preliminary acoustic measurements in the auditorium ...

PRELIMINARY ACOUSTIC MEASUREMENTS IN THE AUDITORIUM “OSCAR NIEMEYER” IN RAVELLO R. Dragonetti, C. Ianniello and R. Romano DETEC, University of Naples - Federico II - piazzale Tecchio, 80 – 80125 Naples (Italy) {[email protected]}

Abstract After years of music festivals that were held in wonderful places like ancient churches and terraces overlooking the sea, the town of Ravello on the hills of the Amalfi coast was endowed with an auditorium conceived ten years ago by the now 102 years old Maestro Oscar Niemeyer. The Institution which the authors belong to was involved under the responsibility of the second author in the consultancy for the acoustics related to the last design of the magnificent, but debated, masterpiece of the famous architect Niemeyer. At the end of January 2010 the auditorium was opened to public performances so the authors had the opportunity to check the room acoustics behavior of the main hall. This paper reports about architectural features of the auditorium and the results of preliminary acoustic measurements performed in the unoccupied main hall. Keywords: Niemeyer, auditorium, measurements, parameters.

1 Introduction Ravello is a graceful town on the hills near Amalfi where breathtaking views of the Mediterranean sea and the astonishing coastline can be enjoyed. The location offers a rich combination of natural beauties, art monuments and cultural memories. Artists, writers, musicians and other famous guests have spent time in Ravello fascinated by its unique treasures. A special mention is due to Richard Wagner who in 1880 signed the guestbook of his hotel with the words “The magical garden of Klingsor is found”. This event gave rise to the belief that the gardens of the ancient Villa Rufolo had inspired his opera Parsifal. Later this fact supported the decision of concerned people to organize an annual festival based on the performance of Wagner’s music to promote tourism and enhance the economy during the difficult years following the II World War. On the occasion of the celebration of the eighty years after the death of Wagner The Ravello Festival was started on June 1953 with a three days performance of Wagnerian music in the gardens of Villa Rufolo. Since this first

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INTERNOISE 2010 │ JUNE 13-16 │ LISBON │ PORTUGAL

date the duration of the festival has increased greatly. Besides Wagnerian production, nowadays the Ravello Festival has grown into a whole summertime presentation of a wide variety of music: orchestral and chamber music, solo music, jazz and pop concerts. Dance and ballet, cinema, art exhibitions, discussion meetings and the opportunity to meet and talk with the participant artists are also offered to the public. To manage and enhance these events and other cultural activities as well, in 2002 a society funded by public and private institutions (Ravello Foundation) was established. Until the end of 2009 Wagnerian concerts and other events have been held outdoors in the gardens of Villa Rufolo with artists performing on a temporary stage protruding in the air like an entity flying over the lovely view of the sea and coastline (Fig.1). Also other beautiful places like historical churches, squares, typical corners, gardens and terraces have served analogous purposes excellently.

Fig,1 – The protruding stage in Villa Rufolo (Ravello). Left: in the fifties; Right: nowadays. The idea of an auditorium was born in July 2000 almost for chance. The Mayor of the time during a relaxed talk with a Brazilian journalist visiting Ravello expressed the need of an auditorium for his town. The journalist suggested that an Italian dear friend of the famous Brazilian architect Oscar Niemeyer – the President of Ravello Foundation – could join him to meet and ask the Master to conceive an auditorium for the town of Ravello. Architect Niemeyer agreed and took seventy days to complete an artistic and architectural preliminary design of the auditorium. He made his Italian friend and the Municipality of Ravello a gift of his work which consisted of a number of drawings and a plastic model (Fig.2).

Fig. 2 – Views of the plastic model of architect Niemeyer,

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Subsequently, Niemeyer and his collaborators signed consultancy contracts for further developments of his architectural preliminary design. One condition agreed upon firmly was that changes of shape and appearance should not be allowed to other involved consultants and contractors without a specific discussion and a personal approval of architect Niemeyer. A definitive design stemmed from the collaboration of the Niemeyer staff, the Municipality of Ravello and an Italian firm; it was ready and approved in May 2004. In the meanwhile local “querelles” of legal, political, bureaucratic, environmental and aesthetic nature have plagued the difficult path toward the realization of the auditorium. Finally, in 2007 the contractor who won the final bidding for amelioration and construction of the auditorium with associated infrastructures signed a contract for acoustic consultancy with the DETEC, the university department which is the work place of the authors. The acoustic job was carried out in close contact with the partners responsible of the architectural aspects who informed the staff of architect Niemeyer about the choices of the acoustic designers to check for their compatibility, even during the construction of the auditorium. So, the restraint of the inherited demanding requirement of untouchable aesthetics was taken into account as much as possible.

2 Highlights of the consultancy for room-acoustics With reference to the activities scheduled by Ravello Festival and carried out since the second half of the nineties the acoustics of the auditorium had to be adapted to many genres of performance. Orchestral music, chamber and solo music had a special role. However, the basic room acoustics behavior inspired to a classical concert hall could not be taken as a goal. The shape of the room, the restraints imposed to its appearance, the needs of a multipurpose hall conjured against this initial preference of the consultants for acoustics. Fig. 3 displays a section and a plan of the auditorium that have been simplified a little with respect to the originals reported in the definitive project. The geometric dimensions given in the definitive project are: volume of the hall about 8600 m3, over all floor surface about 1218 m2 and retractable stage area about 180 m2 (max width = 21 m, max depth = 9 m). 406 seats are arranged on stairs. The contour of the stage and seating area is almost a parabola.

Fig. 3 – Section (left side) and plan (right side) of Niemeyer’s Auditorium (The two drawings are not in the same scale). An initial analysis of the available drawings showed that too much energy associated with first reflections from the curved vault converged toward the very sound-absorbing area occupied by audience. The proposal of flying dishes suspended from ceiling, which could reflect and diffuse the sound impinging directly on the vault, was rejected by Niemeyer staff.

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The auditorium has a plan shaped as an irregular trapezium - recalling a fan shaped hall which is developed much transversally in the area occupied by the audience. This circumstance causes faint first reflections reaching directly the listeners seated far from the lateral walls. To moderate this lack of lateral energy vertical glass panel were suggested along the external edges of the two extreme stairs to reach near seat-blocks. Each row of ascending panels forms a serrated surface able to readdress impinging direct sound emitted from a point source at the center of the stage toward the central part of the seating area. They should do this job for the 1/3 octave band at 500 Hz and higher. A pair of convex panels suspended at each high corner at the back of the hall, suggested for a similar aim in the original definitive project, were also included. The definitive design reported a multi-level stage floor surrounded by an almost parabolic wall with the surface shaped like cylinder sectors. The prescribed minimum height with respect to the local stage floor was 2.5 m. When a whole flat floor is desired, the structure is retracted into a room below. Due to the difficulty to displace vertically and hide the surrounding fixed wall, it was substituted with wheeled and removable transparent (metacrylate) panels having a wavy shape. When used they allow a flexible tuning of the initial reflected sound from the stage to the benefit of both the musicians and the audience. With a similar aim, a removable oval crown of wavy transparent panels can be suspended over the stage area. This solution was accepted by Niemeyer’s staff because all panels were not a fixed fixture affecting the appearance of the hall permanently. The control of the reverberation time was accomplished by lining the ceiling with white wooden panels (thickness 20-25 mm) over an air cavity having a depth of about 15 cm. A layer 30 mm thick of polyester fibrous materials was inserted in the air space. The curvature of the whole vault was preserved quite well. About 350 m2 of paneled surface had invisible perforations to get a wide-band sound-absorbing system. The remaining surface of the vault was covered with the same panels without perforations. The latter realized a membrane-type sound-absorbing system able to absorb low frequency sound. Care was taken to alternate perforated and impervious panels almost randomly over the area occupied by the audience. This arrangement was chosen to gain a little diffusion of the reflected sound. About four hundred upholstered chairs, chosen for comfort and aesthetic reasons, where arranged in three blocks as shown in the plan in Fig.2. They contribute further fixed sound absorption. Variable absorption was obtained with three systems that can be exposed to sound field when a reduction of the basic reverberation time is needed, e.g. amplified music, cinema, meetings with sound reinforcing loudspeakers. A first one is constituted of a layer of polyester fiber 10 cm thick backed by the concrete wall embellished with the large circular window that is displayed in the section in Fig. 3. The fibrous material is hidden behind an articulated wall made of dense-wood panels 40 mm thick. Computer controlled motors can superpose with an almost coplanar motion a number of them to analogous fixed panels coupling hidden porous surface with the sound field in the room. The maximum exposed area is about 100 m2. Two large sound-absorbing panel are hidden in a pocket between the rear wall of the room and the back wall of the control cabin. This long and narrow room with large observation glass panes hosts apparatuses for projection and sound/video recording. When both wheeled panels are extracted from the pocket completely at each side of cabin, they contribute a sound absorbing surface of about 18 m2. Besides the large circular window closed with double panes of sound insulating glass, there are also a curved logenze-like window in the frontal descending vault and the whole left side wall which are double walls made with sound insulating glass panes. All these glass surfaces can be obscured against the daylight with flat porous curtains falling at a distance of more than 10 cm from the backing glass walls. They behave like sound absorbing systems

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constituted of a thin porous panel backed by an air cavity, so the exposed curtains can contribute to variable acoustics of the auditorium.

3 The temporary opening of the Nyemer Auditorium At the end of 2009 the management of Ravello Festival announced the official opening of the auditorium to public performances. A three days winter festival was organized that started with the ceremonial inauguration on Thursday 29th January 2010 and ended on the following Sunday. A military musical band (Corps of Carabeeners), a ballet with reproduced music, a solo saxophone concert, a large orchestra and choir performing the 9th Symphony by Ludwig van Beethoven, pop music with a famous Italian singer with full orchestra, Vivaldi music performed by a chamber orchestra under the direction and participation of a famous Italian violinist and a 3D cinema projection were all offered to public in the Niemeyer Auditorium. Also public conference and discussion panels were kept in the same hall during the threedays “tour de force”. Neither variable sound absorbing devices nor additive reflecting panels were used during all performances. The asset of the hall was the basic one with flat floor. Surprisingly, after its first opening no other event has been kept in the closed auditorium. Fig.4 shows two external views of the built Oscar Niemeyer Auditorium.

Fig. 4 – External views of the built “Oscar Niemeyer Auditorium” in Ravello (Italy).

4 Acoustic measurements After the closing of the auditorium to public performances the authors had the opportunity to carry out acoustic measurements in the unoccupied auditorium in the asset it had been used during the three-days festival. Fig. 5 shows two internal views of the hall with instrumentation and operators. A dodecahedral loudspeaker was located along the median axis of the floor at the height of 1.3 m and at the distance of 5.0 m from the first row of chairs. Powered exponential sine sweeps were used to excite the room. Responses were recorded at nine receiving points located at the height of the head of a seated person in the audience area with non directional, figure of eight and ear microphones. Fig. 6 displays the sound source and receivers locations. The subsequent processing of the recorded responses yielded conventional room-acoustic parameters according to the standard EN – ISO 3382 , 2000 [1]. A power-calibrated sound source was used with a calibrated sound level meter to obtain the steady-state Strength Index G according to equation 1:

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G = Lp - LW + 31 dB

(1)

Where Lp is the sound pressure level (dB re 20 Pa) and LW is the sound power level of the sound source (dB re 1 pW).

Fig. 5 – Internal views of the unoccupied auditorium.

Fig. 6 – Plan of the auditorium displaying the locations of the sound source S and nine receiving points in the audience area. Fig.7 shows single microphone parameters T30, EDT, C50 and C80 and two-microphones parameters LF and 1- IACC for the octave bands with center frequency from 125 Hz to 4 kHz. Each colored line refers to average values for the triplets of receiving points denoted with the same color in Fig.6. Save the reverberation time T30, all other parameters depend on the distance of the triplet of receivers from lateral walls. It may be argued that the central seats are fed with initial reflected sound grater than the one reaching lateral seats. Due to the almost symmetrical location of the sound source and to the shape of the section as well, a

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long circulation of sound energy in the vertical plane containing the sound source can be supposed to exist before a high mixing of reflected sound is established. 1,7

1,5

1,6

right

1,5

lef t

1,3

EDT (s)

T30 (s)

central

1,4

1,1 0,9

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0,7

1,2

lef t 1,1

0,5 125

250

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1000 2000 4000

125

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-4,0

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1000 2000 4000

Frequency (Hz)

C80 (dB)

C50 (dB)

Frequency (Hz)

250

0,0

-2,0

central right

-4,0

lef t

lef t

-6,0

-6,0 125

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125

Frequency (Hz) 1.0

1000 2000 4000

center right

0.8

lef t

1 - IACC

central right

LF

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Frequency (Hz)

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lef t 0.2

0.6 0.4 0.2 0.0

0.0 125

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Frequency (Hz) Frequency (Hz) Fig. 7 – Measured room-acoustics parameters. Average values for each triplet of receivers (color code of lines as in Fig. 6).

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This conjecture can be supported by the comparison between the higher values at central locations with respect to the values at lateral locations for EDT, C50 and C80. These parameters are sensible to the initial energy in the impulse response. A reversed condition can be observed for LF and 1 – IACC which are sensible to the initial lateral energy. The steady-state values of the Strength Index G displayed in Fig. 8 also show a little dominance for the central area occupied by spectators. 12,0 10,0

G (dB)

8,0 6,0 central

4,0

right

2,0

lef t

0,0 125

250

500

1000 2000 4000

Frequency (Hz) Fig. 8 – Steady-state Strength index G. The results of measurements reported above suggest that the objective acoustics of the hall can be considered a good starting point for the multipurpose function of the auditorium. Obviously, the variability of acoustics that can be accomplished with the removable devices described in Sec 2 cannot warrant the performance of the best concert halls. However, the authors are confident that the provided removable reflectors will moderate the lack of field homogeneity in the audience area when they are mounted around and over the multilevel orchestra platform. Besides the preliminary measurements reported in the present paper for the basic asset of the auditorium, further measurements will be carried out to deepen the investigation as soon as the Oscar Niemeyer Auditorium will be reopened. However, judgments and comments about the acoustics of the auditorium have been already published.

5 The responses to a questionnaire and judgments After the three-days festival the Ravello Festival management published the results of a questionnaire proposed to almost 5100 spectators who had participated in the events. More than one thousand respondents expressed their opinion on general impression they had about the whole complex of the auditorium, on its aesthetics, on the acoustics of the hall and the functionality of the architectonic complex. Fig.9 shows the results for acoustics [2]. Only 12% of the interviewed people expressed a negative opinion about the acoustics. Unluckily the data could not be analyzed in terms of type of performance. However, the world-known conductor and violinist Mo Salvatore Accardo praised the acoustics of the hall. A similar opinion was expressed by the Italian pop star Lucio Dalla who had sung accompanied by a

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classical symphony orchestra. Also newspapers wrote that the Niemeyer’s Auditorium had passed the examination on its acoustics quite well.

Fig. 9 – Response to a questionnaire about the acoustics of the hall of Niemeyer’s Auditorium.

6 Conclusion The long story of the birth and the difficult realization of a singular architectural work has been reported briefly. The persons responsible for acoustics have spent many efforts doing their best to balance the constraint of untouchable aesthetics with the needs of roomacoustics for a multipurpose hall. The responses to the questionnaire, the judgment of qualified musicians and the results of the preliminary measurements give confidence to the authors that, with further checks and trims, the masterpiece conceived by Oscar Niemeyer, set in a beautiful view between the sea and the sky, will please not only the eyes but also the ears.

References [1] EN ISO 3382. Acoustics - Measurement of the reverberation time of rooms with reference to other acoustical parameters. [2] http://www.ravellofestival.com/newsletter/nl52/nl52.html (visited 24/02/2010).

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