MIL-HDBK-1191
23.2.1.2
Flanking Transmission. Flanking sound paths are sound paths that
go from one space to another by secondary paths, not through the primary wall
or floor. Flanking paths can be through a corridor, laterally through a roof
or floor plane, and through gaps and cracks in construction. Figure 23.2 and
23.3 indicates transmission paths and some example construction options the
medical facility designer should consider when providing for various levels of
sound isolation for adjacent spaces.
23.2.1.3
Other terms.
Other terms pertinent to sound isolation review are
defined in appendix "E".
23.2.2
Constructions. This section describes different construction
types and explains how they can be evaluated for their ability to block sound.
23.2.2.1
Partitions. The medical facility designer should provide
partitions which meet the requirements found in appendix A. A large amount of
material is available from suppliers which provide examples of standard wall
assemblies and list the associated STC ratings. Typical single layer gypsum
partitions for steel framing (with wall boards staggered) normally can achieve
an STC rating of 40, however with the inclusion of glass fiber in the wall
cavity the STC ratings increase to around 47. Double layer gypsum partitions
have STC ratings ranging from 46 (without cavity bats) to around 53 (with
cavity bats), both having base layers vertical and face layers horizontal,
with joints staggered). All STC ratings are verified with an associated test
number.
a.
Acoustical Insulation: Lightweight porous fibrous insulation can
be a glass fiber or a mineral fiber batt. At least one side of
the insulation should be unfaced. The density of the insulation
should be around 24 to 64 kg per cubic meter (1 to 3 pounds per
cubic foot). Careful consideration should be given to limiting the
use of fibrous insulation in partitions where flexibility is a
concern; the insulation could hamper the ability of adding or
relocating plumbing, voice/data outlets or electrical outlets in
the future.
b.
Flanking transmission: The most common flanking paths at
partitions are the joints between the partition and the adjacent
floor, wall, and ceiling elements. To achieve the full sound
isolating capabilities of a partition, be sure details are
provided for continuous beads of sealant at the floor and ceiling
joints of the partition (Figures 23.1 and 23.3).
c.
Recessed services: Where service elements (e.g., electrical
outlets, telephone or data plugs ) are recessed into sound
isolating partitions, as will often occur, they should be backed
or encased with gypsum board, plaster, or other impervious
material equal to the surface weight of the partition. Designers
should provide appropriate details in design plans.
d.
Surface mounted equipment: Vibrating equipment (such as medical
instruments with electrical motors), should not be mounted on wall
surfaces adjacent to acoustically sensitive spaces.
23.2.2.2
Ceiling Systems. The medical facility designer shall take into
account that ceiling systems are critical factors in sound isolation when wall
constructions do not extend to the floor above. Sound isolation through an
average suspended mineral fiber acoustic tile is seldom greater than STC (or
CAC) 35 to 39. Glass fiber acoustic tile ceilings are far worse, with STC or
CAC ratings less than 25. Sound travels through the ceiling, into a common
23-2
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