L-Acoustics V-DOSC, Руководство оператора

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L-ACOUSTICS V-DOSC Manual Version 2.00 29/06/05 V-DOSC MANUAL V4 0605.doc 120/158
Ratchet Strap Adjustments
Before taking the system to trim, raise the array above the ground to tension the rear ratchet
straps (See Fig 95 w,x). Mounting a remote digital inclinometer on the top enclosure and using a
handheld digital inclinometer for the bottom enclosure is the most accurate technique for
matching the actual installation to the ARRAY 2004 or SOUNDVISION simulation. Essentially,
we want to adjust the ratchet straps so that the installed array has the correct top and bottom
enclosure site angles in order to obtain the correct overall vertical coverage angle (Cell P36 in
ARRAY 2004).
♦
With reference to the remote inclinometer readout, adjust front and rear motors to pre-tilt
the array so that the top enclosure is angled according to the calculated site angle (-1.5
degrees for the example in Figs 93 and 94). Pretilting is important so that ratchet straps are
tensioned while the array is in its’ final focus orientation and the centre of gravity for the
array is correct.
♦
Using a handheld inclinometer on the bottom enclosure, tension ratchet straps so that the
bottom enclosure site angle is equal to Site Angle #N as calculated in ARRAY 2004 or
SOUNDVISION where N= the number of enclosures (-28.65 degrees for the example in
Figs 93 and 94). This procedure will provide the correct vertical coverage angle for the
system (27.15 degrees for the example in Figs 93 and 94).
♦
When the system is flown to the actual trim height, Site Angle #1 will have to be readjusted
using the remote inclinometer readout or with reference to the top cabinet laser (see
below) since chain motors typically do not run at exactly the same speed if the relative load
distribution between them is different (i.e., if the system is pointing upwards or
downwards).
Note: DO NOT OVERTIGHTEN RATCHET STRAPS, especially if the array is tilted upwards. In
general, the goal is to simply take the slack out of the angle straps. Overtightening ratchet straps can
increase the angle between enclosures up to 1 additional degree per cabinet by closing the gap at the
rear of the enclosures (similar to what happens for a stacked system due to gravity).
Important things to note concerning the use of ratchet straps:
Tightly ratcheting flown arrays is not recommended for the following reasons:
♦
Tight ratcheting can increase the angle between flown enclosures up to an additional 1
degree (i.e., a 4 degree angle strap can produce 5 degrees, etc)
♦
This increase in angle can be non-constant vertically along the array and is difficult to predict
or control (typically the bottom enclosures are affected first)
♦
A 5.5 degree angle strap can be modified to a 6.5 degree value with tight ratcheting and
WST criteria will not be satisfied
♦
When ratchet straps are overtightened and the array is excessively tilted upwards, physical
damage can result to the flytrack and/or angle strap fittings
♦
L-ACOUSTICS has developed a spacer block to eliminate the need for use of ratchet straps,
(specifically for the case of arrays with upwards tilt)
Moderately ratcheting flown arrays IS recommended for the following reasons:
♦
Ratchet straps introduce a continuously variable ''tweak factor'' that allows for fine tuning of
coverage down front and greater angle strap resolution when used correctly in conjunction
with top and bottom inclinometers.
♦
When the array is pointing downwards, the centre of gravity shifts backwards and the top V-
DOSC enclosures tend to close naturally, forming a flat long throw section (this is desirable
for flat audience, open air festival situations). For larger 12-16 enclosure arrays, even though
0.75 degree angle straps are used for the first 6-8 enclosures, the actual obtained angles will