Setting up your PA system
Positioning
Your equipment should be set up to suit the audience. The speakers should be ideally mounted with the horns above the height of the audience. You will find that the sound at the back of hall or room will sound flat because the treble will get absorbed by the bodies between the speaker horn and the listener if they are below head height. Also ensure that the speakers are situated in such a way that the audience can’t knock them over, there is nothing better to ruin an evenings entertainment that a heavy speaker landing on someone’s head.
Connections
Connect everything up using suitable connectors and interconnects. Ensure that cables are not in positions where somebody could trip over them; it could injure the person and/or damage your equipment.
Use a Mixer
Class-d would suggest that power amplifiers are used in conjunction with a suitable audio mixer. This allows the correct levels to be achieved, maintained (see step 4) and reduces the possibility of damage to your equipment.
Set your levels
This often overlooked step is actually a very important part of creating a good sound and could prevent serious damage to your PA equipment. Firstly you should set up the volume on your amplifier to the loudest that you will need for your entertainment. To do this, follow the steps below:
- Turn you amplifier down to a low level.
- Play the loudest track you are going to be using.
- Adjust your mixer levels to a point where there the output level meters show levels that peak on or around 0dB. Levels above this show your level is too high and may ‘clip’ causing distorted sound.
- Turn you amplifier up in volume until you reach the desired level (note that a room full of people will mean that the volume needs to be higher than the level for an empty room). If you hear any sort of distortion immediately turn the volume down to a level where there is no distortion. This distortion effectively tells you that you have reached the maximum level you PA system is capable of producing. Prolonged use at levels above this will result in damaged (or burnt out) speakers and possibly damage to you amplifier.
- Important: The Health and Safety Executive has guidelines for the level of sound in live venues, information on this can be found by contacting them or your local council directly.
- If you are using microphones then this is a good time to set the levels and position them (or your speakers) so you can reduce the likelihood of feedback.
- Don’t be tempted to increase your amplifier levels during the entertainment. It can be very difficult to hear distortion in a crowded room and by the end of the event you may find your speakers have been irreparably damaged.
Speaker Damage
Speaker damage usually occurs for one of three reasons, been over-driven, clipping or incorrect frequencies reaching you drivers.
Over-driving – This will occur when you put too much power into you speakers, when using an amplifier that is rated higher than the speakers. The symptom of this is distorted sound. A very simple problem to fix, turn the volume down.Clipping – This usually occurs when using an underrated amplifier turned up full. When this happens the sound will appear to ‘click’ when the amplifier is unable to produce the level of sound you are asking of it. This signal will damage your speaker very quickly. Again turn you amplifier down. Even amplifiers with clipping protection can cause damage to your speakers when used for prolonged periods with the clipping protection cutting in. You may want to consider buying a more powerful amplifier.
Incorrect frequencies – Speakers require crossovers to split the frequencies going into you speaker drivers in to Hi and Low. A poor quality or incorrect crossover could allow for example low frequency sound to get to you tweeter, a sure fire way to blow it. All Class-d speakers have crossovers that will help prevent this problem.
Choosing your amplifier.
The first thing to do when choosing which amplifier to use is to decide what speakers to use with it. It is far better to have an amplifier that is rated the same as or higher than the rating of the speakers (always look for RMS power ratings and use these for both the amp and speakers). This is because is it easy to turn down the amplifier volume on a higher powered amp, but you will have to buy a new amplifier if you are having problems with clipping.
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