MONO – On acoustic, monaural or “mono” is the system of recording and playback sound in that it’s not possible to understand the different positions of sound sources, i.e., all sound is transmitted through a single channel, is also called of “mono system”.

STEREO – In acoustics, stereo is an audio reproduction system that uses two separate monaural sound channels (left and right) synchronized in time. It’s the pattern found to playback the music CD, but it has been replaced in the movies and in some recorded music by the multi-channel audio (5.1/7.1), however, stereo hi-fi devices still mainly use stereo.

DOLBY – It’s a brand created by Ray Dolby, founder and chairman of Dolby Laboratories, a company specialized in audio compression reproduction. The Dolby brand is associated with two different applications: noise reduction and cinema sound.

SURROUND – It’s the concept that expands the image of a reproduction of one dimension (mono or stereo sound) for two or three dimensions. Surround brings a more realistic audio to sound systems in movies, theatres, home entertainment, videos and computer games and is increasingly present in everything and everywhere.

A channel can have more than one speaker but only plays the sound of “one side” of the recording. Let’s see the definitions of the channels for reproduction in order to better understand the sound systems:

• 2.0 – This type of acoustic circuit is composed of two channels, one right and one left, that is the simplest form of stereo that was “revolutionary” dubbed in Dolby Stereo.
• 3.1 – This acoustic circuit has three channels, two of them destined for left and right channels, one for the centre and also a channel for a subwoofer which will only plays the low frequency bass sounds. This model became known as Dolby Surround.
• 5.1 – It’s the most widely used acoustic circuit for “home theatre” and consists of five stereo channels and one for the subwoofer which, in this case, use two channels to right (front and rear), two to the left (front and rear) and a centre channel.
• 7.1 – It’s the latest system, which has seven channels for stereo and a subwoofer, the channels being divided into three front channels and four rear channels to give greater sensation of sound in large rooms (cinema).

Speaker – it’s a transducer device that converts an electrical signal into sound waves. The speakers are divided according to their frequency ranges of work in tweeter, mid-range, woofer and subwoofer:

• Tweeter – It’s a speaker of small size (ranging from 0.5″ through 3″), used to reproduce the high frequency range (above 5000 Hz) of the audible spectrum, i.e., sounds more acute.
• Mid-range – It’s a speaker used to reproduce the midrange frequencies of the audible spectrum, usually between 300 Hz to 5000 Hz, can play most musical instruments. Generally have a size less than 8″.
• Woofer – It’s a speaker used to reproduce bass frequencies and averages, usually between 50-4500 Hz, possess rigid edge and its size can vary from 1.2″ to 18″.
• Subwoofer – It’s a type of loudspeaker used to reproduce low frequencies (bass and sub-bass), usually below 45Hz. As this frequency range the cone needs to move much air, speakers are large diameter and high excursion cone (4 to 20mm range).

dB – Decibel is a unit of measurement of reasons, in acoustics, the decibel is used as a logarithmic ratio of sound intensity and pressure and its power.

Hz – Hertz is the unit of measurement for the frequency or the number of vibrations of the air/duration of a musical note. Thus, each musical note corresponds to a duration and is associated with a frequency, whose unit is the hertz (Hz).