3
1. Preamble –“Why build a 3 capsule microphone ?”
-Pfanzagl-
figure-of-eight capsule, which is added to the well known Blumlein-Pair of two figure-of-8
capsules, which have an included angle of 90° and are oriented at +/- 45° towards the sound
source. The new capsule is pointed directly towards the middle of the sound source at 0°.
Why add a third capsule at all, as the Blumlein-Pair already captures 360° ? The Blumlein-
Pair arrangement is appreciated by m
Dooley, 1985]), which is attributed also to the fact that the signals of the two channels are
largely decorrelated (meaning: very different) also at low frequencies, which is important for
good spatial impression. This is a unique feature which is almost exclusively reserved to
crossed figure-of- -
techniques), as all other microphone patterns (with hypercardioids as an exception) do not
provide similar signal-separation for low frequencies.
As a one-point recording technique with highly directional microphones the BPT-mic is
characterized by providing precise localization.
Tomlinson Holman described this behaviour, which can also be found with figure-of-eight
microphones, with the following words: -pair] aims the
microphones to the left and right of center; for practical microphones, the frequency
response at 45° off the axis may not be as flat as on axis, so centered sound may not be as
This is of course one of the main reasons why it makes very much (sonic) sense to add a
third figure-of-eight microphone or capsule to the -
of
the Center-capsule in relation to the L and R capsule.
For normal recording applications, the level of the center microphone will usually be set
between -6 dB to -3dB in relation to the L and R microphone.
Deviations of this are of course possible and for some applications it might make sense to
set it at -10dB or if it is necessary to emphasize the center of the sound-source it may be
set to 0dB or even more.
In order to shield off unwanted signals from the rear it is preferable to place an acoustic
barrier (for example in the form of a sound-absorptive acoustic panel) behind the BPT
microphone. This helps to achieve a better direct-/diffuse sound (i.e. direct signal /reverb)
ratio and enables the sound engineer to move the system further away from the sound-
source thereby usually achieving also a better balance between instruments (or instrumental
groups) in case of larger ensembles.
(Rem.: If the absorptive panel cannot be used for optical reasons, the three capsules of the
microphone can be switched to cardioid pattern and attenuate sound from the rear in this
manner. However if possible, the use of an absorptive panel is recommended, as this will
result in a much clearer sonic image achieved in the recording, since diffuse sound arriving
from the back is being eliminated more effectively)
