What is a Sound System?
(in Simple Terms)

The simplest sound system is two cans attached to a stretched string. All sound systems work on a very similar principle, just with more refined technologies.

When I yell into Can A the sound waves from my mouth enter the cavity of the can and bounce off the can’s interior bottom. This causes the bottom to flex/vibrate which creates a push/ pull on the string. The string will vibrate (resonate) at approximately the same frequency as this push/ pull energy and the vibration will then travel as a wave down the string until it reaches the other Can (B) exterior bottom surface. The mechanical energy of the vibration causes a push/ pull in the can B bottom which then causes compression and rarefaction of the air within the can. This creates a sound wave coming out of the can for your ear to hear.

Not very efficient, maybe, but it can be improved upon.

The sound source (Can A) will have a more flexible and delicate bottom surface such as a paper or light plastic cone to reverberate from the incoming sound waves. The mechanical energy resulting from this movement will move a small magnet backwards and forwards at the cone’s centre. If the other end of the magnet is inside a small wire tube infused with a small electrical current to create an opposing magnetic field. The magnet is then free to vibrate backwards and forwards in the field and create a magnetic/ electrical flux.

This flux leaves Can A as a generated electrical signal (sine wave or oscillation). Hey presto! I have a dynamic microphone!

Create the same device in Can B in the opposite order. Input the electrical signal into the reverse process and Hey Presto! I have a speaker! The oscillating electrical signal creates fluctuation in the magnetic field which then forces the magnet and the attached cone to oscillate mechanically creating sound waves.

The trick is to make the sound (signal) source in Can A as light and as sensitive as possible and to make the speaker (Can B) as robust as possible while still projecting all the audio frequencies. Both these devices transform the sound or signal from one type of energy to another. This signal transformation or transduction is critical in the live sound and the studio recording processes. Each transformation loses strength (amplitude) for some frequencies and enhances the amplitude of others. Additional frequencies (distortion) may also be added that colour the original signal.

The accuracy of a microphone or speaker’s signal transformation and the colour they add to the resulting sound are the subject of legend. There are a zillion microphones and speakers (transducers) out there, each doing these transformations slightly differently and there are just as many subjective opinions as to their effectiveness in creating a pleasing sound. Do not worry, most of the really good microphones and speakers are easily found with a little legwork.

All that now remains of the original can to can system is the string. At that very least it needs to be replaced with a wire to carry the electrical signal. It is then easy to add an electrical amplifier (amp) to the wire and boost the signal strength by a set or proscribed amount.

There will then be a need to control the signal strength (level) entering into the amplifier in order to adjust the sound volume (level) eventually coming out of the speaker. This is done with the preamp (pre amplifier). Having got this far, adding various tone controls (EQ) will allow changing the amplitude of parts of the electrical signal to add or remove colour and/ or sound levels at specific frequencies.

Hey Presto! I have a sound system! All I need to do is package it

1) Put the preamp, amp and speaker in a box, I have a guitar amp

2) Put the preamp and amp in a box, I have a small powered mixer
with a separate speaker or 2 added. This is usually a poorer
quality or introductory level PA or sound system

3) Have the preamp, the amp and the speaker as separate components and usually this makes a better sound system because a) separate components are usually manufactured to higher standards b) each component is electrically shielded from each other to eliminate more hum and induced noise c) the user has more control over and choice about the optional functions available when components are purchased separately

4) Recently amplifiers have been included in the speaker cabinets. These are more electrically efficient but may make the speakers heavier.

5) Have duplicated components in a sound system and create a stereo (2 channel) system with separate volume and tone controls for each channel

6) The difference between a home consumer stereo and (5) is that the signal source is from recorded media (CD or Tape player) and the design of the components is far less tolerant to the rather huge dynamic signal fluctuation of live sound. It is not recommended to use consumer stereo gear as sound gear except as a signal source (CD player). However, home stereos operate on the exact same principles as above.

In summary, the whole plethora of stuff mentioned above boils down to a:

Signal source - microphone, CD player, Tape player

Preamp - to control and massage the signal

Amp - to boost the signal by a predetermined amount

Speaker - to transform the signal back into sound

All of the above information assumes the signal path remains electrical or analogue in nature. In some components the analogue signal is transformed (there is that word again!) or converted into a digital signal (bits, bytes and data) only to be transformed back again into an analogue signal at the amplifier input.

Every time a transformation occurs a little of the original information about the sound is either lost, coloured or distorted. It is no different for the transformation between analogue and digital. As a rule of thumb, the more expensive the gear the more likely the transducer will do a good job with minimal signal loss or colouration. Some products deliberately add colouration and distortion in a manner that is both sonically pleasing and enhances the sound.

That is why one microphone can sell for US$100 on eBay and another that looks outwardly similar for US$15000. It all in the ear of the beholder.

Good sound systems cost. It is pointless to spend big money if you can not hear the difference (the Emperor’s new clothes). Listen to lots of gear at live events. Find a small system that sounds good to you. Ask the engineer why. And start a new journey into amplified Celtic harp music.

Stephen Vardy
Harpsound Audio
[email protected]