Live Sound Equipment - Speakers

When using speakers in the live environment, it is often best to use passive PA speakers as opposed to active ones. The difference between active and passive speakers is that active speakers have an amplifier built into them, whereas passive speakers require an external amplifier and speaker cables to work. The reason why it is best to use a passive speaker system for live sound is because from the external amplifier, you can get much more output from them due to having a larger wattage. The amplifier used to power them can also vary in size (watts), so you would need an amplifier that can take the power from the speakers, so the larger the speakers, the larger the amp would need to be. The routing of passive PA speakers to a mixing desk is very simple too, as this diagram below will explain:

As you can see from the diagram, the speakers go into the amplifier and the amplifier goes into the main outputs of the mixing desk. The speakers connect to the corresponding left and right inputs on the amplifier via speaker cables (blue wire), and then returned to the mixing desks left and right outputs via XLR cables (red wire). This is very simple set up, and the only thing to consider is getting the left and right speakers the correct way round, and by this, I mean connecting the left speaker to the left input, then taking that input to the left output of the desk, and doing the same with the right speaker. If there is a mix up in the routing then you could potentially have them the wrong way round which would make panning any audio go to the wrong speaker. It is very simple to reverse though, just swap the cables around.

Wattage and resistance

The next thing to consider when using speakers in a live sound environment is the wattage of the speakers and amps, as well as the resistance. The wattage of things is measured in watts (w for short) and wattage is basically the amount of electrical potential that something has. Using guitar amplifiers as an example, a 15 watt amp has less potential energy than say a 50 watt amp, meaning that a 50 watt amp can go much louder. In regards to speakers and amps, it works in very much the same way that the higher the wattage they both have, the more potential volume you can get out of the speaker. You have to be careful with speakers and amps though, because say you have an 800 watt amp and two 500 watt speakers, you would not be able to power the speakers because the amp wouldn’t have enough power. Two 500 watt speakers equals a kilowatt, and the amp doesn’t have a kilowatt of power, so you either need to get a bigger amp with at least 1000 watt of power, just use one 500 watt speaker or get two speakers that equal less than 1000 watt of power. It is best to balance the signal, although leaving about 100-200 watt headroom between the amp and speakers would be beneficial. Having an amp too small for the speakers wouldn’t be enough to power the speakers as I have just mentioned, but having an amp too big for speakers also wouldn’t be good either, simply because running too much power into small speakers leaves the risk of blowing the speakers and ruining them, hence why it is best to balance the signal.

Resistance plays a key part in everything because it determines how loud you can actually get your speakers. The resistance of an amplifier can vary, although they are usually around 8 ohms, ohms being the measurement of impedance (resistance). The impedance of an amplifier is relevant to the wattage and impedance of the speakers, because say for example you have two speakers at 200 watts, 8 ohms, you will be demanding 4 ohm and 400 watt out of your amplifier, whilst still feeding 200 watt in each speaker. This may sound confusing; however it is very simple once you know the formula. This diagram below will show you exactly how it works:

Live Sound Equipment - Mixing Desks

Analogue Desks

The mixing desk that we use in school for live sound is the Behringer Xenyx 3200 (picture to the left). It is a 32 channel mixing desk with 6 aux sends per channel, 4 stereo line outputs and 4 output buses, as well as many more features. This is like most standard live mixing desks, such as the Yamaha MG32/14FX or the Peavey 24FX. Some mixing desks have different features on them that make them distinctively better for live use as oppose to studio use, for instance, a mixing desk with more outputs and auxiliary sends would be better for live use, whereas a mixing desk with MIDI controllers would probably be best for studio use. Desks with more channel inputs would also be preferable over one that has less because the more channel inputs there are, the more instruments/microphones you can have on stage. A mixing desk with say, 8 channels on them will only leave you with 8 possible inputs for microphones/instruments, making it very unpractical for live use. A 32 channel mixing desk would triumph over an 8 channel mixing desk because of the amount of possible inputs available. As well as inputs, a mixing desk would want to have multiple output sends too, allowing multiple amounts of monitors/speakers on stage. The auxiliary sends on a desk would be the main control of the monitors on stage, look at this diagram below:

As you can see by this diagram, the auxiliary send allows you run some external monitors into the desk via an amp going into the mono output of the auxiliary. The monitors are then controlled by the ‘Aux 1’ knob which can be found on all channel input strips, allowing you to adjust the volume of what is going out through the monitors. The more auxiliary outputs that a desk has, the more monitors you can run, so the desk we use in school (Behringer Xenyx 3200) would be very good because it has four mono aux sends, allowing for four sets of monitors on stage. A comparison between the mixing desk in the school recording studio, the Allen and Heath ZED-r16, and the Behringer Xenyx 3200 would be that the ZED-r16 has limited features that make it good for live use. The outstanding features of MIDI controllers, firewire connection and impeccable sound quality mean it triumphs over the Behringer for studio use. The Behringer is far better for live purposes though because it has more auxiliary, FX and main outputs, four different group buses and a maximum of 32 possible channel inputs. The ZED-r16 has only two auxiliary outputs for monitors, one set of main outputs and only 16 channel inputs, making it unpractical for live use. The Behringer has no USB or firewire input setting making it nearly useless for recording purposes.

Another main feature of the Behringer that excels it in the live environment is the four different group buses. What these groups do is they control the volume of a number of channels with just one fader, and the way to send certain channels to a group is by pushing in the group button next to the channels fader. This detailed diagram below shows an exact representation of the desk, explaining how to send channels to a group:

By clicking the button that says ‘group 1-2’, the channel input gets sent to the subgroup output one. By clicking the button that says ‘group 1-2’ on multiple channels, they all get sent to the same subgroup and you can adjust the volume of potentially 32 channels on one fader. A way to use the groups logically is to maybe group all of the drum microphones together, setting the levels first and then sending them to the output. Having control of a whole drum kit on one fader is very useful, because if the whole kit is too loud or too quiet, it makes it easier to adjust the volume accordingly. You could group the whole drum kit on say group 1, then on group 2, 3 or 4, you could control all of the vocal microphones, simply by pressing the relevant button next to the fader. The last button on the channel fader, represented by the diagram above says ‘main’, and that button when pushed in send the channel to the main output. 

Digital Desks
There are many differences between analogue and digital mixing desks, as well as many similarities. For starters, digital desks are far more expensive, due to the added features from analogue, the way the signal goes out the speakers is different, and the amount that you can actually do on them is far more superior over the analogue desk. It works in the same way as an analogue mixer in the way that the microphone gets plugged into an input, someone speaks into it and the signal comes back out again, however on a digital mixer, the signal gets converted from analogue to digital. A digital signal is a lot more clear and sounds better than an analogue signal, which is one feature that separated the digital desk from the analogue. Digital signals are used whenever you are recording using a DAW, it is the exact same process. The signal goes into the DAW as analogue, and gets converted by the DAW, and the digital signals gets sent to the main speakers. A digital desk is a software driven desk, meaning that all of the channels can be controlled by programming into the desk. Like an analogue desk, a digital one uses faders, channel strips, knobs etc. they just have the ability to be programmed and saved. For instance, you can set the levels for a microphone how you want them, get it perfect, and save the setting so you can automatically get that setting up again. This is very useful because you would spend time perfecting the setting, change the fader and knobs around, and still get that perfect setting by just loading it from the desk. Below you will see a picture of a digital desk (the Behringer X32) so you can see what it looks like in comparison to an analogue one:

The specifications of theBehringer X32 includes up to 32 microphone pre-amps with 6 aux inputs, 16 XLR outputs with 6 aux outputs, 25 mix buses complete with 6-band parametric EQ, 8 stereo FX slots for 40 plus effects plug-ins, plus many more.
For a further in depth analysis, clink this link to visit the Behringer website.

This sort of digital mixing desk would be useful for large venues such as the O2 arena in London. The in house mixing console that they use however is the Soundcraft Vi6 digital mixer (click here for more details) and it is a much larger desk than the Behringer, with features including 96 mono inputs, 32 input faders, and 32 fixed send buses. The venue owns two of these mixing consoles, assumingly a spare one just in case, and they only use this mixer for their live performances. 

Live Sound Equipment - Microphones

Dynamic

The most common type of microphone found in live music settings is the dynamic microphone. In most dynamic microphones, a very thin, light, diaphragm moves in response to sound pressure. The diaphragm's motion causes a voice coil that is suspended in a magnetic field to move, generating a small electric current. They are generally less expensive than condenser microphones (although very high quality dynamics can be quite expensive),and dynamics feature quite robust construction and can often handle very high SPLs (Sound Pressure Levels).Arguably, the most popular brand of dynamic microphone for live use are the Shure SM58 vocal microphones and the SM57 instrument microphones. These are reasonably priced (£ 85 - £100) microphones that have the durability and sound quality to be used by large and small venues, from stages and lounges all the way up to the likes of the NEC arena, Birmingham. Dynamic microphones are very versatile and can be used on most instruments, for studio and live use, making them an all-round good type of microphone. The function of a dynamic microphone is to be durable enough to sustain a live performance and to project the audio that is gone through them out of the monitors and speakers on stage. This diagram below shows the source of sound, from the microphone to the monitors (XLR leads are red, monitor leads are blue):

 

Ccondenser

Condenser microphones are less commonly used in the live sound environment because of their more sensitive diaphragm and less resistance to high volumes. To mic up an instrument, amplifier or to be used for vocals, a dynamic microphone would be preferable, although it is down to personal preference of the musician and the technician. Condenser microphones require phantom power in order for them to work, which means that for a live situation you may need to enable phantom power on the desk, as well as an optional external backup supply such as a phantom power box. This just means more cables and hardware which is a lot more complicated than just running a dynamic microphone. A popular use for condenser microphones, both in the studio and live performances, is for overheads when miking up a drum kit. Overhead condenser microphones would be used for larger venues, however on a small stage where the drum kit volume is overpowering enough already, overheads will not be necessary. Condenser microphones are more sensitive than dynamics, so using condenser microphones such as the Samson CO2 pencil, or the Shure KSM44/SL will mean that a lot more background noise will be picked up, which is not good when in a live environment. As well as this, feedback will be a concern. As mentioned earlier, condenser microphones are much more sensitive than dynamics and will pick up a larger range of frequencies, meaning that monitor feedback will be much more common. Feedback from a microphone is something that a sound technician would want to avoid at all times, so using a condenser microphone would be strongly not recommended.

Lapel Microphones

Lapel microphones are small, wireless ribbon microphones that clip onto the performers clothing, allowing for hands free capability. There are run from the mixing desk into a receiver via an XLR cable, and from the receiver it is picked up by a radio transmitter that is connected to the actual microphone head, worn by the performer. Lapel microphones have a high frequency response and are prone to feedback if incorrectly positioned on stage (much like most microphones really) but from my previous experiences, they feedback much easier than any dynamic microphone or some condensers. Lapel microphones are only practical for live use because of the one feature that separates them from any other type of microphone, the hands free capability. It is very common that you see TV presenters, comedians, and theatrical actors using them because they need there hands to perform and they need to move around the stage. This diagram below shows how they are routed through the desk:

The O2 arena, London, holds a large amount of live on stage microphones, however they popularly use AKG dynamic and condenser microphones. As mentioned in previous paragraphs, dynamic and condenser microphones have different purposes for live sound. The O2 arena use similar style microphones to any other venue, even at our school. AKG microphones serve very similar purposes to the shure dynamic microphones, as they are both very diverse, and very good quality. There is no mention of lapel microphones on the website, however they will definitely get used for a large pop/rock venue.

Diagram

This diagram below shows the priory stage set up with all the microphones and cables: