The treble range emitted from a loudspeaker generally
heads straight towards the engineer's ears and the immediate surrounding
area, as if it was a flashlight pointed in the right direction.
The bass does not behave so directionally. The bass part of the
direct wave is quickly modified by the interaction of floor and
ceiling bounces with the air in front of the woofer. The ATTACK
Wall Baffle cleans up the frequency dependant acoustic impedance
mismatch that the woofer feels when it is supported midfield on
a monitor stand out in the open air of a room. An improved and more
accurate direct signal is delivered to the engineer when the speaker
is playing into smooth air, free from acoustic feedback. The next
section of studio design is to develop a reflection free zone for
the engineer to work inside of.
Typical "LEDE" Type ETC Signature
sketch illustrates the various elements involved in a loudspeaker
playing towards an engineer while both are alongside a wall. The
direct signal travels from the speaker to the engineer. The reflected
signal travels out, hits the wall and bounces towards the listener.
Sound waves are a 3 dimensional effect but here, only that part
of the wavefront that actually interacts with the listener is
being traced out. Note that the angle of incidence equals the
angle of reflection.
A speaker and engineer are set up
parallel to the sidewalls and perpendicular to the end walls.
Sound reflects off each sidewall and both end walls. The location
of the reflection point depends on the position of the wall. This
graph plots out the reflection points for any number of side and
end wall configurations. End wall reflection points start behind
the speaker and behind the listener and move back with the wall
position. The side reflection points are always halfway between
the speaker and listener on the surface of the sidewall.
If the speaker is off to the side,
then the direct signal does not take a parallel path to the sidewalls.
The reflection point is no longer at the halfway point on the
wall. For this more general case, the formula can be written so
that the location of the reflection point is known based on the
angle between the speaker axis and the room axis and the distance
the wall is from the speaker and the distance the listener is
from the speaker.
the angle between the speaker and the room axis is known the reflection
points for any side or end wall location can be calculated. When
the results are plotted out, the locus diagram results as shown.
A sample set of room walls is selected to illustrate where the
reflection points would be. The ray tracing between the speaker,
the wall reflection point and the listener is made to further
the reflection path. Note that the farther away the wall is located,
the closer the reflection point becomes to the halfway point between
the speaker and listener. There are no reflection points inside
the smallest imaginary room where the speaker and listener are
in opposite corners of the room. In this study, secondary reflections
are not considered but in a real room analysis, they also should
be included in the evaluation of early reflection points.
taking the single wall reflection diagram and flipping it over
we get the stereo reflection diagram. The graph is a general presentation
of all possible wall reflection points for the iso triangle arrangement
of speakers and listener typically found in the control room of
a 2.0 recording studio. An example room is outlined and the 8
reflection points identified. Then the path of each reflection
is traced, starting at a speaker, connecting at the intersection
of the wall and reflection locus of points and then straight to
the listener. There are 2 reflection points on each wall.