Omni-directional speakers usually send sound in all directions, front and back. They are not standard, and are usually found in outdoor plazas.

Uni-directional speakers only send sound in one direction - forward. This is normal for most PA speakers.

There are also omni-directional microphones, which are not good for live music. It is better to use microphones with a “cardiod” pattern.

The “Sum” is sometimes called “Mono”, as it is the combination (or addition) of the Left and Right signal. Check out the series of lessons Sound Engineering Q&A for more on this topic.

On Guitar Noise

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