Report La Plata's Argentinean Theater (RAYES S - Corrected)

7/30/2019 Report La Plata's Argentinean Theater (RAYES S - Corrected)

1/16

Instruments and acoustic measurements UNTREF Santiago Rayes June 2013

1

ACOUSTIC EVALUATION OF LA PLATAs

ARGENTINEAN THEATER

SANTIAGO RAYES

Universidad Nacional de Tres de Febrero, Ingeniera de Sonido, Buenos Aires, [email protected]

Abstract The purpose of this paper is to evaluate the objective acoustical parameters of the measurements

made in La Platas Argentinean Theater. This evaluation includes the analysis of classic acoustical

parameters as reverberation time, C50, C80 and strength. Also spatial parameters as IACC and Lateral

Fraction where evaluated. The results were compared to the recommended values proposed by Beranek and

Kutruff for this kind of spaces. Calculations show that the hall obtained acceptable results in comparison with

the recommended parameters proposed for opera houses.

1. INTRODUCTION.In order to describe the acoustical characteristics

of a hall it is necessary to make the corresponding

measurements to collect the information needed to

calculate them. Different investigations through

the years have come to a list of different

acoustical parameters that show good

reproducibility in different spaces and have a

connection with subjective evaluations. Some of

these parameters are investigated in this paper.

The standardization of the measurement protocols

and the acoustical parameters used allows the

researcher to compare the acoustical

characteristics of different spaces.

In this paper measurements made at La Platas

Argentinean Theater are described. Some

representative acoustical parameters are calculated

and compared with Beranek and Kuttruffs

recommended values for concert halls and opera

houses .

1. BASIC CONCEPTS.1.1.Reverberation time. [2]

Reverberation time is defined as that time required

for the sound in a room to decay 60 dB. This

represents a change in sound intensity or sound

power of 1 million (10 log 1,000,000 = 60 dB), or

a change of sound pressure or sound-pressure

level of 1,000 (20 log 1,000 = 60 dB). In very

rough human terms, it is the time required for a

sound that is very loud to decay to inaudibility.

Obtaining a nice, linear decay spanning 60 dB or

more as shown in Fig. 1A is a very difficult

practical problem. Background noise, an

inescapable fact of life, suggests that a higher

source level is needed. This may occur if the

background noise level is 30 dB (as in Fig. 1B),

because source levels of 100 dB are quite

attainable.

The situation of Fig. 1B is the one commonly

encountered a usable trace less than the desired 60

dB. The solution is simply to extrapolate the

straight portion of the decay. It has been

demonstrated that in evaluating the quality of

speech or music, the first 20 or 30 dB of decay is

the most important to the human ear.

FIGURE 1 - THE LENGTH OF THE DECAY DEPENDENT ON

STRENGTH OF THE SOURCE AND THE NOISE LEVEL. (A) RARELY

DO PRACTICAL CIRCUMSTANCES ALLOW A FULL 60-DB DECAY.

(B) THE SLOPE OF THE LIMITED DECAY IS EXTRAPOLATED TO

DETERMINE THE REVERBERATION TIME.[2]


2/16


2

(1) () = 0,161 . [.]V = Volume of the room. [m3].

Atot = med.Stot = Total absorption of the room.

[sabins].

med = individual surface absorption index.

Stot = Si = total surface of the room. [m2].

Si = area of an individual surface. [m2].

m = air sound attenuation constant. [].

RTmid is the reverberation time obtained as an

average of the values corresponding to 500 Hz.

and 1 kHz. frequency bands.

(2) = [ (500 . ) + (1 . )]2 []

1.2.Bass Ratio (BR). [3]It can be obtained as the ratio between the

addition of the reverberation times corresponding

to 125 Hz. and 250 Hz. frequency bands and the

addition of the reverberation time corresponding

to 500 Hz. and 1 kHz. frequency bands. It is

related to the subjective feeling of acoustic

warmth.

(3)= [ (125 . ) + (250 . )]

[(500 . ) + (1 . )]

1.3.Brightness (Br). [3]It is obtained as the ratio between the addition of

the reverberation times corresponding to 2 kHz.

and 4 kHz. frequency bands and the addition of

the reverberation times corresponding to 500 Hz.

and 1 kHz. frequency bands.

(4)= [ (2 . ) + (4 . )][ (500 . ) + (1 . )]

1.4.C50. [3]It is defined as the relationship between the sound

energy that arrives to the listener during the first

50 msec. from the arrival of the direct sound

(direct sound and first reflections) and the sound

energy after 50 msec. . [2]

(5)50[]=10log( () /,

())

.

() is the impulse response at a receiver point..1.5.C80. [3]

Indicates the separation degree between the

different individual sounds of a musical

composition. [2]

(6)80[]=10log( () /,

())

.

() is the impulse response at a receiver point.1.6.Lateral Fraction (LF). [3] [4]

Lateral reflections contribute to spaciousness.

Barron [7] found that the contribution of areflection to spaciousness is proportional to its

energy and cos, where is the angle between the

axis through a listeners ears and the direction of

sound incidence, provided delay is in the range

from 5 to 80 msec. This contribution is

independent of other reflections and of the

presence or absence of reverberation. Lateral

fraction (LF) was proposed as an objective

measure for the spatial impression.

(7)= [()] / [()]

()is the impulse response at a receiver point.

1.7.IACC. [3]Inter Aural Cross Correlation can be defined as

the correlation between sound arriving to both

ears. It indicates the degree of similarity that

exists between two signals. If the signals are the

same, then IACC will be 1, while if they are

completely different IACC will have a value of 0.

(8)

0 IACC 1

ir() is the IACF obtained from the ACFs forthe left and right ears and is the interaural time

delay.

mslr 1,)(IACC max


3/16


3

When it comes to an existent hall the measure

associated with IACC is binaural and has to be

recorded using a pair of microphones placed on

the ears of an artificial head (dummy head).

The IACCe (EARLY) corresponds to the first 80

ms. from the arrival of the direct sound, and theIACCl (LATE) is calculated from 80ms to 1s. .

Okano proved that 500 Hz., 1 kHz. and 2 kHz are

the most representative frequency bands. In

consequence the IACCe3 and the IACCl3 appears

as an average of the IACCe and the IACCl using

the above mentioned frequeny bands.

When it comes to comparisons the (1-IACCe3)

value is commonly used.

Beranek compared the (1-IACCe3) withsubjective appreciations. In Table 1 a value of (1-

IACCe3) can be seen with his corresponding

subjective category.

TABLE 1(1-IACCE3) RECOMMENDED VALUES.

1.8.Stage Parameters (ST Early and Late).[5] [6]

The early support (STearly) relates to ensemble,

i.e. ease of hearing each other members of an

orchestra.. Influences of the direct sound, delay

time and the reflections from near surfaces are not

included. The typical range goes from -24 dB to -

8 dB. .

(9)

The late support (STlate) relates to perceived

reverberance, i.e. the response of the hall as heard

by the musician (on the stage). The typical range

goes from -24 dB to -10 dB.

(10)

in both cases is the impulse responsemeasured at a distance of 1 meter from the

acoustic center of an omnidirectional source.

1.9.Sound Strength (G). [3]It is the degree of sound amplification producedby the hall. It depends on the listeners distance to

the stage, the energy associated to the early

reflections, of the surface of the audience and the

level of the reverberant field.

It can be defined as the difference between the

total sound pressure level produced by an

omnidirectional source in a determined position in

a hall (Lp) and the sound pressure level produced

by the same source placed in free field at a 10

meters distance (Lref).

(11)

() is the impulse response at a receiver point.() is the reference impulse responsemeasured at a distance of 10 meters from the

source in a free field.

In the case of the Gmid the sound strength is

analysed in the 500 Hz. and 1 kHz. frequency

bands. Beranek [1] recommends these values of

Gmid for empty concert halls:

4 Gmid 5,5 [dB]

2. EQUIPMENT. Presonus AudioBox 44VSL Audio

Interface + PC.

Motu Traveller Audio Interface + PC.

M-Audio Fastrack Audio Interface + PC. SPS200 Software controlled Soundfield

Microphone.

Outline Globe omnidirectional sourceradiator with sub-woofer.

G.R.A.S. Kemar Dummy Head. 4 earthworks measurement microphones. Svantek SV959 type 1 Sound Level

Meter.

01.0

0

21.0

02.0

2

10

)(/)(log10 dttpdttpSTEarly

01.0

0

20.1

1.0

2

10 )(/)(log10 dttpdttpSTLate

0

2

0

2

10 )()(log10 dttpdttpG ref


4/16


4

3. THE PLACE.La Platas Argentinean Theater is an artistic

complex which has one of most important lyrical

hall in Argentina. It is placed in La Plata city,

capital of the Buenos Aires province (Figure 2).

The Alberto Ginastera is the main hall of the

complex where the measurements where done. It

was opened in the year 1999 and has an Italian

horseshoe style. With its stalls, three levels of box

seats and galleries can hold and audience of 2000

spectators. The space has an opera hall design.

The main usages of the hall are opera, classical

music, choreographic and popular music

performances.

FIGURE 2AERIAL SHOT OF THE THEATER.

4. MEASUREMENTS PROCEDUREThe auditorium was in an unoccupied condition

during all the measurements.

The safety curtain was up and the pit was open.

The stage condition for the measurement can be

seen in Figure 3.

First of all, background noise was measured in 10

different positions. The results are shown in Table

2.

A one minute Leq was used in background noise

measurements.

Background noise measurements were made with

a calibrated type 1 sound level meter.

For the rest of the acoustical parameters 12

representative positions of the theater were used.

These positions are shown in Figure 5.

In the case of the omnidirectional source used for

the measurements, 2 different positions were used.

Position 1 was placed on the stage (Figure 3) andposition 2 on the pit (Figure 4).

Measurements in the above mentioned 12

positions were made using a soundfield

microphone and a dummy head.

The soundfield microphone recorded data was

post processed to obtain the

omnidirectional/lateral sound incidence

information for LF parameter and omnidirectional

information to obtain the rest of the basic

acoustical parameters of the hall.

The signal used for the measurements was a 15

seconds exponential sine sweep from 20 Hz. to 20

kHz.

5. RESULTSBackground noise results are shown in Table 1.

T30 and EDT results are shown in Figure 6.

Stage Parameter results, RTmid, EDTmid, BR andBr are shown in Table 2.

C80 results with the source placed on the stage are

shown in Figure 7.

C80 results with the soruce placed on the pit are

shown in Figure 8.

C50 results are shown in Figure 9.

Lateral Fraction results for some representative

positions measured with the source on the pit are

shown in Figure 10.

Table 4 shows the results for the parameters C50

speech average and C80 music average.

Finally Table 5 shows the Gmid results and Table

6 the (1-IACCe3) results.


5/16


5

FIGURE 5 -MEASUREMENT POSITIONS IN THE HALL.

FIGURE 3SOURCE POSITION 1(ON THE STAGE).

FIGURE 4SOURCE POSITION 2(ON THE PIT).


6/16


6

TABLE 2BACKGROUND NOISE LEVELS IN DBZ AND DBA.

BACKGROUND NOISE

POSITION Leq [dBZ] Leq [dBA] Difference

Stage 62,1 42,7 19,4

1 62,2 34,8 27,4

2 65,8 36,2 29,6

Ground floor lateral box seat 64,8 33,7 31,1

3 62,3 36,2 26,1

9 62,8 40,2 22,6

10 63,5 34,6 28,9

12 65 35,2 29,8

11 63,3 35,7 27,6

13 63,4 40,6 22,8


7/16


7

TABLE 3STAGE PARAMETERS RESULTS (LEFT). RTMID ,BASS RATIO,BRIGHTNESS AND EDTMID RESULTS (RIGHT).

RT mid [s] 1,70

BR 1,20

Br 0,77

EDT mid [s] 1,30

STAGE Parameters [dB]

ST early (s.stage) -20,21

ST late (s.stage) -18,62

ST early (s. pit) -10,50

ST late (s.pit) -10,16

FIGURE 6REVERBERATION TIME (T30) RESULTS AND EARLY DECAY TIME (EDT) RESULTS.

0,50

1,00

1,50

2,00

2,50

125 250 500 1000 2000 4000 8000 16000

Frequency [Hz.]

T30 and EDT [s]

T30

EDT


8/16


8

FIGURE 7C80 RESULTS WITH THE SOURCE PLACED ON THE STAGE.

FIGURE 8C80 RESULTS WITH THE SOURCE PLACED ON THE PIT.

-15

-10

-5

0

5

10

15

20

125 250 500 1000 2000 4000 8000 16000

C80 (Source on stage)

C80 1

C80 2

C80 3

C80 4

C80 5

C80 6

-15

-10

-5

0

5

10

15

20

125 250 500 1000 2000 4000 8000 16000

C80 (Source on stage)

C80 9

C80 10

C80 11

C80 12

C80 13

C80 14

-15

-10

-5

0

5

10

15

20

125 250 500 1000 2000 4000 8000 16000

C80 (Source on pit)

C80 1

C80 2

C80 3

C80 4

C80 5

C80 6

-15

-10

-5

0

5

10

15

20

125 250 500 1000 2000 4000 8000 16000

C80 (Source on pit)

C80 9

C80 10

C80 11

C80 12

C80 13

C80 14


9/16


9

-7

-5

-3

-1

13

5

7

9

11

13

15

125 250 500 1000 2000 4000 8000 16000

Frequency [Hz.]

C50

C50 1

C50 2

C50 3

C50 4

C50 5

C50 6

0

0,05

0,1

0,15

0,2

0,25

0,3

0,35

0,4

0,45

0,5

125 250 500 1000 2000 4000 8000 16000

Frequency [Hz.]

Lateral Fraction (LF)

LF 1

LF 2

LF 3

LF 9

LF 11

LF 13

FIGURE 9C50 RESULTS WITH THE SOURCE PLACED ON THE STAGE.

FIGURE 10 LATERAL FRACTION RESULTS FOR SOME R EPRESENTATIVE POSITIONS.

-7

-5

-3

-1

1

3

5

7

9

11

13

15

125 250 500 1000 2000 4000 8000 16000

C50

C50 9

C50 10

C50 11

C50 12

C50 13

C50 14


10/16


10

TABLE 4C50 SPEECH AVERAGE AND C80 MUSIC AVERAGE RESULTS.

SOURCE ON STAGE SOURCE ON PIT

POSITION C50 "Speech Average" [dB] C80 "Music Average" [dB] C80 "Music Average" [dB]

1 -0,44 1,72 -1,872 -3,58 0,28 -3,56

3 0,93 5,43 -1,53

4 1,70 3,53 -0,69

5 0,28 3,01 -2,35

6 0,02 3,98 -0,92

9 -1,91 3,11 -0,35

10 1,22 2,81 2,01

11 -2,38 2,96 0,69

12 1,49 2,56 1,44

13 -2,41 2,65 1,93

14 3,49 5,40 2,93


11/16


11

Gmid (1 IACCe3)

TABLE 5GMID MEASUREMENT RESULTS. TABLE 6(1-IACCE3) RESULTS.

Source on stage

POSITION Gmid

1 1,20

2 -0,37

3 -2,00

4 0,82

5 -0,47

6 -3,19

9 -0,44

10 -1,74

11 -1,25

12 -2,65

13 -1,65

14 -0,10

Source on pit

POSITION Gmid

1 -0,22

2 -1,15

3 -5,59

4 -0,30

5 -0,32

6 -4,96

9 -0,05

10 -1,35

11 -0,58

12 -2,77

13 -0,02

14 -0,23

Source on stage

POSITION 1 - IACCe3

1 0,46

2 0,51

3 0,60

4 0,62

5 0,65

6 0,70

9 0,66

10 0,51

11 0,72

12 0,62

13 0,68

14 0,42

Source on pit

POSITION 1 - IACCe3

1 0,44

2 0,71

3 0,76

4 0,70

5 0,72

6 0,79

9 0,65

10 0,58

11 0,67

12 0,67

13 0,65

14 0,40


12/16


12

6. RESULTS ANALYSIS.6.1.Background Noise.

Background noise in the hall vary between 62,1

dBZ and 65 dBZ. And from 33,7 dBA to 42,7

dBA. The difference between the values in dBZand dBA vary between 19,4 and 31,1.

This represents a significant difference between de

weightings and it can be caused due to vibration

problems in the hall.

6.2.Reverberation Time.RT and EDT decrease as the frequency is

increased. The highest values are observed at 125

Hz. . 2,24 seconds for the T30 and 1,46 seconds

for the EDT.

Table 3 (right) shows some parameters calculated

from the ones mentioned above. This was made to

compare those parameters with the preferred

values proposed by Beranek for this kind of halls.

RTmid has a value of 1,7 sec. with an empty hall.

Beranek [1] recommends:

Concert hall: 1,8RTmid 2 sec.

Opera house: 0,7RTmid1,2 sec.

These values are calculated for occupied halls.

The RTmid of La Platas Argentinean Theater will

probably decrease with an occupied condition.

It can be said that this hall has a reverberation

time placed between the recommendations given

for opera houses and concert halls. Probably due

to the fact that the usage of the Theater includes

orchestra concerts.

The EDT which describes better the liveness of

the hall has a value of 1,3 seconds. While Beranek

recommends a value of EDT similar to the RTmid

for concert halls.

6.3.Bass Ratio (BR) & Brightness (Br).The BR for this hall has a value of 1,2. While the

Br has a value of 0,77.

BR fulfills the recommendations for a concert

hall, while the Br is slightly lower than therecommended values.

6.4.Stage Parameters.There are calculated values for the different

positions of the source during the measurement. In

the case of the source placed on the stage the

STearly is -20,21 dB while de STlate is -18,62 dB.

For the pit source position the STIearly is -10,50

dB and the STIlate is -10,16 dB.

All the values are into the typical range for the

stage parameters.

6.5.C80.C80 values for all the measurement positions are

presented from 125 Hz. to 16 kHz. but the C80

music average was evaluated. When the source

is placed on the stage the Music Average has

values between 0,28 and 5,43 dB.

When it is on the pit the values are between -3,56and 2,93 dB .

The values are clearly lower when the source is

placed in the pit. Analyzing these results (source

in the pit) it can be seen that the C80 music

average on the positions placed on the ground

floor and the central position on the 1st floor give

positive values, while the rest of the values are

negative.

Ground floor measurements and central position

on the 1st

floor with the source on the pit are theonly values that fulfill the recommendations given

by Beranek [1] for this parameter.

6.6.C50.C50 values for all the measurement positions are

presented from 125 Hz. to 16 kHz. but the C50


13/16


13

speech average was evaluated. Only the results

with the source placed on the stage are considered.

The values goes from -3,58 to 3,49 dB. .

The higher value is surprisingly placed on of the

furthest position from the source (Position 14 onthe side box). It can be noticed that there are C50

speech average positive values in the side boxes

measurements while in the center positions of the

1st, 2nd and 5th floor the values are negative.

6.7.Lateral Fraction (LF).Lateral fraction values calculated for some

representative positions in the hall (the ones

placed near the center).

Values from 125 Hz. to 16 kHz. produce results

that vary between 0,04 to 0,5.

6.8.Sound Strength (G).The values given for the Sound Strength (G) are

measured with the source on the pit and on the

stage. In both situations the values calculated are

lower than the ones recommended by Beranek [1]

for concert halls (4Gmid5,5 dB).

This is probably because the theater was not

designed as a concert hall.

6.9.IACC.The (1-IACCe3) parameter was calculated in all

the positions with the source on the pit and the

stage. Taking Beraneks recommendations for this

parameter the hall has values that go from

acceptable to excellent category.

The best positions are: Position 9 (with source on

the stage and pit), position 5 (source on the stage)

and positions 11,12 and 13 with the source on thepit.

7. CONCLUSIONS.Background noise level in the theater is high for

this kind of applications. But it is important to

consider that during the measurement there were

people working on the stage.

The difference between the background noise

measured in dBA and dBZ is considerable

(between 19,4 and 31,1 dB). These results show

that the Theater might have vibration issues on the

hall.

The hall has a classical opera design. The RTmid

is 0,5 seconds higher than the maximum

recommended by Beranek [1] for theaters. And

0,1 seconds lower than the minimum

recommended for concert halls. This shows that

despite being designed as an opera house the hallhas a long RT for this usage.

It is important to keep in mind that the

recommended values for this parameter were

calculated for occupied halls, so the RTmid for

this Theater would be much closer to the

recommended values for these halls than the

measured one. Considering that this measurement

was performed under unoccupied condition.

As is usual on this type of halls, there are longer

RT at low frequencies and shorter at highfrequencies.

The hall it is also used as a concert hall, so this

last feature might help achieving better results for

this kind of usage.

BR and Br values show acceptable results. Br is

0,1 points lower than the minimum recommended

value (Br 0,87 with occupied hall). If the

measurement would have been performed with an

occupied hall this value would probably be even

lower than it was. It is important to consider thatthese parameters are recommendations for concert

halls.

Stage parameters are between the typical range of

values on the stage and the pit.

Results show that the recommended values of C80

music average are only achieved with the source


14/16


14

on the pit only on the ground floor and the central

position measured on the 1st floor.

C50 speech average results are below the

recommended ones (C50 music average> 2dB,

occupied hall). The values obtained where

measured with an empty room and will probablyget closer to the recommended ones in an

occupied hall situation.

Kuttruff [4] proposes to average Lateral Fraction

values from 125 Hz. to 1000 Hz. due to the fact

that the low and mid-frequency components

contribute most with the sensation of

spaciousness.

Recommended values by Kuttruff [4], for large

halls vary from 0 to about 0.5. That

recommendation is achieved in all the measuredpositions.

(1-IACCe3) values are between the

recommendations given by Beranek [1]. On one

hand, the lowest values are founded on one the

nearest position from the stage (Position 1) and on

the side box seat position (Position 14). On the

other hand the positions where the higher values

of (1-IACCe3) are founded (Positions 3 and 6) are

the positions were the lower values of Gmid are

obtained.

This situation can be caused due to the fact that

both microphone positions (3 & 6) were placed

under the 1st floor balcony. Gmid on these

positions can be improved with electroacoustic

support.

8. BIBLIOGRAPHY.

[1]Beranek, L. L. (2005 (2nd. Ed)). Concert

Halls and Opera Houses: Music,

Acoustics and Architecture. Springer.

[2]Everest, F. A. (2001). The Master

Handbook of Acoustics. McGraw-Hill.

[3]Isbert, A. C. (1998). Diseo acstico de

espacios arquitectnicos. Barcelona,

Espaa: Edicions UPC.

[4]Kuttruff, H. (2009 (5th. Ed)). Room

Acoustics. New York: Spoon Press.

[5]Gade. (1989). Acoustical Conditions

Preferred for Ensembles.Acustica 69

1437-1442.

[6]al., Marshall. et. (n.d.). Acoustical

Conditions Preferred for Ensembles.

JASA 64 1437-1442.

[7]Barron, M. (2010 (second edition)).

Auditorium Acoustics andArchitectural Design. New York: Spon

Press.


15/16


15

APPENDIX.

TABLE 7BERANEKS RECOMMENDED VALUES FOR ACOUSTICAL PARAMETERS ASSOCIATED TO A CONCERT HALL.[3]

TABLE 6BERANEKS RECOMMENDED VALUES FOR ACOUSTICAL PARAMETERS ASSOCIATED TO A CONCERT HALL.[3]


16/16


16

TABLE 8ACOUSTICAL PARAMETERS RECOMMENDED VALUES BY BERANEK ASSOCIATED TO A THEATER.[3]

TABLE 9(1-IACCE3) RECOMMENDED VALUES BY BERANEK.[3]

Report La Plata's Argentinean Theater (RAYES S - Corrected)

Documents

Transcript of Report La Plata's Argentinean Theater (RAYES S - Corrected)