142 Chapter 6
part of the design criteria. There are a few general rules
that will help with the acoustics of these small rooms:
- Like the precision rooms, these rooms will work
better if the proportions of the room result in
optimal modal distribution. - Unlike the precision rooms, studios and vocal
booths often work best when they are not
symmetrical. - Avoid parallel surfaces if possible.
- Use treatment that is as linear as possible, both
statistically and by direct measurement of reflected
sound. - Avoid treating entire surfaces with a single form of
treatment. For example, covering an entire wall
with an absorber will usually be less effective than
treating some areas and leaving some alone. - Listen carefully to the kinds of words the end user
employs to describe the space either in terms of
what is desired or in terms of something that need
modification. Words like intimate, close, dark,
dead, quiet are usually associated with the use of
absorption. Words like open, live, bright, airy are
often used in conjunction with diffusion. - Placing absorption in the same plane as the micro-
phone will increase the apparent MFP and result in
a longer ITG (initial time gap). This often makes
the room seem larger. For example, in a vocal
booth that is normally used by standing talent,
place the absorption on the walls such that both the
talent and the microphone are in the same plane as
the absorptive area. In a conference room placing a
band of absorption around the room at seated head
height will help improve the ability to communi-
cate in the room.
6.9 Rooms for Entertainment
There was a serious temptation to call this section
“Rooms That Sound Good.” The temptation was
resisted to avoid the criticism that the section titles
would thus imply that precision rooms don’t sound
good. It is a matter of goals. As was pointed out, the
purpose of the precision room is analysis. This section
will cover rooms that are designed for entertainment.
Of course it is much more difficult to set out design
criteria for a good sounding room. As with any subjec-
tive goal it comes down to the tastes and preferences of
the end user. To a great extent how one approaches an
entertainment room depends on the type of system to be
used, and the type of entertainment envisioned. An
audiophile listening room will be treated differently
from a home theater. It should be noted that in the world
of home entertainment there exists a very rich audio
vocabulary. Some of the words that are used like
spaciousness and localization have meanings that are
consistent with the use of these words in the scientific
audio community. Subjective words like air, grain, defi-
nition, impact, and brittleness are much more ambig-
uous and are not yet mapped into the physical domain
so that we know how to control them. One of the chal-
lenges is when the end user wants two mutually exclu-
sive aspects optimized! The so-called Nippon-Gakki
experiments of 1979^24 quite elegantly showed how
different subjective effects can be created by simply
moving acoustic treatment to different locations in a
room, Fig. 6-19. Note that when localization is rated
good, spaciousness is rated poor and vice versa.
Some general points:- In home entertainment systems the distribution of
room modes is somewhat less important. Having
modal support in the low end although inaccurate
can result in rooms that sound fuller. This might
enhance a home theater system. - Absorption should be used sparingly. These rooms
should be quiet, not dead. If absorption is to be
used, it must be linear. - Remember that everything in a room contributes to
the acoustics of the room. Most home entertain-
ment rooms will have plush furniture that will be a
significant source of absorption. The furnishings
should be in place before the final treatment is
considered.
The furnishings should be in place before the final
treatment is considered.- Lateral reflections should be emphasized by using
critically placed diffusers. Lateral reflections can
dramatically increase the sense of spaciousness in a
room. - Absorptive ceilings tend to create a sense of inti-
macy and a feeling of being in a small space. If this
is not desired, use some absorption to control the
very early reflections but leave the rest live.