BSS 366T OmniDrive [57/112] Method

BSS 366T OmniDrive [57/112] Method
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FDS-366T
The Alignment Assistant is an advanced loudspeaker measurement function
built-in to the FDS-366T for directly measuring the delay and phase
relationships between drivers (using a measurement microphone), and
automatically adjusting the settings to accommodate these. The Alignment
Assistant has the ability to ‘see’ past the crossover filters, and is thus able to
compensate for the drivers and enclosures themselves, leaving the crossover to
do exactly what it was intended to do, and present a precisely aligned acoustic
wavefront. The Alignment Assistant can measure and compensate for:
Physical alignment of drivers within an enclosure
Driver or enclosure phase anomalies near the crossover point
Relative distance correction of arrayed boxes
Note that Alignment Assistant will not alter the phase response of the selected
crossover alignment. This will be preserved by the Phase Compensation
feature, dependent on the Phase Compensation Defeat setting in the Utilities.
Alignment Assistant uses a special stimulus signal that is sent to the outputs of
the FDS-366T during measurement. Each band output is stimulated in turn (via
the normal crossover filtering and equalisation). A measurement microphone
plugged into the C input of the FDS-366T picks up the stimulus reproduced by
the driver under test, and records the result for analysis. The special nature of
the stimulus signal allows not only the delay (distance) from driver to
microphone to be established, but also the impulse response of the driver/
enclosure, from which phase details can be calculated.
Once all the bands have been measured, the delay and phase results are stored
and used to determine the band delays to be applied to make the wavefront
from the system coherent between drivers and between cabinets. Various
options allow the measurement to be biased towards driver alignment within a
cabinet, cabinet alignment, polarity correction, or a combination of these.
The microphone must be placed far enough away from the loudspeakers so
that the vertical placement of drivers does not give rise to differential delays
which the listener will not normally be subjected to. It must be close enough
that a reasonable level of acoustic energy of the stimulus is achieved and
thereby ensuring that there is good signal-to-noise ratio. A good placement
would be a forward listener position.
If an array of two or more cabinets are to be aligned, then the microphone
should be placed centrally between the cabinets. If the drivers within a cabinet
are to be aligned then better signal-to-noise conditions will exist closer to the
cabinet. The microphone should then be optimally placed on the central axis
of the cabinet at a distance of perhaps 3 metres (10 feet) or so. Care should be
taken to place the microphone away from acoustically reflective surfaces such
as walls, pillars etc.
The microphone must be plugged into Input C. When the automated
measurement process is running, it is important that the microphone is not
moved. A microphone stand is highly recommended. Although the system is
quite tolerant of noise, It makes sense to keep the environment as quiet as
possible.
Microphone
placement and
connection
Method
6. Alignment
Assistant
Utilities - Alignment Assistant

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