Figure 21: Multipurpose auditoria and stage flexibility

Multipurpose Auditoriums:

As seen in the adjoining images, A multipurpose auditorium can be used in multiple ways just by changing the way function of the stage by using acoustical barriers/shells. For example, • An orchestra needs space for the choir to assemble. • For an opera or dance event, a wide proscenium is needed. • For a jazz performance, there should be a proper strip of standing area. • In the case of a drama event, the stage is reduced to a smaller area. • For conferences and talks, the stage is very small and a projection screen is installed. • For cinema, a screen and speakers are installed, again, making the stage smaller in size.

Figure 21: Multipurpose auditoria and stage flexibility

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7.2 Acoustics: Absorb, Block, and Cover

A balanced acoustic design absorbs, blocks, and covers (the ABCs of acoustics) sound. This can be achieved by employing sound masking technology and installing interior products with acoustic properties. 1. Absorb Sound The most direct way to address the control of unwanted noise within a space is to properly treat its shell (floor, ceiling, and walls). A room filled with hard finishes can cause echoes and reverberation sound and can make communication difficult. To eliminate these problems, products and systems with sound-absorbing characteristics should be carried out. These porous/fibrous sound-absorbing materials soak up sound waves by trapping them in an internal maze of air pockets.

Ceilings can absorb sound and they can control sound in other ways as well. They can also be used to deflect or distribute sound more evenly throughout a space. The NRC rating is between 0 and 1. To absorb more, the NRC rating should be higher. Certain materials are more noise absorbent - for instance, fiber glass has a high NRC. Ceilings should have closure/seal components to prevent sound leaks through return-air grills, lay-in light fixtures, sprinkler heads, and other utility penetrations.

Installation of carpets with cushioning has numerous advantages that includes the absorption of airborne sound and reduced footfall noise. Also, a carpet helps to create an aesthetic ambiance conducive to lowered voices, a heightened sense of privacy, and reduced distractions. Polyurethane cushion-backed carpet has a higher NRC rating when compared to bare concrete and

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conventional jute-backed carpet. Cut-pile (vs. loop pile) carpet with a permeable carpet backing laid over cushion has higher NRC ratings.

2. Block Sound Sound absorption is just one way to improve acoustics, blocking sound from spreading into adjacent areas is equally important. Both walls and carpet block sound transmission. The best sound absorption relies on lightweight, porous materials, the best sound-blocking materials (solid masonite, metal, or hardboard) are dense and heavy. With no air spaces for sound waves to slip into and through, panels containing these tightly packed interiors essentially cut off the direct path into adjacent spaces. These divider panels can be extremely effective at blocking and absorbing sound simultaneously. To be effective at both and provide non-intrusive levels of speech privacy, the panel should meet the following criteria • Panel heights should be a minimum of 60 inches; 72 inches is preferred. • The recommended NRC is 0.60. • A Sound Transmission Class (STC) rating between 18 and 20 is ideal. Panels should be high enough to block conversational noise from traveling over the top of partitions into adjacent spaces. The higher the panel, the sounder the blocking is. Sound-blocking benefits level off in panels that are 75 inches or higher.

3. Cover Sound Instead of eliminating noise, environments should have a mixture of noises than complete silence. Even the slightest of sounds will be heard, if there isn’t any ambient noise. After the interior shell is equipped with products that absorb and block sound,

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the final step is to cover the sound with masking technology. The sound masking system slightly raises the overall structure’s sound level, covering or dampening the sound of a typical conversation. The sound emitted by the masking system is similar to that produced by HVAC equipment – HVAC equipment emits sounds that are evenly distributed.

The system consists of a set of electronic components and speakers, and can be installed above a suspended ceiling system, pendant-mounted in areas with open ceilings, or placed under access flooring. Sound masking systems provide benefits in most indoor, non-industrial spaces. Once the system has been purchased and installed, it is tuned to a specific frequency. Tuning should take place after the space is fitted out, but before occupation. The best tuning capabilities will adjust the spectrum of the masking sound being emitted to the specific acoustical signature or physics of the individual room. Good acoustical performance requires a balanced approach of absorption, physical barriers, and sound masking.

7.3 Acoustic Materials

Barrier Materials

• Barriers must be nonporous—that is, they must block the passage of air through them. • They must have sufficient mass so that the sound traveling through the barrier is significantly less than the sound diffracting over or around the barrier. Barriers should be built of a material having a total surface mass density of at least 20 kg/sq. m • They must be weather resistant and properly designed to withstand wind and other structural loads appropriate for the location.

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