What do I need?
A basic sound system
A sound reinforcement system and a recording setup have two major components in common, microphones and mixers. Microphones are used to capture the sound, and the mixer is used to combine those signals together. The output of the mixer, instead of feeding a recording device, is connected to a power amplifier, which boosts the signal to "speaker" level. One or more loudspeakers are connected to the outputs of the amplifier. At this point the signal is converted from the electrical domain back to the variations in air pressure we recognize as sound, albeit at a much higher level.
Signal processors are devices, usually connected between the mixer and power amplifier, used to enhance the signal or fix problems with the sound. The most common types of signal processors are equalizers, effects processors, and compressors. An equalizer is basically an extremely selective set of tone controls that allow you to boost or cut specific frequencies. Typical applications for equalizers are tone shaping and feedback control. Effects processors are used to create special sound effects, such as reverb (sounds like a big, reverberant room) and delay (echo), among others. Compressors control varying signal levels. A loud signal that passes above the compressor's threshold is reduced (or compressed) by a given amount. A compressor can also help prevent distortion or damage to the loudspeakers. Of the processors listed above, the equalizer is the most useful in just about any sound reinforcement application.
Many of the same microphone rules used in recording apply equally as well for live sound reinforcement.
A major difference between microphone placement in live sound versus recording is proximity to the sound source. The goal in sound reinforcement is to get the microphone as close as possible to the sound source for two reasons:
- Primarily, placing all microphones as close as possible achieves maximum sound level before feedback occurs.
- Secondly, close-miking improves isolation of the desired sound source and reduces pickup of unwanted sounds.
Other general recommendations for live sound microphone techniques include:
- Try to get the sound source (instrument, voice, or amplifier) to sound good acoustically before attempting to put a microphone on it.
- Use as few microphones as necessary. The more microphones you use, the more likely you are to have feedback problems. Using fewer microphones will allow more volume before feedback occurs.
- When multiple microphones are used, the distance between microphones should be three times the distance from each microphone to its intended sound source. This prevents comb filtering, an unpleasant, hollow sound created when two or more microphones pick up the same sound source. This technique is known as the 3-to-1 Rule (see figure 8).
Large Ensembles (Band, Orchestra, Choir)
Large ensembles generally do not need much sound reinforcement, unless the performance area is unusually spacious. For choirs, use a technique known as area miking. To determine the right number of microphones, use one for every 10-15 voices. Remember not to use more microphones than absolutely necessary and follow the 3-to-1 Rule. As in recording, use a flat frequency response condenser, preferably in a cardioid-pattern. If the microphones will be suspended from the ceiling, make certain they are aimed towards the singers' mouths, not at tops of their heads. Handheld, dynamic microphones are designed for up-close use only, and are not appropriate for choir-miking under any circumstance.
Similar techniques apply to orchestras and concert bands. Depending on the size of the ensemble, use at least one microphone per section. Remember to keep the microphones as close in as possible and as far from the loudspeakers as possible. For soloists or lead instruments, consider using a microphone attached directly to the instrument. Miniature condenser microphones can be attached or clipped onto the bells of brass and woodwind instruments or the chin rest of string instruments.
Recommended Equipment for Large Ensembles
One condenser microphone per section; cardioid
Soloist microphones - (horns, stand-mounted or horns or strings, clipped-on); cardioid
Choir microphones - (permanent install, hung from ceiling or stand-mounted); cardioid
An assortment of XLR microphone cables in varying lengths
A mixer with enough input channels
Signal processors (if desired)
Small ensembles (jazz combos, string quartet, vocal jazz groups)
For smaller groups, close-miking becomes essential for reducing leakage between the instruments. Let's examine each instrument type individually.
Lead Vocal - Use a handheld, directional microphone. The microphone should be touching the lips or just a few inches away. The same technique applies to background vocalists.
Electric Guitar Amplifier - Use a cardioid dynamic microphone roughly 1-4 inches from the loudspeaker, pointed toward the center of the speaker cone.
Drums (Jazz Band) - Generally, three microphones are sufficient to achieve an authentic jazz drum sound. Place one directional dynamic microphone in front of the kick drum, and use a pair of decent directional condenser microphones above the kit for cymbals, toms, and snare drum.
Drums (Rock Band) - To get a "big" rock sound, try to place a microphone on every drum.
Snare Drum - Use a dynamic microphone on a short boom stand. Aim the microphone at the top head, just above the top edge of the drum.
Kick (Bass) Drum - Use a front drum head that has a hole in it, or remove the front head altogether. Mount a microphone on a short boom and position it inside the drum a few inches from the beater head, on axis with the beater. Use a wood beater to get more "attack", or stuff the drum with a blanket or pillows to reduce boominess.
Tom-toms - Use one microphone for every two toms. Position them close to the heads, in a similar method as used for the snare drum. If enough microphones are available put one on every tom-tom.
Cymbals - Place a condenser microphone above the hi-hats, pointed down and slightly away from the drummer. Or, angle the snare mic slightly towards the hi-hats. To pick up the rest of the cymbals, place another condenser near the ride cymbal, a foot or two above.
Piano - Open the lid and aim a condenser microphone just over the top, above the treble strings (see figure 10).
Grand Piano - Use two flat-response condenser microphones, one positioned 12 inches above the treble strings and the other above the lower strings. Both mics should be about 8 inches from the hammers.
Upright Bass - For the most natural sound, place a condenser about 6 inches in front of the bass, just above the bridge.
String Quartet - For violins and violas, use a miniature condenser microphone clipped to the instrument. The best place to attach a microphone without altering the sound of the instrument is the chin rest. For cellos, use a stand-mounted condenser microphone aimed at the bridge, about a foot away.
Saxophone (see figure 11) - Again, a miniature condenser microphone clipped to the instrument and aimed into the bell yields good, up-front sound quality with great isolation. Alternatively, a dynamic microphone on a stand provides similar results, but restricts movement.
Brass (Trumpets, Trombone, Tuba) - Similar to the saxophone, clip a condenser to the bell of the instrument. If the sound seems excessively bright, especially the trumpet, try slightly off-axis to get a more mellow tone.
Vocal microphone; cardioid
Guitar amplifier microphone; cardioid
Drum microphones, cardioid
Piano microphone; cardioid
Woodwind microphones; cardioid
Brass microphones; cardioid
Stringed instrument microphones; cardioid
An assortment of XLR microphone cables in varying lengths
A mixer with enough input channels
Signal processors (if desired)
Mixers, Amplifiers and Loudspeakers
As in recording, mixers are used to combine microphone signals together. Mixers designed for sound reinforcement of musical instruments usually feature a set of extra controls for each microphone beyond just a volume control. These typically include a gain, or "trim" control, an EQ section, a set of auxiliary send volume controls, a bus section, a pan control, and a fader for volume control (see figure 12).
The gain control boosts the signal from microphone level up to line level. The next stage is the EQ, used for tone shaping. A typical mixer will have knobs to boost or cut the highs and lows. Also common is a "sweepable" midrange, which utilizes two controls. One knob selects the frequency, and the other one boosts or cuts that frequency.
Auxiliary sends are additional outputs from the mixer that can be used to route the microphone signal to other devices without affecting the main output of the mixer. Common applications for auxiliary sends include stage monitors or effects processors. The bus section is used to assign the microphone signal to the main outputs of the mixer. The pan control typically serves two functions, either working with the bus section to choose which output the signal is routed to, or to adjust the left-to-right balance if you are using a stereo sound system. At the bottom of the channel strip is the fader, which gives you precise control of the volume of each microphone that is assigned to the master outputs of the mixer.
Amplifiers and loudspeakers work together to reproduce the combined microphone signals from the mixer at a much higher level. A typical power amplifier has two inputs (left and right) and two outputs to connect to loudspeakers. Note that amplifier outputs are designed for loudspeakers only! The signal at this point is much too high to connect to any device besides a loudspeaker. Most amplifiers also have input sensitivity controls as well.
Loudspeakers (see figure 13) come in many shapes and sizes, choosing the right one depends largely on the individual application. Some things to consider the size of the auditorium, portability requirements, and budget. Most sound reinforcement loudspeakers are multi-way devices, which means each speaker cabinet includes two or more) individual loudspeakers, each optimized to reproduce a specific frequency range. Two-way boxes with a woofer for low frequencies and a horn for highs are the most common variety. This type of loudspeaker is appropriate for applications involving voice reproduction and most musical instruments that do not require a good deal of low-end response. Subwoofers can complement the two-way boxes for rock bands or music with a considerable amount of low frequency content. Large touring sound systems occasionally employ up to a five-way system.
For ease of setup and portability, these devices are occasionally combined into one unit, either a powered mixer (mixer/amplifier) or powered loudspeaker (amplifier/ loudspeaker).
A signal processor enhances the audio signal, or can assist in correcting imperfections in the sound system. While not usually essential to the operation of a sound system, they offer some significant advantages. Signal processing equipment includes equalizers, special effects processors, and dynamic processors.
Equalizers come in two basic varieties: graphic and parametric. The graphic equalizer see figure 14) is the most common type. The controls on a graphic equalizer consist of a row of faders that are used to cut or boost specific frequencies. The more faders there are, the more precise the level of control. Each fader represents a "band": common graphic equalizers are 5-band, 10-band, 15-band, and 31-band. Graphic equalizers give the user visual "feedback" (no pun intended) by graphically representing which frequencies have been cut or boosted. While easy to use, graphic equalizers only allow alteration of the frequencies shown on the front panel. For example, a 31-band equalizer allows you to cut at 400 Hz (Hertz) and 500 Hz, but not anywhere in between. A cut at 450 Hz could be simulated by reducing both 400 and 500 Hz, but this results in cutting more frequencies than is necessary. A parametric equalizer, on the other hand, offers more precise control. Fully parametric equalizers consist of three controls, frequency boost/cut, and bandwidth. The frequency control permits the user to select a specific frequency, the boost/cut control selects how much that frequency is raised or lowered, and the bandwidth control selects how many adjacent frequencies are affected by the adjustment.
Equalizers are often employed in an attempt to control feedback. While not the ultimate solution, they can be a useful tool in this application. To begin, turn on all microphones, and raise their individual levels to the point where they will most likely be used during the performance. Slowly bring up the master output level of the mixer until feedback occurs. Now go to the equalizer and pull down the offending frequency roughly 3dB (decibel). If the feedback is a "hoot" or "howl" try cutting in the 250 to 500 Hz range. A "singing" tone may be around 1 kHz. "Whistles and screeches" tend to occur above 2 kHz. Very rarely does feedback occur below 80 Hz or above 8 kHz. It takes practice to develop an ear for equalizing a sound system, so be patient. After locating the first feedback frequency, begin turning up the system again until the next frequency begins ringing. Repeat the above steps until the desired level is reached, but do not over equalize. Keep in mind the equalizers can only provide a maximum level increase of 3 to 9 dB. Parametric equalizers, though more confusing to the novice user, allow for more precise control of feedback frequencies.
Automatic feedback reducers will accomplish the same results as above. They find and cut the frequencies that are feeding back automatically. The same precautions listed above apply to feedback reducers as well as equalizers. Automatic feedback reducers are very helpful in wireless microphone applications. Remember that microphone placement is crucial to eliminating feedback, and the temptation to wander away from the ideal microphone position when using a wireless is great. If the performer gets too close to a loudspeaker, feedback will result, a good feedback reducer will be able to catch and eliminate the feedback faster than a human operator.
One of the most commonly asked questions in professional audio is "What microphone can I use that doesn't cause feedback? The answer to the question is, of course, that no such microphone exists. Feedback results from a combination of many factors, including loudspeaker placement, microphone placement, the frequency response of both devices, and room acoustics.
What is feedback?
Feedback is characterized by a sustained, ringing tone, which can vary from a low rumble to a piercing screech. Echoes and reverberation caused by room acoustics, as well as ground buzz and other extraneous noises, are not the same thing as feedback, and cannot be cured in the same manner.
What causes feedback?
Feedback occurs whenever the sound entering a microphone is reproduced by a loudspeaker, picked up by the microphone, and re-amplified again and again. The familiar howl of feedback is an oscillation that is triggered by sound entering the microphone. The easiest way to create feedback is to point a microphone directly into a loudspeaker. (We don't recommend you try this!) Placing the microphone too close to the loudspeaker, too far from the sound source, or simply turning the microphone up too loud exacerbates feedback problems. Other contributing factors are too many open microphones, poor room acoustics, and uneven frequency response in either the microphones or loudspeakers.
What can I do about feedback?
The single easiest way to reduce feedback is to move the microphone closer to the desired sound source. Additionally, using a directional microphone (cardioid, supercardioid, etc.) will typically increase the amount of gain before feedback. In live sound reinforcement, reducing the number of open microphones with an automatic mixer will also improve the situation. Try to keep microphones and loudspeakers as far away from each other as possible. Lastly, acoustically treat the room to eliminate hard, reflective surfaces such as glass, marble, and wood.
When all of the above solutions have been exhausted, the next step is to look towards equalizers and automatic feedback reducers.
Compressors, as mentioned above, are used to control varying sound levels. When a singer is performing, certain notes or phrases tend to be louder than others. Typically, that singer's volume is set to the maximum possible level without causing distortion further downstream in the sound system. In a loud environment, quieter passages will get lost unless someone "rides the vocal fader to boost the singer during these quiet passages. The volume then needs to be reduced to prevent distortion when the singer gets loud again. A compressor allows the volume to be left at the boosted" level by reducing the peaks (loud parts) by a preset amount so they don't cause distortion. An unfortunate myth that arose from this practice promotes the idea that the compressor actually makes quiet sounds louder. Two controls common to most compressors are threshold and ratio. The threshold determines at what point the compressor function activates, and ratio controls how much the signal is compressed. A lower threshold causes the compressor to activate on quieter sounds, while a higher threshold requires louder sound to activate. Similarly, a lower ratio control reduces the level by a small amount(e.g. a ratio of 2:1 results in a level half of what it would normally be.) A higher ratio (such as 10:1) would reduce the signal to a much greater degree.
A specialized form of compressor, called a limiter, uses a very high ratio (often 0:1) that prevents any signal from surpassing the level set by the threshold. Limiters are primarily used as overall system protection at the output of the mixer, while compressors are typically employed on an individual channel basis.
Finally, special effects processors allow the user to add ambience (reverb) or create unique sounds (chorus, flange, delay)
Hooking it Up
Step 1: Position the microphones as per the previous instructions.
Step 2: Using the XLR microphone cables, connect the microphones to the mixer inputs (see figure 15).
Step 3: If you are using condenser microphones, be sure phantom power is turned on at the mixer.
Step 4: Connect the outputs of the mixer to the inputs of the signal processors (if any) and then to the inputs of the power amplifiers.
Step 5: Connect the speaker outputs of the amplifiers to the inputs of the loudspeakers.
Step 6: IMPORTANT! Always turn the mixer and any signal processors on first. Then turn the amplifiers on. This prevents possible damage to the loudspeakers. When powering down the system, always turn the amplifiers off first.
Step 7: Begin setting levels by placing all the input and master faders at 0". Check each microphone one at a time by bringing the gain control up (while the musician plays) until the output level meter reads "0", then back down the gain slightly. Repeat this step for each microphone. NOTE: At this point the amplifier inputs should be all the way down.
Step 8: While the ensemble plays, bring up the input level controls on the amplifier until the sound reaches the desired level.
Step 9: Adjust the faders to achieve the proper blend of the instruments. Avoid pulling any faders down to the bottom part of their travel. If a particular channel needs a drastic reduction in level, reduce that
Sound Reinforcement for Theatre
The Realities of Theater Sound
Microphones for Everybody!
Most theaters that operate on a limited budget try to use as few microphones as possible. Common techniques include hanging a few microphones overhead, and maybe a few boundary (or surface mount) microphones at the front of the stage. Mary inherent problems exist with these techniques, including, but not limited to:
- Reduced gain before feedback due to too many open microphones too far away from the actors
- Comb filtering (that thin, hollow sound) resulting from multiple microphones picking up the same actor
- Increased pickup of stage vibration noise, reverberation, and other unwanted sounds.
- Varying sound levels as actors move in and out of the pick-up areas of different microphones
How do professional theaters deal with these issues? Easy. they don't. Every performer on stage gets a Wireless microphone. Most Broadway productions use over a hundred thousand dollars worth of wireless microphones for a single show. A basic rule of microphone technique for any application is to get the microphone as close as possible to the desired sound source. Therefore, even though you can't always see it, each actor has a small lavalier microphone clipped, taped, glued, or sewn to some part of the face, hair, or costume. Having every actor "close-miked" eliminates all of the above problems encountered with distant miking. The distance between the microphone and the actor's mouth remains constant, thus providing a constant output level. High sound level shows go a step further, using headworn microphones to get the microphone even closer to the sound source.
The Overhead Dilemma
Okay, so your budget doesn't quite get up to Broadway standards. Using a few overhead microphones for smaller speaking parts can be an acceptable alternative, but be realistic about what to expect. Consider the following example:
Two actors on stage, one is wearing a lavalier microphone six inches from his mouth, the other is standing six feet from the nearest overhead microphone. The actor wearing the lavalier will be four times louder than the other actor will! Turning the microphones up louder is not always an option, either. For any given sound system, the farther the microphones are from the sound source, and the closer they are to the loudspeakers, the less you can turn them up before feedback occurs. Multiple open microphones will further increase the chances for feedback. In addition, distant microphones will pick up more ambient sound, making the actors sound farther away, when compared to close-miked actors. If you choose to use overhead microphones, pay close attention to where the actors are standing when they speak. If the actors are always as close to the microphones as possible, sound quality will improve. Turning down unused microphones will also help.
For downstage areas, or runways where it is not practical to hang an overhead microphone, boundary microphones are often used. These small, flat microphones are usually placed at the edge of stage, where they will be out of the actors way. Boundary microphones are not magic; they are subject to the same limitations as overhead microphones, with the additional issue of stage vibration pick-up.
Overhead and boundary microphones that you may see in a Broadway production are not necessarily used for sound reinforcement; many times they are used for hearing assist, backstage cues, or recording.
One final note on microphones: shotgun microphones are never used for sound reinforcement! The shotgun microphone was designed for film and video production work, where the microphone signals are going straight to tape. It does not "focus" on the sound coming from the stage, nor does it filter out unwanted sounds. A shotgun placed at the back of the hall will pick up everything that happens between the microphone and the stage.
Another issue that can plague amateur theater is poor acoustics. The typical "cafe-gymna-torium” that is used for many school and church theatrical productions is, acoustically speaking, the worst possible place for sound reinforcement. These rooms tend to be extremely "echo-y” which limits intelligibility (the ability to understand what is being said) and decreases gain before feedback (how loud you can turn up the sound system). Professional productions are done in quiet, non-reflective, controlled environments that are optimized for theater sound. Many theaters also employ a distributed sound system, which uses many speakers placed throughout the venue that are divided into zones. Each zone is fed a varying amount of signal, depending on how far they are from the stage. Loudspeakers nearest the stage get very little, if any, signal, while those at the back get proportionally more. This also allows the overall volume level to be lower, which improves intelligibility in a poor acoustic environment.
Know Your Performers!
Lastly, remember to keep in mind the skill level of the performers involved. Professional actors and singers know how to project their voice, which creates more signal level at the microphone. Children, especially shy ones, do not make much sound, which further necessitates close-miking techniques. As mentioned above, turning distant microphones up louder will most likely result in feedback. Remember, if you can't hear what the actors are saying from six feet away, the microphone certainly can't either!
If the above examples seem to paint a grim picture, don't despair. Placing the microphones as close as possible to the actors mouths will always result in improved sound quality. Just be aware that overhead microphones, used carefully, can increase intelligibility for smaller speaking roles. What they cannot do, however, is create a Broadway-like experience. Wireless microphones and carefully controlled, expensive sound systems operated by top-flight sound technicians are the science behind the illusion in professional theater.
Lavalier Microphone Techniques for Theater
The object of most theatrical microphone techniques is to make the mics as inconspicuous as possible and provide the actors with freedom of movement, while still providing a high level of sound quality. The obvious choice is wireless lavalier microphones, which are becoming increasingly popular. Today it is common to find Broadway productions that incorporate twenty to thirty wireless microphone systems on a nightly basis. This section presents a few tips and techniques to get the best results from lavalier microphones.
Place the microphone near the top of the chest, above the ear, or in the hair line.
(See figure 16) A common mistake is to place the mic near the throat, but this will lead to an unnatural sound due to a "shadow” created by the chin that will block high frequencies from reaching the microphone.
Use an omni-directional mic if you have to position it above the ear or in the hairline. A side-effect of directional mics (cardioid, supercardioid, etc.) is off-axis coloration, an uneven pickup of the sound that results when addressing a directional microphone from the side or rear (off-axis). A mic placed on the head will, of course, always be off-axis unless it is right in front of the mouth. Omnidirectional mics will sound more natural when placed away from the mouth
Consult the wig master on securing mics near the hairline. Mic cables can be secured in the hair in several ways, including wig clips, comb clips, sewing them into barrettes, bobby pins, and elastic headbands. Also, the mic can be mounted on the temple of eyeglasses.
Never use "Gaffer" tape to secure a cable to the skin. The adhesive found on this tape can cause skin irritation, as well as just being too sticky, Suggested alternatives include surgical tape, spirit gum, medical adhesive, and clear bandage tape.
Be sure to provide strain-relief for the mic cable behind the neck. The point where the neck bends needs to be the most secure. If no strain relief is present, a sharp neck movement could tug the mic out of place. Again, surgical tape and elastic headbands are good choices for securing the mic cable to the neck
Be careful not to get make-up in the opening of the microphone element. Any makeup that gets into the mic element will alter the frequency response, and could destroy the element altogether.
If the mic cable is run inside clothing, tape the mic and cable to the fabric to prevent contact noise. Contact noise is caused by clothing rubbing against the mic capsule or cable. A little tape and some careful positioning can help eliminate this problem. Also, tie a simple knot in the mic cable near the microphone. This will also assist in blocking cable noise from getting into the microphone.
Consult the wardrobe master to help prevent clothing noise. Clothing noise is caused by garments rubbing against each other. There is no practical way to shield the mic from this noise, so it is a good idea to plan ahead with your wardrobe people. Generally, synthetic materials make more noise than natural fabrics, such as cotton. Also, ask wardrobe to tape or sew together multiple layers of clothing to prevent rustling.
Don't be afraid to use equalization. Judicial use of high frequency boost can help brighten a mic covered by clothing or positioned in the hairline. Low frequency cut reduces cable noise, breath pops, and wind noise.
Keep spare mics on hand at all times. Many professional theater companies consider lavalier microphones a disposable item. Condenser microphones especially can be easily destroyed in such an abusive environment. Sweat, make-up, and constant tugging on cables and connectors can quickly wear out even the highest quality microphone. Try to inspect your mics on a regular basis by plugging them in and listening for any odd noises and crackling, or degradation of frequency response. Wiggle the cables and connectors to check for loose connections.
Take the headworn approach. More and more, actors in Broadway musicals use headworn microphones. The mic placement is always consistent and right in front of the mouth for best sound quality and better gain before feedback. Headworn mics also give you that "hip, 21st century" look!
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