Figure 202 Balcony Design

Balconies

Angle underside of balcony upwards

Angle underside of balcony upwards

Fair leading edge to reduce reflections

Figure 20.3 Flying Balcony Design

balcony overhang is very deep, both direct and reverberant sound have difficulty penetrating. A sound system can augment the direct sound, using loudspeakers located on the underside of the balcony. A concave or semicircular-ceiling cavity under the balcony can help generate a localized reverberant field to offset the effect of a deep overhang.

In rare instances, halls have been built with a flying balcony, separated from the rear wall of the room as in Fig. 20.3. This allows the sound to flow around the upper balcony to reach the rearmost under-balcony seats. It is an expensive solution, since it presents structural challenges, even when beams support the balcony from the rear.

Ceiling Design

The ceiling of an auditorium or theater is more complicated than those found in a lecture hall. When auditoria are designed for speech, strong overhead reflections are preferred, whereas for music, a ceiling that diffuses the sound and aids in the sense of envelopment, or feeling surrounded by the sound, is best. A flat ceiling can yield excellent results for speech if it is not too high and if the floor rake is sufficient. In auditoria and lecture halls, particularly when the floor is flat or slightly raked, a shaped ceiling is helpful. This type can be designed by dividing the surface into angled planes or separately supported reflectors, so that there is an even distribution of reflected sound over the audience.

The surface above the proscenium arch is particularly important. Figure 20.4 shows an example. The first reflecting surface should be convex and horizontal at the proscenium wall. Such a shape aides in the reflection of sound to the seats in the center of the orchestra section, which is the most difficult to cover. It is also more forgiving of changes in the source position than a sharply slanted reflector. By controlling the curvature the clusters, loudspeakers can be nested above the reflector where the shielding helps control feedback. One or more rows of theatrical lighting must be accommodated, located at 45° and 55° from a downstage actor. Consequently there is a scramble for the ceiling space in the third of the ceiling closest to the proscenium, which must include passive acoustical reflectors, loudspeakers, catwalks, and theatrical lighting.

Figure 20.4 Design of Proscenium Reflectors

Figure 20.4 Design of Proscenium Reflectors

Procenium HeightArchitectural Reflecters

Ceiling reflectors can be flat or convex shaped but are not concave or coffered. Some designers prefer to use individual panels, or clouds, since they are more easily adjusted after installation, and are in some cases less expensive. When this type of ceiling system is used, the reflectors should be arranged along a single planar or curved surface so that interference patterns due to Bragg imaging do not occur. Reflectors should be large enough that the frequencies of interest are scattered more or less specularly. Using a group or array of reflecting panels can help offset this limitation and assure that low frequencies are also reflected (Leonard, Delsasso, and Knudsen, 1964). In Chapt. 7 we discussed the effects of reflector size on the frequency of the scattered sound. Where ceilings are very high or when there are ceilings at different heights, as is the case in some religious structures, the highest surfaces should be the first choice to receive absorptive treatment. These spaces sound best if the reverberation times are matched. Application of absorption to the whole area may not be required, but if some is treated the rest should maintain a consistent appearance whether treated or not. Where a highly diffuse ceiling is used, clarity is likely to suffer in the rear of the auditorium and in the balcony seats during unamplified use.

Audio Visual Considerations

As auditoria and religious structures become larger, they must rely on audio and video reinforcement systems to transmit the message to the audience. Floor layouts must accommodate sight lines, not only to the talker, but also to video screens and loudspeaker locations. If large loudspeakers are necessary to provide the directivity required for speech intelligibility, then the architectural real estate necessary to accommodate them must be included in the design. Loudspeakers should be arranged so that the source image is preserved, and frequently a central cluster above the proscenium is the best solution. When this does not match the visual expectation of the design team, enclosures can be incorporated to soften their visual impact.

If there are projected images in a theater, church, or lecture hall then the seating layout must accommodate the requirements of the screens. Figure 20.5 shows seating arrangements based on front and rear projection screens. The front row of seats should be no closer to the screen than one and one-half screen heights (1.5 H) or about one and one-eighth screen widths (1.125 D). The rearmost seat should be no more than 8H or 6D from the screen. In some cases screen sizes become very large and multiple screens must be used. This is particularly true in large fan-shaped churches where no single screen can be seen by the entire congregation.

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