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SQ, SQL and SPL are terms used the describe the orientation and aim of an audio system build.
I shall start by answering the first part, what is SQ?
SQ stands for Sound Quality.
In a SQ system, the aim is to get sound reproduction just as it was recorded or just as the artist(s) intended it to be heard. The main emphasis is on accurate sound reproduction, detail, staging, tonal accuracy, imaging, stage height and depth. When all done correctly, it should make the listener feel like as if he/she was in the studio or live venue where the music source was recorded and hears the sounds just as they were produced.
For a detailed information on these terms (which are only a part of the total aspects of a SQ system) please refer to google and wikipedia. If something is unclear then i and other members can help you understand.
You hear a guitar play on a sq system, you hear the exact timbre, tone, presence, dynamics of a guitar note , sound of fingers running down the guitar strings, pluck of a guitar string just as it would sound when listened to it live. You listen to someone sing, you hear the chest resonate, vocalizationnof words, breaths between verses etc. No detail is missed. Each and everything is in balance without a single frequency range over whelming the others. Staging and imaging refers to the fact that for example while listening to music recorded at a live performance, the listener should be able to realise and appreciate the position of different artists on the stage as it was on the actual stage where and when the music was recorded. Stereo systems use two speakers to reproduce that data while surround systems utilise multiple speakers to accurately and more realistically reproduce the stage in all three dimensions.
To achive the highest quality possible, a sq system utilises many principles and equipment. Starting from the headunit right down to the speakers everything is selected with great care including amplifiers, digital signal processors, fibre optic cables, RCAs, speaker wires, power wires, capacitors etc so that each component in the system compliments others.
A good headunit with decent digital to analogue convertors (DACs) and ability to play uncompressed music (usually CDs), noise resistant directional rcas, amplifiers with good rated power, damping factor, signal to noise ratio, slew, total harmonic distortion, stereo separation, ohm load compatability etc, speakers (usually component speakers) with a flat frequency response and transparecy etc etc these are just a few examples of the considerations when selecting equipment for sq system.
What is flat response? Linear response? When the music is analysed on a sq system using RTA or spectrum analyzer etc, the frequncies in the spectrum should be equal to each other in magnitude and no band should over power other, thus giving a flat line or flat response, but thats just about it. Flat freq response is only an important part of equipment selection so that there is no big peak in the system and thus requiring less EQ = lesser digital artifacts. The fact is that no one can listen to a flat response music system. Thus a reference curve is used as an industry standard where the lower end of specturm is boosted slighlty and the uppper end is similarly rollled off slightly, and this curve results in a very very smooth and natural sounding sound system.
Dsps are an integral part of a sq system. They allow you to time align different speakers in the system so that the sound from all speakers reach listener's at the same time(in a car listener is never at the central sweet spot as in a home audio enviorment and thus Time alignment is a must)
Dsps also give the user power equalizers or EQ used to achieve the target reference curve.
All said and done, loudness is never really a priority in a sq system but pristine sound precision and quality is. And unfortunately owing to these facts SQ system tend to be more expensive and labor intensive due to all the considerations like reflections, rattles, sound dampening etc. But sq systems are pure joy to listen to, which uou can enjoy for hours without ear fatigue and headaches and for these reasons, sq systems are very addictive.
I hope i have helped you understand what SQ is all about. The points i missed shall be explained by other SQ experts around here.
Cheers!
