The recording engineer needs to work in a reflection
free zone in order to listen to the speakers without experiencing
distortion in musical tone or image position due to early reflections.
By knowing the path each early reflection takes and blocking it,
a reflection free zone can be created. Here, we take note of the
set of reflections that cause distortion in stereo mixing in any
sized room and arrange to block all of them with a simple gobo type
well-known stage in the evolution of a recording studio occurs after
all the electronic equipment is loaded into the room, set up, plugged
into power and each other. Like a race car before the shock absorbers
are installed, it starts and feels great, you can rev it up a few
times, but back it out of the driveway and take it out on the road
and you quickly find yourself dangerously loosing control. Hence,
the birth of studio acoustics.
first set of reflection points that need controlling are those that
cause flutter echoes. They are easily demonstrated as a low frequency
pseudo-tone caused when a high frequency clicks emitted by the speaker
bounces back and forth over the same path between parallel walls.
The engineer hears the sound emitted from these multiple reflections
even though the listening position is not directly in line with
the flutter paths. The ability for the sound to travel along a repeating
path must be eliminated from the control room.
before, the locus of all possible early reflection points can be
plotted out for any speaker/listener combination. By overlaying
the graph with wall positions, the exact location of the wall reflection
can be determined.
This demonstrates the path taken by that part of
a sound wave that hits a wall and then reflects back towards the
listener. Only the first half of the total path between the speaker/wall/listener
is shown. In order to eliminate a wall reflection it is necessary
to block the ray of sound that is traveling on the reflection path
between the speaker and the listener. One way to block the sound
path is to add sound absorption at the reflection point, a common
practice in recording studios and other high performance audio rooms.
However, it can also be done by blocking the path at any other location
along it's path.
arrangement of acoustic baffles is called the ATTACK Wall. It effectively
blocks all early reflection paths regardless of how close or far
any of the walls are located to the mixing set up. This same system
can be set up at either end or directly in the middle of any room
and not experience early reflections. It can be set up off axis
in a room with the distance to each wall being different and there
are no early reflections. The ATTACK Wall configuration of baffles
effectively blocks all possible paths that cause flutter echoes
or early reflections.
Here is seen what happens when 5 speakers are set
up in the official surround format, speakers at 0, 30 and 110 degrees.
A pattern of baffles can be developed that effectively blocks all
possible flutter paths and early reflection paths. At the mix position
there exists a reflection free zone for any sized rectangular room.
Likewise for any location within any room as long as the audio axis
is kept parallel to the room axis. The theory behind this design
scheme is perfectly general and can be applied to any playback configuration
with any orientation in any shaped room.
The acoustic signature of a recording studio requires
a clean direct signal followed by about 25 milliseconds of time
that is free from "early" reflections. The baffle/stand
system presented here has been shown to clean up and present a strong
direct signal in an early reflection free environment. This can
also be accomplished by simple covering all the walls, floor and
ceiling with deep sound absorbing materials, an anechoic chamber.
Although engineers could work well in such a space, they soon become
exhausted, the engineer has no late night endurance. People don't
like sensory depravation. Adding a diffusive tail, a time-delayed
backfill of incoherent sonic chaos finishes out the task of acoustic
design in any studio.