Martin Audio MLA MINI, Руководство для продвинутых пользователей

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MLA Mini Display 2.2 V1.0
120
MLA MINI
DISPLAY 2.2
This shows a system that has been set up with the reference point in the centre of the audience
region and a start and finish delta of + and – 2dB respectively. Because the reference point is
central, the SPL drops evenly from start to finish, down 4dB from the loudest point at the start
of the coverage.
The next diagram shows a system where the front of house position is around three-quarters of
the way back from the front but the start and stop deltas are still at +/-2dB:
As you can see, the level drops gradually over three quarters of the venue back to front of house
and then drops rapidly back to the audience finish. Decidedly strange and in most (but not
necessarily all) circumstance, unwanted. To get the same smooth 4dB drop you should enter the
start delta as +3dB and the finish at -1dB. But that only works if front of house is exactly three
quarters of the way back! In the majority of cases you are far better of leaving the reference at
the halfway point to make it easier to easily calculate how the loudness contour will flow from
start to finish.
Of course they are many applications when it may be desirable to have the SPL rapidly drop
off behind the reference point, at outdoor events where noise pollution is an issue, the ability
to move the reference point to dictate the contour in front and behind it individually is another
very useful tool at the system technicians disposal to create the ideal coverage for difficult
environmental conditions.
The default setting is +/-3dB with the reference point in the centre, this is unquestionably a
very good place to start and works very well, unless you have a very large array or need to try
something slightly unusual it is advisable to stock with these settings.
As mentioned, setting the start and stop delta is simply a case of entering the required figure
in dB. As with entering hard avoid regions, it is prudent to be mindful of how hard your DSP is
going to have to work to achieve the results you have requested. With a huge array of 22 MLA
enclosures, it was possible to achieve a 0dB start/stop delta in the Tokyo Dome, the furthest
seat being around 550 feet from the array. It would however be very difficult to get such an
astonishing result from say an eight box MLA Mini array. The height of the array also has a
significant effect, a ground stacked system will not be able to achieve low figures for start and
stop as a flown array. In actual fact, a 0dB start/stop sounds very unnatural and because you are
used to hearing an array get louder as you get closer, you actually get the distinct impression
that it is getting quieter as you get closer to the array. The other issue is that multicellular
optimisation is only effective down to around 300Hz, low and sub frequencies will still behave as
you would expect reducing in SPL by 6dB for every doubling of distance. If the optimisation from
front to back is set to a target of as little as a few dB this will obviously differ drastically from
the behaviour of low frequencies meaning that the will be a very noticeable difference in tonal
balance across the audience coverage with the loss of low frequencies being very apparent as
you go towards the back as the mid and high frequencies hardly drop in level. It is recommended
therefore that unless you have specific reasons to do otherwise, that you use figures of +/-3dB.