Handbook for Sound Engineers

Acoustical Noise Control 83

The design of rooms to achieve maximum isolation
from airborne and structure-borne sounds is a highly
specialized undertaking, ordinarily entrusted to consul-
tants expert in that branch of acoustics. However, a
sound engineer, charged with the responsibility of
working with a consultant or doing the design person-
ally, is advised to become familiar with the sometimes
conflicting claims of suppliers and the literature on the
subject.

4.3.9 Acoustical Doors

Every part of an acoustical door is critical to its perfor-
mance. Special metal acoustical doors are available with
special cores, heavy hinges, including special sealing
and latching hardware. Their acoustical performance is
excellent and their higher cost must be evaluated against
high labor costs in constructing an alternative. There are
two design elements required in considering what kind
of door to utilize. There is the transmission loss of the
door itself and there is the sealing system. The sealing
system is the more critical of the two. Whatever system
is used, it must hold up over time and withstand the
wear and tear of use. Doors and their seals are difficult
to build and are often the weak point of a sound room.
There is good reason to design sound room access and
egress in such a way that excessively high performance
is not required of a single door. Use of a sound lock
corridor principle places two widely spaced doors in
series, relieving the acoustical requirements of each,
Fig. 4-31.

Homemade Acoustical Doors. An inexpensive door,
satisfactory for less demanding applications, can be
built from void-free plywood or high density particle

board. It is also possible to start with a core material of

particle board and laminate it with gypsum board if

sufficient care is taken to protect the fragile edges of the

gypsum board. Doors for acoustical isolation must have

a solid and void-free core and be as massive as prac-

tical. Most residential grade doors are hollow and

approach acoustical transparency. Some commercially

available solid core doors are made of laminated wood;

others, of particle board with composition board facing.

The latter has the greater surface density. The 5.2 lb/ft^2

of the particle-board type gives an STC value of about

35. An STC-35 does not do justice to, say, STC-55
    walls. Nevertheless, for doors separated as they are in
    the case of a sound lock, the TL of one door comes
    close to adding arithmetically to the loss of the other
    door. Two doors, well separated, approach doubling the
    effect of one.
    All this implies a perfect seal around the periphery of
    the door attained only by nailing the door shut and
    applying a generous bead of acoustical sealant on the
    crack. A practical operative door must utilize some
    form of weatherstripping or other means for its seal.
    Fig. 4-32 illustrates different approaches to sealing a
    door.^13 Many of these, especially the wiping type,
    require constant maintenance and frequent replace-
    ment. One of the more satisfactory types is the magnetic
    seal, similar to those on most household refrigerator
    doors. Zero International manufactures a system of door
    seals specifically designed for acoustical applications,
    Fig. 4-33. This type of commercially available acous-
    tical door seal is a good way to get results from a home-
    made door that approaches the performance of a
    proprietary door at a fraction of the cost.

Proprietary Acoustical Doors. By far the more satis-

factory doors for acoustical isolation in sound rooms are

those manufactured especially for the purpose. Such

doors offer measured and guaranteed performance over

the life of the door with only occasional adjustment of

seals. This is in stark contrast to the need for constant

seal maintenance in the homemade door shown in Fig.

4-32. Each manufacturer has its own strengths. Some

doors like the Overly and the IAC use cam lift hinges,

which actually lift the door as it opens.

Manufacturers of building elements that need to be

rated for sound transmission use ASTM standards in

measuring their products. ASTM e-90 is the appropriate

standard for sound transmission measurements. Copies

of the standards are available at http://www.ASTM.com. Most

manufacturers build a range of doors to suit specific

needs. IAC builds doors ranging from an STC-43 to an

impressive STC-64, Fig. 4-34.

Figure 4-31. Sound lock corridor.

Studio

Path 1

Path 3

Sound

lock

Path 2

Entrance hall

Control

room