4
are not even multiples (1:1.15:1.42, etc.)
will space the modes more evenly.
However, this technique alone is no
substitute for adequate amounts of
diffusion and absorption. In most
rooms, with enough absorption and/or
large and irregularly shaped objects,
the decay (Rt60) time or room character
can be effectively smoothed or
neutralized.
Some would advocate the use of
non parallel surfaces. However, it
should be pointed out that this
technique is not unlike the dimension
ratio technique. That is, it moves
modes around in the frequency
domain but does not decrease their
number. It is, however a much more
complex job to predict their locations.
As an element of diffusion and/or
reflection control, non parallel surfaces
along with adequate absorption can be
part of a total acoustical solution in
some applications. Be aware that as a
room is dampened, some discrete
echoes can develop if absorption
and/or diffusion is not applied in all
room axes i.e., floor/ceiling, side
wall/side wall, front/back, diagonals,
etc.
Westlake Audio offers, for a fee,
total acoustic design and consultation
for clients requiring a high degree of
acoustical performance.
THE LISTENER/SPEAKER/ROOM
INTERFACE:
We have already commented on
several aspects related to this LSR
relationship but here are some more
basics. Always place the speaker
system on a secure surface with front
board flush with adjoining vertical
surfaces. Place a thin rubber or felt
mat under the speaker to reduce
structure borne transmission. For more
bass move the speaker or listener or
both, closer to large objects or the room
boundaries (wall, floor, ceiling, etc.)
For less bass move the speakers and/or
listener towards the center of the room.
One particularly effective set up is to
place the listener near the wall at the
back of the room and position the
speakers 1/3 of the way into the room.
This places the listener at the rear wall
and thus puts the direct wave and the
rear wall reflection essentially in phase
at low frequencies. The listener is
sitting in a high pressure (low
frequency) area while the speakers are
located in an area of neutral or average
pressure. This allows the speakers to
be tuned to some degree, moving them
closer to the front wall will tilt them
towards a more bassy sound, moving
them towards room center will reduce
the bass but increase the direct field
over the room character. Moving the
speakers towards or away from the
side walls will have a similar effect
depending on how close they are in
relationship to the room size. When
the speakers are relatively close to the
listener is sometimes referred to as
near or close field monitoring, which is
often used in professional recording
studios. This type of configuration has
the advantage of presenting the direct
sound to the listener as quickly as
possible thus allowing the listener to
get an accurate assessment of the
sound field before the room field has a
chance to build up, possibly masking
details. It also allows the loudest peak
levels to be presented to the listener
while keeping the average room SPL
down. This eases the work the
speakers have to do and reduces the
neighbor interference factor.
It may also be beneficial to try
locating the listener and speakers on
the long wall of rectangular rooms.
This will put the side wall reflections
further away (in time) from the direct
signal and obviously promotes a closer
field experience. In very small rooms
however, this may preclude the afore-
