Townsend Labs Sphere L22 Precision Microphone System Guide
Off-Axis Correction
36
Setting the Controls
The Sphere plug-in’s Off-Axis Correction section has four controls and an enable button (See
Off-
Axis Correction
on page 21
for a complete description of its controls). When the enable button is
engaged, the Pattern control in this section overrides the mic model’s pattern, although the mic
model pattern controls continue to affect the on-axis frequency response.
Figure 5-4
Sphere plug-in
’
s
OFF-AXIS CORRECTION
controls
The
ON DIST
and
OFF DIST
controls specify the on- and off-axis distance, respectively, to the sound
sources. Let’s say you have two room mics that are 2 m from a kick drum that face directly away from
the kick. You might set the polar pattern to cardioid to minimize kick drum leakage into the room
mics. However, conventional cardioid mics typically have a lot of leakage, especially at low
frequencies, where the pattern moves towards omni or figure-8.
By enabling Off-Axis Correction (
IN
is on) and setting the corresponding
PATTERN
control to
cardioid, it is possible to have a much more accurate polar pattern. In this case, set
OFF DIST
to about
2 m. Set
ON DIST
to a larger value because most of the sound reaching the front of the mic will have
traveled further after reflecting off walls, ceiling, and floor.
The distance can be estimated by calculating the path length of the first reflection, although there is
usually no need to be exact. It normally works well to set the controls approximately and then dial them
in by ear. The actual distance value assumes the sound originates from an infinitely small sound source.
When the sound source is relatively large, you can think of the distance value as corresponding to the
average distance to the source.
For example, with a mic on a guitar cab’s grill, some sound is picked up from the center of the cone
and some from the edges. The average distance corresponds to a point somewhere in between. There
is no need to take measurements; just make an estimate and dial it in by ear. Typically, when
ON DIST
is set properly, enabling and disabling Off-Axis Correction results in a minimal change for on-axis
sources. Adjust
OFF DIST
until off-axis sounds have the highest amount of rejection. If in doubt, start
with these default settings:
ON DIST
= 20 cm; and
OFF DIST
= 1 m.
The
AUTO
button essentially disables Off-Axis Correction below about 1 kHz, so the response is
equal to the mic being modeled. Auto mode can be useful if there are multiple sources at different
distances or the sources are moving. We normally recommend leaving Auto mode off, but use the
setting that sounds best. With Auto mode on, both distance controls are disabled.
