Page 9 - ACCENT Aug 10
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ACCENT Special Edition - August 2010                                 9

Wireless microphones                                                                                             ü Primary
                                                                                                                 ü Secondary
A practical guide to choosing wisely                                                                             ü Tertiary

                          Shure SLX series                       all are analogue systems. This is important     Choosing your first system
                  (up to 12 systems per band)                    as digital radio transmission is not yet fast   Something often overlooked when purchasing
                                                                 enough for live sound and you would expe-       your first wireless system is what you may want to
Convenience and mobility are                                     rience latency or delay in the reception. You   do in the future. A single system is quite straight
the major advantages of wireless                                 may have noticed this effect with a digital     forward... say a true diversity, modest cost, hand
microphones. But there is a little                               TV if you have also had an older analogue       held system. But what if you might want to have
more to it than simply plugging in                               TV on the same channel. The digital TV is       more wireless mics in future, perhaps for a band,
and switching on.                                                slightly delayed. In a wireless mic system      jazz choir or theatre performance.
                                                                 this would make it impossible to talk flu-
Wireless microphones are in fact small FM                        ently or sing in time.                          This is when you will need to know what frequency
             radio stations. The microphone includes                                                             bands and channels your systems are using and,
             an FM transmitter and this signal is then                  Diversity ... and why                    more importnantly, how many simultaneous non-
received by an FM receiver that is usually plugged                        you might want it.                     interfering channels can your system use. For this
into a mixer or amplifier.                                                                                       reason it is highly recommended you consider this
                                                         Diversity is a common term in wireless mic              BEFORE you purchase that very first system.
Sounds simple, but like any radio transmission a         systems, but there is often confusion about its
wireless microphone can be subject to noise, inter-      meaning. At the simplest level it refers to a system    Lower cost systems often have up to 16 preset
ference or even dropouts of the signal.                  that has two antennas on the receiver to reduce         channels available, but only 4 of these systems may
                                                         dropouts. Dropouts are mostly caused by phase           work together. As the quality (and costs) increase,
Regardless of what type you choose or how much it        cancellations of reflecting signals (called multi-path  the number of simultaneous channels increases... a
costs there are some basic things you should do to       nulls). In theory, by having two antennas separated     measure of their greater radio tuning stability and
minimise the likelihood of any of these problems.        from each other, there would be less chance that        tighter bandwith tolerance of both transmitters and
                                                         both would dropout simultaneously.                      receivers.
   • Ensure you keep the distance between transmit-
     ter (mic) and receiver as short as practicable      In practice, simply having two antennas is not that     The more advanced systems also have a wider
                                                         much better than one.                                   range of accessories available for combining and
   • Whenever possible avoid any walls or obstruc-                                                               boosting antennas for the receivers and provid-
     tions between the transmitter and receiver          Passive Diversity - Very low cost systems usually       ing convenient power and mounting (usually rack
                                                         only have a single antenna. These are referred to as    mounts).
   • Use new batteries in the transmitter for any        “non-diversity” systems. Other low cost systems
     important occasion. Better quality systems          that have two antennas are typically labelled as        It should also be remembered that the quoted
     usually give an indication of typical battery life  “diversity” systems. But these are technically de-      maximum number of simultaneous systems in
     in the operating manual as well as a “low bat”      fined as “passive diversity”. Effectiveness against     manufacturers’ literature assumes ideal operating
     indicator on the transmitter.                       dropouts is modest but may be quite acceptable in       conditions. In practice this number may be lower.
                                                         static situations. However, if you are moving (with     Hence it is always recommended that you err on the
   • Make sure the transmitter and receiver are          your mic/transmitter), or other people or objects are   higher side.
     set to the same channel (someone may have           also moving about then dropouts are still likely.
     changed one). Some systems have automatic                                                                   And finally, when choosing multiple systems it
     channel setup, usually a “Sync” button on the       True Diversity - These systems are more costly but      pays to stick with a particular brand and series
     receiver.                                           substantially eliminate dropouts due to multi-paths.    (e.g. Shure PGX, SLX, ULX or Senneiser EW100,
                                                         These systems actually use two separate receivers       EW300, EW500).
   • Test the transmission with the mixer/amp vol-       internally with an antenna for each. The receivers
     ume turned down. When both the mic/transmit-        monitor the radio signal strength and seamlessly             For specific recommendations on
     ter and receiver are working there is usually       switch the audio to obtain the best signal at any        wireless mic systems to suit your needs
     an indicator light or meter on the receiver         point in time.
     (sometimes labelled signal or RF).                                                                                          call Music EDnet
                                                         System configurations                                                   Ph 1300 723 700
   • Turn on the mic (often there is a mic mute but-     Wireless microphones generally come in the same         
     ton that is separate from the power switch)         variety as wired mics, except that the mic must
                                                         contain or be attached to the transmitter.                    Sennheiser EW100 series
   • Turn up the mixer/amp and walk around the                                                                        (up to 12 systems per band)
     area where you will use the mic to test for         Hand held - the most common type, where the mic
     any blank spots or droput zones. If there are       and transmitter are a single unit. The better quality
     any, you may need to relocate the receiver (or      systems include popular good quality
     antenna), upgrade your antenna and/or upgrade       “capsules” such as Shure SM58, Sen-
     to a true diversity system (see below)              nheiser E835 and so on.

Of course this will all be routine after you have        Lapel or Lavalier - clip on mics
done it a couple of times.                               that plug in to a separate bodypack
Wireless System Basics
All wireless mics these days use FM radio trans-         Headset - mount on the head or over
mission and although many are digitally controlled,      the ears and the capsule is reasonably
                                                         close to the mouth. These are best perfo-
                                                         ming for hands free operation and are also
                                                         available in miniature, skin toned forms for
                                                         theatre productions. Plug in to a separate bodypack
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