FBT MBT 8008 - Manual (Page 26)

UK
24
cardioid microphone polar pattern
panoramic microphone polar pattern
PUBLIC ADDRESS SYSTEMS
The aim of a public address system is the
communication of spoken announcements. The
broadcasting of music for entertainment purposes is,
when required, done at a low volume.
The above systems are mainly used in public venues,
such as shopping centres, railway stations, hospitals,
sports and cultural venues, in which even sound
distribution and the intelligibility of the messages
broadcast are a priority. In such installations, the
dislocation of single loudspeakers in relation to the
different frequencies is found to be of greater
importance that the high fidelity of the source in
relation to the music signal. There is however a
tendency to use higher quality components with a
more extensive frequency response. Attention should
be paid to the acoustic characteristics and the use of
the environment; these are the factors that will
determine the configuration of the entire project.
Stereophonic coding of the signal is not usually used,
given that the number of loudspeakers and their
position would not allow correct reproduction of the
stereophonic image.
An electrical sound system can perform different
types of functions:
- Amplification of sound: in churches, theatres,
conference rooms, etc.
- High-level diffusion: for addressing the public in
factories, the streets (in the case of assemblies),
distribution of sound and announcements in sporting
venues, communication frommoving vehicles.
- Low-level diffusion (background music): hotels,
offices, shops, supermarkets, waiting rooms.
- Mixed: with background music combined with the
possibility of public address functions, calls,
announcements, alarms, etc..
THEMICROPHONE
The microphone is a device that transforms the
variations in acoustic pressure into electric energy,
thereby allowing the transmission and amplification of
sound
. This conversion of energy operates on the basis of
inductive phenomena, in the case of ribbon
microphones, or capacity variation, as in the case of
condenser microphones. These two types account
for the large majority of professional microphones
used today.
The ribbon microphone is the most common, due to
its good quality and solid structure, that makes it
resistant to the effect of atmospheric humidity, and all-
round performance.
Due to its low voltage output, the condenser
microphone must be used in conjunction with a
preamplifier, which is usually incorporated into the
microphone itself, to lift the output signal and thereby
give an excellent degree of sensitivity. The condenser
microphone is powered either by a small battery
(usually incorporated) or (if prearranged) by the
amplifier by means of the same lines used for the
signal (phantom power).
The results are excellent, though are produced at a
high cost, which is why the condenser microphone is
almost exclusively used for high-level professional
applications.
In no case should microphones be oriented towards
the loudspeaker or its scattering zone, as this will
cause sound feedback. In the event of the latter, lower
amplifier volume, adjust the tone control, or if
necessary, install a graphic equaliser (or even better,
a parametric equaliser) to filter out the frequencies
causing feedback.
When connecting the microphone to the amplifier,
prefer short, twin-wire shielded lines. Microphone
lines should be kept at least 30-50 cm from
loudspeaker and other electrical equipment lines. If
these lines are particularly long (i.e. > 6/8 m), connect
the microphone to a balanced amplifier input to
eliminate the risk of interference (even with lines
dozens of metres long). In the case of longer
microphone lines, it will be necessary to use
microphone preamplifiers with balanced lines (in this
way, distances of over a kilometre can be covered).