Acoustical Design and Materials for a Concert Halls

Acoustical Design and Materials for a Concert HallsPrepared by :Ayessa Ann DesaporadoPamela PenaroyoAlvin SabiagaIntroduction:The concert hall conveys orchestral sound to the listener through acoustic reflections from directions defined by the room geometry. When sound arrives from the sides of the head, binaural hearing emphasizes the same frequencies produced by higher orchestral-playing dynamics, thus enhancing perceived dynamic range. Many studies on room acoustics acknowledge the importance of such lateral reflections, but their contribution to the dynamic responsiveness of the hall has not yet been understood. Because dynamic expression is such a critical part of symphonic music, this phenomenon helps to explain the established success of shoebox-type concert halls.

In concert halls acoustic design there are two basic discipline:

Room AcousticsNoise control - whose needs and solutions are different, though they must often be achieved in the sane wall,floor, or ceiling detail. Sometimes the same materials are used for different reasons, and their material;s specification s are simply separated.Analysis:The responsiveness of a concert hall to dynamics can be traced to the interaction of three factors: the characteristics of the orchestra sound, the reflections provided by the room, and the directional sensitivity of hearing. In this article, the combined effect of these factors is quantified as binaural dynamic responsiveness (BDR). The hypothesis is that lateral early reflections, such as those that occur in historically successful shoebox halls and some modern designs, increase the halls responsiveness to orchestral dynamics due to the interaction between orchestral spectral excitation, spatial sound transmission, and emphasized high-frequency content in directional hearing.These elements correspond to the three elements of the transmission chain: source, the orchestra; path, the room; and receiver, a listener.Sound of the Orchestra. In the realm of dynamics, the orchestra sound involves crucial effects related to the harmonic structure of the sound. A natural effect with higher playing dynamics is the perceived intensification of the instrument sound. An important phenomenon is the nonlinear change in the overall spectral shape. For most orchestra instruments, more higher harmonics are excited with a more forceful playing style.

The Effect of Lateral Reflections. In modern times, performance venues are often designed to replicate the sound quality of the famed classic halls, but are also subject to demands for larger audiences and alternative seating configurations. Larger audiences preclude copying the small spaces where classical music originated, structural technology allows larger and more flexible spaces than before, and new hall typologies, such as the vineyard-style hall, offer an enhanced social experience

The Effect of Lateral Reflections. In modern times, performance venues are often designed to replicate the sound quality of the famed classic halls, but are also subject to demands for larger audiences and alternative seating configurations. Larger audiences preclude copying the small spaces where classical music originated, structural technology allows larger and more flexible spaces than before, and new hall typologies, such as the vineyard-style hall, offer an enhanced social experience.

Directional Binaural Loudness. It is a well-known effect that shading from the head, shapes of the pinnae, and reflections from the listeners body cause alterations in the frequency content entering the ear canals, depending on the direction of the incident sound. The direction-dependent filter created by these effects is known as the head-related transfer function (HRTF).

One discipline is the design of the auditorium itself; the volume, shaping, finishes, and furnishings necessary to achieve the best acoustical environment for the natural (unamplified) sounds of musical instruments. This discipline is called room acoustics.For a Concert Hall, good acoustics involves: - good distribution of sounds to all the seats, which depends on proper shaping and finishes of all interior surfaces.Natural sound diffusion and envelopmentA sense of intimacy for the audience and a sense of ensemble for both musicians and audience- Proper reverberation times throughout all frequencies, which depend on the rooms volume and the total sound absorption of all materials

Freedom from acoustical faults of echoes, flutter, and fucosFreedom from disturbing noises Surface Materials and Constructions:

To achieve the designed acoustical objects and considering the decoration effects, the materials and constructions for the surfaces of the concert hall are assigned as follows:

(1) Side walls of stage and oblique parts of side walls of auditorium: 25mm wood planks (or 2 layers 12mm fiber reinforced gypsum boards covered with wood skin) decorated with MLS construction.(2)Parallel parts of side walls of auditorium: 25mm wood planks (or 2 layers 12mm fiber reinforced gypsum boards) designed as column form to diffuse sound waves.(3)Rear wall of auditorium: QRD diffusers made of wood. Absorptive curtain with a density of 750 g/m2 is hung in front of the rear wall to change RT value and eliminate echo when holding conference evens.(4)Rear wall of stage: Diffusers shaped like pyramid is designed in the back wall of the stage. The moveable partition is build with wood planks. The two sides of the partition are reflective or absorptive respectively. The absorptive surface is covered with absorbent having noise reduction coefficiency larger than 0.5. When holding conference, the absorptive side will appear.(5)Ceiling: The ceiling is made of fibre reinforced gypsum boards with density large than 40kg/.(6)Floor of auditorium: Wood planks adhered to the floor slabs.(7)Floor of stage: Wood planks built on stilts.Sound Insulation and Noise Control To achieve the requirement for the background noise level of the hall, sound insulation and noise control have to be carefully considered:

- The surrounding walls of the hall consist of two layers made of light concrete blocks. In the gap between the two layers wall, air-conditioning tubes are placed. To increase the sound insulation ability of the surrounding structures, fiber reinforced gypsum boards backed rook wool sheets are added on the inner layer. The partitions on stage are made of reinforced concrete. The doors of the hall consist of sound locks with two door panels. Their sound insulation index each must be not lower 30dB.

- Noise control methods include choosing lower noise level ventilator, using flexible pipes to connect the vibrating equipment, setting absorptive materials inside the ducts and isolators to support the packaged air-conditioning system and so on.AcousticalMaterials

Reverberation Conditions:The most important and well-known element of natural acoustics is reverberation. There are three General reverberation conditions that most commonly occur:

a relatively short reverberation that allows clearly intelligible speech but which tends to frustrate and repress music and congregational response .

a medium or compromise reverberation that serves all types of speech and music acceptably but usually serves none exceptionally .

a long reverberation that imparts a glorious and resounding character for spoken and sung responses of the assembly, pipe organ and traditional choir yet, if excessive, can render speech virtually incomprehensible and reduce contemporary and folk music groups to muddled noise.

Natural AcousticThe following factors are recommended in providing appropriate natural acoustics in the architectural and acoustical design:

- Provide a reverberation period of at least 2 to 3 seconds.

- Minimize the amount of sound absorbing materials. In all cases, sound absorbing materials must not be located near the important sources of sound: the assembly, the music. Since all of these sound sources are at floor level, floors cannot be carpeted and pews cannot be covered with upholstery or cushions.

- Provide properly oriented, hard-surfaced materials around sound sources. All surfaces (including floors, walls, and ceilings) near and around, musicians, and the assembly must have hard surfaces.

- Avoid or minimize the use of lightweight surface materials such as gypsum board or thin wood panels. If wood paneling is desired, and if it occupies a large area, it should be attached directly over solid, massive structural materials. Do not use suspended acoustical ceilings.

Music:Benches or chairs for the seating of those engaged in the ministry of music, instrumental or choral, should be so constructed and arranged that they have the advantages described for congregational seating and also that they are clearly part of the assembly. Yet, the music should be able to sing and play facing the rest of the audience.Sound IsolationSound isolation involves the acoustical insulating properties of building elements (walls, doors, etc.) to minimize sound transmission between rooms and other areas.Sound isolation must be provided for all spaces within the building where silence, privacy, solemnity, and confidentiality are required for the special needsSound Reinforcement: The most important function of a sound reinforcement system is to provide excellent speech intelligibility. It must do this within the reverberant environment needed to support the audience and music in a concert hall. Care must be taken in the design and use of sound systems so that the audience voice is not overpowered or made less significant by amplified sounds.The preferred loudspeaker design is a central cluster. This may be composed of several loudspeaker horns assembled into a single array or of several cabinets that house the necessary components. One major advantage of the central cluster design is directional realism: the audible impression that sound is coming from the talker rather than from the loudspeaker. There are other loudspeaker configurations that may be appropriate under certain conditions, but these must be evaluated on a case-by-case basis.

- Traditional music (vocal and instrumental) should require no amplification. The naturalacoustics of the concert hall should be adequate to support voices and traditional instruments. It may be necessary in some cases to provide supplemental electronic support or enhancement for small bands, but this should be done with great care to preserve the purity of natural vocal sounds and to prevent overpowering the audiences.

Now you learned something?Thanks :DThe End