Flanking can significantly degrade carefully designed separations between studios and listening rooms. When a large conduit, duct, or plumbing pipe penetrates a sound-rated wall, as is often the case in TV studios, there can be significant sound transmission through the opening. Small openings can also make a significant difference and should be closed off.

Since there are large bundles of heavy wire in studios and since changes must be made to the cabling, a permanent seal is not possible. In permanent installations the opening is closed off with drywall and plastic pipe packed full depth with fiberglass or safing, and the cracks sealed with caulk on both sides. In flexible installations closed cell foam, fire stop compound, or other malleable materials can be used to seal the ends of a pipe. In some cases commercial isolation clamps are built into the common wall.

Where pipes, ducts, and conduits penetrate separated walls they must not form a bridge between the isolated structures. A structural break is required in these elements, particularly when studios utilize floating construction. Piping can be isolated using flexible no-hub connectors. Flexible conduit can be used and ductwork can include flexible connections.

Occasionally there are cases where a wire way is used to carry cabling between critical spaces. In these cases, it may be possible to fill the cavity with fiberglass batt or safing and

Figure 21.17 Separation Walls for Music Spaces to Provide a Given Noise Reduction between Adjacent Rooms (Klepper, Cavanaugh and Marshall, 1980)

Construction A - NIC 35

Figure 21.17 Separation Walls for Music Spaces to Provide a Given Noise Reduction between Adjacent Rooms (Klepper, Cavanaugh and Marshall, 1980)

Double layer drywall on resilient spring hangers

Double layer drywall on metal studs

Fiberglass in air space

3" (2OO mm; ASTM C145, normal weight grouted CMU (along corridor, b" - \50mm)

Concrete slab on unit Isolators (May be replaced with slab perimeter isolation joint on-grade if water table conditions permit;

Construction B - NIC 51

Remove drywall on one side. Replace floating slabs with two layers of 1 1/2" (33 mm) wood flooring on 2" (5O mm; thick b Ib/cu ft (lOO kg/cu m) pressed fiberglass board. This can usually be omitted when the slab is on grade.

Construction C - NIC 43

Remove drywall on both sides. Replace floating slabs with two layers of I 1/2" (33 mm; wood flooring on 2" (50 mm; thick b Ib/cu ft (lOO kg/cu m; pressed fiberglass board. This can usually be omitted when the slab is on grade.

cover it with a heavy lid that can be removed to access the wire. The object of any filler material is to block off the air passage between the two spaces or to provide a long path with a high attenuation.

HVAC Noise

HVAC units are a major source of noise in studios and listening rooms. For low-background levels flow-generated noise is particularly important to control. Terminal devices with adjustable dampers should be avoided. Volume control units should be located well upstream of the termination. Klepper et al. (1980) recommend that for an NC 20, dampers be located at least 15 ft (4.5 m) upstream; for an NC 35, the minimum distance is 5 ft (1.5 m). This assumes flexible duct or sheet metal duct with a minimum 1" (25 mm) liner between the device and the termination.

Both supplies and returns must be ducted. The final run to the terminal unit should be made with flexible duct that is not kinked or severely bent. Lining is required but may not be necessary for the entire length of the duct. The added duct area gained by removing duct liner near the terminal can be more important than the attenuation the liner provides. Silencers, preferably low-frequency traps, are almost always necessary near the mechanical units.

Packaged HVAC units, fan coils, and condensers should not be located directly above studios and sensitive listening rooms. In large studios and dubbing facilities this may require a separate structural support system for the equipment. In small studios it may be sufficient to locate fan coils over nonsensitive spaces such as bathrooms or closets with vibration isolation and silencers as required. Even when packaged rooftop units are remotely located there is still a possibility that low-frequency rumble can be transmitted into the roof via the ductwork. Duct runs, particularly those supported on lightweight roofs, should be vibration isolated. Even when there is a flexible connection between the ducts and the fan, low-frequency rumble in the air stream can be transmitted into the duct walls and down through the supports. Vibration isolators, having a deflection equal to that of the fan, are prudent for the first three points of support and half that thereafter. Detailed recommendations were discussed in Chapt. 11. Silencers placed at the roof penetration serve to counteract exterior noise breaking into the ducts from aircraft or other sources. Down shot units should be avoided unless there is sufficient room underneath to locate silencers and construct breakout enclosures.

Ductwork can transmit noise between rooms. HVAC ducts serving adjacent spaces must be routed so that they provide noise isolation equal to that of the other paths. Figure 21.18 gives an example of a duct layout for contiguous music practice rooms. The ducts here are assumed to be lined with 1" (25 mm) duct liner. In critical installations silencers also may be required between rooms.

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