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  PA Proverbs
(Hints and Tips)

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A collection of short hints, tips and other PA wisdom shared to assist you in your use of PA systems. If you have any such advice or comments of your own that you would like to submit for possible inclusion on this page, please email me (or put your suggestion in a comment on the blog associated with this site). Minor alterations may be made to accepted contributions, to suit the general style of this site. Contributors will not be identified on this page unless they request to be. Many thanks to all our contributors.

Please note that some items on this page do not fall neatly into the section headings, so you might want to look at two or more sections. For example, tips about the connection of a cable to a microphone might be found under 'Cables', 'Microphones' or 'System Assembly and Interconnection'. (If anyone can think of a better way to organise them, please let me know!)

My apologies if you are offended by the seemingly obvious nature of some of the items. However, it can be useful to be reminded even of the obvious, and some less experienced engineers than yourself might find them them helpful! Please remember that these 'proverbs' are just opinions on what is (or is not) good or useful practice. They may need adaptation to specific circumstances, and other opinions may differ.


"What really gets me into trouble is not what I don't know, it's what I know for sure, but just isn't so." − Mark Twain.


Contents


General

  1. Never just assume that anything is going to operate as it should at the moment it's needed, without having checked it first. Equipment goes faulty, cables get connected incorrectly, controls get misadjusted. Always test everything, well before the event starts, to give plenty of time for correcting (or working around) any problems you find. [See Rig check, Line check and Sound-check − Ed.]
  2. Once equipment is unpacked, and especially during an event, keep all food and drink well clear of it − and make sure everyone else does too. This is especially important for equipment such as mixers and graphic equalisers that have lots of sockets and/or slots for slider controls. Anything that gets into these is sure to cause problems sooner or later.
  3. The better packed your equipment is, the less likely it will be to get damaged during transit. Good quality flight cases are expensive, but so are repairs − and inconvenient too.
  4. To help keep on good terms with hire companies, always normalise their equipment before returning it to them.
  5. When cleaning CDs, always wipe in straight lines from the centre outwards (this minimises the effect of any minor abrasion caused by the cleaning). And if cleaning to try to correct a problem with a particular track, remember that track number 1 is the innermost track on the disc.
  6. Remember that most types of silver-coloured gaffer tape incorporate an electrically conductive layer (made of aluminium). When used to secure cables, in some cases this layer may increase the pick-up of interference by the cables or may increase unwanted capacitive coupling between adjacent cables. Therefore, it's best not to use the silver-coloured type on cables except where essential for aesthetic reasons. But in any case, never use it on or near to exposed connections of any kind. [No colour of gaffer tape is suitable for use as an insulating tape, so must never be applied directly to exposed electrical connections or conductors. Where an insulating tape is required, use only suitable purpose-made tapes (e.g. PVC tape, where suitable) − Ed.]
  7. Maintain all equipment in good condition. In particular, regularly check cables for damage and check equipment dust filters and cooling fans for any build-up of dust.

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Microphones

(Also see the Microphones page.)

  1. Always use the appropriate kind of mic for the job (see the microphone selector).
  2. After speakers, this is the part of the system that will make the most difference, in terms of sound quality, so don't compromise. In general, avoid budget types. Only use high-impedance or unbalanced types if essential − they require suitable connection arrangements to avoid sound quality problems.
  3. Although capable of a better quality sound, condenser mics can be more prone to damage by rough handling. So for rough stage vocals use, use a rugged good quality dynamic mic such as the Shure SM58, and only use condenser mics where really necessary, such as for drum kit overheads.
  4. To avoid the embarrassment of flat batteries, use phantom powered condenser mics and DI boxes rather than battery-powered ones. (Some are capable of being powered either way.)
  5. Don't test mics by blowing into them or tapping them, as this can cause damage. Speak or sing into them instead. The spoken words "one", "two", "test" and "check" are 'tried and tested' words to use. When adjusting the mic channel EQ, listen to "one" to adjust the bass, "two" and/or "test" to adjust the treble, and "check" to adjust the mid-range frequencies. Alternatively, if a mic needs to be checked during an event and speaking into it would be inappropriate, lightly scratch the basket of the mic with a fingernail.
  6. When using multiple hand-held radio mics, or if wired mics need to be moved around on the stage (or are liable to be taken off their stands and replaced on different ones by vocalists!), identify each mic with a different colour of self-adhesive tape − stick a piece of the same coloured tape against the relevant fader of the mixer, so you can readily keep track of which fader controls which mic. Wrap a band of the tape around both ends of the held part of the mic, as either end may be at some time obscured by the performer's hand.
  7. Encourage performers in correct microphone technique, such as holding the mic at an appropriate distance for the particular use, and at the correct height and angle. (However, don't forget the visual aspect − there's little more frustrating to an audience than never being able to see the performer's lips, even if the sound is superb − especially when close-up video is in use.)
  8. Try to discourage vocalists from wrapping their fingers around the basket of the microphone, as obstructing the entry of sound into part of the microphone can significantly alter its directional characteristics and may make feedback more likely and/or cause undesirable tonal colouration.
  9. Try to discourage vocalists from holding radio mics at the very bottom end, in the case of types that have a projecting aerial there, as this would reduce the effective power of the transmitted radio signal, and so increase the likelihood of reception problems.
  10. If possible, avoid using wired mics that have on/off switches. Some performers have a habit of switching them off accidentally (or deliberately and then forgetting they've done so), or leaving a mic switched off for a later performer who expects to find it switched on. If you do need to use mics with readily accessible switches and these mics will be handled by performers, or their switches might be accidentally knocked, then put some suitable tape over the switches to avoid accidental operation.
  11. Correct placement of mics is often critical to achieving the best results, especially when close-miking acoustic instruments. When deciding where to place a mic, it's worth considering that the mic will 'hear' much the same sound as if you placed your ear in that position, pointing in the same direction. (But only try this if the sound level at that position isn't so high as to risk damaging your hearing.)
  12. When miking-up a multi-driver instrument cab, listen to the cab first to check that the driver you choose to mike-up isn't a dodgy-sounding one. (Again, beware of high sound levels − they may occur suddenly.)
  13. When a mic is used with a tight-fitting mic clip, be aware that the pressure of the clip can cause the XLR latch to be released as the mic is removed from its stand by the performer, with the possibility that the XLR plug can then lose electrical connection with the mic, or even fall out completely. If this looks a possibility, be sure to place the mic into the clip with the XLR latch-release button in line with the slot of the clip, and ensure that the performer knows to replace the mic similarly.
  14. Inferior quality windshields can seriously damage your sound!
  15. When using condenser mics with phantom powering, check that the voltage of the available phantom power (48V from nearly all modern PA mixers and mic pre-amps) is correct for your microphones before connecting them. Most condenser mics intended for use on stage are designed for 48V powering but you unless you are certain it is still wise to check.
  16. When using several condenser mics and/or DI boxes with phantom powering, check that the the total current demand of all the phantom-powered devices connected to the mixer does not exceed the total phantom power current available from the mixer.
  17. If using a ribbon mic, it is best to avoid applying phantom power to it if at all possible, as a fault in the mic cable can easily cause the mic to be seriously damaged.
  18. When using a ribbon mic, never blow into the mic, as this is almost certain to cause serious damage to it.
  19. If a mic is suspected of being faulty, don't put it back in the box with the others, to be taken out again and be used another time. Put it separately (preferably marked in some obvious way) until it has been checked and repaired.
  20. When attaching a lavalier mic to its user's clothing, get them to tilt their head fully forwards and ideally clip the mic at a height about 2 cm (1 inch) below the point on their chest where their chin touches it. If the user is to be facing forwards for the majority of the time, then preferably clip it at a central position. If the user is to be predominantly facing towards one side (as in some interview situations), then clip the mic at that side of centre.
  21. If a new mic has to added, or a faulty one replaced, during a performance, it is often inappropriate for it to be tested in the normal way, by someone speaking into it. Even if the mic is not routed to FOH during the test, seeing a person speak into it can be a visual distraction. In such cases the basic operation of the mic can be confirmed by activating the PFL on the relevant channel, turning up the headphones level control, and listening for the ambient sound picked up by the mic. (It may also be necessary to temporarily turn up the channel gain control, depending upon the sound level in the vicinity of the mic.) The only problem with this is that it doesn't confirm that you really are listening to the new mic (it may have been plugged into the wrong channel on the stagebox!). So if the mic is being placed by someone other than yourself, a better approach is to have them lightly scratch the basket of the mic with a fingernail, while you listen for this distinctive sound via the channel PFL. The assistant can be given a 'thumbs up' signal when this check is completed.
  22. If a performer insists on swinging a mic on its cable, do not rely on the latch of the XLR connector to secure the mic to its cable. Use only a heavy-duty mic cable in good condition, and check the tightness of the XLR's cable clamp. Wrap plenty of gaffer tape around the mic, the connector and at least the first 150 mm (6") of cable (taking care not to tape over the XLR latch release button!). Also, to help ensure that there is no possibility of the mic or its cable striking another performer, crew personnel, or object, securely attach some coloured tape to the cable to indicate the furthest distance from the mic that the cable can be safely held by the performer, when swinging it.
  23. When using microphones some distance from the sound source (for example in the case of drum kit overheads, choir mics or rifle mics), and monitor speakers are in use, take care to avoid the sound from those speakers being picked-up by the mics along with the wanted sound, as that can degrade the FOH mix. This can be a particular problem with drum kit overheads, because most dummers like their monitors loud. Consider using headphones or IEMs instead. Otherwise, minimise problems by using positioning and directionality of both the mic(s) and the monitor(s), and keep the monitor(s) levels down to the minimum acceptable.
  24. When an acoustic guitar doesn't have a built-in pickup, close-up use of a stand-mounted microphone is best avoided if the guitarist is standing, because even slight movement of the guitar body relative to the mic can significantly affect the nature of the picked-up sound (as well as its level). In a live situation when close-miking of a guitar is required, the guitarist should be seated (and should take care to hold the guitar in a fixed position) or else a miniature gooseneck mic, or a suitable temporary pick-up, should be attached to the guitar. (In a studio recording situation, use of a stand-mounted mic may be suitable if it can be placed at a sufficient distance from the guitar to make any small changes in position and distance less significant.)
  25. Be sure to adequately tighten mic stand boom adjustments, to avoid unintended changes in position or height. Tightness is particularly important when a heavy mic is used with a boom covering a horizontal distance of more than 45cm (1ft 6in), in order to avoid a gradual sagging in height due to the weight of the mic.
  26. When a vocalist is to sing into a mic on a stand, be sure to set the height of the stand correctly. An incorrect height may cause the vocalist to stoop or to stretch, neither of which is helpful for good vocal technique.

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Other On-stage Issues

  1. Ensure that all guitarists and other musicians with hand-held intruments that connect to on-stage equipment and/or the PA system using an unbalanced connection (usually a jack-to-jack cable) are aware of the need to avoid creating the loud impulsive noises that can result from plugging-in or unplugging instrument cables (at the instrument end), as these noises can be seriously damaging to equipment and very unpleasant for audiences.

    Turning down the volume control on the instrument will never be effective in preventing these noises. [They usually originate mostly from the tip of the plug unavoidably contacting the sleeve of the instrument's jack socket as the plug enters/exits, and in the case of instruments equipped with a battery-powered pre-amp, from the switching on/off of the battery by insertion/removal of the plug. Self-shorting jack plugs can sometimes be helpful in avoiding these problems, but are not always effective.]

    When the instrument is amplified by the PA system, the sound engineer should mute the relevant channel(s) on the mixer, before the instrument is unplugged, and there needs to be a pre-arranged cue for the sound engineer to do that. Muting at the mixer in this way will avoid unpleasant noises from the PA system FOH and monitor speakers and will protect them from possible damage.

    However, if the instrument has a connection to backline equipment then the only way to protect and avoid the noise from that equipment is for the musician to either turn down their amplifier or to interrupt the signal to it, before unplugging the cable from their instrument. Interrupting the signal can often be conveniently achieved by use of an appropriate pedal, or by unplugging the instrument cable at the non-instrument end before unplugging it from the instrument.

    As a last resort, the noise created by unplugging from the instrument can sometimes be significantly reduced if the musician first grasps an earthed metal part of the jack plug (i.e. a part that connects with the sleeve of the plug) and then touch the metal sleeve or nut of the instrument's jack socket with a finger of that hand, maintaining contact until the plug is fully in or out and taking care not to touch the tip of the plug. If the instrument socket has no touchable metal parts (e.g. is recessed), then instead of touching the socket with a finger use the other hand to touch an earthed metal part of the instrument (e.g. the pick-ups).

  2. It can be helpful in keeping stage sound levels under control if, when asking band members if they can adequately hear what they need to, they are also asked if there is anything that is swamping what they need to hear and would be usefully reduced in level.
  3. When giving advice to band members, e.g. on microphone technique, it can be useful to remember that people often find it easier to keep in mind something to aim for rather than something to avoid. For example, it will often be more effective to say "It would be helpful if you could hold the mic closer to your mouth", rather than "It would be helpful if you didn't hold the mic so far from your mouth".
  4. It's worth giving some serious thought to the type and brand of batteries that you use in your radio mics and in beltpacks for body-worn mics, wireless instrument systems and IEM systems, especially if operation for several hours between battery changes is a requirement. Zinc types are best avoided. A useful comparison of many AA-sized alkaline (and a few lithium) UK brands can be found at batteryshowdown.com. System manufacturers generally recommend avoiding the use of rechargeable types − mostly because their life between recharges is quite limited and reduces unpredictably as the battery ages. To be sure of avoiding battery failure, many professional users use a new set of alkaline batteries for every show. But in less critical applications where budget is tight and where each use is shorter than around 1.5 hours, with plenty of time for recharging in between, using good-quality rechargeable types can be very convenient and cost-effective.

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System Assembly and Interconnection

(Also see the System Assembly page.)

  1. When deciding on the location of the front-of-house mixer, don't assume that a position on the centre-line of the venue will give the best listening position. Although this is often the best choice, sometimes sound reflections from surfaces (especially curved ceilings) can cause problematic cancellations at a central position, so a position slightly to one side may be preferable in such circumstances.
  2. For rapid location of a desired channel during an event, when cabling-up the system assign the stage signal sources to the mixer channels in the same order that they are positioned across the stage (as viewed from the mixing position). As it's usually helpful to keep the channels used for vocals next to each other, assign those channels (in stage position order) first, followed by the instrument channels (in stage position order). [Or, use a standard ordering such as the one shown here − Ed.]
  3. To avoid dangerous and/or expensive mistakes, don't use the same kind of connectors for different purposes in the same system. In particular, beware of multiple uses for Socapex connectors (mains power, balanced audio lines or amp-to-speaker connections) and for XLRs (balanced audio lines or low-power amp-to-speaker connections). This is especially important for touring systems, and even more so when unskilled people are assisting in assembling the rig. (If such mixed use of connectors is unavoidable, ensure that all the relevant connectors are very clearly labelled.)
  4. If it is desired to extract a line level signal from one or more individual channels of a mixer, e.g. to feed IEM transmitters for individual performers, or for multi-track recording purposes, and there is no 'direct out' facility, you can use the channel 'insert' facility of your mixer (if it has that!). For each channel of interest, you need to make (or otherwise obtain) a special cable, consisting of an unbalanced screened cable terminated in a 3-pole ("stereo") jack plug. The screen of the cable is connected to the sleeve of the plug (as usual) but the 'signal' (hot) conductor is connected to both the tip and the ring of the plug. This plug then connects into the 'Insert' socket on the relevant mixer channel; the link between tip and ring connections prevents the signal path through the mixer from being broken. The other end of the cable is terminated normally in whatever kind of connector is needed for the equipment you are feeding the signal into.

    The internal wiring of the 'Insert' socket on some mixers supposedly avoids the need for such a special cable, allowing a signal to be extracted by inserting an ordinary 2-pole ("mono") jack plug only partially into the socket − just to the first 'click'. However, this is not recommended because in a large system it would be too easy to forget which plugs are deliberately partially inserted − it would be all too likely (especially for some other 'helpful' soul) to think that the plug had not been properly inserted, or had subsequently taken a tug on its cable, and push it fully in. The consequences would not be good.

  5. Most tape, CD, and DAT recorders reproduce their input signals on their output connections when in record mode. Therefore, when such a machine is connected to a mixer for both recording and playback, there is a likelihood of an electrical feedback loop being created which can seriously damage speakers, etc. So unless you are sure your machine does not have this facility, or has a foolproof way of disabling it, always use the designated 'playback' inputs on the mixer (which usually do not feed to the 'record' outputs − but do check this!), rather than using normal channel inputs. (Alternatively, use an auxiliary output on the mixer, rather than the 'record' output, and be very careful not to turn up that Aux Send on the channel(s) used for playback. For a mix the same as the main mix, use a post-fade auxiliary and set all the required Aux Sends to 3 o'clock − or to '0 dB' if marked.)
  6. Be aware that most mixing desks do not isolate the XLR (mic) input of a channel when a jack is inserted into the channel's line input. So it's always best to ensure that there is no plug in the XLR input when the line input is being used, to avoid the possibility of interference with the line-level signal caused by connections made to the other end of any XLR cable that usually plugs into that channel. (Such connections, e.g. to an usused DI box, may be more easily overlooked or accidentally made if the XLR cable is routed from a stagebox.) [Of course, the converse also applies: don't have anything plugged into the line input if using that channel's XLR input − Ed.]
  7. To assist in balancing Left and Right speaker levels, use the same length of speaker cable for both Left and Right speakers − even when the Left and Right amplifiers are located together and closer to one side than the other. (But don't have the unused speaker cable length coiled on a reel, as this may impair its ability to lose heat and so cause overheating.)
  8. Consider using a 2-channel amplifier configuration, with separate 'Left' and 'Right' connections from the mixer, even when you're mixing in mono. That way, if an amplifier fault or an amplifier feed fault develops during an event, you'll probably only lose half of the system rather than all of it.
  9. When not a safety hazard or too unsightly, coil any excess length of stage cables at the source (e.g. mic) end of the cable. This avoids the stagebox area being cluttered-up with all the spare cable (which can make later access difficult) and makes those last-minute changes of mic location much easier to cope with − especially when the cable run to the stagebox has been taped down. If for some reason the coils can't be at the source ends, make them a metre or so away from the stagebox − and use a releaseable cable tie around each coil to prevent them getting jumbled.
  10. When connecting any unbalanced source (e.g. most instruments, iPADs®, notebooks, etc.), to a balanced mic input of a mixer or stagebox, always use a DI box. Don't be tempted to use an in-line adaptor to convert from an unbalanced jack to an XLR, as these don't provide a balanced signal to the mixer and can cause serious damage to the source equipment if the mixer has phantom powering switched on.
  11. Not all balanced outputs are designed to cope with phantom power being applied to them. For example, when linking a mixer's balanced outputs to another mixer's mic inputs (cascading), to avoid possible serious damage be very sure that phantom power isn't activated on those input channels before making the connections. To be certain of avoiding damage (e.g. if phantom power were accidentally activated later), use a suitable 1:1 isolating transformer in each feed. (If possible, it's always best to have phantom power deactivated on channels where it's not needed, even when using source equipment that is designed to cope with it.)
  12. When connecting balanced outputs to unbalanced inputs, or connecting to them using unbalanced cable, check the manufacturer's instructions for the source equipment, on how to make such a connection. If making such a connection from a balanced output of the quasi-floating type, it is important to link the unused cold leg of the output with signal earth, in order to avoid the possibility of relatively high levels of noise being added by the output.
  13. If your speaker cables have jack plugs at the end that connects to the speakers, don't plug-in or unplug the jack at the speaker end while the other end of the cable is connected to an amplifier that is switched on. (As the plug goes in or out, the sleeve contact inside the socket could bridge across the insulation between the sleeve and tip of the plug, short-circuiting the amplifier output and damaging the amplifier.) In any case, it is not recommended to connect or disconnect speakers from amplifiers that are switched on. − Also see the next tip.
  14. Unless your speaker cables have connectors with protected contacts (such as Speakons) at the speaker end, don't leave that end of the cable unplugged while the other end of the cable is connected to an amplifier that is switched on. (The 'signal +' (hot) pole of the plug could make accidental contact with earthed metalwork, short-circuiting the amplifier output and damaging the amplifier. And, in powerful systems, touching that pole could be an electric shock hazard.) − Also see the previous tip.
  15. Preferably, avoid connecting speaker outputs of backline amplifiers to DI boxes. (Instead, use a mic on the speaker, and/or use a line-level output into a DI box.) If you must do this, only use a DI box that has a specifically-designated speaker input, only use a passive DI box, use a correctly-wired speaker cable to make the interconnection and take great care to make sure that the DI box's earth lift switch is in the 'LIFT' position before you connect the amplifier to it. [Also see the previous two proverbs, and see Emulated line output − Ed.]
  16. If you are faced with a backline amp that has an intermittent or crackly output, first check if it has effects loop jack connectors that are not being used. It's a frequent problem on older amps that the internal switch contacts on these connectors, that complete the signal path when no plugs are inserted into them, fail to make good electrical contact. Sometimes putting a plug rapidly in and out of the relevant connector (usually the Return − but sometimes the Send!) lots of times will clean the contacts sufficiently to provide an adequate short-term fix, but a much more reliable quick solution is to use a short jack-to-jack patch cable to link the Send and Return connectors.
  17. When assembling large systems, keep an eye on mains power requirements. As a rough guide, amplifiers providing a total of 2 kW output power is the maximum that should be supplied through any one 13 Amp socket outlet of the building's fixed electrical installation.
  18. When connecting several speakers to one channel of an amplifer, take care not to go below the minimum load impedance catered for by that particular model of amplifier.
  19. When connecting an unbalanced XLR output of a mixer to an unbalanced XLR input of an amplifier, be aware that equipment differs in which pin of the connector is used as the 'hot' connection. Most British equipment uses pin 2 for the 'hot', but some older US equipment uses pin 3. So, if these types of equipment are being interconnected a special cable will be needed to make it work. N.B. Pin 1 is always used as the 'earthy' (screen) connection.
  20. When connecting a mic cable to a microphone, be sure that the XLR is pushed in hard enough for the latch to click into place (greater pressure is needed for XLRs having a rubber sealing ring). This is especially important if the mic is to be removed from its stand by the performer, and/or is likely to be treated roughly. Plugs falling out of mics during a performance is not good news.
  21. When running out audio XLR-to-XLR cables such as mic cables or feeds to amplifiers, it can be helpful to remember that the pins of the connectors 'point' in the direction of the signal flow. So, the end of the cable with a female connector needs to be at the 'source' end of the run, and the end with a male connector at the 'destination' end. N.B. DMX lighting control cables are the opposite to this!
  22. When running out an induction loop cable, avoid including the stage within the area of the loop if at all possible. This will reduce the likelihood of magnetic feedback problems caused by guitar pick-ups etc. picking up the field from the loop. (Note, however, that the field is not contained entirely inside the loop area − there is some degree of 'overspill' − so the further the loop area from the stage the better.)
  23. Wrapping a mic cable a couple of turns around the vertical pole and boom arm of a mic stand is a good way to keep the cable tidily in place (when your stand isn't supplied with the nice clips for that purpose). However, don't do this (still less use the nice clips!) on a vocal mic stand unless you're sure that the vocalist will not want to remove the mic from its stand and hold it, at some point during the performance.
  24. When a stereo source is to be connected to a stereo rig, the ideal would be to use a fully-featured stereo input channel on the mixer. However, many professional mixers do not have these (e.g. so-called 'Tape/CD' inputs often have very limited EQ and Aux Send facilities). In such cases it may be necessary to use two normal mono channels of the mixer, one for the Left signal (panned hard left) and one for the Right signal (panned hard right). When doing this it is necessary to ensure that the channels are set-up identically, and that any subsequent adjustments are made to both of them.
  25. When a stereo source is to be connected to a mono rig, it is necessary to decide whether or not the Left and Right signals must be summed, or if just one of them can be used. For recorded material, the signals must usually be summed in order to avoid losing content (in case of any hard panning in the recorded mix), but for stereo instruments often just the Left channel is used. (Many stereo keyboards provide a summed mono output from the Left output jack if the Right output jack is not used − but some musicians might query the lack of two cables...)

    If summing is required, then if the mixer has an available stereo input with sufficient features this may be used provided that the relevant Left and Right busses get summed at some point into the mono signal that is used (e.g. by these busses being routed to the same Mono output of the mixer).

    If a suitable stereo input is not available then a 'Y-splitter' may be used 'in reverse' to combine the source's Left and Right output signals by direct connection of both of them to a single mono channel of the mixer. However, do not do this if the signals come from a very low-impedance source (such as a headphone output) − otherwise there would be a risk of distortion or even possible damage to the equipment, due to current overload. There is not usually any problem in making a direct connection between line-level Left and Right outputs of semi-professional or consumer-type CD decks etc. If there is any doubt about the suitabililty of directly connecting Left and Right together, then it is necessary to use two mono channels of the mixer, one for the Left signal and one for the Right. The two channels must be set-up identically (routing both to the same bus), and any subsequent adjustments must be made identically to both of them.

  26. Problems (typically intermittent operation, or distortion) are sometimes experienced on particular mixer channels, due to oxidation of the normalling contacts of the Insert jack sockets. (This is more likely to occur if the contacts have been held separated for a very long period of time, by a plug remaining inserted.) Until the socket is replaced, the problem can be solved by use of an insert lead with its 'send' and 'return' connectors at the far end linked together, or by use of a 3-pole jack with its tip and ring terminals connected together (and no cable attached).
  27. When connecting or disconnecting to/from a live 3-phase supply (for example by inserting or removing a 4-pole CEE-form connector), there is a possibility that the connections of two or more of the phases may momentarily make contact without the Neutral connection. This could potentially result in serious damage to any equipment currently connected to the distribution arrangement that is being connected or disconnected. Therefore, it is strongly recommended that all equipment is isolated from the distribution arrangement (e.g. by removing their plugs) before connecting or disconnecting the arrangement to/from a live 3-phase supply. (It is not sufficient to merely ensure that the equipment switches are in the Off position.)
  28. When using equipment that requires an external power supply unit, use only the make and model of unit advised by the equipment manufacturer. [For an explanation of this advice, see this question on the FAQ page − Ed.]

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Mixing

(Also see the Intro for Mixing Engineers page and the Mixing Facilities page.)

  1. Always set the channel gain controls first, using the mixer's built-in level indicators. Note, however, that a subsequent large change to the channel EQ settings will often change the overall level of the signal. If an EQ boost significantly increases the level, it may be necessary to decrease the setting of the channel gain control in order to restore the required headroom (which in turn may necessitate re-adjustment of the channel fader).
  2. After the initial rig check, set up monitor mixes before the front-of-house mix, as this enables the total on-stage sound level to be assessed and controlled early on. Also, when the band are desperate to start their rehearsal (because of delays to the set-up schedule, or because insufficient time has been scheduled for a rehearsal after the sound-check), having the monitors set up first will enable the band to start rehearsing sooner.
  3. It is common for vocalists to sing louder, and for musicians to play louder, when the audience are in place for the event (as compared to how they performed in the sound-check). So it can be helpful to set the gain controls a little on the low side during the sound-check, to accommodate the higher levels expected later.
  4. It can sometimes be difficult to see which switch-buttons on a mixer are 'In' and which are 'Out' − especially in poor lighting conditions. To help with this, some mixers (e.g. Mackie) have a line drawn around the buttons (e.g. a white line on grey buttons). If you can see the line above the mixer panel then the button is 'Out'; if you can't then it's 'In'.
  5. To avoid overloading the mixing amp of the desk, when creating mixes start with the faders at their '−5dB' positions (approx 60% of travel), then vary them from there − mostly with reductions. If during sound-check you end up with any channel faders exeeeding '+3 dB' (85% of travel), more than 10% of them exceeding '0 dB' (75% of travel) or more than a quarter of them exceeding '−5 dB', then increase the main fader setting and back off all the channel faders by a corresponding amount. (See also the next proverb.)
  6. To maintain a satisfactory signal-to-noise ratio from the the mixing amp of the desk, if during sound-check you end up with all the channel faders at below '−15 dB' (approx 30% of travel), then decrease the main fader setting and increase all the channel faders by a corresponding amount.
  7. Only mix in stereo when there's a real benefit (e.g. special effects) − and only when the layout of the venue is such that the majority of the audience are covered well by both the Left and Right speakers (this is very rare!).
  8. Make good use of your mixer's grouping facilities (e.g. vocals in one group, drum mics in another, guitars in another, etc.), so that the level of these sets of channels in the mix can be adjusted as a whole, using the group faders. If your mixer doesn't have a grouping facility, but has Left, Right and Mono (L+R) master faders, then by panning the vocals to hard left and the instruments to hard right you can use the Left and Right master faders as group faders (in which case of course you use only the Mono output to drive the front-of-house amplifiers).
  9. The sound throughout a venue will be different at different locations − and not just louder nearest to the speaker stacks. What's more, the sound will often change significantly when the audience enters − there will be less natural reverb and the high frequencies will tend to be reduced towards the back of the venue as they are absorbed much more by the audience than are the bass frequencies (see grazing effect). So familiarise yourself with the sound in different parts of the audience area, and during the event be aware that members of the audience are not all hearing the same sound as you − especially if you are mixing from the very back of the venue.
  10. When setting the individual channel EQs during sound-check, it can help you to focus on the sound via the channel to be adjusted if you first temporarily raise the level of that channel in the mix. After setting the EQ, restore the channel fader to its correct position (which may be slightly different to its previous position, because of the effect of the changed EQ) before moving on to the next channel.
  11. One possible way to set sweep EQ controls is as follows:
    • After setting the Low (LF or Bass) and High (HF or Treble) controls as required, make sure that the cut/boost control(s) of the sweep EQ is set flat (i.e. to '0', 12-o'clock).
    • Now listen to the sound and decide what you don't like about it most of all.
    • Next set the cut/boost control of the sweep EQ to give a large amount of boost (about 10 to 12 dB) and set the Q control (if you have one) to about 2.5.
    • Set the Frequency control to minimum, then slowly rotate it up to its maximum setting, noting the position that makes what you don't like about the sound (as noted above) become significantly worse. When you have swept the whole range, return the Frequency control to that position, and return the cut/boost control to '0' (flat), so that the original sound is obtained.
    • Now slowly rotate the cut/boost control anti-clockwise until the best sound is obtained, in conjunction with adjustments to the Q control (if you have one).
    • Finally, make any necessary re-adjustments to the High and Low controls (and to other sweep EQ controls on that channel, if it has any others).
    • If you have other sweep EQ controls on that channel, proceed to adjust them in like manner.
  12. When using a multi-amped system (i.e. separate amplifiers for each frequency range, e.g. bass, mid, high), keep the main graphic equaliser flat until the crossover(s) have been properly set and the amplifier levels for each range have been properly balanced.
  13. When graphic equaliser sliders have a very small travel (35 mm or less), an adjustment of just one or two mm can have a very significant effect on the sound. Check the 'Range' setting, if there is one (e.g. 6 dB or 12 dB).
  14. Remember that the FOH graphic equaliser affects the total mix, so don't be tempted to adjust it based on the sound of a single source. (The exception is playback of a pre-recorded track that you are very familiar with the correct sound of − in which case first be sure that the relevant channel EQ is set flat!) An ideal way to set up an FOH graphic is using pre-recorded test tracks corresponding to each frequency band of the graphic, and checking the sound level of each band at several places in the venue using a good quality sound level meter (this takes a long time!) − Again, first be sure that the EQ is set flat on the channel used for playing the test tracks! [Analysis tools are now a popular alternative method for setting FOH grahics. Monitor graphics are often best set up using the ringing out method − Ed.]
  15. It is unusual for controls to need to be at their minimum or maximum settings (with a few obvious exceptions, such as unused Aux Send controls and faders at minimum). Such a setting is generally undesirable, as it gives no further room for adjustment and implies that an 'ideal' setting cannot be reached. If you find that it is necessary to set a control this way without an obvious explanation for the need, then it may be an indication of an underlying problem that would be better corrected in another way.
  16. Treat any comments from the audience judiciously. Enquire at what time(s) during the event the comments relate to, and where abouts in the venue the person was located. Show interest, be courteous, and remember that tastes differ from person to person.
  17. Get to know your mixer well − e.g. which Aux or Effect sends are pre-fade and which are post-fade, and whether they are pre-EQ or post-EQ.
  18. Activate the channel Low Cut switches on all channels with no wanted deep bass content − especially on microphone channels used for vocals, strings, drum overheads, etc.. This reduces pick-up of unwanted bass leakage, handling noise, etc. on those channels. [However, check that these switches are not activated on channels with wanted bass content, such as kick drum, keys, bass, etc. − Ed.]
  19. Keep alert, even when things seem to be going smoothly. The unexpected can and does happen, and a rapid response is sometimes required.
  20. If you are using a channel input for the return from an effects unit, be very careful not to turn up the relevant effect send control on that channel. If you do, the resultant electrical feedback could seriously damage your speakers. Preferably, mark the control in some way, as a reminder.
  21. Once a satisfactory mix has been established, and changing circumstances then require further adjustments to be made, take care to make only small adjustments (in the first instance). All the hard work done during sound-checks and rehearsals can be rapidly undone by a few large changes here and there.
  22. Remember that ambient noise sources (such as HVAC, or sounds from outside the auditorium) may have a significant impact on the overall signal-to-noise ratio perceived by the audience − especially in low-level applications such as speech amplification. When the PA system signal-to-noise ratio is satisfactory but the perceived signal-to-noise ratio is poor, and a further increase in amplified sound level is not possible (e.g. because of feedback), steps may have to be taken to reduce ambient noise levels.
  23. When using a monitor mixer, with mixes created using the auxiliaries, use post-fade auxiliaries. This enables the channel faders to be used as overall level controls for the individual sources, allowing convenient and rapid adjustment of a source in all the mixes simultaneously when required (e.g. due to feedback or a sudden change in source level).
  24. When using a monitor mixer, patch graphic equalisers into the inserts of the mixer outputs (usually the auxiliary sends) rather than routing the outputs via the graphic equalisers. This allows the effect of the appropriate graphic equaliser to be taken into account when monitoring a particular output using its AFL (but check that the AFL monitors the signal post-insert!).
  25. When using a monitor mixer, if at all possible use a listen wedge that is identical to the monitors being used by the performers, so that you get the best possible match to the sound that they hear from their monitors.
  26. When playing pre-recorded material that is routed via pre-fade auxes (e.g. to stage monitors) as well as via the channel fader, remember that if the track needs to be manually faded out then you must fade down the relevant aux send(s) as well as the fader − otherwise even with the fader fully down the audience will probably still hear the material via the monitors. (In such cases, consider having the relevant aux send on that channel switched to post-fade, if your desk has that facility.) Obviously the same applies to manual fade-ins.

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Amplifiers

(Also see the Amps & Speakers page.)

  1. Be sure that amplifiers have an adequate output power rating − at least 30% above the power input that the speakers require in order to achieve the desired sound level − to maintain headroom on signal peaks. But don't misuse the spare power by over-driving the speakers.
  2. Remember that the maximum output power that can be obtained from a particular channel of an amplifier is not a fixed value − it depends on the overall impedance of the speakers that are connected to that channel.
  3. Before switching on the amplifiers, switch on mixers, graphics, etc., and check that the amplifier level controls are set at minimum. Likewise, before switching off any other equipment set the amplifier level controls to minimum and switch off the amplifiers. [For more detailed information on this, see Switch on/off procedure − Ed.]
  4. When using a multi-amped system (i.e. separate amplifiers for each frequency range, e.g. bass, mid, high), be sure that the main graphic equaliser is flat before starting to balance the amplifier levels for each range. The only proper way to balance the amp levels is to use an analysis system or to use an audio test CD having test tracks for each frequency range, and check the sound levels at several places in the venue using a good quality sound level meter. (First be sure that the EQ is flat on the channel used for the audio test CD!)
  5. Never connect a speaker output of an amplifier to anything other than a speaker. Doing so can cause all kinds of expensive damage.

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Speakers

(Also see the Amps & Speakers page.)

  1. In terms of sound quality, this is the part of the system that will make the most difference (closely followed by microphones), so don't compromise on choice. It isn't possible to properly compensate for poor quality speakers by using equalisation.
  2. When choosing speakers, compare the sensitivity figures. This is a guide to how much sound level you will get from the speaker for each watt of power input from the amplifier, and can vary hugely between different types of speaker. Remember, however, that the easiest way for the speaker manufacturer to achieve an impressive sensitivity figure is to compromise on sound quality, so be sure to check that too.
  3. To get the best out of your speakers, be sure that they are at the correct height for the situation are that they are positioned and angled correctly. This can make a very significant difference to the quality of the sound perceived by the audience! For example, locating speakers inward from the side walls, and/or angling them slightly inwards towards the centre of the room, can help to reduce troublesome reflections from the side walls (especially in long, narrow rooms). And raising the height of the speakers and angling them slightly downwards can help to reduce the difference in sound level between the front and back of the room. (See also the next tip.)
  4. When setting the position and angle of front-of-house speakers, use the 'line of sight' method to help with the alignment of the high-mid cabs and HF horns. This is especially helpful to get an initial position, before the system is ready to be switched on and listening tests done. First stand behind (or under) the speaker to judge what area it is covering, and make adjustments to its position and angle as necessary. Then walk around the listening area, looking at the relevant speakers − you should be able to see into the speaker horns. (Remember to take into account any obstacles that might not yet be in place, such as a standing or dancing audience.) These methods work because it is the high audio frequencies that carry the intelligibility and clarity of the sound, and these travel in substantially straight lines, just like light.
  5. If you are connecting speakers of different impedance to the same amplifer, the speakers having the highest impedance will take the smallest amount of power from the amplifier (and will therefore probably produce the least sound).
  6. Configure the speaker system according to the programme material. Powerful bass bins are not required for reproduction of speech, or of music with minimal bass content.
  7. When positioning monitor speakers close to microphones, take account of the polar pattern of the microphone in order to ensure minimum pick-up of the monitor sound by the microphone, and so reduce feedback problems. For cardioids, the monitor should be on the rear axis of the mic, i.e. directly behind it. For super-cardioids use two monitors, each at an angle of 55 degrees from the rear axis. For hyper-cardioids the two monitors should each be at an angle of 70 degrees from the rear axis.

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Cables

  1. For ease of recognition, put similar markings on cables of the same type (mic cables, speaker cables, instrument cables, etc.), and store similar types together. They can be marked at the ends with coloured tape, with clip-on identification rings, or the cables themselves could be of a different colour.
  2. Don't coil cables by wrapping them around your arm − this stresses the cable and puts a twist in it at each turn of the coil. Instead use a good cable coiling technique, such as the 'over-under method'.
  3. Releaseable cable ties and Velcro® ties are a real boon. Use them around cables in storage or transit to prevent them becoming tangled with each other; use them on-stage to keep coiled excess cable lengths neat and tidy. 200 mm is a good length to use for most cables. For bulkier coils (such as speaker cables), two of these ties can simply be linked together to make one (nearly) twice as long.
  4. If you plug together the two ends of XLR-XLR cables as soon as you have coiled it for storage or transit, the ends can't fall between the turns of the coil and create knots.
  5. If a cable is suspected of being faulty, don't put it back in the box with the others, to be taken out again and be used another time. Put it separately (preferably marked in some obvious way) until it has been checked and repaired.
  6. Cable faults are often intermittent, so if a cable seems to be faulty and then seems OK again, mark it as suspect and don't use it until it has been fully checked out − otherwise it may unexpectedly fail again during use.
  7. Always use proper speaker cables that are adequately rated for each partcular job. Don't use instrument jack-to-jack cables or microphone XLR-to-XLR cables for the interconnections between power amplifiers and speakers, or between backline heads and their speaker cabs. Inappropriate cables can be damaged by the high current and voltage of speaker signals (which may in turn cause equipment damage).
  8. It's worth investing in good quality cables − but the hyper-expensive types (such as are sometimes advocated by audiophiles and audiophile equipment suppliers) rarely give much added benefit in the context of PA systems. Manufacturers well-known for the high quality of their cables include Belden, Canare, Klotz and Van Damme (the links are to their websites, and open in a new window).
  9. Check mains cables frequently for signs of damage, and get them promptly and properly repaired or replaced. [See PAT − Ed.]
  10. When removing cables that have been gaffer-taped to the floor, don't pull up the cable from the floor with the tape still attached to the cable. Rather, while pulling the tape from the cable with one hand, hold the adjacent loose part of the cable down on the floor with the other hand. This will prevent the edges of the tape curling around the underside of the cable − if the sticky sides touch they are almost impossible to get apart again and the tape will require time-consuming removal from the cable afterwards by tearing or cutting, with a risk of damage to the cable.
  11. In large systems, it can be helpful in tracing cables (when you need to fix a problem or to make changes) if all cables have a unique reference number at both ends. Clip-on numbered plastic rings are available for this purpose.
  12. Don't use XLR cables that have the shell of the connectors connected to the cable screen (pin 1). This avoids the possibility of earth-loop problems being caused by the connectors at cable joints coming into contact with each other, or with adjacent metalwork.
  13. When wiring XLR connectors to make balanced cables, the name 'XLR' can be used as a mnemonic for which pin is which: pin 1 = X = Earth, pin 2 = L = Live (hot), pin 3 = R = Return (cold).
  14. The mnemonic 'Tip-To, Ring-Return' can be used to help remember the (most common) wiring of mixer TRS insert jacks. So, the signal is fed To the effect unit via the Tip connection, and it Returns to the mixer via the Ring connection.
  15. When making cables to connect from a 3-pole (stereo) mini-jack headphone output of a laptop, MP3 player, etc. to a Line input (e.g. of a mixer), it can be useful to wire a pair of resistors into the connector(s) at the other (i.e. destination) end of the cable. This avoids the possibility of damage to the laptop or player if the hot pole of the destination end connectors make accidental contact with something earthed while the mini-jack is still plugged into a headphone output. (Such an accidential short-circuit can only easily occur if the destination end is a jack or phono connector − e.g. if jack connector tips make brief contact with signal earth as they are plugged in to a jack socket.)

    Wire a 1 kilohm resistor in series at the Left hot conductor's connection, and another in series at the Right hot conductor's connection.

    This also provides protection against damage, or current-overload distortion, due to the Left and Right headphone outputs being connected directly together. This might be a permanent connection, as in the case when the stereo output cable is wired into a single mono connector at its destination end. Or it could occur if the two separate Left and Right connectors at the destination end get plugged into linked input sockets (such as a pair of linked input sockets on a single channel of a DI box), in order to create a mono signal.

  16. When doing special things inside connectors, as suggested in the previous entry, it's wise to label the cable accordingly, to avoid confusion later. (Also because such cables may be indicated as faulty by a cable tester, even though they're wired as intended.)
  17. Keep all cabling well clear of transformer power supply units (whether of the plug-in or in-line types), as the stray magnetic field from the transformer can induce a hum current into the cable conductors. Even mains power cables should not be located close to such power units (including any excess length of their own supply cables), as a hum current can be induced into the earth conductor of the power cables − this is more likely to cause a problem if you have any unbalanced signal interconnections. Preferably, route all 3-core mains cables directly away from power supply units.
  18. When packing away bodypack units, don't wrap the mic/earphone cable around the bodypack. These thin cables are very easily damaged, and repeated bending of the same points along the cable around the corners of the bodypack can cause problems to occur at those points.
  19. In an installed system, if you need to trace the route of a cable that has been run out of sight within a wall, floor or ceiling, then this can be done by passing a suitable current through the cable and using a pick-up coil to detect the resulting magnetic field produced by the cable. If the current passed through the cable is at an audio frequency then the signal from the pick-up coil can, after amplification, be fed to headphones or earphones. It can be convenient to use a frequency of the order of 400 Hz and to use an induction-loop pick-up tester to detect the field. The test signal can be obtained from any suitable source and amplified using an PA amplifier to provide a suitable current level, in which case a series resistor of suitable value and power rating will be needed, to limit the current level. Alternatively, an induction-loop driver can be used as the amplifier, in which case no series resistor is needed. The current can be passed down one conductor of the cable and returned to the amplifier through another − be certain, however, that the selected conductors are not connected to any other equipment, or to earth. The amount of current required through the cable is dependent upon a number of factors, including the sensitivity of the pick-up equipment and the distance between the accessible surface(s) and the cable. Care must be taken, however, not to cause damage to the cable by passing so much current that its conductors overheat − extra care must be taken with small-gauge conductors such as those within a multicore.

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This page last updated 27-Nov-2016.