Sound And Light Training SALT Manual by Ken Ellis

5. Components of a Sound System - Sound Source

• Connecting Electronic Sound Sources


In order to connect an Electronic sound source to a sound system, you usually just "plug it in". That is, an Electronic sound source usually outputs an electronic signal suitable for direct connection to a sound system (the mixer).


• CD, Record, and Cassette Tape Players



• CD, record, and cassette tape players all have "RCA jacks" on them which can be used to connect them to the sound system. Some mixers also have RCA jacks for input, but many only have XLR and 1/4" jacks. In this case, an RCA to 1/4" adapter is needed.



• If you have enough channels on the mixer, you may connect the left and right signals from the CD, record, or cassette to two mixer channels. However, if channels are scarce or if the system is being run mono (rather than stereo), then you may use a Y-adapter to bring both signals into the same channel.



• If you are playing "Split-Track" performance tapes where the music is on one track (i.e. the right) and a rehersal version of the singing is on the other track (i.e. the left), then you MUST connect to two mixer channels in order to be able play just the music for the performance.



• If you try to connect a record player to a mixer, you should be aware that older record players put out a special signal called "Phono" which requires special equalization to make it sound normal. If your mixer does not have a "phono" input (and most don't), then you may need to make drastic changes to the tone controls (equalizer) to get the records to sound OK.






• Electronic Instruments - Keyboard, Electric Guitar, Electric Drums, etc.



• "Electronic" instruments such as guitars have a built in microphone or magnetic "Pickup". Keyboards output an electronic signal. These signals may be connected to a guitar or keyboard amplifier and/or the sound system mixer.



• If the distance between an electronic instrument and the mixer is much more than 25 feet, a "direct box" should be used to convert the un-balanced high impedance signal from the instrument into a balanced low impedance signal which can travel a longer distance (hundreds of feet) without picking up significant noise. The direct box has an input jack that accepts the 1/4" plug of a guitar cord and an output jack that accepts the XLR plug of a microphone cord.



• Usually, an electric guitar player and often a keyboard player will want to have their own guitar / keyboard amplifier. This serves two purposes: a) the musician can hear what they are playing better with a dedicated amplifier than they can through the monitor system and b) the musician may want to add special effects that are only available on the guitar / keyboard amplifier. If the guitar / keyboard amplifier is being used to add effects, then it a direct box cannot be used. In order to get the "sound" that the musician wants, you have to place a microphone in front ot the guitar / keyboard amplifier to pick up the sound of that instrument for the "House mix". Usually a desk mike stand (6") with a Goose neck (12") works best in this application. If the amplifier has treble and bass speakers, place the microphone half way between them. If it has several full range speakers, place the mike directly in front of one speaker.



• Another way to connect electronic instruments to the sound system is via an FM transmitter and receiver. This is most appropriate for guitar and horn players that want freedom of movement. The FM transmitter has a guitar cord which plugs into the instrument and the FM receiver has another guitar cord which plugs into the mixer.







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• Connecting Acoustic Sound Sources


To connect an Acoustic sound source to a sound system, you usually need to use a microphone to convert the "acoustic" sound into an "electronic signal".

Acoustic sound or "sound waves" are rapid minute variations in air pressure created by a person's voice or an acoustic instrument. A microphone is used to convert these sound waves into electrical signals suitable for input into a sound system.


• Voices - Talking or Singing


To get a person's voice into a sound system, you need a microphone. There are many different types of microphones which can be used depending on the particular situation.


• Wired / FM Microphones:



• Most microphones require a cord to carry the electrical sound signal from the microphone to the mixer.



• When the cord presents a problem such as a trip hazard or limits the movement of the performer, then an FM microphone should be used.



• FM microphones contain a small FM transmitter which sends a radio signal through the air to an FM radio receiver. The FM receiver is then connected to a mixer input.



• Placement of the FM radio receiver and its antenna(s) is very important. It should be close to the microphone (20 to 100 feet) and not near sources of electronic interference (i.e. CD player, effects processor, keyboard, or computers).



• You get what you pay for in FM microphones! The more expensive units are called "True Diversity". That means they have two antennas to receive the radio signal from the microphone. The purpose of two antennas is to minimize the multi-path cancellation effect. If one antenna is receiving the signal directly from the microphone and also receiving a reflection of the same signal (i.e. off a metal object), the two signals may be out of phase and cancel each other out, causing "drop-out". However, with a second antenna (properly located), it should not be receiving the same reflected signal and therefore its signal will not be canceled out (at the same time). The receiver automatically switches to whichever antenna is receiving the strongest signal.



• If several FM microphones are used at the same time, each must operate on a different radio frequency.



• The newest series of FM microphones are called UHF. This means they operate on a very high radio frequency around 900Mhz. Usually they will provide better performance than the VHF units.






• Unidirectional / Omnidirectional Microphones:



• Unidirectional (also called Directional or Cardoid) microphones "hear" or pick up much better from the front than they do from the sides or rear.



• Unidirectional microphones are usually best for sound reinforcement to prevent feedback (because they don't pick up much sound from the main or monitor speakers)



• Omnidirectional microphones hear or pick up sound from all directions equally.



• Omnidirectional microphones cause feedback easily.



• Omnidirectional microphones sometimes sound more natural for recording purposes.






• Laveler Microphones:



• A Laveler microphone is a small microphone which usually has a clip to attach it to the performer's clothing.



• Laveler microphones provide "hands-free" operation.



• FM Laveler microphones provide the greatest freedom of movement.



• Laveler microphones usually do not sound as natural as hand held mikes and are less desirable for singing.



• Depending on the clothing being worn, location of a Laveler mike is sometimes a problem. It needs to be located as high as possible and centered with the mike pointing straight up. The best location is clipped on a tie, just below the knot. If the performer is not wearing a tie or a buttoned shirt, it may be difficult to find a place to clip the mike.



• In theatrical performances, they often hide an FM Laveler mike in the performer's hair either over one ear or above the forehead.



• It looks better if you get the performer to wear the FM transmitter in a pocket or under their clothes and route the wire to the microphone through their clothes to minimize visibility of the microphone.






• Headset Microphones:



• Recently, Headset microphones have been gaining popularity. Many professional performers use a Headset microphone.



• A Headset microphone provides the "hands-free" operation of a Laveler with superior sound quality for singing and better feedback control.



• An FM Headset microphone provides the best sound quality along with "hands-free" operation for a singer.



• When combined with an FM Instrument pickup, an FM Headset mike gives a singer / instrument player complete freedom of movement.






• PZM Microphones:



• A PZM (Pressure Zone Microphones) looks like a flat metal plate with a small raised area containing the microphone element. It may be placed directly on a flat surface such as a floor or table top to pick up sounds from as far as 10-12 feet away. Sometimes, a shield is used to limit the sound pickup angle.



• Tonal quality of a PZM microphone may not be as good as other mikes, but they are useful when it is not practical to directly mike the performer.







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• Acoustic Instruments - Piano, Guitar, Horn, Drum, etc.


There are a great number of ways to mike acoustic instruments. Experiment to find out what works for you and the performer!


• Acoustic Guitars



• First, hope that the performer is using a guitar with a good quality built-in Pickup. This can be directly connected to the mixer. If the mixer is more than 25 feet away, a direct box should be used.



• If the guitar doesn't have a pickup (or has a pickup that doesn't sound very good), use a directional microphone on a boom mike stand. Place the mike as close to the opening in the guitar as possible without being so close that the performer will hit the mike when playing the guitar.



• Similar to electric guitars, an accoustic guitar can be used with an FM transmitter and receiver to connect it to the sound system and allow the performer freedom of motion.






• Horns



• A good quality Laveler microphone clipped onto the bell of the horn often works well (be careful not to scratch the metal of the horn or you will have a very angry performer on your hands!). An FM Laveler gives the performer freedom to move. Some Laveler style microphones come with a special clip for horns which is padded with felt so it doesn't scratch the horn. It also allows the microphone to face into the bell of the horn.



• A directional microphone on a straight, goose-neck, or boom mike stand can also be used.






• Pianos



• On a Grand Piano, the lid should be opened (probably on the short stick). An omnidirectional microphone on a boom stand can be positioned so that it hovers near the middle of the strings. Tonal quality can be changed by moving the mike towards lower or higher strings.



• An alternative is to use a PZM microphone attached to the inside of the Piano lid or possibly attached to the bottom. If you are in a hurry, you can even place a PZM on the floor under the piano.



• Since the wood of the Piano tends to direct sound from the speakers back to the microphone, feedback may be a problem.



• An upright Piano can be miked with a PZM inside the lid or a mike on a boom stand behind the Piano. Tonal quality varies greatly with mike placement.

• Phantom Power:



• Some microphones contain circuitry which requires power to make the microphone operate. Condensor microphones are one example. Some mixers provide "Phantom Power" for this purpose. Phantom Power is usually 9 to 48 VDC.



• If the mixer has Phantom Power, it usually has a switch to turn it on or off. Sometimes there is a switch for each channel and sometimes the switch applies Phantom Power to 4 or 8 channels at a time. Be sure the Phantom Power switch is turned off if you are not using microphones that need it. Try not to leave Phantom Power turned on to a mixer channel connected to a Dircet Box or to a microphone that has an On/Off switch - it may cause problems.






• Microphone Proximity Effect:



• Directional mikes always have a "proximity effect". When a person is in close proximity to the microphone (2" or less), there is a dramatic increase in the low frequency (bass) response.



• The proximity effect can be used to advantage by constantly staying close to the mike (less than 2") for a more POWERFUL sounding voice.



• Occasionally getting close for effect adds variety.



• When a large number of microphones are used for a singing group, the proximity effect is usually a disadvantage: Most of the time, singers are to far away from the mike (8" to 18") for the proximity effect, so the sound system is set up to sound best without the proximity effect. On solos, singers get in close (2" to 4") and the proximity effect makes them have too much "bass".



• When the system is set up primarily for people using mikes at distances > 8", then individuals should not get closer than 3" to prevent excessive bass.






• Miking Techniques:



• As mentioned above, the distance the sound source is from the microphone is very important. For singing and speaking, 2" to 4" is the optimum distance.



• Equally important to distance is the angle of the microphone. When using a hand held microphone, it should be positioned just below the mouth, even with the chin. The microphone should be held almost vertical with only a slight tilt toward the mouth. You should speak or sing across the top of the microphone. If you speak directly into the top of the microphone it will cause excessive breath noises and "P-popping".






• Mike Stands:


When a hand held mike or a laveler is not appropriate, then a mike stand is probably the best solution. Again, the proper choice of mike stands can make a big difference:


• Straight stand - usually suitable for a speaker or singer or a group of people.



• Boom stand - helps get the mike closer to a person playing a piano, keyboard, guitar or other instrument.



• Goose-neck stand - often useful to get a mike close to an acoustic instrument.



• Hanging mikes - sometimes the best way to mike a choir is to hang microphones above and in front of them.



• Podium - often a lecturn or podium has a goose neck microphone built in.






• Connecting Cords


It is important to understand the different types of cords that are used to make the connections between the various parts of a sound system. All cords used to connect inputs to a sound system or to connect the various parts of the sound system together MUST be shielded cable in order to prevent the system from picking up hum and noise. The only exception to this is the connection between the amplifier and the speakers which does NOT need to be shielded.

The cords used to connect sound sources to a mixer fall into one of two categories:


• Unbalanced



• The term "unbalanced" refers to a two conductor cord where one conductor is a grounded shield and the other conductor caries the sound signal. However, the sound signal must also return via the shield. The connection is referred to as "unbalanced" because one conductor is grounded and the other is not.



• Unbalanced cords may use RCA jacks, or 1/4" plugs.



• Unbalanced connections generally should not be used for distances much greater than about 25'. At greater distances, an unbalanced cord picks up too much electronic "hum" and noise. Although the shield protects the inner conductor from picking up hum and noise, since the sound signal must return via the shield, it is affected by the hum and noise picked up by the shield.






• Balanced



• The term "Balanced" refers to a three conductor cord where the outer conductor is a grounded shield and two inner conductors carry the sound signal. The connection is referred to as "balanced" because the two inner conductors that carry the sound signal are "balanced" at the same voltage level.



• Balanced cords can carry sound signals much further than unbalanced cords, typically several hundred feet. Balanced cords are not nearly as susceptable to picking up hum or noise because the sound signal only goes through the inner two conductors and never uses the shield. Therefore hum and noise picked up by the shield is simply grounded.