PROCEEDINGS of the
23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

The Teatro Colón in Buenos Aires as a double- function hall
Gustavo BASSO1
1

IPEAL, Facultad de Bellas Artes, Universidad Nacional de La Plata, Argentina

ABSTRACTThe Teatro Colón in Buenos Aires is well known for its acoustic quality. It is considered not only one of thebest opera houses in the world, but also an exceptional space for symphonic music, as highlighted by Leo
Beranek and colleagues in two articles published in 2000 and 2003. The architectural and acoustical analysisof the hall shows some of the possible causes of this dual behavior, derived from a specific combination ofarchitectural features such as the shape of the horseshoe, the height and depth of the boxes at the upper levels
and the design of the proscenium and pit. These components contribute to create a very enveloping soundfield when used for symphonic music, similar to those of a shoebox auditorium, and allow the maintenanceof the acoustical balance between the singers and the orchestra when used as an opera theatre. As can be seenfrom audience opinion polls on the sound perceived, acoustic measurements and the outcomes of a digitalmodel, this behavior is more noticeable on the main floor. In this work, the acoustic quality of the Teatro
Colón as a double-function hall is analyzed.
Keywords: Opera house, acoustical quality, lateral reflections

1. INTRODUCTION
The Teatro Colón of Buenos Aires, which opened in 1908, is well known for its excellent acousticalquality. General opinion considers that it is not only one of the finest opera theatres in the world, butalso one of the best halls for symphonic music. Along with the usual sources of information, based on
the opinions of the audience, musicians and critics who have attended functions during its history, theassumption that the Teatro Colón has a superior acoustical quality was supported by two extensive
research works developed at the beginning of the 21st century. The first of them, published in 2000,
was carried out by Takashuki Hidaka and Leo Beranek (1). In that paper, they surveyed 22 musicians,
who had vast experience performing in halls around the world. The musicians were asked to rate theacoustic quality of 23 well known opera houses and the theatres were then ranked on a scale from"poor" to "very good". The Teatro Colón was not only among the best, but actually placed highest of
all the theatres. In another article, published in 2003, Beranek repeats the previous methodology andclassifies the auditoriums for symphonic music according to their acoustical quality (2). In this paper
the Teatro Colón was placed joint top, with the same rating as two shoebox -shaped concert halls built
specifically for that purpose: the Vienna Musikverein and the Boston Symphony Hall.
Why is the acoustic of the Teatro Colón so good? Perhaps one possible answer to this question
could be that the Teatro Colón behaves like a double hall, with some features typical of opera theatre
and others of an auditorium for symphonic music.
In order to understand the physical origins of the acoustic quality of the hall, it was decided toanalyze the acoustic field of the best seats beyond the limits imposed by ISO -3382 standard. Some
theories, based on the structure of the lateral reflections, as the cause of the strong sound presence
and the great enveloping sensation experienced in the room, were then considered as possible
explanations of its acoustical behaviour. The main objective of this work is to present part of theoutcome of this analysis, in which some of the architectural causes of the acoustic fingerprint of theTeatro Colón were exposed. Part of the material shown has already been presented in previous
congresses and scientific meetings, but in this case a more comprehensive perspective is followed.

1

gusjbasso@gmail.com

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2. METHODOLOGY
In order to determine the possible architectural causes of the acoustic behaviour of the Teatro Colón,
several activities were carried out:
1. Analysis of historical records and opinions of well-known artists. A new series of opinion polls
was also performed to complete the picture from the point of view of the audience.
2. Acoustic measurements of the hall based on the ISO-3382 standard (3).
3. Simulations in a digital model, developed using the software CATT-Acoustic, which was finetuned using the data collected from the measurements described in point 2 and with the dataobtained taken of measurements of the acoustic materials–seats, chairs, curtains and carpets–in a certified laboratory (4).
4. Analysis of the relationships among the physical data collected and the outcomes of thesubjective evaluations of the hall.
5. Analysis of the probable architectural causes of the acoustical quality of the hall, based on the
conclusions obtained in point 4.
Following the methodological process listed above, the condensed results of this stage of theanalysis are described in the next subsections. The results are presented in two parts: firstly inreference to the theatre as an auditorium for symphonic music and secondly regarding its use as atheatre for opera.

3. THE TEATRO COLÓN AS AN AUDITORIUM FOR SYMPHONIC MUSICThe results of the opinion polls about the acoustic quality of the hall as a auditorium for symphonicmusic were, in general, expected. They describe the sound differences at different levels and revealed
some well-known small sectors of the main floor with a sound quality below the average. However,
the item "comments", in which the listeners could express themselves freely, was very revealing. T hemajority highlighted the presence of the sound–one of them said it was "tangible", the feeling of being
immersed in sound, and that the acoustic fingerprint of the room was maintained at the highest levelof quality throughout the entire dynamic range, from the pp to the ff. Some musicians with vastinternational experience compared the quality of the main floor with the stalls in some of the best
shoe-box auditoriums–Boston Symphony Hall and Vienna Musikverein were mentioned. This wasquite unexpected, since in the Italian horseshoe halls, the highest acoustic quality is usually found at
the upper levels, not in the stalls. The following section will focus principally on the main floor.
The signal in Figure 1 shows the impulse response at a seat near the centre of the main floor.

Figure 1 – The first 250 ms of the binaural impulse response measured at a seat near the centre of the mainfloor
It can be seen that there is a very rich texture after the first significant reflection, which arrives 21
ms after the direct sound. Further analysis shows that the signal has a lot of early lateral energy
arriving from angles of 15º to 80º in the horizontal plane and of 10º to 50 º in the vertical plane, givena polar system with its origin in the line of sight of an observer faced to the stage. This kind of
acoustical field is shared quite well by almost the totality of the seats on the main floor (4).

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3.1 Architectural origins of the lateral reflections on the main floor
The first geometrical feature that stands out is the shape of the horseshoe plan view, which isslightly different from those of other Italian opera theatres. Figure 2 shows that its proportion issomewhat oblong in the longitudinal axis, and the first section of the horseshoe, near the stage, is nearrectilinear with an angle of divergence of about 9º, which is quite small. This shape produces a lot oflateral early reflections that cover a big area of the main floor, in a way similar to that of a shoebox
type auditorium.

Figure 2 – Horseshoes plan views of some opera theatres: Teatro alla Scala/Milan (magenta), Royal Opera
House/London (blue), Staatsoper/Vienna (green), Opera Garnier/Paris (light blue) and Teatro Colón (red).
After (5)The rear part of the horseshoe of the Teatro Colón is comparable to a traditional horseshoe andallows even distribution of the energy to the audience on the back area of the main floor. The
combination of the two parts of the plan view, the first with its shoebox type behaviour and the second
with its horseshoe contour, seem to generate the even distribution of the acoustic energy on the main
floor that was evidenced in the measurements.
The shape of the plan view does not produce by itself the reflections towards the audience on themain floor. It is necessary that the energy reaches a surface capable of reflecting it back to this area.
The main origin of the strong lateral reflections that have been measured is, clearly, the dihedral angle
created at the encounter of the rear wall and the ceiling of the boxes that surround the stalls. The
height of the balconies in the Teatro Colón is particularly effective in that sense, because there is a lotof free space in the boxes above the heads of the audience that allows the energy to return unobstructedto the stalls. As an example, Figure 3 shows a comparison of the longitudinal section of the Teatro
Colón and the Teatro alla Scala in Milan, Italy. The two theatres have the sa me number of levels, but
the Teatro Colón has a greater height (approximately 30% higher). The energy returns clearly to themain floor in the case of the Teatro Colón, whereas in other examples much of it is trapped andabsorbed by the public, the curtains and the carpets present inside the boxes (4).

(a)

(b)

Figure 3 – Longitudinal section of the Teatro Colón (a) and the Teatro alla Scala of Milan (b). After (4)Even with boxes of a considerable height, the energy could be confined inside them if they were
too deep. In the case of the Teatro Colón, this does not happen as the boxes near the stage have rearwalls that are very close to the front, allowing space for only two rows of seats (Figure 4). This patternis repeated on almost all the levels of balconies.

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Figure 4 – Boxes of the first level near the stage. The free path for the reflections from the wall/ceilingencounter can be easily seen
As an example of the efficiency of the three mentioned factors when they are combined, Figure
5 shows the origin of some strong lateral reflections in one seat on the main floor when a sound source
is located on the stage.

Figure 5 – Main lateral reflections at the same seat on the main floor coming unobstructed from thedihedral angles wall/ceiling at three balconies levels. After (4)Those reflections have a broadband spectrum and the sound arrives at the main floor from almost
ideal angles, well above the critical angle needed to avoid the seat-dip effect. Their delay and intensity
are well within the Haas effect limit. The perceptual field is, therefore, very enveloping and, at thesame time, the localization of the sound sources on the stage is clear and the timbre of each instrument
is well preserved. These characteristics are like those that can be found in the best shoebox-typeauditoriums.
3.2

Acoustic field at the upper levels
At the upper levels the situation is completely different. The acoustic field is formed by the global
acoustics of the hall, defined by the values of Reverberation Time TR, Bass Ratio BR or Strength G
at each position, and from the early reflections generated by the stage floor, by the surfaces thatsurround the proscenium arch, and by the surfaces near the box that is being considered –such as its
own ceiling and rear wall. This behaviour will be described in the section dedicated to the hall as an
opera theatre.

4. THE TEATRO COLÓN AS AN OPERA THEATRE
The Teatro Colón of Buenos Aires is mainly an opera theatre. Unlike auditoriums for symphonicmusic, in which the orchestra and the audience occupy the same architectural space, opera theatres
have three different conjoined spaces, each with different acoustic functions: the stage tower, the area

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for the audience and the orchestra pit. The importance of the voice in this genre is obvious, so thesound balance between the singers on the stage and the orchestra in the pit is considered one of the
key factors that determine the acoustical quality of an opera theatre. Simplifying the subject, thesingers need clarity, intelligibility and timbre preservation, whereas the orchestra requires
reverberation and spatial impression (6). The singers are at a disadvantage with respect to the orchestra,both in terms of their number and the power of the sound they produce, but these disadvantages canbe mitigated by two concurrent factors: the nature of the sung voice, trained in the western operatic
tradition, and the acoustics of the theatre. The singer can be heard over the orchestra in the frequency
region of the so-called "singing formant", a fifth formant that usually lies in the frequency range of
2000-3000 Hz. In this spectral region, the singers’ voice can overcome the sound of an orchestra andcan be heard clearly (7, 8). There is another feature that contributes to the audibility of the singers:
their position on the stage from where the sound projection reaches the listeners without obstacles.
The orchestra, on the other hand, is located in the pit, a space acoustical ly separated from the area
occupied by the audience (9). There are two additional factors: one is the complex dispersion of theaudience in a traditional opera theatre, with listeners located in the stalls and in boxes at different
heights. The other is the changing nature of the opera sets, with different scenery and constant changes
in the location of the opera singers. This complexity of variables makes the task of finding average or
global balance values unrealistic: the low acoustic homogeneity of such theatres forces us to study thebalance of each source-receiver pair and try to obtain valid averages by audience zones alone.
4.1

Singer-orchestra balance

One of the problems in trying to characterize the balance is that it is not standardized. It does notappear, for example, among the parameters defined by the ISO -3382 standard. Nor are themeasurement conditions stipulated. As we will see, the scenography and the location of the singer onstage could substantially modify the values of balance obtained. From all the existing definitions, wefound it most appropriate to apply those of John O'Keefe and Nicola Prodi in the case of the Teatro
Colón. O’Keefe suggested putting a directional sound source on stage and an omni -directional soundsource in the pit (9, 10). In the Prodi proposal the Balance coincides with the difference in G values
from stage and pit when both sources are omnidirectional and has the advantage of not needing thepower equalization between the sources. In the case of the Teatro Colón, a complete set of GSTAGE andG PIT measurements in the main floor and from several locations in the upper levels were available.
The Strength was measured on the main floor with omnidirectional sources located in the pit and on
the proscenium, with the textile curtain in position. Most of the data of B obtained falls within the
average limits advised by the specialized literature. Some authors suggested the range from -2 dB to+4 dB (9, 11), while others go up as high as +7 dB (10). The spectral distribution of the balance is as
important as the value of B. Figure 6 shows that the stage/pit balance in the main floor reaches its
maximum in the region of the singers’ formant, even in the seats in the stalls furthest away from thestage (6).

Figure 6 – Spectral characteristics of the balance on the main floor. Pla1 to Pla7 are seats on the main floor.

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In order to identify the origin of the described acoustical behaviour, the digital model was used
to replicate the values obtained in the measurements with two omnidirectional sources and the textile
curtain. These balance values could be suitable reproduced from 500 Hz, while for values below 200
Hz the simulation proved ineffective because of its inability to solve the phenomena related to wave
acoustics (i.e. diffraction and seat-dip effect). A characteristic stage set-up of an opera was simulated,with materials with an absorption between 10% and 30% in the mentioned frequency range. With anomnidirectional source in the pit there is no direct sound coming from the pit on the main floor, as
can be seen in Figure 7. The first discrete reflections arrive 50 ms after the emission, later than the
diffuse reflections.

(a)

(b)

Figure 7 – Major early reflections on the main floor from an omnidirectional source in the pit. (a)Reflectogram; (b) origin of the reflections. After (6)With a directional source on the stage the sound of the singers benefits from the specificarchitecture of the Teatro Colón, as in a symphonic concert with the orchestra on stage as shown in
Section 4. Figure 8 a shows the simulated impulse response at a seat near the centre of the main floor.
We can see that the first significant reflection arrives 21 ms after the direct sound (5).

(a)

(b)

Figure 8 – Early reflections on the main floor from a directional source on the stage. (a) Reflectogram; (b)origin of the reflections. After (6)The ability to hear the voice on the stalls is supported by the direct sound and its first reflections,which arrive much earlier than the reflections coming from the pit. This feature, added to the spectral
reinforcement of the zone of the singers’ formant, explains in part the good balance that the audiencehas on the main floor. However, if the source is placed well inside the stage (12 m from theproscenium) and the scenery is very absorbent, the balance is drastically reduced, falling below therecommended values (6).
Contrary to in the stalls, at the upper levels there is a direct line of sight to instruments in theorchestra in the pit. In the stalls, the sound of the orchestra is attenuated by the barrier effect of the3948

pit and the fence between the pit and the audience. Due to the diffraction and the excellent low
frequency diffusion provided by the lateral boxes and the sides of the proscenium, this attenuation
affects the low frequencies less. At the upper levels, this barrier disappears and the sounds of medium
and high frequency grow at relative values. The digital simulation shows that, although the balance at
higher levels loses part of the spectral advantage that the theatre has in terms of the stalls, this change
is compensated for by the emergence of the powerful reflection of the singers' voices on the stage
floor. This reflection is useful only for the voices and is almost non -existent for the audience on themain floor. This fact, plus the appearance of early reflections from the ceiling, allows the balance tobe maintained within appropriate values at the upper levels. The contribution to the balance of thereflection on the stage floor is very important. If a carpet is used, the balance is reduced by an averageof 2 dB. At the upper levels, the influence of the stage set-up is less pronounced than on the main
floor when the singers are located well inside the stage box.

5. DISCUSSION
The aforementioned measurements and digital simulations of the main floor of the Teatro Colónshow an acoustic field with a large amount of non-frontal energy, in which a dense structure of earlylateral reflections appears behind the first significant reflection. These reflections fall well within theHaas limit, minimising echoes and colorations and, at the same time, increasing the perceived
spatiality. From the answers obtained in the surveys on acoustic quality it is known that the sound in
the Teatro Colón is very immersive and that it has a strong sound presence. It is interesting to pointout that these characteristics are found in both uses of the hall, as an opera theatre and as an auditorium
for symphonic music. In some sense, the theatre seems to behave acoustically as a doubl e hall, as if
it were a combination of an Italian horseshoe opera house and a shoebox -shaped auditorium.
The question that arises is: are the usual physical characteristics sufficient in describing the soundperceived by the audience? In a first attempt to answer this question, some descriptors defined byISO-3382 standard were applied, such as the LF or the IACC, but these parameters do not take into
account the specific time, level and direction of arrival of each individual reflection, and therefore
they could not explain an acoustic field in which, seemingly, these features were critical. In a second
attempt, some objective theories and methods were used in order to predict the acoustical quality ofhalls for music, among them Beranek’s AQI. This method did not explain the quality, however, withthe best seats of one of the best halls for music obtaining only average ratings (12).
Nevertheless, a series of conjectures has been developed that could explain, at least qualitatively,
the relationship between the existence of powerful early lateral reflections and the acoustic fields ofhalls such as the Teatro Colón. Among them, is an early work by Rüdiger Wettschurek who, in his
PhD Thesis, pointed out the differential perception of lateral energy at differ ent sound levels. In his
own words, a musical crescendo was as a kind of “awakening” of the room through the increasing of
the subjective room presence –(13), cited from (14).
More recently some authors, including Tapio Lokki, Jukka Pätynen and Eckhard Kahle, among
others, have pointed out the importance of the strong lateral reflections in order to obtain a very
immersive, enveloping acoustical field. They sustain that the presence of this kind of reflections
increases the subjective dynamic spatial responsiveness [26, 27], the enveloping sensation and thepresence of the sound (15, 16). Furthermore, these strong lateral reflections increase the emotional
impact of the music and make the acoustics of auditoriums more engaging (16, 17).
Another notion put forward is the amount and nature of the diffusion needed inside a hall: toomuch diffusion would preclude the necessary reflections required in order to achieve an immersive
acoustic field but, conversely, an insufficient or misplaced diffusion would prevent the homogeneous
distribution of the acoustic energy. According to Kahle, some halls that lack quality do so as a resultof having excessive diffusion (18). In this sense, the Teatro Colón seems to have a proper balanceamong reflective, diffusive and absorptive surfaces.

6. CONCLUSIONSThe Teatro Colón seems to behave like a double hall, with some features typical of opera theatre
and others of an auditorium for symphonic music. As an auditorium for symphonic music it seems to3949

perform, on the main floor, like a combination of a shoebox-shaped hall and a horseshoe theatre. At
upper levels it behaves like a traditional Italian horseshoe hall (4). As an opera house, the Teatro Colóncombines two complementary situations: on the main floor, the voices of the singers are accompanied
by a large number of early lateral reflections that, combined with the masking of the sound that comesfrom the pit, reinforce them in the singer's formant region. At the upper levels this spectral advantage
disappears but is compensated for by the arrival of powerful reflections from the stage floor and theceiling (6).
The theories that emphasize the importance of strong lateral reflexions not only coincide withthe physical acoustic field observed in the Teatro Colón and with the subjective reactions it produces,
but also help to understand some of its architectural characteristics. However, up to now the physicaldescriptors used in those new theories are mainly qualitative, so we need to develop some quantitativedescriptors to analyze existing spaces and design new ones. The main goal is to find a new set ofobjective parameters that properly describe the acoustic fingerprint of a hall for music.

ACKNOWLEDGEMENTS
The author acknowledges María Andrea Farina for her contribution about architectural acoustic
and graphic design; also, Rafael Sánchez Quintana and Alberto Haedo for their role during therestoration of the Teatro Colón.

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