14,49

51,4

0,27

0,35

Second Floor results Table 14. Acoustical parameters results. Second floor.

Source Position

Positio n

A B




D50 (%)

Gmid (dB)

Ts (ms)

LFCE4

IACCE3

6

1,20

2,05

3,97

57,7

13,66

76,3

0,29

0,36

6

1,35

-3,36

0,30

29,2

6,29

109,9

0,23

0,31

Stage and Orchestra Pit

21


PART III – “Teatro – “Teatro Margarita Xirgu” Table 15. Acoustical parameters results. Stage.

Source Position

A (Stage) B (Orchestra Pit)

Acoustical Parameter ST1mid (dB) -14,9 -12,5

Early Decay Time [EDT mid] The EDT results are strongly related to the sound source and microphone positions, so it would not be correct to take an average value of this parameter. The EDTmid values obtained for the sound source position B are about 0,17 s greater than those obtained for the sound source position A. It may be related to an increase of the reflections energy coming from the back wall of the stage (sound source position B is closer to that wall regarding the A position). Another important fact is that the EDT mid values decrease as the microphones/dummy head position moves away from the sound source positions. So, the lower values were obtained in the measurement positions 3 and 5. In addition, the measurement position 5 is located below the second floor balcony, which reduces the amount of reflections coming from the ceiling and therefore produces a considerable decrease of the EDTmid value. This phenomenon tends to decrease the subjective sensation of liveliness for any musical activity, but it will not affect considerably the theatrical presentations.

Speech Clarity [C 50 (“speech average”)]: The C50 (“speech average”) parameter results have interesting considerations. Except the measurement positions 4 and 6 (for the sound source position B), the C 50 (“speech average”) values are acceptable for theatrical presentations. Due to the shape of the hall, and the sound source position (B), the measurement position 4 may be located at a high lateral reflections receiving point, which produce lowers values of this parameter. The same consideration is applied to the measurement position 6. But, in any case, these results must to be investigated further.

Music Clarity [C 80 (“music average”)]: The results for the C 80 (“music average”) parameter have the same behavior that those for the C50 parameter regarding the sound source position and the audience areas under balconies. The failures noted in the previous section for measurement positions "4" and "6" now are beneficial for musical clarity. But, this also leads to that in the rest of the measurement positions, the C80 (“music average”) values are too high (excessive early sound energy) which suggests that the performance of the room to musical activities is not satisfactory.

Definition [D 50] Since this parameter is strongly related to the C 50, there is no appreciable difference between the results behavior in both cases, and the conclusions obtained for the C 50 (“speech average”) parameter can be also applied to the D 50 results.

Centre Time [T s]:

22



A relationship between the (subjective) syllable intelligibility V S and the center time T s is given 18 by Kürer by the following correlation rule:

Ts in ms. For a syllable intelligibility of V S ≥ 80 % the results according to the above -mentioned rule are Ts ≤ 130 ms. So, as it can be observed from the results, the T s measured are optimal in all measurement positions.

Lateral Fraction [LFCE4]: The LFCE4 values in the measurement position 1 (near the longitudinal axis of the room ground floor) are lower than those positions located in the sides, as it can be expected. It is interesting to note that in the measurement position 5, the LFC E4 values are the higher, even when this position was located near to the longitudinal axis of the room. Again, the shape of the room may produce reflections focusing at that point. It is important to remark that there are considerable differences in the result according the sound source position. For the sound source position B, the results are greater. It is because that position was displaced from the longitudinal axis of the room, so the lateral energy arriving to the measuring points increases. The results obtained are optimal, but is not enough to classify the room according to its musical performance as it is described in the previous parameters evaluated.

Interaural Cross Correlation Coefficients [1-IACC E3]: The 1-IACCE3 results obtained have the same behavior of those for the LFC E4 regarding the sound source and microphones positions. The conclusion is the same: even though the results are optimal, the room does not offer good acoustic comfort for musical activities.

Room Support [ST1 mid]: There is an important consideration regarding the results obtained for the ST1 mid parameter. If we compare these results with those recommended we can conclude that the musician’s capacity to hear themselves and the rest of the orchestra is optimal. However, the recommended values were obtained for big concert halls, which have noticeable constructive differences regarding the hall volume, audience area size, stage dimensions, etc. The “Margarita Xirgu” theater is considerably small in comparison with that kind of concert halls (cannot accommodate large orchestras) so it is not correct to use the recommended values to make a global assessment of the hall. May be, for a small chamber orchestra we can say that the results obtained are optimal.

GLOBAL ASSESSMENT OF THE HALL The theater "Xirgu Margarita" has a high degree of acoustic comfort for theatrical presentations. This was evident from the results obtained for the reverberation time and the parameters that define the quality of speech intelligibility. On the contrary, the room does not have good performance for musical activities (except those using electroacoustic amplification systems, which can improve the performance of the room using, for example, artificial reverb).

18

Kürer, R.: “A simple measuring procedure for d etermining the "center time" of room acoustical impulse responses” . 7th Intern. Congress on Acoustics, Budapest 1971.

23



This is compounded by the small size of the stage for this type of activity, although it can be developed presentations of small chamber orchestras.

24


ANEX

ANEX 19

FORMULATION OF ACOUSTICAL PARAMETERS Monaural Parameters: Reverberation time (s):

Early decay time (s):

Bass Ratio:

Brightness:

Voice Clarity (dB):

Musical Clarity (dB):

19

Dr. Wolfgang Ahnert and Dr. Wolfgang Schmidt: “Fundamentals to perform acoustical measurements” . EASERA user manual.

25


ANEX

Definition (%):

Strength Factor (dB):

: Reference sound pressure level measured at 10 meters in free field.

Central Time (s):

Lateral Efficiency:

: Impulse response instantaneous sound pressure measured with a microphone with figureeight pattern.

Binaural Parameter: Interaural Cross Correlation Coefficients:

Left ear impulse response. Right ear impulse response.

26


ANEX

Stage Parameter: Room Support (s):

27

Acoustical Parameters - Teatro Argentino de La Plata and Teatro Margarita Xirgu

Recommend Documents