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WHICH SPEAKER AND AMPLIFIER DO I NEED ?

The choice of speaker / amplifier depends on several factors;

  1. The location i.e. indoors / outdoors.
  2. The size of the area to be covered
  3. The use i.e. PA announcements, Disco, Live music or Theatre

SPEAKERS & IMPEDANCE

Most speakers currently available will be 16, 8 or 4 ohms; or 100Volt line

  • It is advisable only to use speakers of the same impedance to ensure correct operation
  • It is also important to match your speaker to the amplifier output.
  • Do not mix low impedance speakers with 100V line equipment.

Speakers come in a variety of types and styles,

  • The most common is a Full Range speaker using a cabinet combining a bass driver and horn using a passive crossover to give a good overall sound.
  • The next stage is a full range speaker incorporating a mid range driver these speakers are often preferred by vocal artists.
  • To compliment the Full range speaker a Bass cabinet is often used, this provides improved bass frequency response and is almost essential with modern Disco music.
  • The bass speaker can be added to the existing amplifier using a passive crossover
  • Or can use its own amplifier in this case an active crossover must be used.
  • High powered systems will usually use an active crossover sometimes called a system controller, at all times this ensures that the speakers are always working within their designed frequencies.
  • Failure to use the crossover will result in poor sound quality and may lead to damage or failure of the speakers.
  • Special application speakers are available i.e. :-
    • Stage monitors these are used to provide foldback to the performer and are usually wedge shaped or fitted with an angle mount.
    • Foldback monitors are usually full range and are supplied by a separate amplifier. Some may have an internal amplifier.
    • Outdoor speakers will be weatherproof
    • for long cable runs 100 Volt line systems will be used as this system has reduced losses
    • However it is best used only for announcements and background music.
Positioning the speakers will affect their performance, try not to position the speakers where the sound will be muffled be any obstruction.
Raising speakers on stands will improve the mid and top response while Bass speakers are best mounted at floor level.

AMPLIFIERS

Amplifiers are rated in Watts. Always use the RMS rating as this gives the true power.

N.B. some systems may be rated as Music power this can be 3 times higher and is an inaccurate measurement system

  • Power amplifiers should be selected to have an output close to the rated input of the speakers but not exceeding the rating. Ensure the speaker impedance is within the output range of the amplifier.
  • When connecting an amplifier always turn the gain controls to minimum to avoid a power surge which could damage the equipment.
  • Always connect the speakers and inputs before turning on the power.
  • Use the shortest cables possible from the amplifier to the speakers, use cables large enough for the output power i.e. 1.5mm cable as a minimum
  • When driving a load an amplifier will become hot it is important to ensure that the ventilation holes are not covered, also do not place the amplifier near to a heat source i.e. a radiator.
  • It is advisable to let the amplifier idle with no load for a few minutes to allow it to cool before switching off N.B. on larger fan cooled amplifiers let the fan do its work
  • If using the amplifier outside you must protect it from the weather by using a suitable enclosure with good ventilation.
  • It is preferred to operate an amplifier and speaker below its maximum to minimise distortion and to prolong the systems life.
  • When using multiple amplified systems always use an active crossover in the input line for maximum efficiency as passive crossovers will result in large system losses

WHICH MICROPHONE DO I USE ?

  • DYNAMIC MICROPHONE
        • This type of microphone creates its signal by moving a magnet relative to a coil.

  • CONDENSER (CAPACITOR ) MICROPHONE
        • This type of microphone creates its signal by moving two charged plates, A condenser microphone requires a power supply to opperate its internal pre-amplifier. The power may be supplied from an internal battery or from a phantom powered mixer

  • IMPEDANCE.
        • Two types of microphone are in common use;
          • Low impedance 200/600 ohms.
          • High impedance 50000 ohms.
        • Low impedance types are usually used as they are less affected by cable losses

  • UNBALANCED
        • An unbalanced signal uses only two conductors, One for the signal the other is a ground reference (screen)

  • BALANCED
        • A balanced signal need an overall screen but the signal is carried on two conductors working together in a push/pull arrangement. Any noise e.g.. hum that is induced in the conductors is summed in the input, these are out of phase with each other (opposites) and are equal so they cancel.

  • BALANCED INPUT
        • Balanced inputs use either a transformer or are electronically balanced (common mode rejection).

  • The best possible combination for theatre use i.e.. Long lines with excellent rejection of 'Thyristor Buzz' is Low impedance Balanced working.

WHAT IS A PICKUP PATTERN ?

With the exception of the OMNI(directional) microphone all microphones are more sensitive in some directions than others. In choosing which microphone to use start with a type that has the directional characteristics that suit the particular job you want it to do.

  • CARDIOID
        • Good rear rejection wide (high) frontal pickup
        • Float (front of stage) microphone.
        • not so good if you have to avoid picking up the orchestra
  • SUPER CARDIOD
        • Better at rear rejection, narrower frontal pickup.
        • Good Float (front of stage) microphone.
  • SHORT SHOTGUN
        • Excellent rear rejection, very narrow frontal pickup
        • Good overhead for up stage pickup
        • Useful for float microphones if you have enough to avoid gaps appearing between microphones
  • RIFLE
        • Very tight frontal pickup.
        • Use only if you can guarantee where the cast will be
        • i.e. exactly in the right spot every time - otherwise they won't be heard

WHAT IS A GOOD VOCAL MICROPHONE ?

  • No handling noise
  • a pop proof windshield
  • supercardioid
  • mechanically robust
  • and a presentable appearance
    are all qualities for a hand held Vocal microphone.
We recommend the SHURE SM58 as near ideal.

WHAT IS A GOOD FLOAT MICROPHONE ?

  • Rejection of orchestral noise
  • good sensitivity (especially in the upper frequencies)
  • and a reluctance to feedback are required here.
  • Condenser microphones are more effective.
  • You may find PZM (Pressure zone microphones) will work for you,
    they sit on the stage {beware of cast with big feet!}
    and need a good surface but can give astonishing results
    and are near invisible.

WHAT IS A GOOD FLY MICROPHONE ?

  • Here we need a microphone that is sensitive at longer distances
  • but not so directional that hot and cold spots appear.
  • The condenser short shotgun is the answer.

WHAT IS THE BEST MICROPHONE FOR OUR SHOW ?

  • There is no scientific way of answering this one.
  • Study your needs
  • study the microphone
  • ask other people with more experience (especially at your venue!)
  • THEN make a stab at it.
  • Listen carefully during the show so that next time you know what worked and what didn't
  • change things accordingly then repeat for every show.

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last modified: 1st July 2003