This introduction to PA Sound systems series was originally presented as an online self study course which I designed, and I am now presenting it in the form of a series of blogs.
The aims of the series are as follows:
- To enable readers to select appropriate equipment for basic systems
- To enable readers to set up and operate typical systems
- Give an understanding of common problems
- Introduce concepts of advanced operation
The first section covers the basics, such as types of connection and base components. Then we cover these in more detail before looking at the types of equipment required for a variety of scenario’s.
Next we look at a "typical" set of controls for a professional mixer and a tour of the real thing. The final section of the course looks at common problems and some advanced techniques
The Basics - Balanced and Unbalanced signals
We are not talking about the state of mind of the Sound Engineer based on the supply of tea or coffee, but rather the type of audio signal being sent.
It is important to cover this right at the begining, because if you do not understand the difference between the types of signal it can cause you serious grief later.
A basic audio signal varies between earth (0v) and a positive value, for the scientists among you, its called a sinewave. The problem is, these singnals a very likely to pick up stray electrical interference.
The picture below shows the signal in black and the interferance in yellow.
This basic signal is known in audio circles as 'unbalanced'
Imagine you had a signal source at one end of a room and it was connected to an amplifer at the other end by a long cable, all the interferance would be amplified too.
A balanced signal is sent down two conductors, a third overall screen is also usually found on good quality cable. The diagram below shows that the audio signal is sent as + and - and out of phase with each other.
This means that when the audio signal is recombined by the audio equipment any interference (signified by the yellow arrows) is cancelled out.
The advantage of using balanced audio signals is that long cable runs become possible, that is why most professional equipment allows the use of balanced audio signals.
The point to remember is that if you take a professional balanced microphone, and plug it into a portable amplifier/speaker combination that only has unbalanced inputs you will loose half your signal.
Thats all very well, but how can I tell from looking at a cable which it is?
As a rule of thumb, if you see a cable that looks similar to the one shown below, it is a balanced cable and can be used for connecting microphones to mixers, or mixers to amplifiers
Typical PA equipment
- MICROPHONES (MIC's) - the microphone component takes physical sounds and converts them into electronic signals.
- MIXER - the mixer component takes inputs from MIC's or Electronic sources such as CD players or Keyboards
- AMPLIFIER - the amplifier component takes an output signal from the mixer and increases (amplifies) the signal to drive speakers.
- SPEAKERS - These reverse the process begun with the MIC's and convert the final electronic signal into physical sounds
You can get "powered mixers" that combine the functions of mixer and amplifier and these can be useful but if you later want a larger mixer you would have to replace both components.
You can get "Combi units" that combine the functions of mixer, amplifier, and speaker. These can be useful but if you need a high power output (for large open spaces) or more than a couple of inputs then a powered mixer with modern portable speakers may be a better solution.
|3 Pin XLR
||1/4 inch Mono Jack
The 3 pin XLR connectors are industry standard for balanced connections, although some equipment uses Stereo Jacks. In a 3 Pin XLR, Pin 3 is negative (cold), Pin 2 is positive (hot), and pin 1 is earth. In a Stereo Jack, the RING is negative (cold), the TIP is positive (hot), and SLEEVE is earth.
¼" Mono Jack
the ¼ mono jack is a common connector for unbalanced inputs/outputs. On older equipment wear in the jack sockets can cause poor signals. In a mono Jack, the TIP is positive (hot), and SLEEVE is earth
Speakon connectors come in two and four pin varieties, they usually connect speakers and amplifiers. In a Speakon connector you will have 1 or 2 pairs of connectors, each pin will be marked to indicate + or - and its pair. For example 1+, 1-, 2+, 2-
To be continued ........