PRESONUS ULT-series, Owner'S Manual

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4 Loudspeaker Placement and System Configuration
4.1 Recognizing Problem Rooms
ULT-series
Owner’s Manual
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4.1.2 Wall and Corner Loading
Very low frequencies are not directional, so they radiate out of the sides
and back of the loudspeaker, as well as out of the front. If you place a
loudspeaker against a wall, the rear sound propagates back into the
room. This can increase output of bass frequencies as much as 6 dB,
and as much as 12 dB if you put the loudspeaker in a corner.
In order to have the most control over your sound, it’s best to always
start with the flattest response, so you normally should avoid wall and
corner placement. On the other hand, if you need some extra bass boost,
this technique may be worth a try. It is important to be aware of what’s
happening and be prepared to take advantage of it or compensate for it.
Power User Tip:
Because a floor monitor placed on the stage is
unavoidably subject to half-space loading, the Monitor Preset on your
ULT-series full-range loudspeaker is specifically designed to compensate
for bass buildup and maintain a tight mid-bass response.
4.1.3 Maintain a High Direct-to-Reverberant Ratio
Another way a room interacts with sound waves is through reflectivity. Like
most room anomalies, reflections can be good and bad. Consider the effect of
a cathedral’s reflections on a choir or a piano. This type of reverberation (reverb)
is quite desirable. But not all reverb is good reverb. Reflections can also cause
comb filtering. For example, if a speaker is placed near a reflective surface (such
as a concrete wall), the direct sound coming from the speaker and the reflected
sound coming from the wall can arrive at the listener’s ears out of phase with
each other, causing cancellation and reinforcement. If they’re 180 degrees
out of phase with respect to each other, they will cancel each other out.
If you are using your loudspeakers in a reverberant environment, position
them so that as much sound as possible is focused on the audience area and
steered away from reflective surfaces. ULT-series full-range loudspeakers have a
nominal 110-degree horizontal and 50-degree vertical coverage pattern. When
you do your placement and positioning, it’s a good idea take some time to do
a “walk around” of your loudspeakers, playing either pink noise or program
material, so you get a feel for how the sounds are translating into the room.
4.2 System configuration suggestions
The following subsections will demonstrate some system configurations for
common rooms. The size and shape of your room and the application for which
it will be used determine, to a large extent, how many speakers you will need
and where they should be placed. In every situation, keep in mind two important
design factors: your loudspeaker’s coverage pattern and half-space loading.
Both full-range ULT-series loudspeaker offers offer the same 110˚H x 50˚V coverage
pattern. Be sure to pay close attention to these angles when using your speakers.
Rotating the cabinet changes the horizontal and vertical coverage. Both full-range
ULT-series loudspeakers support rotating the horn if you would like to install them
in a horizontal orientation but still maintain the 110˚ x 50˚ dispersion pattern.
When configured for stereo use, make sure the cabinets are not placed
too wide for the room or too far back into the corners. Too wide of a
placement will direct too much energy onto the walls and can potentially
add destructive interference to the room. Adjust the left and right speakers,
as well as the toe-in angle, to produce the best stereo image. If a room is
very narrow, a mono cluster might be a better choice than stereo.
Wherever you place your loudspeakers, you should be aware of half-space
loading. Half-space loading occurs when a speaker comes in close contact with,
or touches, a hard surface like a floor or wall. As its name indicates, this type
of summation happens when the circular radiation of the speaker is blocked
by a hard surface and forced to radiate in a crescent shape. Depending on
the proximity and position, there may be a boost in low-frequency energy.