Sound for the School Stage

Looking at all of the settings, it was quite clear to me that the person who had set it up simply did not know what the controls were for and had just left them where they were when he removed the mixer from its box. His placing of the mixer behind curtains reinforced this impression, because the curtains would have deadened any sound that came to him as he set the levels because the curtains were behind the speakers, and all he would have heard would be the low frequencies, muffled by the curtains, so if he had made any attempt to set the levels correctly he would have boosted the high and mid frequencies, not the bass. That person - for you could not call him a sound operator - simply did not have the first idea about stage sound!

Acoustics

To understand stage sound properly, you need some knowledge of the science of Acoustics so that you can work out what equipment you will need and what that equipment does to the sound.

First of all, sound is merely vibrating air. Of course, vibrations can occur at different speeds: the faster the vibration, the higher-pitched the sound. We count the number of times a sound vibrates in one second and call this the frequency of the sound. Frequency is measured in Herz (pronounced like "hurts"), abbreviated to Hz, and kHz (kiloherz, i.e. 1000Hz). Frequencies are usually divided into high (above 10kHz), mid-range, and low (below 100Hz).

High frequencies are directional: that is, they tend to move in the direction in which the source is pointed. If a loudspeaker is pushing out high frequencies you hear the sound best in front of the speaker, less well to either side, and poorly, if at all, behind. Low frequencies, however, are omni-directional: that is, they tend to spread equally in all directions. So if you are listening to a rock group, you will hear the bass guitar almost as well if you are behind the speaker as you would if you were in front.

This can cause problems, in particular feedback (or howlround as it is sometime known). What happens here is that sound from a speaker is picked up by a microphone and fed back through the system, producing that awful shriek or howl which we have all heard at one time or another. Often reducing the bass response of the amplifier (see later) will get rid of the problem.

Before we can go any further there is one other term with which we must become familiar - the Decibel (dB). This is not a unit in itself, like a volt or watt or Herz, but a comparison between two levels. Usually we use it in reference to sound pressure level (SPL), the level of sound. 0dB is defined as the smallest sound the ear can hear at a frequency of 1000Hz (1kHz). Because decibels, like our ears, work on a logarithmic rather than a linear scale (and I won't even try to explain that!), an increase of 3dB means a doubling of the sound. If one sound is 100 times louder than another, we can say it has a ratio of 100:1 or 102:1. We could also say it is 20dB louder. Thus if the ratio of sound A to sound B is 1000:1 (or 103:1), we can say it is 30dB louder. You will find that the gain, equaliser and fader controls on mixers are calibrated in decibels. The "normal" position will be marked as 0dB and increases marked with a plus sign (+6dB) and decreases with a minus (-6dB).

To complicate matters - and they're rarely simple in sound! - at the input stage, the above is true, but when we refer to the output, when sound pressure is doubled, it increases by 6dB! You don't really have to remember all this: just as most people know the difference between a 60W bulb and a 100W but would be pushed to tell you exactly what a Watt is, so we can treat the decibel as a measure of the difference between two sounds without knowing exactly what a dB is.

Microphones

The first stage of sound reinforcement is to pick up the sound. This is done with a microphone and there are a number of different types on the market: the omni-directional, the cardioid, and the hypercardioid. There are also specialist mics such as Pressure Zone Microphones (PZM), Boundary Microphones, and Phase Coherent Cardioids (PCC). Details are as follows:

Omni mics pick up sounds coming from every direction equally;

Cardioids have a kind of heart-shaped pattern of pick-up, being most sensitive in front, less so at the sides and not at all behind;

Hypercardioids (also known as uni-directional) only pick up sound from directly in front. These are sometimes referred to as shotgun or rifle mics;

PZM and Boundary Zone mics work on the reflected sound principal. Usually hemispherical in shape, they are placed on the stage floor or other sound-reflective surface and pick up sound from all around. They are very similar to condenser mics and need a battery or phantom power (see later) to drive them. If you watch ITV's The Bill look carefully at the interview room wall where the tape recorder is: you'll see a square object with a wire leading from it. That's a pressure zone mic;

PCC mics pick up sound from a 180 sweep in front and none from behind. They are very expensive!

You may occasionally come across ribbon mics: they are great for recording and broadcast purposes but totally useless for stage work. They have an almost perfect figure of eight sensitivity, picking up sounds from immediately in front and immediately behind, but not at all from the sides.

Mics can also be dynamic or condenser. There is no point in going into the differences in construction here: all we need say is that dynamic mics are more hardwearing but less sensitive and the condenser needs a power supply. PMZ, Boundary zone mics and PCCs are all condensers.

Dynamic Microphones

Dynamics are usually used as vocalists' mics. Their rugged construction makes them fairly insensitive to handling noise and they are usually held close to the mouth. It often looks as though singers are trying to swallow the mic!

Some dynamics do not have a flat frequency response, and so tend to "colour" the sound a little. What this means is that they are more sensitive to certain frequencies and so emphasise them. As any frequency emphasis should be added at the mixing stage so you should look for mics with the flatest frequency response. Inevitably they are the most expensive! My own experience is that the cheaper dynamics tend to emphasise the high frequencies so that the sound has to be altered fairly drastically at the mixing stage.

There is a big range of dynamic mics on the market, ranging in price from about £12 to a couple of hundred. Remember: as in everything, you get what you pay for and you cannot expect first-class sound from a mic that costs less than a CD!

Condenser Microphones

Condenser mics are excellent for picking up general stage sound, i.e. for reinforcing everything spoken or sung on stage. They are not really suitable for hand-held work and they require a power supply.

The power supply for the cheaper condenser mics is usually a battery or batteries. Most use three or even four 'AA' size batteries (i.e. Duracell MN1500 and equivalents), although some use the oblong 9 volt batteries. The more expensive condensers are phantom powered. What this means is that they have an additional wire in the cable which connects them to a mixing desk (see later) along which the driving current is fed by the mixer. Phantom power is usually 48 volts. A mic driven by phantom powering will normally give a flatter and wider frequency response than one driven by betteries, and in fact those mics which can be battery or phantom powered perform better with phantom powering.

Mics are usually low impedance and balanced (unlike line level input - I'll explain that later! -which is low impedance, unbalanced). Again, there is no need to go into the technicalities, except to say that you can use longer runs of cable with low impedance mics without risk of interference.

Radio Microphones

The signal from mics can be input into the mixer or amplifier by cable or by radio transmission. Radio mics can be either lapel (or tie-clip), hand-held or worn around the head. They have a built-in transmitter and an aerial which send signals to the receiver which is plugged into the mixer. They need batteries delivering, usually, nine volts of power, and if the battery is running low, the signal may very well break up. If two or more radio mics are in use, they have to operate on different frequencies or they will interfere with each other and the sound quality will deteriorate. It is worth pointing out that radio mics which are close to each other in frequency, but not the same, can also interfere with each other.

In the UK there are stringent licencing regulations regarding radio transmitters and only certain broadcast frequencies can be used by radio mics. Of this narrow range of frequencies, there are five which can be used without a licence. They are usually designated by colour - red, green, blue, yellow, white - and they cannot all be used together because of cross-talk interfence. These frequencies are the ones used on the cheaper ranges of radio mics, intended for amateur use. They have a short range and work best when the receiver is in line-of-sight with the transmitter.

The other frequencies are used for professional equipment and require a licence, which costs over £100 a year. Similar arrangements exist in most other countries, especially Europe, the US, Canada, Australia and New Zealand, and may vary from country to country. Use of an unlicensed radio mic rendes you liable to presecution and a large fine!

In the equipment catalogues you will find mention of Diversity Receivers. These are a particular kind of radio mic which transmits and receives on two frequencies: the signal input into the mixer is the stronger of the two at any given moment. Some non-diversity mics have two antennae which are normally placed at different sides of an auditorium. This is because, as the performer moves across the stage, it is possible for the signal to be weakened in certain places whilst remaining strong in others. The two antennae compensate for this.

Another problem which can occur with radio mics is worth mentioning, and best explained by an example. I was acting as sound engineer for an operatic society and was proudly told that they had a new, professional radio mic. Wonderful! It didn't work!

Actually, it worked perfectly well, except in their theatre. This was because the room, which had metal struts across the ceiling, acted as a kind of giant Faraday Cage, blocking the particular frequency of this mic, whereas my school's much cheaper, amateur radio mics worked perfectly! I offered to swap, but they weren't interested: they simply got a mic with a different frequency!

Using Microphones

As I've already said, cardioid dynamic mics are the best for general vocal work. For picking up everything on-stage (sound reinforcement) there are numerous possible approaches: an omni-directional dynamic mic suspended above the stage is all that is normally required for relaying the show to the dressing rooms, but the quality is not good enough for relay to the audience through the sound system. The best results come from the use of PCCs, Boundary Zone mics, PZMs or condenser cardioids or hypercardioids at five foot intervals across the stage. Hypercardioids are best used some distance from the stage..

It is worth mentioning that sound reiforcement mics are not a replacement for vocalists' mics. They do not dominate in the way a hand-held, almost swallowed dynamic mic does! Rather they simply lift the general level of sound coming from the stage to make it more audible.

As far as prices in general are concerned, they can vary from around £12 (a Realistic dynamic from Tandy) to well over £300. The mic which comes nearest to being what we might call the industry standard is the Shure SM58 (a dynamic mic) which has a fairly flat frequency response at 50Hz to 15kHz and costs around £100. Best budget buy is probably the AKG D70ME at around £40 (these prices ex-VAT), although there are some new Beyer mics which are just as good and in the same price range.

There are a number of radio mics on the market, ranging in price from the Soundlab at around £200 to top of the range auto-diversity models at well over £1000. My favourite for school use - we've used one for a number of years and even dropping hasn't spoilt it! - is the Trantec S1000 system. Schure, Beyer, Sennheisser and TOA also produce very good radio mic systems but they are, on average, about £300 - £500 more than the Trantec. PCC mics are very expensive: the excellent Amcron PCC200, which includes a noise gate, retails at around £300, plus VAT. The best PZM and Boundary mics sell at about the same price, but they are coming down in price. We are now using AKG shotgun mics for sound reinforcement and the total package for two mics, 25M of cable for each, a two-way phantom power supply and cables for connection into our non-phantom powered mixer, cost around £800 plus VAT a year ago.

Mixing Desks

The next stage in the chain is the Mixer, in which the sound from the various mics (and other sources such as musical instruments, tape decks, and so on) are mixed together to achieve the right balance. Inputs to mixers for stage use are normally in multiples of four, and eight is the lowest number worth getting. The highly regarded and popular Allen and Heath SR series offer 8, 12, 16 and 24 inputs.

Each input should have the following controls:

Gain This adjusts the sensitivity of the input. You may have to contend with a singer with a loud voice who holds the mic up against the mouth and another with a quiet voice who holds the mic a foot or more away both at the same time. The gain control (a kind of coarse volume control) will enable you to bring the input levels closer together. Some mixers have an additional control (a "pad") which automatically cuts the input by 12dB or so when the channel begins to overload.

Tone A good mixer will allow for the adjustment of the tone of each input in at least three frequency ranges (low, mid and high), and some will have a further two controls (mid-low and mid-high). The most useful controls for the voice are the mid-range. Normally these will cut or boost the appropriate frequencies by up to 12 or, better, 16dB. Once you start rading about sound in real detail you will be told that that some frequencies are best cut and boosted, and others are best shelved. Don't worry about it! It's important for recording or broadcast applications, but for school shows...... Well, with the equipment we can afford in school, the effect wouldn't be noticed!

Aux. You may want to add echo or reverberation (or any one of a number of other possible effects) to the incoming signal. Some mixers can do this themselves, but with the majority you need to use an external signal processor. The auxiliary sends allow this: with them you can control the amount of signal to be sent from the mixer to the processor. Most mixers have at least two auxiliary sends: the better ones have four.

Monitor Musicians like to hear what they are playing, and rock musicians in particular like to have on-stage loudspeakers pointing towards them. This is called foldback or monitoring and any good mixer will have a monitor send on each input channel. In many mixers, one of the auxiliary sends doubles as a monitor send.

Pan A pan pot places the sound in a stereo image. By turning it fully to the left, you send all of the signal to the left output channel only, and by turning it fully to the right, you send it all to the right channel. By turning it half to the right, you send two-thirds of the signal to the right and and one third to the left, and so on.

Fader The fader is the volume control for the channel. By adjusting the levels of the faders, you alter the balance of the output sound. Thus, for instance, you can make a singer louder than his backing, or further balance the two singers we mentioned above.

These are the basic input controls, but there are others found on more advanced (i.e. expensive!) mixers. PFL (pre-fade listen) is a very useful feature which enables the operator to listen to the sound before it goes to the fader, thus enabling him, at the flick of a switch, to compare the unmixed sound with the mixed, to check that mics are working, and to line up a cassette or CD exactly before it is to be played. Overload indication (and, in some cases, clipping) is useful. A light comes on to show that a channel is reaching overload point, thus enabling the operator to move the fader enough to avoid distortion. Some mixers will actually clip (that is, reduce) the sound at this point by, normally, 3 or 6dB.

On price, as always you get what you pay for, and you should not expect to pay less than £500 for a mixer with sufficient flexibility. A British company, Dynamix, does produce an 8 channel mixer for around £200 but it is very basic and once you really start using it you will find it very limiting. Brands to consider include Soundcraft, Tascam and Yamaha. The professional brand leaders in the UK tend to be Allen and Heath whose SR Plus mixers start at over £650 for the 8 channel model, rising to over £1000 for the basic 16 channel desk. All mixer prices are ex-VAT.

The Amplifier

The mixer feeds the sound to an amplifier, or, more properly, a number of amplifiers, as each output channel needs it own. Every mixer has two outputs (left and right) - some have four, six or even eight - and provides the facility to route the sound to any number of these outputs in whatever balance you want. This is particularly useful for large auditoria where you may want to have speakers at various points down the length of the room. This can form the basis of a very complex system in which the sound played through the speakers is delayed for a fraction of a second so that it arrives at the same time as the unamplified sound from the stage. Without this delay the two would be slightly out of phase - not, perhaps, enough to be noticed by the audience, but enough to give the sound a rather fuzzy edge, making it more difficult to follow. You'll possibly have heard this effect at outdoor events which use a fairly basic PA system with a large number of speakers. However this is far beyond the scope of anything we may use in school, so we'll leave it there!

All an amplifier does is increase the volume of the sound fed into it and feed it on to a loudspeaker - and it really is best to have one amplifier per speaker, otherwise you don't get the full power of the system. The power of an amplifier is best expressed in RMS (root mean square), which is the average power it can deliver for long periods without overload or distortion. Sometimes this is referred to as continuous power. Some manufacturers of mainly domestic equipment use the term Music Power (more properly known as peak power) to give a more impressive appearance to their advertising. However Music Power simply means the maximum the system can deliver for a short period of time. Running the system at this full power for any length of time will cause overload, distortion and damage to the speakers. Peak power is usually twice RMS so an amplifier rated at 80 watts RMS is actually considerably more powerful than one rated at 100W Music Power!

Amps provide master faders for each output channel and, often, a more complex graphics equalizer than the simple three or five frequency tone controls on the input channels of a mixer. Generally these will be seven or eight band equalizers (an equalizer is really a filter), each cutting or boosting by, preferably, up to 16dB, an octave of frequencies. An octave is the term given to the distance between two frequencies which differ by a ratio of 2:1: for instance, 100Hz and 200Hz, 10kHz and 20kHz. Built-in equalizers normally operate at octave centres (this is, the frequencies double between each filter), leaving a lot of frequencies barely touched, so for really critical work (and way beyond the needs of a school!) professional sound engineers use graphics equalizers that operate at one-third octave intervals. These are the fabulous - and horrendously expensive! - 15 or even 30 band equalizers you will see advertised in professional sound catalogues.

Also useful is some kind of graphical indication of output, which can come in the form of an illuminated bar graph (which is normally green, with a couple of red sections at the top to indicate overload) or a VU meter. Personally I prefer the bar graph because, in the heat and stress of a show, it is easier to read the moving lights of a bar graph than make out the figures on an admittedly more sensitive VU meter.

Amplifier prices vary considerably, beginning at around £500 plus VAT and running into thousands. It is safe to say that for the majority of makes, the higher the price the higher will be the power output. Cheaper amplifiers are available, but they tend to be Public Address amps which cannot handle complex musical mixes without distortion. And by the way, don't use a hi-fi amp: you simply won't get the quality.

Powered Mixers

Because of the expense of buying one amplifier per speaker, many schools (my own included) compromise by buying a powered mixer, which is essentially a mixer and amplifier in one. The best, again, use more than one amplifier. We use a Studiomaster 8/2 (now obsolete and replaced with a more advanced model - isn't everything!) which has three amps: one per output channel and one to drive a monitor. If you use a separate mixer, or your mixer/amp does not have a monitor (foldback) amp, then you will need to buy a speaker with a built-in amp in order to use the monitor section.

Powered mixers are, of course, more expensive than ordinary mixers, but do, generally, work out cheaper than separate mixers and amps. HIT produce a 5 channel unit at around £550, but you will probably find five channels too limiting. The Yamaha EMX series have a good specification and prices start at around £900, and there is Studiomaster whose entry-level model is about £800.

Loudspeakers

The final link in the chain is the loudspeaker, and let me be perfectly plain here: it is totally false economy to buy an expensive amp and/or powered mixer and use it to drive cheap speakers. In fact, in our system the speakers (JBL Control-10s) were more expensive than the powered mixer! The speaker is the end of the line: it is the part which produces the sound that your audience will hear and it must be capable of reproducing all of the frequencies which make up the sound. Now the frequencies a speaker is capable of handling depend upon the size of the cone, the heart of the system, so it is perfectly obvious that one cone cannot reproduce every frequency. For schools the ideal is far too expensive to be obtainable, but the best compromise is to buy a speaker with three cones: one for the bass, one for the mid-range and one for the high frequencies. Our Control-10s have a 300mm bass driver, a 130mm mid-range and a 25mm tweeter (for the high frequencies). This sort of speaker includes a crossover which splits the sound into the different frequency ranges. Ideally the crossover should come before the amp but this is prohibitively expensive, requiring three amps for every speaker! You will notice, however, that rock bands usually use a range of speakers, from huge bass bins to tiny tweeters, all stacked on top of each other.

The loudspeakers you are most likely to use are these cone (moving coil) speakers, as they are the most economical. There is another type, however, which is, arguably, better suited to the mid to high frequencies. These are horns (compression drivers) which work in a different way and offer greater clarity and control over sound direction, but they do it at a price which puts them beyond the reach of most schools. The JBL Control-12SR speakers, for instance, include a 44mm horn, but they cost almost £200 per pair more than the 10s. Having said that, however, horns are becoming more affordable and may become standard in future. After all, it is not that long ago that crossovers and multiple cone speakers were horrendously expensive and speakers using a 12 inch (310mm) cone were the norm.

Incidentally, one tip: if you need to use a long run of cable from amp to speakers, use the heaviest gauge cable you can afford, because the thinner the cable, the more resistance it offers and the more loss of power there is.

As I said earlier, it is false economy to buy a good mixer/amplification system and then use low cost speakers. Spend as much as you can afford. I rate the JBL Control-10 speakers very highly, but they do cost about £1000 (plus VAT) the pair, whilst the Control-12SRs mentioned above are around £1200. If you expect your speakers to be moved around a lot or transported from building to building, you should consider the ruggedness of Bose. The best - the "Industry Standard" - will set you back (with controller which has to be inserted between mixer and amp) well over £1300. However Bose do produce a portable system, which retails rather more cheaply.

Incidentally, many schools still have column speakers, installed during the sixties. These consist of a number of cones (usually 12 inch), one above the other. Apart from the fact that they cannot deliver the range of frequencies which even the cheapest of modern speakers do, they have a further disadvantage: when "crossed" (i.e. turned so that they face diagonally into the audience) there is distortion at the crossover point. Only use them if you're forced to do so, and never cross them.

I know that I have been talking what most schools would term "silly money", but it really isn't that silly. Our own system, built up over quite a number of years, cost well over £3500, but we bought it in stages and it has proved its worth, not only in the quality of sound which is produces - which is excellent - but also in its ability to stand up to hard knocks. It is frequently carried by hand around the school, or in the back of my car to other venues, or even in the aisle of a bus. It is well used, not only for shows (four or more a year), but also for other school events, such a our speech day which is held in the Sports Hall where the acoustics are dreadful. Without the system more than half the audience wouldn't hear a thing!

Other Equipment

Once you get into sound, you'll find that there are other things you will want: for instance, a playback cassette player which plugs into the mixer, and a signal processor. We managed to find a lovely machine which gives us all we need: reverb, echo, reverse reverb, flanging, chorus, and various combinations (99 in all!) of these, all for under £200. This is the ART Multiverb and I can recommend it very highly. There are a lot of these processors on the market, but they do tend to be very expensive. The ART, for me, gives the best balance of features and price.

With CDs becoming the norm for recordings nowadays you'll probably also want a CD player which can be linked into the system and you may even find that you need to be able to input MIDI instruments as well. Neither of these is a problem: you just need more money!!!

By the way, there's another technical term, which I've already mentioned, which needs explaining, nd this is the right pklace to do it. The term is line-level and it refers to the characteristics of the signal produced by electronic musical instruments, electric guitars, tape decks and CDs. It differs from the signal produced by microphones in that it is high impedance and unblanaced. Again, there is no need for me to go into technicalities: suffice it to say that you should not plug a line-level source into a mic level input, or vice versa, because you'll get lousy sound quality and could cause damage to your mixer.

We have also just solved a major problem. Many of our shows use what is basically a rock band: a couple of keyboards, lead, rhythm and bass guitars, and drums. The kids like to play loud and it's difficult to stop them inching up their guitar amps from the setting which we establish in rehearsal. We therefore needed to be able to control the volume of the sound they produce so that it balances properly with the vocals. The only way this can be done is to channel the instruments through the mixer. That causes two problems: first the amplifier-induced distortion characteristic of rock music will go, and second, we only have eight channels on the mixer, and six of them are already in regular use.

What we needed was a sub-mixing system for the band, and effects pedals for each guitar. The effects pedals, which reintroduce the distortion, cost about £40 each and we would need three. This problem was very easily solved: the kids bought their own because they were playing in bands outside of school. But the sub-mixing was another thing entirely. We needed another mixing desk, the output of which would be fed into the powered mixer through one of the inputs channels, so the sound engineer would have complete control over the whole sound balance, leading to a much better sound balance.

What we did was to buy a mixer which, on first sight, would seem a bad choice: it was a six channel job from Yamaha with only two channels capable of accepting low impedance mic input. The rest would only accept high impedance line level input, from cassette decks, for instance, or from electric instruments. So we now use the two mic inputs to mic up the piano and the others for the three guitars and the synthesiser. The mixer sits beside the MD who sets the balance of the instruments on it, and the output is taken from there to the powered mixer where it is mixed into then whole sound picture. No more itchy fingers! No more lead guitars drowning everyone out! Wonderful!

That's the great thing about a sound system: you can expand it without having to replace what you already have. We could, for instance, have bought a 12-channel mixer and additional mics, and routed the band's sound to the left channel and the mics' to the right, take each of these into the main powered mixer, where they can be further modified and balanced, and then reintroduced into the stereo image, thus giving us full control, not only of the sound balance, but of which speaker each sound comes from and at what level. Great! - but we couldn't afford it!

Remember, you're going to have kids who are interested in sound and what can be done with it. They deserve the chance to develop their skills as much as any actor, dancer or singer; and, in fairness to the actors and the singers, they need the best quality sound that you can produce. You won't be able to buy your whole system at once: we've been bulding up ours over a period of years, and will continue to do so. Start simply: the best powered mixer and speakers you can afford, with some relatively cheap mics. Then you let the type of show you do dictate what comes next. Initially you may have to make do with existing equipment (speakers in particular) which is far from ideal. Don't worry: make do until you can afford something better. We hired a radio mic for a few years until we could afford our own, and we continued to slap the itchy volume-control fingers of our guitarists until just a few weeks ago!

Operating the System

There's just one further point to be made: the best equipment in the world will be useless in the hands of an insensitive operator, so it is worth setting up an operating system which will get the best out of the equipment, even in the hands of an inexperienced operator. Here are some suggestions.

First of all, your sound operator must hear the same sound as the audience. He should not be in a sealed control room because, even if he has the best monitors in the world, he won't hear the sound that the audience hears. The best place - and the place where I always put our operator - is at the centre back of the hall (towards the front of the back-stalls in a real theatre!). Incidentally, for the same reason he should not use headphones. Their only use in a theatre context is to line up tapes or check that mics are live when you have a pre-fade listen capability on the mixer.

It is best to get your output equalizers set up first, for they determine the final quality of the total mix and if they're not right, you'll never get a good sound. The thing to remember is that the output equalizers are there to counter any peculiarities in the acoustics of the hall. Once they have been set up for that hall, there should never be any need to alter them. In fact it is possible to get units which are microprocessor controlled, and by following their test procedure you will get a graphical read-out of the frequency response of the room, and then you simply line up the band settings on your graphic to get the correct curve on the read-out and bingo! it's all done.

Most of us, of course, can't afford such sophistication, so here is the system that works for me. Connect a tape deck to one of the input channels and insert a tape which you know well. Move all settings (gain, input graphics and volume fader) on the input channel to 0dB: this will replay your tape without any alteration. Now set your master output volume to 0dB and centre all the slides on the output graphic. Play your tape and you will hear that it does not sound the way you like it. Adjust the bands on the graphic carefully one by one until you have a sound which seems right to you. Make a note of these settings! With minor alterations they will be the basis of your system. Now try another well-known tape. Does this sound right? If it does, you've got the right settings: if not, go back to the flat (i.e. central) settings and start again. When you are satisfied, compare the settings with those for the first tape. If they are very close, try your first tape at the settings for the second. If you're happy, then you have the right settings: note them down and use them as the basis for your sound mix every time you work in that hall. If you're not happy, you'll just have to keep working at it with different tapes until you reach an acceptable compromise.

Then it is time to start working on the settings for the input channels. These will be very variable, depending upon the sound you are reproducing (usually the voice of the singer/speaker) and the frequency response of the mic you're using. For each singer or instrument you are using you must adjust gain and input equalizer controls to get an attractive sound. Gain comes first, then I prefer to adjust the mid-range control next. The human voice has a comparatively limited frequency range, most of which falls in the mid-range band of a three band equalizer; adjusting the high and low frequency bands will normally only affect the harmonics, not the basic sound.

With instruments the situation is different: many produce a wide range of frequencies (notably the piano and strings), whilst others are limited to the upper or lower bands (although again the harmonics must be taken into account). With instruments that produce a high pitched sound, adjust the high band first, and do the opposite for low pitched instruments. To get the best reproduction of a piano you really need two mics and two input channels. Use cardioids pointed into the innards of the piano, one to pick up the high frequencies (i.e. the right half of the keyboard) and one for the low (the left). Naturally each will probably need totally different (input) graphics settings.

Now do the same for any tapes (sound effects or music) which you may be going to play through the system. And make sure you note every setting!

All of this, of course, should be done at a technical rehearsal: you can't possibly do it on the first night! Having to do it at a tech does cause a problem: the sound you hear in an empty hall will be different to that you will hear in the same hall full of people. Your output graphics settings, however, will be close enough for minor adjustments to be made on the night. That's why it's a good idea to have music playing (from a tape) as the audience come in. You can use that as your test.

Sound is important. The trouble is, you don't really realise how important until you hear it reproduced correctly. Many people are satisfied with nothing but amplification and so if they can hear the singer at the back of the auditorium above the band and without feedback, then they are happy. Sound reproduction is much, much more than that, and you owe it to your singers and your Musical Director to get the best possible quality from the available equipment, and if the available equipment doesn't deliver good quality, then I'm afraid you need to start spending money, or at least do the sort of show which doesn't require Sound Reinforcement!

Finally, an important piece of sound equipment which the audience never hears! This is the intercom system which allows the various backstage departments to talk to each other and, most important of all, allows the assistant director (or stage manager) to cue lighting and sound. Unless everyone who will be using the intercom is insulated from the audience so that anything that comes over the intercom will not be heard, then forget the cheap but effective baby-minder type of intercom with the buzzer to attract attention. You must go for a headset intercom. These consist of a belt-pack with call and speak buttons, and a set of headphones (double or single muff) with a little boom microphone. The industry standard is the Techpro system which is extremely rugged and reliable, but very expensive and very, very heavy. Like the Bantam, a cheaper version made for the amateur theatre, it is a cable-based system and requires a master station to be plugged in to a mains outlet and heavy duty cables with XLR connectors to carry current and signals.

These two systems, Bantam and Techpro, are perfect for permanent installations which will receive a lot of use, but they do have the disadvantage that they restrict the movement of the user to the length of cable from his outlet. The weight is also a disadvantage: when I'm using a Techpro belt-pack I feel as though someone is trying to pull my trousers down!

My own preference is for a radio headset intercom system. A professional one, of course, is very expensive, but there are two - Realistic from Tandy, and Maxon - which are lightweight and cheap. They operate on CB frequencies and so don't need a licence, but, because of this, they do have the theoretical disadvantage that they could be liable to interference from other CB users. I have never found this actually to happen, mainly because of their limited range, which is about 200 metres, quite enough for most theatre purposes.

They also run from batteries which are available in shops all over the country. I remember once, about half an hour before the show was due to begin, discovering that the batteries in one of our headsets were flat and I was able to rush out to a local garage and bought batteries for all of them, just in case. Incidentally, always use long-life batteries: the cheaper ones might last one evening, but that's all. I've now started using rechargeable Nicad batteries. In the long run they're cheaper! Another advantage is that the belt-packs are very small and light and can actually be slipped into a pocket - no more nervous clutching at waistbands! And finally the user is not restricted by trailing cables.

In this case, what does "cheap" mean? For the Realistic system (one channel only) you'll pay a little over £50 a pair (ex-VAT), and for the Maxon five channel model £70 each. Compare that to the Techpro where you'll pay £140 for the power supply, just over £400 for a master station, £58 each for single muff headsets and £90 for each belt-pack, plus, of course, all cable and connectors (and XLRs cost about £2 each). The Bantam system costs just over £100 for the power supply and £95 for a single headset and belt-pack, plus - again - cables and (XLR) connectors.

Thus a six-station Realistic system will cost a little over £150, as compared to almost ten times as much for a comparable Techpro system! Of course it won't take the same amount of punishment, nor will it last anywhere near as long, but it's all that any school is likely to need. And you won't believe the advantages being in constant touch gives until you try it for the first time - then you'll wonder how you ever did without it.

At this point I must emphasise that prices change with alarming rapidity (especially if they're going up!) so please regard the ones I've given as a ball-park figure and not an accurate guide. They've probably changed as I was writing this!

One final point (I think this is actually about the third final point!): any sound system has a lot of trailing cables, often running through the audience - they'll certainly be running through the audience if you position your sound desk in the auditorium - and this can be dangerous: you could be in for a very expensive claim if a member of the audience trips over a trailing cable and injures himself. Don't just run cables under mats! It's very tempting, I know, but dangerous, even though the cables carry very little current. It is possible to buy half-trunking which fastens to the floor and has a kind of tunnel through which the cable runs, but it is very expensive, albeit the best solution. The cheapest - at about £5 a roll - is gaffer tape. This can be put down on all kinds of floors and will stick firmly, yet it will come off quite easily when you want it to without leaving any mark even on the most delicate floors. It's normally available in silver-grey or black. Use the silver which it is more visible, so audience members see it and are more likely to mind their feet. Actually, it's worth always having a roll in stock. I always intend to but forget and so the day before a show we're rushing round trying to buy some!

And by the way, you always use more than you think you will! I reckon we use 2-3 rolls per production - and that's apart from what the caretaker pinches when we're not looking!

Author: Written by Peter D. Lathan, http://www.britishtheatreguide.info