Choir Tech Know-How: Part 2
In my previous article, Choir Tech Know-How: Part 1, I gave you an overview of the different parts making up a sound system and different types of sound systems you can use for your choir. In this article I am now going to delve a little deeper, looking at the music player, amplifier and mixer and what they do.
To play backing or rehearsal tracks for your choir, you could simply use an Mp3 player or CD plugged into a speaker system. This will work fine, but has some drawbacks, particularly for rehearsals. Mp3 players are designed to play one complete track after another. That’s great on the train, but when you’re learning a song, it’s less effective. Not being able to easily go back to a particular point in the music is frustrating. Listening to a 16-bar introduction every time you want to play part of the track is a waste of your time and will quickly get boring for your choir. Larger tablets are better for this as they often allow you to drag the play bar back to roughly the right position, but it can be tricky to do accurately and you can’t mark positions on the tracks. My preferred solution is using a DAW (digital audio workstation) program on a laptop.
A DAW is a program designed to record, edit and play back music. I use it because it allows me to mark various places in a track, play different choir parts from a particular point, and generally see what is happening in the music. I will explain in further detail how I use the DAW in a dedicated article. The important point to note is that you will need to play the same track many times, often starting in different places, while you are learning your songs and this is a speedy and effective method.
The amplifier/mixer part of the equipment comes in many forms. It can either be one item or two or more separate items. Put simply, the amplifier boosts the signal coming in from the music player so that it is strong enough to be used by a speaker. The mixer allows you to have more than one audio source entering the amplifier at one time. How these two interact is often the biggest cause of confusion.
You will need a mixer if you want to have more than one source of audio playing through your speakers. These sources could be a backing track, microphones or instruments. All good mixers allow you to mix two or more signals and balance (ie change the relative levels) of each audio source. This is important in order to get a good blend of sound.
Mixers come in all shapes and sizes. You do not need a complicated mixer for rehearsals. You just need to ensure that you have enough channels (one for each sound source coming into the mixer) for your particular set up. At Total Voice Contemporary Choir, we use one stereo input for backing tracks and between one and four channels for microphones, depending on whether there are soloists or not. Each channel should have input level gain control (which allows you to balance the strength of the signals coming to the desk), some EQ, and channel faders to control the volume of each sound source. The desk should also have a master volume. On small desks these volume adjusters are often rotary knobs, on larger desks they are likely to be sliders – I find sliders are easier to work with as they show you the relative volumes more explicitly. It is important that the desk has enough outputs to allow you to attach the various speakers you want to use.
Other features that are nice to have include left and right pan options on the channels, auxiliary channels (that allow you to have more than one mix of the sound) and mutes on each channel (so you can cut off the microphones when necessary). Solo buttons (that cause just the selected channel to be sent to the headphone socket), and a headphone socket (so whoever is operating can hear what is happening on each channel) are also very handy. All this sounds a lot but most of it is found on even the smallest general purpose mixer.
In portable combination systems, the mixer can be part of the speaker. Each input will generally have its own gain adjustment (“gain” is how strong the signal is) and an overall volume (how loud the speaker is). It is important to get these two clear in your mind when you are trying to solve problems, but more of that later. In these systems you never actually see the amplifier as it is built-in to the whole system. For larger multi-speaker systems, it is normal to have a separate mixing desk and amplifier. There are two main types – a passive desk and active speakers, or an active (or powered) desk and passive speakers. Each system has its advantages and disadvantages.
Passive desk, active speakers – here the sound goes into the mixing desk where it is combined before passing along cables to one or more speakers which each have an amplifier in them. Each speaker will have its own volume control and sometimes will have the ability to act as simple mixers as well. Our main speaker can, for example, take the audio signal from an mp3 player and a single microphone. The advantage of this system is that each amplifier is separate; if you blow an amp outdoors on a wet day, you can continue with the other speaker. The desk is lightweight, but the speakers are heavy and require mains power.
Active desk, passive speakers – here the sound signals go into the desk where they are either amplified in the desk itself, or are amplified in a standalone amplifier before passing down special cables to your speakers. In general, these speakers do not have volume adjustment on them as this is done from the amplifier. In this case, if an amplifier blows you will lose all sound. The advantage is that the speakers are light and do not need mains power so are more portable. The desk and amplifier are heavier though, and you need to understand how to match your amplifier to your speakers for both watts and ohms.
When it comes speakers, size matters. Speaker sizes are measured in watts rather than physical dimensions. What does that mean for us? Watts correlate with how much sound the speaker can make – bigger wattage speakers generally make more noise. For rehearsals, you do not need massive speaker systems. We rehearse a choir of sixty with a single 150W foldback speaker and we have plenty of volume in hand should we need it. So somewhere in the 1 -2 watts per person is fine. For a gig, you hopefully will have more people in the audience than the choir – so you will need more powerful speakers.
As a very rough rule of thumb for indoor performance, you can get away with about 5W per person in the audience, ie a 150 seat hall would need about 750W of power. If you need to amplify in an outdoor venue you need to approximately double the amount of power per person, so an outdoor venue for 150 would need closer to 1500 watts of speakers. These are obviously very rough figures and depend on whether you are going to amplify the singers or not. If you are not amplifying your singers then you need to match the backing track volume to what they can produce. There is no point having a 1000W of speakers pumping out a backing track if you have a unamplified choir of twenty.
I hope you found this article helpful. Next time I will be focusing on microphones. I will also be putting together some video posts on desk set up and management. In the meantime do send in your comments and queries and I will be happy to help.