In part 1 we examined home audio. Now, in part two, I would like to take a look at two big parts of speaker systems. How the speakers themselves work, and how systems are put together when focusing on live sound.

Live Sound

There are 3 basic parts to any sound system

  • Soundboard
  • Microphones
  • Speakers

These three are all it takes to get stage music going. In theory, nothing more is required. However, there are subcategories, and a few other things that you can use to make it better.

Soundboard

Many people think that to play live music you just plug your instrument into the speakers and that’s the end of it, however that is not the case.

Soundboards (known to the professional as a “mixer”) are a rather simple idea: Bring in all the data from the instruments and microphones and send them to the appropriate speakers. However it is much more complicated in practice.

A soundboard is essentially made up of channels. Each channel corresponds to one input (can be instrument, mic, our anything else that can output sound). each channel has its own set of controls for volume and various other effects. The larger and more expensive the board, the more options you have on the soundboard.

A standard mixer

Most boards have a few effects that they the are capable of achieving. The most important, the pan effect. Allows a particular instrument to be sent to only one half of the speakers. There are also various reverb and delay effects. However these are most often applied by the instrumentalist himself before the signal even gets to the soundboard.

Microphones & Other Inputs

Different microphones are made for different tasks.  A condenser microphone, for example, is perfect for use in studios. It provides pristine sound quality and frequency response (in other words, it can record very high and very low sounds). The only problem with condenser microphones is that they are very sensitive to loud noises (which abound in concerts). Condenser microphones are also quite expensive, and unable to stand up to the abuse they might receive in a lively concert. Condenser microphones also require their own source of power (48 volt “phantom” power). For these reasons, condenser microphones are generally not used in concert.

Dynamic microphones, on the other hand, make a lot more sense in a concert situation. They are considerably cheaper then condenser microphones, but are much more rugged. Chances are that dynamic microphone that looks like it’s been to hell and back will still sound as good as the day it came out of the box.

The difference between these two types of microphones lies in the technology behind them, which I will discuss in a later post.

The Shure SM58 dynamic microphone. This microphone is considered a standard for all performances.

Microphones, of course, are not the only things that supply input to the soundboard. In fact, a large percentage of the inputs in, say, a rock concert, are not microphone generated. Some will come from an electric guitar. Others will come from keyboards, or any of the numerous non-acoustic instruments. These take input from the musician and convert them into an electrical signal which can then be sent to the soundboard to be processed. In the average rock lineup, the only true microphones are for the drums and the vocals. However many other instruments, such as acoustic guitars, may require microphones.

Speakers

This is the part that everyone understands at least on a rudimentary level. The speakers are what make the sound, simple as that, however there is a set of speakers that many people don’t even realize are there, in fact, they aren’t even meant for the audience.

The are called monitors. It can be hard to hear yourself when all the speakers are pointed away from you and towards the audience. In general, it is nice to be able to hear what you are doing. This is what monitors are for. In larger concerts, they generally will take the form of an earbud or some such thing. But in smaller or low budget performances, they will most often take the form of speakers pointing towards the performers instead of the audience.

Different kinds of speakers are, naturally, used for different purposes. In a large performance there may be dozens of speakers working together to make the sound. Everything is huge. Loudspeakers can push out incredibly high amounts of sound.

Although I am not particularly knowledgeable in this area I can tell you this. Speakers like this are big, loud, heavy, expensive, hard to manage, and take a long time to set up properly. However, the results can be rather rewarding.

Although there are many intricacies in a sound system (amplifiers, effects modules, etc.) these are no doubt the most important. In fact, I get buy using just these three (and an instrument of course) when I play for certain groups.

How Speakers Work

I have touch briefly in the past about some of the basics of sound, however now might be a good time for a little refresher. Sound travels through the air in the forms of vibrations. When those vibrations reach your ears, a signal is sent to your brain in the form of electrical impulses, which is then interpreted by the brain as sound.

A speaker microphone systems uses this same principle. When sound enters a microphone it vibrates a diaphragm which converts the vibrations into an electrical signal and sends it through it’s chord to the soundboard, much like the human ear. The electrical signal is then sent to the correct speaker, which then is able to reproduce the vibrations exactly, kind of like the reverse of the microphone. But how is this done?

Like microphones, speakers also have a diaphragm. The diaphragm is a flexible cone generally made of paper, plastic, or metal. The large end of the cone is the end that points outwards. On the small end, however, is where the magic happens.

Attached to the back of the diaphragm is an electromagnet called a voice coil. A speaker actually has two inputs. When an electrical current is sent one way, it causes the poles of the electromagnet to point a certain way. When the electrical current is reversed, so are the poles. In every speaker there is a static magnet. This magnet interacts with the electromagnet just like it would any other magnet. When the poles of the electromagnet are facing one way, the two magnets attract and move closer together, when they face the other way, the magnets repulse and move farther apart. This happens many times a second, creating the vibrations needed to produce sound.

I hope you liked this in-depth (if rather long-winded) explanation of in concert sound systems and speakers. Although there is tons more to learn, I think this is a good start.

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