d&b audiotechnik A1 Mainframe F-Series, Руководство пользователя

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(4.0E) 5-1
5. System operation
5.1. Setting up/stacking the loudspeakers
To get the best out of any high quality loudspeaker system it must
be properly set up. Care and attention needs to be paid to the po-
sition of the loudspeaker cabinets relative to each other and also
to how they are angled and aimed towards the audience.
5.1.1. Vertical coverage
The aiming of the loudspeaker in the vertical plane is responsible
for the coverage all the way from the stage to the furthest listening
point. Both the height and vertical angle of the loudspeakers need
careful adjustment.
Speaker stands, mounting brackets and rigging fittings can be used
to vary the height and angle of cabinets used on their own or as
part of a speaker array. F1220 cabinets can either be flown or fit-
ted with a swivel frame and placed on a stand. F2 cabinets can be
rigged and flown.
The lower the loudspeaker height, then the greater the sound level
difference between the audience area at the front of the stage and
the audience area at the extreme range of the loudspeaker co-
verage. To minimise the sound level difference between the stage
and the back of the room and ensure a more even level distributi-
on the loudspeakers need to be placed as high as possible - within
reason.
In relatively confined spaces there is a risk of aiming too much
energy towards the rear wall and ceiling of a room, increasing the
reverberant component of the sound in the room. In the worst ca-
se, bad speaker aiming can create a highly audible slap echo from
the rear wall of the room - slightly tilting the loudspeaker cabinets
down towards the audience can reduce and alleviate this problem.
5.1.2. Arraying mid/high cabinets
With more than one loudspeaker source in a room, comb filter ef-
fects can create coverage problems. An unavoidable problem with
multiple sound sources, comb filtering creates a regularly spaced,
uneven frequency response across a coverage area due to con-
structive and destructive interference between the sources. The ac-
tual character of the comb filtering which occurs is related to the
physical spacing of the sound sources. Minimising this effect requi-
res some experimentation - altering the distance between the cabi-
nets to try and minimise path length differences between the loud-
speakers and the listeners can help. Sometimes even small alterati-
ons to loudspeaker positions can have a dramatic effect on parti-
culary prominent combing frequencies. Fortunately, in real situati-
ons, the masking effects of room reflections, room absorbtion, and
absorbtion due to the presence of an audience, all help to conceal
combing related coverage problems.
A related problem due to interference effects can occur when clo-
sely arraying loudspeaker cabinets. Arrays need to be constructed
so that the coverage patterns of the individual loudspeakers com-
bine with minimal overlap. This problem has less to do with path di-