Section 4. SPECIAL DESIGN FACTORS
General Comments. The material in NAVFAC DM-1 is useful,
particularly with respect to acoustic isolation. However, there are some
issues in chapel design that make the judgment of an acoustic consultant who
has experience in places of worship particularly urgent, and the Contracting
Officer may require that such a consultant be engaged.
Room Acoustics. Large places of worship can be a difficult acoustic
problem because they must accommodate to both the reverberation period
desirable for speech and that desirable for music; the compromise must be
carefully resolved. In addition to the leaders of worship, members of the
assembly must be able to hear each other in speech and song, this presents
problems very different from those of other auditoriums. The practice of
building dry rooms and depending on loudspeakers to distribute sound is not
In rooms for assemblies of fewer than 500, it should be possible to avoid
the use of public address systems by proper design. This implies sufficient
volume overhead. together with proper shapes and surfaces. Overhead surfaces
should be generally reflective because absorptive surfaces inhibit musical
resonance and distribution. Hard floors are also valuable.
Cushioned seating, because it absorbs sound when vacant and none when a
person is present, tends to stabilize the reverberation time in a room, and is
Air and motor sounds in ventilating systems should be reduced
aggressively by duct lining, bends, sound traps and velocity control
to a Preferred Noise Criterion (PNC) of 20.
Isolation of Sound. Internal isolation problems focus on a few
spaces that need particular attention. One group is the rooms that serve for
the penitential rites or as counselling rooms, including chaplains' offices,
where the sound of conversation must not pass out of the room. Partitions must
be full height, sound traps may be required in ductwork, and sound seals at
doors. An STC of 50 is satisfactory. Places where musicians rehearse should
also be isolated by location or by control devices so as not to be disturbing;
an STC of 55 is appropriate. It should be possible, also, to isolate kitchen
noises from events in the social hall. A server between kitchen and
hall can be most helpful in this matter.