1 ADA Acoustics & Media Consultants GmbH, Arkonastr. 45-49, D-13189 Berlin / Germany
2 University of Architecture and Urbanism “Ion Mincu”, Str. Academiei 18-20, RO-010014 Bucuresti / Romania
Popular version of paper 4aAA5, “The National Opera in Bucharest – Update of the room-acoustical properties” Presented Thursday morning, November 5, 2015, 10:35 AM, Grand ballroom 3
170th ASA Meeting, Jacksonville
The acoustics of an opera hall has changed dramatically within the last 100 years. Until the end of the 19th century, mostly horseshoe-shaped halls were built with acoustically high-absorbing wall and even floor areas. Likewise, the often used boxes had fully absorbing claddings. That way the reverberation in these venues was made low and the hall was perceived as acoustically dry, e.g. the opera hall in Milan. 100 years later, the trend shows opera halls with more live and higher reverberation, preferred now for music reproduction, e.g. Semper Opera in Dresden.
This desire to enhance the acoustic liveliness in the Opera House in Bucharest led to renovation work in 2013-2014. The Opera House was built in 1952-1953 for around 2200 spectators and it followed a so-called style of “socialist realism”. This type of architecture was popular at the time, when communism was new to Romania, and the building has therefore a neoclassical design. The house was looking inside the hall like a theatre of the late 19th century. The conditions in the orchestra pit for the musicians, as far as mutual hearing is concerned, were bad as well. So, construction works took place in order to improve room acoustical properties for musicians and audience.
Fig. 1: Opera hall after reconstruction
The acoustic task was to enhance the room acoustic properties significantly by substituting absorptive faces (as carpet, fabric wall linings, etc.) by reflective materials:
Carpet on all floor areas, upholstered back- and undersides of chairs
Textile wall linings at walls/ceilings in boxes, upholstered hand rails
Textile wall linings at balustrades, upholstered hand rails in the galleries
All the absorbing wall and ceiling parts were substituted by reflecting wood panels, the carpet was removed and a parquet floor was introduced. As a result, the sound does not fade out anymore as in an open-air theatre but spaciousness may be perceived now.
The primary and secondary structures of the orchestra pit were changed as well in order to improve mutual hearing in the pit and between stage and pit. The orchestra pit had the following acoustically disadvantageous properties:
Insufficient ratio between open and covered area (depth of opening 3.5 m, depth of cover 4.7 m)
The height within the pit in the covered area was very small.
The space in the covered area of the pit was highly overdamped by too much absorber.
Fig. 2: new orchestra pit, section
The following changes have been applied:
The ratio between open area and covered area is now better by shifting the front edge of the stage floor to the back: Depth of opening is now 5.1 m, depth of cover only 3.1 m.
The height within the pit in the covered area is increased by lowering the new movable podium.
The walls and soffit in the pit are now generally reflective, broadband absorbers can be placed variably at the back wall in the pit.
After an elaborate investigation by measurements and simulation on site a prolongation of the reverberation time of 0.2-0.3 s was reached to actual values of about 1.3 to 1.4 s.
Together with alterations of the geometric situation of pit, the acoustic properties of the hall are now very satisfactory for musicians, singers and the audience.
Beside the reverberation time, other room acoustical measures such as C80, Support, Strength, etc. have been improved significantly.
If the MP’s speeches don’t put you to sleep, at least you should be able to understand what they are saying.
Using state-of-the-art audible simulations, a design team of acousticians, architects and sound system designers is working to ensure that speech within the House of Commons chamber of the Parliament of Canada now in design will be intelligible in either French or English.
The new chamber for the House of Commons is being built in a glass-topped atrium in the courtyard of the West Block building on Parliament Hill in Ottawa. The chamber will be the temporary home of the House of Commons, while their traditional location in the Center Block building is being renovated and restored.
The skylit atrium in the West Block will be about six times the volume of the existing room, resulting in significant challenges for ensuring speech will be intelligibility.
Figure 1: Existing Chamber of the House of Commons, Parliament of Canada
The existing House chamber is 21 meters (70 feet) long, 16 meters (53 feet) wide, and has seats for the current 308 Members of Parliament (to increase to 338 in 2015) and 580 people in the upper gallery that runs around the second level of the room. Most surfaces are wood, although the floor is carpeted, and there is an adjustable curtain at the rear of the MP seating area on both sides of the room. The ceiling is a painted stretched linen canvas over the ceiling 14.7 meters (48.5 feet) above the commons floor, resulting in a room volume of approximately 5000 cubic meters.
The new House chamber is being infilled into an existing courtyard that is 44 meters (145 feet) long, 39 meters (129 feet) wide, and 18 meters (59 feet) high. The meeting space itself will retain the same basic footprint as the existing room, including the upper gallery seating, but will be open to the sound reflective glass roof and stone and glass side walls of the courtyard. In the absence of any acoustic treatments, the high level of reverberant sound would make it very difficult to understand speech in the room.
ARCOP / FGM ARCHITECTS
Figure 2: Early Design Rendering of Chamber in West Block
In order to help the Public Works and Government Services Canada (PWGSC) and the House of Commons understand the acoustic differences between the existing house chamber and the one under design, and to assure them that excellent speech intelligibility will be achieved in the new chamber, Acoustic Distinctions, the New York-based acoustic consultant, created a computer model of both the new and existing house chambers, and performed acoustic tests in the existing chamber. AD also made comparisons of the two room using sophisticated data analysis and tables of data an produced graphs maps of speech intelligibility in each space.
An early design iteration, for example, included significant areas of sound absorptive materials at the sides of the ceiling areas, as well as sound absorptive materials integrated into the branches of the tree-like structure which supports the roof:
Figure 3: Computer Model of Room Finishes
The dark areas of the image show the location of sound absorptive materials, including triangularly-shaped wedges integrated into the structure which supports the roof.
Using a standardized measure of intelligibility, AD estimated a speech quality of 65% using the Speech Transmission Index (STI), a standardized measure of speech intelligibility, where a minimum of 75% was needed to ensure excellent intelligibility.
The computer analysis done by Acoustic Distinctions also produced colorful images relating to the degree of speech intelligibility that was to be expected:
Figure 4: Speech Transmission Index, single person speaking, no reinforcement
Talker at lower left; Listener at lower right
Dark blue to black color indicates fair to good intelligibility
While these numerical and graphical tools were useful in understanding acoustic conditions of the new room, in order to make it easier for the client and design team to appreciate the acoustic recommendations made by the consultant, Acoustic Distinctions also produced computer simulations of speech within the new room, enabling the team to hear the way the new room will sound when complete.
This approach, known as audible simulation or auralization, has been used to analyze a variety of room design options, and as the design progresses, new analysis and simulations are produced.
This first audible simulation is made using the room model shown above. The talker is an MP standing near the center of the bright yellow area in the STI map above. The listener is an MP seated in the opposite corner of the room, where the dark blue to black color confirms the STI value of just less than 0.70, corresponding to “good” intelligibility.
Audio file 1: Speech without Sound System. STI 0.68
(CLICK ON ABOVE LINK TO PLAY WAV FILE)
To increase the intelligibility to values above the 0.75 minimum design goal, we add the sound system, being designed by Engineering Harmonics, to our model. With the sound system operating, STI value are increased for the above talker/speaker pair to 0.85. Speech will sound like this:
Audio file 2: Speech with Sound System. STI 0.85
(CLICK ON ABOVE LINK TO PLAY WAV FILE)
While these examples clearly show the benefit of a speech reinforcement system in the Chamber, the design and client team were not satisifed with the extent of sound absorptive materials in the ceiling of the Chamber that were required to achieve the results of excellent intelligibility. An additional goal was expressed to reduce the total amount of sound absorptive materials in the room, to make the structure and skylight more visible and prominent.
Acoustic Distinctions therefore made changes to the model, strategically removing sound absorptive materials from specific ceiling locations, and reconfiguring the absorptive materials within the upper reaches of the structure supporting the roof. Computer models were again developed, and the resulting images showed that with careful design, excellent intelligibility would be achieved with reduced absorption.
Figure 5: Speech Transmission Index, single person speaking, with sound reinforcement
Talker at upper left; Listener at lower right
Bright pink to red color indicates excellent intelligibility
Not surprisingly, communicating this to the design team and House of Commons in a way that provided a high level of confidence in the results was required. We again used audible simulations to demonstrate the results:
Audio file 3: Speech with Sound System, reduced absorption. STI 0.82
(CLICK ON ABOVE LINK TO PLAY WAV FILE)
The rendering below shows the space configuration associated with the latest results:
ARCOP / FGM ARCHITECTS
Figure 6: Rendering, House of Commons, West Block, Parliament Hill
Proposed Design Configuration, showing sound absorptive panels
integrated into laylight and structure supporting roof
END OF PAPER
Audible Simulation in the Canadian Parliament The impact of auralization on design decisions for the House of Commons