Country Home Products Wireless Microphone Systems - Manual (Page 46)

Occasionally it is found that certain wireless
microphone systems do not initially work well with certain
instruments. Symptoms may include poor frequency
response, distortion or noise. In most cases this can be
traced to an impedance or level mismatch between the
two. Frequency response changes are most often due
to impedance problems. Make sure that the
transmitter has sufficiently high input impedance.
Distortion is usually due to excessive input level to the
transmitter. Instruments with active circuitry (battery
powered preamps) often have very high output levels
which may need to be attenuated for some
transmitters. They may also suffer from RFI caused by
the wireless microphone system. This may reduced by
the addition of RF filters in the instrument.
A common type of noise that is heard in wireless
microphone systems is often called modulation noise.
This is a low-level hiss, which accompanies the actual
instrument sound. Though it is usually masked by the
instrument sound certain factors may make it more
pronounced. These include low audio signal levels,
low RF signal levels and high RF noise levels.
Modulation noise can be most noticeable when the
wireless microphone system is connected to a high
gain instrument amplifier with boosted high
frequencies and distortion circuits engaged. The
apparent level of modulation noise can be reduced by
setting the transmitter gain as high as possible (without
causing distortion), maintaining adequate RF signal
level and avoiding sources of RF noise.
Some electric guitars and basses used with wireless
microphone systems may also exhibit intermittent noise
when their control pots are moved to or from the endpoints
of their rotation (full-on or full-off). This is due to metal-to-
metal contact, which occurs at these points in certain
potentiometer designs. A different type of pot may need to
be substituted.
Microphones for acoustic instruments may be omni- or
unidirectional and are usually condenser types.
Microphone selection and placement for acoustic
instruments is a subjective process that may involve a
certain amount of trial and error. See the references in the
bibliography for suggestions.
It is advised to consult the manufacturer of the wireless
equipment and/or the manufacturer(s) of the instruments,
microphones and transducers if problems persist. They
may have details of suggested modifications for one or
both units.
One wireless benefit of interest to guitar players is the
elimination of the potential shock hazard created between a
wired electric guitar and a wired microphone. Once the
hardwire connection between either the guitar and amplifier
or between the microphone and the PA system is removed
the polarity of the
guitar amp is of no
consequence.
VOCALISTS
The usual
choice for vocal-
ists is a handheld
wireless micro-
phone system
for close pickup of
the singing voice.
It consists of a
suitable vocal
microphone
element attached
to a handheld transmitter used with a fixed receiver.
The microphone/transmitter may be handheld or
mounted on a microphone stand. Microphone
technique is essentially the same as for a wired
microphone: close placement gives the most
gain-before-feedback, the least ambient noise pickup
and the most proximity effect. An accessory pop filter
may be used if wind or breath blast is a problem. If the
transmitter is equipped with an external antenna avoid
placing the hand around it. If the transmitter has
externally accessible controls it may be useful to
conceal them with a sleeve or tape to avoid accidental
switching during a performance. Some transmitters
can be set to lock out the controls. Battery condition
should be checked prior to this if the indicator will be
covered. Transmitter gain should be adjusted for the
particular vocalist at performance levels.
The receiver should be located at a suitable
distance and in line of sight to the transmitter. Since
this is often at the mixer position, check for possible
interference from nearby digital signal processors.
Again antenna and audio connections should be
well-shielded and secure.
The primary considerations for sound quality in a
hand-held wireless microphone system is the
microphone element and its proper integration with the
transmitter. The choice of element for a wireless
microphone system would be made according to the
same criteria as for a wired microphone. Ideally the
wireless version of a microphone will sound identical to
the wired version. Ultimately this is up to the
manufacturer of the wireless microphone system. For
this reason it is highly recommended to compare the
performance of the proposed wireless microphone
system to its wired counterpart to make sure that any
differences in sound quality or directionality are minimal.
47
Selection
and Operation
of W
ireless Microphone Systems
C
H A P T E R
5
Application Notes