wood for concert hall acoustics springer

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30 Wood and Wood-Based Materials in Architectural Acoustics

3.3 Wood and the Acoustics of Concert Halls

There are many cases of the improvement of room acoustics when wood materialis used. Moreover, it has been recognized that the acoustical quality of rooms isa matter of subjective judgement. Even today, the design and construction of aconcert hall can be defined as «an art» in the classical meaning of the word, de-

spite the fact that scientific knowledge in this field is advanced (Muller 1986). Thesound field in a real room is very complicated and it is not open to exact math-ematical treatment. The large number of vibrational modes of the sound field aswell as the totality of possible data require the introduction of average functionsand of the statistical treatment of data.



Two points are relevant in the fundamental aspects of room acoustics: the gen-eration and the propagation of the sound in an enclosure, and the physiologicaland psychological factors that give the idea of «good or poor acoustics» of concerthalls, opera houses, lecture rooms, churches, restaurants, offices, etc. The first

aspect is related to the physical phenomenon of wave propagation and sound fielddescription. The second aspect is related to a subjective perception of sound bythe listeners.

A newly built room has several requirements:− The exact definition of the practical purpose of the room (concerts, drama and

opera, pop, jazz, rock concerts, sports events, etc.), which must be related tothe values of sound field parameters such as the reverberation time, the localor directional distribution of sound, and the limitation and peculiarities ofsubjective listening abilities.

− The architectural plan or design of the hall − the shape and the dimensions of

the hall, the position of the sound sources, the stage enclosure, the arrange-ment of audience and seats, the walls, the ceiling, the floor. The positions ofthese last elements are essential in keeping the frequency spectrum of the re-flected sound similar to that of the direct sound.

− The materials used for the construction. Wooden-plated panels in front of anair cushion are used for the absorption of low frequencies. Wooden plates actas resonators, whereas the basic resonance frequency is related to the massper square unit and to the stiffness of the air cushion behind. Wooden liningslead to a bright sound because of low-frequency absorption. Other systemssuch as Helmholtz resonators and thin gypsum plates can be used for this pur-

pose, with more or less success. The absorption of high frequencies in normalauditoria is caused by the audience (the effects of clothing fabrics, etc.) andthe volume of the air. It is interesting to note Beranek’s (1988) statement: «theabsorbing power of a seated audience, orchestra and chorus in a large hall formusic increases in proportion to the floor area occupied, nearly independentof the number of seated persons in those areas.» The acoustic quality of hallsis strongly dependent on the initial-time-delay gap (<20 ms) and is definedas «the difference in the time of arrival at a listener’s ear of the first of the re-flected waves and the direct sound wave.»

The subjective preference of the sound in concert halls is related to the psycho-acoustic parameters, as defined by Ando (1985): the preferred initial-time-delaygap, the preferred listening level, the preferred reverberation time subsequentto the arrival of early reflections, and the magnitude of the preferred measuredinteraural cross correlation. «As different music is performed in a hall, the totalpreference value changes according to the autocorrelation function of the music»(Ando 1985).

It is difficult to cite only one type of hall with excellent acoustics. Beranek(1992, 1996) points to four basic concert hall design types: the rectangular hall

(e.g., Musikvereinsaal, Vienna), the large fan-shaped hall (e.g., Tanglewood Shed,USA), the hall with a segmented nonsymmetrical audience arrangement of “vine- yard ”-type (e.g., Berlin’s Philharmonie Hall), and the hall with extensive use ofmultiple upper-side-wall reflectors in an oval-shaped hall (e.g., ChristchurchTown Hall, New Zealand). The oldest is the rectangular hall (or the “shoe box”).Examples of halls with very good acoustics built in the last century are the ViennaGrosser Musikvereinsaal and Boston Symphony Hall. Both are characterized by arectangular shape and by sound-diffusing interior surfaces on ceiling and walls.

Wood and the Acoustics of Concert Halls 31




The first large concert hall built after World War II in Europe (1951) was theRoyal Festival Hall in London, followed by very prestigious halls in Europe (Ber-liner Philarmonie − 1964, Beethoven Hall in Bonn − 1959, Barbican Concert Hallin London − 1982, Gasteig Philarmonie in Munchen − 1985, Opéra Bastille inParis − 1989, Teatro Carlo Felice in Genova − 1991, etc.). Around the same time,construction began in North America on the Avery Fisher Hall and Metropoli-tan Opera in New York, the Joseph Meyerhoff Symphony Hall in Baltimore, the

Orange Country Performing Arts Center in South California, the Meyerson Sym-phony Center in Dallas, Tanglewood Music Shed in Lenox, Massachusetts, theRoy Thompson Hall in Toronto, etc.), in South America on the Municipal Theatrein Lima, in Australia on the Sydney Opera House, and in Japan on the BunkaKaikan Hall in Tokyo, among others.

Several physical parameters can help in the judgement of concert hall acous-tics, such as:− whether there is a good connection between the orchestra, the musicians, and

the listeners;− whether there is sufficient reverberation time to give tonal quality to the mu-

sic;− whether there is a reasonable balance between strings, woodwinds, and per-

cussion in the orchestra;− whether there is sufficiently loud sound, without distortion, echoes, or unde-

sirable noise;− whether musicians are able to hear themselves and the other players.

Table 3.5. Musical qualities of concert and opera halls affected by acoustics. (Beranek 1996,with permission)

Musical factorsa Acoustical factors

Fullness of tone or its Reverberant time; ratio of loudness of direct sound to loudnessantithesis, clarity of reverberant sound; speed of music

Intimacy Short initia l time-delay gap (18th century music room) Medium initia l time-delay gap (19th century concert hall) Very long initia l time-delay gap (cathedral)

Spaciousness Difference in early sound at two ears at mid frequencies; soundlevel at lower frequencies

Timbre and tone color Richness of bass, treble; tonal distortion; texture; balance; blend,irregular surfaces in hall; focusing

Envelopment Difference in reverberant sound at the two ears

Ensemble Musicians’ ability to hear each other

Dynamic range Loudness of fortissimo; relation of background noise to loudnessof pianissimo

a Beranek (1996) defined the following terms: clarity is the degree to which discrete sounds in amusical performance start apart from one another; spaciousness has two components: (1) ap-parent source width − the music appears to the listener to emanate from a source wider thanthe visual width of the actual source; and (2) listener envelopment − a listener’s impression ofthe strength and direction from which the reverberant sound seems to arrive; intimacy is thedegree to which the music played gives the impression of being played in a small hall.



Beranek defined seven musical subjective factors that can be related to the acous-tical parameters which can be measured (see Table 3.5).

The acoustical response of a concert hall can be deduced from the correspond-ing “signature.” This occurs when excitation is produced with a loud impulsivesound, generated by pistol shots or, better, with an omnidirectional dodecaederloudspeaker system, giving pulses of 1 ms duration (Muller 1986).

ISO 3382-1975(E) “Measurement of reverberation time in auditoria” allows thecomparison of acoustical quality of different halls expressed by the reverberation

time. As defined by Morfey (2001), the reverberation time in rooms is the “timetaken for the energy in an initially-steady reverberant sound field to decay by60 dB.” The preferred range of reverberation time is from 0.6−0.8 s for elemen-tary classrooms and from 1.5−2.3 s for symphonic music.

Figure 3.6 shows the reverberation time versus frequency in several unoc-cupied famous halls (the Concertgebouw, Amsterdam; Symphony Hall, Boston;Metropolitan Opera House, New York; Teatro Alla Scala, Milan; Royal OperaHouse, London; Municipal Theatre of Lima, Lima). At 500 Hz the reverberation

Fig. 3.6. Reverberation time vs frequency in several concert halls. (Jimenez Carlos 1992, withpermission)





Table 3.6. Wood material used as an insulator in different European concert halls. (Data fromGade 1989, with permission)

Parameters Description of hall

Philharmonie Hall, Gasteig, Munich, Germany Function Symphonic concerts 85%, drama and opera 5%, rock, jazz,

pop concerts 5%, miscellaneous 5%

Inaugurated 1985

Geometrical data Volume 30,000 m3, platform area 300 m2, seating area 1,500 m2,seats number 2,387

Acoustical data Reverberation time 2.2 s unoccupied, 2.1 s occupied,1.95 s at mid frequencies

Ceiling Suspended convex and concave elements of 60-mm wood

Walls 38 mm veneered wood fiberboard in front of concrete;wooden reflectors on major sidewall areas

Floor Parquet on concrete, platform floor of 44-mm wood over air spacewith a very flexible hydraulic riser system supplemented with loosewooden riser elements

Chairs Fixed, wooden folding chairs with 8 cm upholstery on seat andbackrest; rear sides of backrests are made of plywood

Barbican Concert Hall, London, England

Function Symphonic concerts 86%, recitals and chamber music 10%, rock, jazz, pop concerts 10%, miscellaneous 20%

Inaugurated 1982

Geometrical data Volume 17,750 m3, platform area 200 m2, seating area 1,050 m2,seats number 2,026

Acoustical data Reverberation time 2.0 s unoccupied, 1.7 s occupied

Ceiling Concrete with exposed concrete beams and ventilation ducts

Walls Wood panels in front of concrete

Floor Parquet on hard surface; platform floor 22 mm parquet on 22 mmplywood and gypsum over air space; a wooden canopy is suspendedover the platform

Chairs Fixed wooden chairs with upholstered seats and backrests

Musikverein, Vienna, Austria

Function Symphonic concerts 75%, recitals and chamber music 25%

Inaugurated 1870

Geometrical data Volume 15,000 m3, platform area 125 m2, seating area 620 m2, seatsnumber 1,600

Acoustical data Reverberation time 3.2 s unoccupied, 2.1 s occupied

Ceiling Gilded and painted plaster on wood

Walls Plaster on brick, wooden doors, wooden paneling around platform,

balcony fronts are plaster on wood

Floor Linoleum on wood with carpet; platform floor is wood over air spacewith steep, fixed risers

Chairs Fixed wooden chairs with upholstered seats



time varies between 1.25 and 2.6 s. Timbre-related effects, recorded on the spec-trum of sound levels in three concert halls (Amsterdam, Boston, and Vienna),were largely commented on by Bradley (1991).

In all concert halls, wood was used as acoustic material in walls, ceiling, chairs,and floor (Gade 1989), as can be seen from Table 3.6.

Figure 3.7 presents the complex structure of the module of a coffered ceiling.Maximum absorption was obtained at 200 Hz. This maximum is probably due tothe mass of the plates and the stiffness of the air cushions; on the other hand, itmight be due to the resonance frequencies of the wooden elements. This type of

wooden structure shows the “favorable inf luence on acoustics of wooden panel-ing, wooden stages and vibrating wooden floors. The corresponding absorptionat low frequencies is a welcome complement to the medium- and high-frequencyabsorption of the audience” (Cremer et al. 1983).

Fig. 3.7. Absorption coefficient for a coffered ceiling, measured in a reverberant room. (Cre-mer and Muller 1982, with permission)





3.4 Summary

Wood and wood-based composites are basic building materials and acousticinsulators used for floors, ceilings, and walls, for the reduction of indoor and

outdoor noise. Indoor noise sources include automatic home appliances, suchas heating, air conditioning, and sanitary systems, entertainment devices, mu-sical instruments, conversations, floor-impact noise, the activity of adults andchildren, etc. Three-way sound transmission is possible: through the adjacentwall, the ceiling, and the floor. The acoustic capacities of a wall are expressed bytwo factors: noise reduction and transmission loss. Heavier materials providebetter sound isolation. According to the “mass law” for building materials, thetransmission loss increases by a factor of about 5 for each doubling of surfaceweight. The higher the sound transmission class rating, the more efficient theconstruction in reducing sound transmission. Outdoor noise can be reduced by

the windows. The attenuation of the windows can be improved using thick glassand proper joints, almost hermetically sealed.

Another very important field of utilization of wood and wood-based compos-ites as acoustical insulators is in the acoustics of concert halls, opera houses, lec-ture rooms, etc. The sound field in a room is very complicated and not open toprecise mathematical determination. Two points are relevant to the fundamentalaspects of room acoustics: the generation and propagation of the sound in an en-closure and the physiological and psychological factors that provide clues aboutgood or poor acoustics. Wooden-plated panels in front of an air cushion are usedfor absorbing low frequencies. Wooden plates act as resonators, wherein the basic

resonance frequency is related to the mass per square unit and to the stiffness ofthe air cushion behind. Wooden linings lead to a bright sound because of low-frequency absorption.

wood for concert hall acoustics springer

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