Acoustic enhancement in the Aylesbury theatre with the CARMEN electroacoustic system

Transcription

1 Acoustic enhancement in the Aylesbury theatre with the CARMEN electroacoustic system Isabelle Schmich 1, Christophe Rougier 1, Helen Butcher 2, Delphine Devallez 3 1 Centre Scientifique et Technique du Bâtiment, 24 rue Joseph Fourier, Saint Martin d Hères, France 2 Arup Acoustics, Parkin House, 8 St Thomas Street, Winchester, SO23 9HE 3 48 avenue Victor Hugo, Boulogne Billancourt, France Abstract: The 1200 seat Aylesbury Waterside Theatre opened in October 2010 in the UK. The theatre needed to be flexible enough to accommodate events and performances from pop to classical music, as well as opera and drama. To host the different performances in the best acoustic conditions, it has been decided to design an acoustics adapted to amplified musi c (RT = 1,1 s at mid frequencies) and to install an acoustic enhancement system in order to adapt it for other music events. The CARMEN electroacoustic enhancement system, designed by CSTB, has been chosen and installed. This paper presents the design and results of the installation of the CARMEN system in the Aylesbury Waterside Theatre. It details the CARMEN electroacoustic design and explains the tuning and fine-tuning session with musicians. Detailed explanations are given for the use with orchestral music. Measurement results and the subjective evaluation with the feedback of acousticians and musicians are finally presented. Keywords: room acoustics enhancement, electroacoustics, tuning, subjective evaluation 1. Introduction The 1200 seat Aylesbury Waterside Theatre opened in October 2010 in the UK. It was designed by Arts Team of RWHL architects with acoustic design by Arup and needed to be flexible enough to accommodate events and performances from pop to classical music, as well as opera and drama. The CARMEN electroacoustic enhancement system 1 was chosen and installed to adapt the acoustics of the hall to the performance hosted. Based on the acoustics of the hall, the system is tuned to fit the final user demand. This paper presents the passive acoustic design for amplified music in the Aylesbury Waterside Theatre. It also presents the design and results of the installation of the CARMEN system and explains the tuning and fine-tuning session with musicians, especially for the orchestral music settings. A subjective evaluation of the system has been done including the feedback of acousticians and musicians which is analysed and presented in this paper. 2. Acoustic design of the hall The primary function of the theatre was to be a touring house, presenting musicals, pop concerts and light entertainment, all with use of amplified sound. The theatre s use for opera, ballet and classical concerts was of lower priority in terms of importance and frequency of events. The demands of a truly multi-purpose venue are acoustically challenging. Generally, halls when the natural acoustics of a hall is in priority aimed for classical music, the hall is built with a concert hall acoustic volume and 1

2 reverberance is reduced for other uses. In the Aylesbury Waterside Theatre the decision was made early on that the theatre would have a natural acoustics beneficial to amplified music, and the acoustics would be electronically enhanced for music events. Reverberance was designed to be about 1.1 s mid frequency unoccupied, with limited bass rise. This limited the volume of the room required (actual volume 8800 m 3 ), saving building height, overall cost and cost for physical variable elements. The seating is well upholstered and the upper levels have broadloom carpet throughout. Otherwise, wall finishes are plastered block or timber; the characteristic stacked timber providing a high degree of sound diffusion. A curved reflector over the 5.5 m deep forestage (or pit) provides physical support to the acoustics for the performers. Figure 1 View of the main volume from the stage, and orchestra set-up on forestage for the fine-tuning and subjective evaluation On completion of the auditorium, the objective room acoustic parameters were measured. With the safety curtain down, the mid frequency reverberation time unoccupied was 1.14 s (see Figure 6), rising to 1.39 s at 125 Hz. With the safety curtain up, the reverberation time increased to 1.4 s mid frequency and 2 s at 125 Hz. At the time only the house curtain and three sets of borders were hanging in the flytower. More sound absorption would normally be expected for any staged production. These results informed the final tuning of the CARMEN system. 3. Design of the electroacoustic system The electroacoustic enhancement system, totally separated from the house sound system, was installed to add reverberation to the hall as well as to provide early reflections and control balance and clarity of the acoustics. CARMEN is a regenerative system which is based on the virtual wall principle 1,2. The local reaction of the cells is achieved by placing a microphone close to the corresponding loudspeaker 3. The system in the Aylesbury Waterside Theatre has 28 cells, each composed of a microphone and a loudspeaker. The exact position of each cell in the theatre has been carefully designed through common study with the architectural team 4. Cells positioned on the lateral walls provide lateral energy and reverberation to the public and contribute to reinforce the listener envelopment. Cells in the ceiling above the audience provide late reverberation to the public and reinforce the reflections coming from the ceiling. Three cells on the movable forestage reflector contribute to give support to the performers on stage and in the orchestra pit, and to audience in the front stalls. Some cells are located under the 1 st and 2 nd balcony ceilings providing early reflections and reverberation to the audience below the balconies and to get a better coupling of these areas to the main volume. In addition, two directional forestage microphones situated approximately 10 m from the stage opening, hanging from the lighting bridge, are used to achieve voice reinforcement for speech drama and opera. It complements the function of the locally reacting cells. 2

3 The tuning of the following five presets was agreed with the client, the acoustician and the end-user: Table 1 List of the requested presets for the Aylesbury Theatre Preset n Use RT mid (s) Description 0 Conference, Amplified Music 1.1 System off 1 Speech Drama 1.1 Stage reinforcement for voices 2 Ballet (orchestra in the pit) 1.6 Homogeneous effect 3 Opera (orchestra in the pit) 1.7 Stage reinforcement for voices 4 Symphony 2.0 Homogeneous effect 5 Chorus 2.2 Homogeneous volume effect 4. Tuning of the system and fine-tuning with musicians for the symphony setting 4.1 Tuning of the electroacoustic system The tuning takes into account the microphone and loudspeaker exact positions in the auditorium and requires complete silence on stage and in the auditorium. Each step of the electroacoustic system tuning for the different settings is described in a previous paper 4. It leads to a stable system, tuned to fit the requirements of the acoustic brief and the final user. The sound sources commonly used for this tuning step are loudspeakers (MLS noise and anechoic music) as well as hand claps. Each preset tuning is done manually (with a semi-automatic part): no automatic tuning exists because the subjective listening of the CARMEN tuning experts to the effect of the system on the acoustic field is more precise than any existing measurable parameters. 4.2 Fine-tuning of the symphony setting Directly after the tuning sessions, a fine-tuning was done by using a real sound source on stage to finely adjust the already tuned parameters. The fine-tuning session was done with an amateur choir for the Chorus setting, and with a professional actor for the Speech Drama setting. This section focuses on the Symphony setting for which a fine-tuning session with professional musicians was done.. The used source should respect the width, frequency response, sound dynamics and all the other characteristics of real performers. For the Symphony setting, an orchestra was playing on the stage. The orchestra was small (30 musicians), but all symphonic instruments were represented (violins, viola, cello, double bass, oboe, flute, clarinet, bassoon, French horn, trumpet, trombones, percussion), see Figure 1. This ensured that the frequency spectrum produced in the theatre by a symphonic orchestra was representative during the fine-tuning session. Specific parts of the symphonic repertoire were repeatedly played by the orchestra to give the possibility to the listeners to compare the response of the hall for different types of sound source excitations. A non-exhaustive list of specific passages is given in the following: loud staccato or longer notes for the reverberation perception, fast music phrase for clarity, parts with cello and double bass for bass frequency response of the system, etc. The goal was to ensure with the system enough early reflections for a high quality intimate sound and at the same time to adjust the bass/treble balance in the hall. Careful listening to homogeneity of sound, frequency balance as well as the arrival times of direct sound and reflections resulted in a high quality setting. During thee fine-tuning session, the hall was empty except for a few listeners and the orchestra located on the forestage with the safety curtain closed to avoid the loss of sound energy into the stage tower. Indeed, no electroacoustic or traditional orchestra shell was designed in order not to clutter the stage house where complete flexibility was required to be able to host multi-purpose performances. 3

4 5. Subjective Personal data evaluation of the Symphony setting Which age group do you fit in? < > 65 Approximately how many music performances have you attended in the last tw elve m A subjective What type of music evaluation do you like and listen was to? done with a contractual symphonic listening chamber panel (5 opera people) poponce other the different settings were tuned. According to the listening panel If other, what feedback types?... some adjustments of the tuning Do you have hearing problems? yes no parameters been made. To assess the acoustics of the theatre, a psychoacoustic questionnaire (see Are you a musician/singer? yes no Figure 2) was distributed during the fine-tuning session of the CARMEN system for each settings. If you are a musician/singer, are you professional amateur General aspects Type of musical ensemble currently performing on stage Visibility of the performers is The comfort of the chair is The architecture and the decoration of the hall seem to you drama opera ballet orchestra choir very good good poor very poor don't know very good good poor very poor don't know very nice nice poor very poor don't know Detailed acoustic perception LOUDNESS (perceived amplification of the hall) loud moderate subdued quiet don't know CLARITY (perception of musical details) muddy blurred distinct clear don't know REVERBERANCE (persistence of the sounds) dry quite dry quite resonant resonant don't know ENVELOPMENT (sensation of being surrounded by sound) frontal quite frontal quite enveloping enveloping don't know INTIMACY (impression of being in a small enclosure) intimate close distant remote don't know BALANCE Treble dominant slightly dominant balanced w eak don't know Bass dominant slightly dominant balanced w eak don't know BACKGROUND NOISE inaudible acceptable tolerable intolerable don't know OVERALL IMPRESSION OF THE ACOUSTICS OF THE HALL very good good poor very poor don't know Only for performers How clearly do you hear your ow n instrument/voice back? clear distinct blurred muddy don't know How clearly do you distinguish the musicians/singers playing nearest your position? clear distinct blurred muddy don't know How comfortable are you w ith playing/singing in the group? very good good poor very poor don't know For all How loud do you hear the follow ing instruments? (w hen applicable) strings w eak strong don't know w oodw w eak strong don't know brass w eak strong don't know percuss w eak strong don't know How loud do you hear the different voices of the choir? (w hen applicable) soprano w eak strong don't know alto w eak strong don't know tenor w eak strong don't know bass w eak strong don't know How loud do you hear the soloist(s)? (w hen applicable) w eak strong don't know Final questions Figure 2 Extract from the psychoacoustic questionnaire distributed to the audience and to the musicians How do you appreciate the piece of music that is being performed? very good good bad very bad don't know When did you fill in this questionnaire? during performance during break after performance Comments and observations: The symphony setting offers the highest number of collected questionnaires: 17 musicians and 11 members of the audience. Members of the audience can be divided into three groups, according to their knowledge of music: naïve, amateur musicians, and professional musicians. An analysis of these three groups shows that members of the audience that are amateur or professional musicians/singers give similar judgments, therefore their answers are aggregated to get more significant results. The main acoustic descriptors are presented in the Figure 3 and 4. Figure 3 [Reverberance] / [Clarity] assessment results, cumulated number of answers. 4

5 Figure 4 [Intimacy] / [Overall impression of the acoustics] assessment results, cumulated number of answers. These acoustic descriptors received good scores. More precisely, the audience members, naive and musicians, experienced the hall more resonant and the sound clearer than musicians on stage (see Figure 3). The clarity is judged «blurred» by 5 people: 3 musicians on stage and 2 members of the audience. An analysis was carried out from answers given by musicians on stage, to assess the stage acoustics. The clarity of the musicians own instrument (Figure 5) is good for all musicians (only one violinist answered blurred ). Three musicians thought that there was a lack of clarity of close instruments (1 violinist, 1 cellist and 1 horn player). Only the cellist associated that lack of clarity with a poor comfort of playing in the group, but overall the Comfort of playing in the group is judged to be good. Figure 5 [Clarity on stage] / [Comfort playing in the group] assessment results, cumulated number of answers. Most of the time, the naive members of the audience rated the acoustical descriptors of the hall higher than the audience members with some musical knowledge of the audience and the performers on stage. This phenomenon was already observed in other studies 5. The contractual listening panel judged the sound to be natural and coming from the physical location of the source. Moreover, discussions with the conductors of the orchestra and choir provided feedback on the global ensemble sound impression, and discussions with musicians revealed a real fear of the impact of the electroacoustic system on their instrumental sound. This observation completes other ones made in previous works Measurement results Objective measurements were carried out once the different settings were tuned and the fine-tuning validated with the listening panel. The measurements of the room acoustic criteria in the unoccupied auditorium were carried out 4 with and without the system according to ISO Results for the Symphony setting are shown in Figure 6. The loudspeaker (Genelec 1031 AM speaker) was located in the centre of the stage at 3 m from the front edge, and a multi-directivity microphone (Sennheiser MKH80-P48) was positioned in 11 positions in the theatre. After request of the listening panel, the Symphony setting is finally slightly lower in RT (1.85 s mid frequencies, see Figure 6) than what was requested in the brief (2.0 s see Table 1) because reverberance and strength of the sound became out of proportion with the visual size of the auditorium. 5

6 Figure 6 Mean values without the system (blue) and for the Symphony setting (red) : RT30, EDT, Clarity, and SPL increase. 7. Conclusions The successful installation of an electroacoustic enhancement system in the Aylesbury Waterside Theatre allows its use for several types of performances with a dedicated acoustics for each one. The RT at mid frequencies varies from 1.1 s without the system to 1.9 s when it is used in the Symphony setting. This setting has been tuned and then fine-tuned with an orchestra composed of professionals playing on stage. This ensures that the electroacoustic is tuned for the real conditions use. In parallel, a subjective evaluation has been done with a psychoacoustic questionnaire. The effect of the system on acoustics is globally appreciated, even if some few musicians felt a lack of clarity on stage. Still most of them mainly appreciated a good clarity on stage with the system turned on. The discussions with the orchestra musicians revealed that some of them had a fear of such electroacoustic systems.. References and links 1 I. Schmich, J-P. Vian, CARMEN A physical approach for Room Acoustic Enhancement System, Proc. 7 th CFA /DAGA, Strasbourg (2004). 2 CARMEN commercial leaflets, > Products > CARMEN section (CSTB, 2008). 3 O. Vuichard, X. Meynial, On Microphone positioning in Electroacoustic Reverberation Enhancement Systems. Acustica 86, , (2000). 4 I. Schmich, H. Butcher, C. Rougier, The benefit of a CARMEN electroacoustic system in the Aylesbury theatre, Proc. Auditorium Acoustics, Dublin (2011). 5 N. B. Tamer, A Comparative Study of Four Concert Halls in Istanbul: Correlation of Subjective Evaluation with Objective Acoustic Parameters. Proc. Acoustics 08. Paris, France (2008). 6 I. Schmich, Musiciens, acousticiens et systèmes électroacoustiques Proc. 10 ème Congrès Français d Acoustique, Lyon, France (2010) 7 ISO Acoustics Measurement of room acoustic parameters: Performance spaces, International Organisation for Standardisation, Geneva (2009). 6