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THE DESIGN OF A MEDIUM-SIZED CONCERT HALL FOR LARGE SYMPHONIC ORCHESTRA: CASE STUDY LE ROSEY CONCERT HALL

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Proceedings of the Institute of Acoustics
Vol. 37. Pt.3 2015
THE DESIGN OF A MEDIUM-SIZED CONCERT HALL FOR
LARGE SYMPHONIC ORCHESTRA: CASE STUDY LE
ROSEY CONCERT HALL
Alban Bassuet Tippet Rise Art Center, Fishtail, Montana, USA alban.bassuet@tippetrise.org
Anne Guthrie Arup Acoustics, New York, NY, USA anne.guthrie@arup.com
1 INTRODUCTION
Located in the town of Rolle in rural Switzerland, half-way between Lausanne and Geneva, Le
Rosey Concert Hall first opened its doors to the public in October 2014. The new building is part of
the renowned Swiss boarding school Le Rosey Institute. Designed by Bernard Tschumi Architects,
the futuristic dome shape building is conceived as a hub for the arts contrasting with the traditional
architecture of the historical campus. It includes a 900-seat concert hall, a 200-seat black box studio
theater, a 50-seat music salon, music practice rooms, a library and visual art workshop spaces. The
concert hall is used primarily for symphonic music including international touring orchestra to
provide students with unique musical immersion opportunities, but also for student orchestra
activities, film and amplified music.
Determining the number of seats for the main hall had been set by a number of different influencing
factors. Firstly, the center is remotely located reducing the number of potential audience members
coming from larger cities. It is also to be used for a wide range of smaller musical ensemble
activities with smaller audience attendances across the year. Finally, the owner, a passionate music
lover, was keen to create a hall that would be louder and more intimate than larger concert halls of
audience capacity typically above 2,000. After reviewing other benchmarks in Europe, the hall
seating capacity was then set to a maximum of 1,000. The design of the hall was therefore
challenged by the requirement to accommodate large symphonic works but for a smaller audience
than larger concert halls. This article describes how this challenge was handled in the design of the
hall and experienced after its first musical season.
The team also picked a reverberation time target to balance the usage of the hall for symphonic
works but also student orchestra and chamber music. The target was 1.8 seconds. Other features
of the hall includes deployable acoustical curtains for amplified events or rehearsals. The hall also
includes a built-in cable distribution infrastructure for multi-media and immersive works.
It is interesting to note that because the project was shaped as a dome with a total building footprint
which could be controlled by its radius, the height of the building was used as a unique parameter to
not only control reverberation time but also to calculate the total cost of the project and the total
habitable area regulated by the Swiss building authority.
The structure of the main hall is isolated on springs to limit structure-born noise from nearby
passing trains from the railway connecting Lausanne and Geneva located less than 60 meters away
from the building.
The hall opened with the Royal Philharmonic and St. Petersburg Orchestras and soloist such as
Hélène Grimaud. The hall has received very positive reviews overall for its acoustics and
architecture.
Proceedings of the Institute of Acoustics
Vol. 37. Pt.3 2015
Figure 1: Interior view of the Hall with the Royal Figure 2: View to the front
Philharmonic Orchestra
Figure 3: Arial view of the building next to the existing school campus
2 DESIGN IDEAS
The main challenge of the acoustical design of the hall was to prevent from excessive loudness
while preserving reverberation for large symphonic works. As pointed out recently by David Kahn
and Indi Savitala1, smaller halls used for symphonic music can result in introducing an amount of
absorption that can compromise reverberation. A design option offered by Savitaka and Kahn
proposes the use of reverberation chambers to increase volume lowering loudness and increasing
reverberation while preserving a small audience chamber.
While also making use of coupled volumes, but smaller ones, the design for Le Rosey took a
slightly different direction. The building overall design did not offer opportunities for large empty
volumes around the hall and the design team did not want to conceal “out-of-view” additional
volumes than the one seen and experienced by the audience in the hall as one auditorium
chamber. So instead of relying primarily on coupled spaces, the design of the hall was based on
increasing the volume per seat of the main audience chamber by raising the ceiling to increase RT
above the target value and to introduce shaping on the surfaces of the hall to lower reverberation
and loudness parameters to the desired target ranges. It basically consisted of making the hall more
reverberant than it would with typical hard surface materials traditionally found in concert halls like
plaster for example, and to introduce wall shaping to lower RT by diffusion and absorption effects
until RT reached its target value. This chosen design strategy presented more risks than adding
Proceedings of the Institute of Acoustics
Vol. 37. Pt.3 2015
large coupled spaces as surface shaping cannot be changed as easily after the fact and predicting
dissipation effects are uncertain. Predictions of sound attenuation had to include scattering due to
the shaping geometry and the added absorption due to the increase of material surface area.
The reverberation time could also have been lowered using acoustical curtains instead of using
dissipative elements on the walls, but the team did not want to impact the reflection sequence of the
space with heavy drapery occluding important reflective surfaces in the hall.
Increasing surface shaping would also inevitably lower the intensity of early reflections. The shape
of the hall was therefore designed as a narrow shoebox to reinforce the intensity of lateral
reflections, hoping those would be attenuated by the wall shaping and become in balance with the
response of the room.
Other features of the hall included a shallow raked audience floor which uses the grazing effect of
direct sound to increase the attenuation of direct energy with distance and be in balance with the
response of the room and control loudness. A balcony gallery was added with a flat ceiling and no
shaping to create upper lateral reflections on the audience’s main floor by cue-ball effect with the
outer lateral walls. Those were meant to balance the lower lateral reflections (from the walls) with
the upper lateral reflections (from the gallery ceiling) favored by the author2 to enhance the
impression of envelopment (Figure 6). The gallery was set high to make a tall rear wall to bounce
rear lateral reflections to the audience on the main floor. It was angled by 2.5° to prevent from slap
back echo to the stage.
The architect was interested in the concept of creating a rectangular concert hall contrasting with
the dome building shape. These two shapes intercept on the ceiling of the concert hall, which was
made to follow the same curvature as the roof as a continuity with the building exterior but also to
maximize the hall’s acoustical volume. Creating a large concave surface, it was imperative to find
solutions against the ceiling focusing. Coffers were created for sound diffusion functioning along the
wall shaping to control loudness. More importantly, three orchestra canopies were suspended
above the stage to prevent from the sound of the stage to bounce of the ceiling and provide a
uniform support to the orchestra on stage.
For interior surface finish, the design team researched materials which could easily be shaped and
cut to create geometrical patterns on the walls and with a fine texture finish for high frequency
scattering (to soften higher partials of musical instruments). After reviewing a wide range of
composite wood material with different veneer finish, OSB (orientated strand boards) picked the
interest of the design team because of its interesting appearance and flexibility of use. OSB is a
very standard material for constructing partitions or framing, but it is also very rarely used as a finish
material, especially in a concert hall. Bringing a sense of irony and lightness, OSB became the main
surface finish in the hall but also in the rest of the building. OSB has texture which can provide an
interesting dissipation effect at higher frequencies, but it is also very porous, especially on its edges,
and lightweight, with sometimes a non-uniform density – both effect which are great acoustical
challenges.
Including its 2.5 m extension, the stage is roughly 240 m2 and can fit up to 115 musicians. The
balcony behind the stage can serve alternatively for audience sitting or choir. The stage extension
can be lowered to create an orchestra pit with additional available space underneath the main
stage. The space underneath the gallery serves as storage for the orchestra risers.
Proceedings of the Institute of Acoustics
Vol. 37. Pt.3 2015
Figure 4: Cross and longitudinal sections of the building and the Hall
Figure 5: Stage plan Figure 6: Desired reflection paths
3 SURFACE SHAPING, DESIGN AND SIMULATION
3.1 Geometry and Early Predictions
The surface shaping geometry used on the walls to lower reverberation was conceived as 3D
corners along the walls which, in addition to providing scattering, return an array of sound
reflections coming from the back of the audience’s heads reinforcing acoustical intimacy and
envelopment. Larger vertical beams are repeated every 4.2m, intercepting with larger horizontal
beams at various height along the walls (Figure 8). The intersections of those beams create 200mm
deep corners acting as cue-ball reflectors. In-between larger beams are laid out 60mm and 30mm
deep joists for diffusion at higher frequencies.
The design team developed a number of different geometrical patterns as shown on Figure 7 and
different densities of shaping were experimented and tested with computer models until the desired
RT was obtained. Before the final design and OSB material were tested in a reverberation chamber,
the design had to be progressed using predictions of what would be the absorption values resulting
from the different geometrical shaping. The equivalent absorption was estimated for each option
Proceedings of the Institute of Acoustics
Vol. 37. Pt.3 2015
and then applied to flat surfaces without shaping in computer simulations of the hall. The equivalent
absorption was estimated following the following methods:
By calculating the unfolded surface area of material and correspondingly increasing the
absorption values of the wall surfaces
By comparing with measured absorption data of sound diffusers such as QRD Diffusors
published by Peter D’Antonio3. Measured absorption data of sound diffuser can provide a
useful reference point between a densely shaped wall panel and its equivalent absorption
coefficient. With a simple rule of three one can estimate the absorption coefficient for
another ratio of unfolded surface area to actual panel size.
By predicting scattering and absorption coefficient using AMFG SoundFlow and Reflex
calculation programs
Sound absorption for OSB was estimated using measured values of un-finished wood (Figure 12).
Figure 12 compares the predicted absorption coefficients of the final geometrical pattern with the
measured data of the actual wall sample tested in reverberation chamber. It is interesting to notice
that it was possible to estimate with a relatively good accuracy the absorption of the shaping
between 250 Hz and 2 kHz. The differences shown here were due to panel absorption effect under
250 Hz which were reduced in the actual wall sample bonded directly to the floor of the
reverberation chamber (or to the concrete walls of the hall once installed), and to a lower absorption
than predicted above 2 kHz as in fact the sealant applied to the OSB greatly reduced its porosity
and made it more reflective than un-finished wood.
Figure 7: Studied geometrical patterns Figure 8: Close-up view of the final wall shaping
3.2 Measurement in Reverberation Chamber
Once the geometry was optimized to meet the acoustical targets, mock-ups of OSB panels were
constructed for reverberation chamber tests. The tests included measuring the effect of the sealant
used on the face of the OSB to seal its porosity, different OSB panel thicknesses, and three
Proceedings of the Institute of Acoustics
Vol. 37. Pt.3 2015
geometric patterns, variations around the final design of the walls. Measurements were conducted
in Switzerland, according to ISO 354:2003.
Figure 9: Close-up view of the OSB with Figure 10: Measured absorption comparing
sealant thickness and surface treatment
Figure 11: Four different pattern densities Figure 12: Measured versus predicted data
Conclusions from the tests were as follows:
For equal shaping and surface treatment, the tests revealed that the 12.5 mm thick board
had a higher absorption at mid-frequencies than a 25 mm board (Figure 10). This can be
explained by the fact that the 12.5 mm board requires less pressure to be compressed as a
single panel than a thicker board, therefore becoming less dense. 25 mm thick board rigidly
bonded to the concrete walls were chosen for final construction.
As expected, increasing the quantity of surface shaping increased the measured absorption
coefficient, and there is a significant increase between a flat board and the same board with
shaping applied (Figure 11). The construction opted for the 14% reduction in joists which
matched the expected data calculations from simulations.
As shown by comparing the veneered and un-veneered 25 mm thick board test data, the
veneer has the significant impact above 2 kHz reducing the OSB’s porosity (Figure 10).
As pointed out earlier, the predictions of absorption for OSB and shaping with the measured
data are not too different between 250 Hz and 2 kHz (figure 12). One can also see that by
comparing data of un-finished wood with veneered OSB, it is possible to achieve a very
reflective OSB material without the risk of excessive porosity at higher frequencies.
Proceedings of the Institute of Acoustics
Vol. 37. Pt.3 2015
4 COMPUTER SIMULATIONS AND FINAL MEASUREMENTS IN
THE HALL
4.1 Computer Simulations
Three models were progressed during the design phase to compare the variations of acoustical
indexes:
Hall with no shaping and hard material such as plaster
Hall with no shaping but OSB as finish material, (measured data, 25 mm thick board and
veneer finish)
Hall with shaping and OSB as finish material, (measured data, 25 mm thick board and
veneer finish)
Reverberation time, loudness indexes and SPL are plotted on Figure 13 through 15, observations
below:
Reverberation time gradually reduces from 2.38 sec (solid plaster) down to 1.75 sec with
OSB and joists (target 1.80 sec), showing the effect of increasing wall shaping
Loudness index reduces from 5.5 dB to 4.0 dB on average in the hall. This difference does
not appear significant at first, but it is in fact important as in such a small room direct sound
can be the prime factor controlling the impression of loudness. This shows that the wall
shaping can provide an overall reduction of loudness even in a smaller concert hall where
direct sound is inevitably dominant.
SPL data excluding direct sound shows a clear reduction of levels in the order of 3 dB
averaged across the hall, confirming the results mentioned above
Figure 13: SPL mapping comparing a smooth plaster finish with veneered OSB and wall shaping
Proceedings of the Institute of Acoustics
Vol. 37. Pt.3 2015
Figure 14: Simulated and measured data Figure 15: Predicted Loudness index, full audience
with a full audience
4.2 Validation Measurements
Sine sweep measurements were conducted in the finished hall with and without the presence of an
audience, using a Bruel & Kjaer dodecahedron, a Genelec Subwoofer, Earthwork and Soundfield
microphones.
The reverberation time with a full audience is presented on Figure 14. Temporal and spatial
distributions are shown on Figure 16 (unoccupied conditions only).
Figure 14 shows a good match with the predictions. Slightly higher values were measured above 2
kHz, which most likely reveal the effect of the sealant finish applied to the OSB preventing from
porosity effects (mid-frequency RT of 1.78 seconds).
Figure 16: Temporal and spatial energy distributions for a position on the main floor and at the
balcony
Proceedings of the Institute of Acoustics
Vol. 37. Pt.3 2015
On the main floor, the temporal energy distribution show the presence of strong early reflections
within 15 to 40 ms, important for intimacy and envelopment. A cluster around 40 ms from the sides
seems to be coming from the ceiling above the gallery providing upper lateral energy and balancing
the lower lateral reflections for a more surrounding acoustical effect. Another cluster can be visible
around 100 ms (typical clusters of classic shoebox historical concert halls - 20 ms, 40 ms, 100 ms
clusters4).
At the balcony, the spatial distributions show the effect of the curved ceiling channeling sound from
the stage to the rear of the hall. It results in a concentration of energy within the 15 to 40 ms time
frame compensating for the distance to the stage resulting in an intimate and also very immersive
sound.
5 CONCLUSION
This study shows how a smaller concert hall can be designed to accommodate large orchestra
forces by increasing its volume per seat and adding scattering. The result has proven to be a viable
solution to control loudness while maintaining reverberation. The study also demonstrates that an
un-usual material such as OSB can be used in concert halls, provided that a sealant is applied to
prevent from the material’s porosity. The work has led to an original architectural design as noted in
the architectural and design press.
The shaping on the walls creates the desired attenuation effect. It is interesting to note that the hall
can contain orchestras Fortissimo while providing intimate sound for smaller ensembles – an
advantage of a smaller concert hall compared to larger halls. The author also notes however that
while the 3D corners have the benefit to return an array of reflections to the back of the audience’s
heads, they also occlude a portion of the grazing energy reaching the rear of the hall by acoustical
shadowing. As a result there is maybe less energy bounced from the rear wall than anticipated.
Le Rosey Concert Hall has received good reviews for its acoustics since its opening. A number of
reviews and critics of the hall have mentioned its clarity and crystalline qualities, which could be in
connection with the increase of high frequency reverberation provided by the sealant on the face of
the OSB, but also by the basic shape and size of the room supporting early reflections. The hall has
also been described as enveloping and rich by teachers and users of the space, and as one of the
best halls in Switzerland by musicians and conductors.
6 ACKNOWLEDGMENT
The authors would like to thank the team members at Arup who collaborated on the project
including Matt Mahon, Adam Foxwell, Joseph Digerness, and Brendan Smith. Thank you to
Bertrand de Rochebrune from D’Silence who acted as the local acoustician in Switzerland during
construction and commissioning and Pascal Schwab for his craft and millwork of the OSB material.
7 REFERENCES
1. D. Kahn and I. Savitala, Acoustical Design of Concert Halls with Small Seating Capacities,
Proc. ISRA, Toronto, Canada (2013).
2. A. Bassuet, New Acoustical Parameters and Visualization Techniques to Analyse the
Spatial Distribution of Sound in Music Spaces, Proc. ISRA, Melbourne, Australia (2010).
3. T. Cox and P. D’Antonio, Acoustic Absorbers and Diffusers, Theory, design and application,
Spon Press (2004).
4. A. Bassuet, N. Woodger, Acoustics of Early Music Spaces from the 11th to 18th Century:
Rediscovery of the Acoustical Excellent of Medium-Sized Rooms, 147th ASA Meeting, New
York, NY (2004)
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Acoustical Design of Concert Halls with Small Seating Capacities
  • D Kahn
  • I Savitala
D. Kahn and I. Savitala, Acoustical Design of Concert Halls with Small Seating Capacities, Proc. ISRA, Toronto, Canada (2013).
Acoustics of Early Music Spaces from the 11 th to 18 th Century: Rediscovery of the Acoustical Excellent of Medium-Sized Rooms
  • A Bassuet
  • N Woodger
A. Bassuet, N. Woodger, Acoustics of Early Music Spaces from the 11 th to 18 th Century: Rediscovery of the Acoustical Excellent of Medium-Sized Rooms, 147 th ASA Meeting, New York, NY (2004)