WHAT
IS IT?
The
SoundField ST250 is a very unique microphone that
applies the SoundField concept to "on location"
applications.
In its most basic form, it is a
mono and variable angle stereo Microphone with
remotely variable pick-up patterns plus the option
to deliver Mid/Side and B Format output formats.
The ST250 System consists of two parts that are
used together, a SoundField microphone and a miniaturized
DC powerable SoundField Processor. Sharing design
principles and sound character with the entire
SoundField family, it is the model most chosen
by engineers and hobbyists who record live concerts,
shows and documentaries.
WHAT
MAKES IT DIFFERENT?
The
SoundField microphone itself contains four capsules,
mounted in a tetrahedral array (tetrahedral describes
an equilateral triangle). This tetrahedral capsule
array, combined with the SoundField Processor/Preamp,
allows the ST250 to become different kinds of
microphones by varying individual capsule combinations.
It can be a conventional mono omni, cardioid,
hyper-cardioid, figure eight or anything in between.
It can be a stereo variable angle omni, stereo
cardioid, or stereo figure eight. It can also
be a complete Mid/Side system for those with sum/difference
matrix decoders. And it is the one and only portable
B Format microphone for use as a multi-channel
source with the upcoming SoundField 5.1 Decoder.
Or, when ST250 B Format recordings are played
back through a MKV Processor in Post Production,
you can alter microphone position within an existing
B Format recording to yield a final stereo or
mono output.
Perhaps
the key advantage of the SoundField system is
that unlike separate or even stereo microphones,
the error between capsules is resolved within
the SoundField Processor. This capsule error is
similar to the time arrival error experienced
by a listener offset between 2 or more spaced
loudspeakers.
The
benefit in resolving this error is significant
in that you can simply "point and shoot"
a SoundField microphone regardless of mode. SoundField
avoids lengthy set-up time typical of separate
microphones and there is no phase cancellation
when shifting between mono and stereo modes. Stereo
imaging is rock stable and absolutely breathtaking.
With multi-channel looming on the horizon, the
SoundField ST250's B Format is already delivering
an output that can be decoded into 5.1 and beyond.
In fact, the forthcoming SoundField SP451 Surround
Processor which is a dedicated B-Format to 5.1
surround converter will make the ST250 the only
5.1 location microphone on the market.
HOW
DOES IT WORK?
The
SoundField System relies upon B Format and its
processing at its core. The advantage of B Format
is that everything begins as a phase accurate
3 dimensional representation of an acoustical
event. Phase accurate means that all sound is
recorded from the same central "single"
point. This is the core difference between SoundField
and traditional stereo or multi-mike set-ups,
in that all other methods (other than a single
mono mike) capture audio from different points
in space. From SoundField's single "point
source", all three acoustical dimensions
are defined, not just two or one as in other microphone
set-ups. The 3 dimensions are: front to back (X),
left to right (Y) and up and down (Z). B Format
offers each of these 3 dimensions as an individual
output plus the point source reference called
W, across 4 channels. A complete three dimensional
graphical representation of B Format is shown
in the drawing to the right. The beauty of B Format
is that it through processing, any type of output
(omni, cardioid, hyper-cardioid or figure eight)
in any form (mono, stereo, or extra wide stereo)
can be derived. In addition, special output forms
such as mid/side and B Format are just a push
button away. This makes the SoundField the most
flexible microphone on the planet, and one that
offers a long future in a multi-channel world.
HOW
DO I USE IT?
SoundField
is used as a normal mono omni microphone in that
you just set it on a stand and go. Moving the
microphone around can vary the relationship between
ambient and direct sound, so some experimentation
with placement is likely. It can be pointed directly
at the source like a shotgun microphone (end fire
mode), hung upside down from a fishpole or boom
(invert mode), used in a "blimp" Rycote
Kit (for location or outdoor work) or set on a
stand like an ordinary mike. The Processor stays
with the user, connected via a supplied 5 metre
SoundField cable (longer lengths available), so
pattern and stereo angle (width) can be changed
and the result monitored with headphones.
The
ST250 can be powered in three ways: from 2 "C"
Batteries (installed inside the Processor), from
externally supplied phantom power (to the Processor),
or from AC mains power. All three modes yield
the same performance. The ST250 is designed to
operate at lower voltages for DC capability, so
you cannot plug an ST250 Mike into any other SoundField
Processor (SPS422 or MKV), nor can you use any
other SoundField Microphone (SPS422, MKV) on an
ST250 Processor. B Format recordings made with
a ST250 are compatible with the MKV Processor
for remixing.
ABOUT
THE FUTURE OF MULTI-CHANNEL AND MICROPHONES
The
future of multi-channel presents some serious
problems in microphone technique as documenting
a real event in 5 channels is not so easy. 5 microphones
at 5 different locations will present significant
capsule error, and will make such a recording
not compatible with mono or even stereo playback
or broadcast systems without significant post
work. The potential of SoundField microphones
to function equally well in multi-channel, stereo
and mono environments is a key advantage. Backward
compatibility is likely to be an important practical
issue as recordings may be distributed to the
International and rapidly evolving Domestic marketplace.
Because
SoundField starts with B Format as a phase accurate
3 dimensional representation, deriving multi-channel
is a matter of decoding only. Right now, most
SoundField multi-channel users apply analog matrix
devices for this purpose. Some use a console,
with advanced matrix options built-in. Some use
custom built analog matrix devices. Shortly you
will be able to purchase a dedicated SoundField
B Format to 5.1 Multi-channel Decoder from our
dealers to go with the ST250 and MKV SoundField
Systems.
SOUNDFIELD
ADVANTAGES
1)
Only a SoundField via B Format acts as a "single
point source", all but eliminating phase
error between capsules, making it backward compatible
down to stereo or mono without cancellations in
response.
2)
As a small "handheld size" integrated
multi-capsule microphone, it offers ease of handling
and mounting compared to traditional stereo mikes,
making recording a "point and shoot"
process.
3)
Variable Pattern control and stereo X/Y Angle
(width) controls are remotely located with the
user on the shoulder carried ST250 Processor,
4)
The B Format potential of the ST250 reaches beyond
the capabilities of all other stereo mikes to
recover and document 3 dimensional information
for use in future multi-channel playback environment.
ST250
ACCESSORIES
AND FEATURES
1)
The ST250 Microphone itself looks and sounds identical
to other SoundField microphones. However, it is
a different microphone than the SPS422 or MKV,
as it is designed to operate at a lower supply
voltage. The SoundField mike "head"
is larger than normal (to hold the 4 capsule array),
with a narrow handle and special 12 pin output
connector (to use with the supplied 5 Meter SoundField
6 pair cable). All 4 capsules are hand made and
fitted in the UK at SoundField Research LTD factory.
The microphone body has no switches or controls
on it, as all operational controls are located
on the SoundField ST250 Processor. Note that the
ST250 mike and ST250 Processor are not interchangeable
with other SoundField microphones and Processors.
2)
A Mic Clip, a standard plastic stand mounted mic
clip to hold the ST250 Microphone body to a conventional
mic stand, fish pole or boom. Many people opt
to purchase the optional Rycote Accessories, including
a blimp and woolly windscreen.
3)
A
5 Metre SoundField Cable is included (about 55
feet long) to connect the microphone to its 1U
processor. It is a flexible 6 pair cable, which
is a similar diameter to standard mic cable and
manufactured for SoundField by the Belden Cable
Co.
4)
A ST250 Portable Processor/Preamp accomplishes
all the math and matrix operations to make it
extremely easy to operate with virtually no training
or study. You do not need to have in-depth understanding
of B Format to successfully use the ST250 as XLR's
on the back supply a normal stereo (or mono) output.
The ST250 Processor is essentially microphone
preamplifiers (delivering a very hot mic level,
almost line level output), capsule compensation,
capsule [array] pattern control, stereo width
control (stereo X/Y angle) and a built-in headphone
monitor.
Specific
Features include:
a)
"Bass" switch, a 120Hz roll-off filter
for wind noise or low frequency control
b)
"Atten" (attenuation) switch, a 20 dB
input pad, for increasing maximum input from 115dB
SPL to 135dB SPL.
c)
"End" switch: Sets the processor to
operate the microphone when it is horizontally
"pointed" at a source, allowing the
pattern and stereo width controls to operate normally
from this mic position. This is important for
blimp mounted uses or handheld applications. Correct
microphone position in end fire mode is logo facing
down.
d)
"Invert" switch: Sets the processor
to operate the microphone when it is vertically
hung (head end pointed down, connector up). This
is important for fishpole or boom operation. Correct
invert position is logo facing out.
e)
"M/S" mode switch: This sets the ST250
to deliver 2 channel Mid/Side mode recordings.
Mid Side output requires a user provided "sum
and difference" matrix for decoding.
f)
"B" (Format) switch: This sets the ST250
to deliver unbalanced B Format when used in conjunction
with the optional ST250 B Format cable (Part number
NN2914). Basically, B Format offers 4 outputs
that are X, Y. Z, and W (an absolute pressure
reference). The purpose of B Format is the ability
to create a 3 dimensional sphere of audio originating
from a single point in space. The advantage of
B Format is that because all information is referenced
to a single point, all output modes (mono, stereo,
Mid /Side or B Format ) are phase consistent.
B Format also opens up multi-channel realms, where
custom matrixes can be built to pull off X/Y/Z
point specific information used in directionally
accurate multi-channel playback.
g)
"Battery" switch: switches power from
external AC or Phantom to Internal Battery power
using 2 ordinary C Cells user installed within
the ST250 Processor. Battery life is impossible
to predict as it varies with batteries, use and
signal level, but it is estimated at between 3
hours and 24 hours. Typical is 5 hours.
h)
Pattern Control: This control varies the polar
pattern of the entire array as a single point
stereo device, and is continuously variable from
Omni to Figure Eight. It is extremely useful in
tuning the "acceptance angle" of the
array. In figure eight mode, the microphone "sees"
more information from the front(direct information)
and the rear (ambient information), rejecting
information from the sides (direct and/or ambient).
In Cardioid mode, it is rejecting more information
from the rear. In Omni, it picks information equally
in all directions. This is helpful in deciding
what balance of direct vs. ambient information
is desired, and from what direction that ambient
information is gathered. It is also helpful in
operating the microphone (in mono) as a conventional
variable pattern condenser when close miking.
i)
Width Control: This control varies the stereo
image from zero (mono) to extra wide. It is perhaps
easier to envision the SPS422 as a stereo pair
that can be gradually decreased in angle to deliver
mono (0 degrees) or increased in angle to stereo
(90 degrees) or "wrap around stereo"
(180 degree). You'll love this control for the
creative options it opens up to you in close and
distant miking situations.
