2 4
16.0
Phase Adjustment
One of the characteristics of the Linkwitz-Riley filter response is that at the
'corner' frequency between two adjacent bands the phase of the signal from
each band is the same. i.e. the two output signals are in phase. (Some small
departure from this occurs in band-pass outputs due to residual effects from the
opposite 'corner' frequencies).
In order to assist in obtaining accurate acoustical summation of the signals
from adjacent speaker units in a loudspeaker system, it is desirable to be able
to adjust the phase of the signal from one frequency band to that from the next
frequency band to properly allow for any phase errors that occur in the actual
loudspeakers and cabinets themselves. The three 'phase' controls on the
FDS-
360
are provided for this purpose.
It will be noticed that a small arrow associated with the graphics around this
phase control indicates which frequency band is being moved 'with' reference
to the other adjacent band, and that band four having no such control operates
as the starting reference.
In operation, phase alignment should commence at the highest frequency
band being used, and all other bands then adjusted in sequence down from
this band. Owing to residual effects as mentioned above, if after initial
adjustment some further re-adjustment is done on any band, then the lower
bands will need re-adjusting to compensate.
The polarity switch associated with each band can also be used to provide
further control range. If having rotated the phase control fully clockwise,
phase alignment is not achieved, then the polarity switch can be operated.
Returning the phase control to zero will then give the previous setting,
allowing a further 180 degrees of control. It should be remembered that this
phase adjustment is designed to assist in obtaining correct phase alignment
around the crossover frequencies of the speaker system, and is not the
equivalent of inserting digital delays into the frequency band. Should this be
required, then you should
refer to section 13.0
of the manual.
To assist in setting up the phase controls, a number of methods can be tried:
•
Using pink noise and a spectrum analyser will provide a pictorial view of
the acoustical energy around the crossover regions, and operation of the phase
controls should be made to give the flattest response.
•
Careful listening test to the speaker system whilst operating the phase
controls will provide another method of alignment.
•
Applying a sinewave signal at a frequency equal to each crossover point in
turn, through the speaker system will allow operation of the phase control to
achieve a minimum speaker level. i.e. a cancellation. Pressing the polarity
switch will then invert one of the outputs to achieve a true summation.
Phase Adjustment
Summary of Contents for FDS 360
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Page 51: ...51 User Notes...
Page 52: ...52 User Notes...
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