This is starting to
cover very large subject areas and could take pages and pages to even scratch the surface. Hopefully you will learn some ithings n school, including a lot of the theory and basics behind audio and
acoustics, but much of itthe
practical application may have to be learned through experience and other education.
For example, for reflections a simplified answer is that as gafftaper noted, it depends upon the application. Where you are relying heavily on the sound
system for all audio, you typically want to eliminate reflections and reduce reverberation as much as possible, effectively removing the room and relying solely on teh sound
system. For speech intelligibility the same may apply, however some natural reinforcement through specifc reflections and a slightly 'liver' space may be desired as well. For music performances, the environment becomes part of the performance and you start looking at aspects like Early
Decay Times, Initial Time Delay Gap, Direct/Reflected energy ratios, Early/Late energy ratios, Clarity, Loudness, Spaciousness, Sound Strength and so on. What is really the issue is both the 'liveness' of the room in general and how a sound from the
stage arrives at the listeners. In general, you do not want any very early arriving reflections and want a gap of maybe 10-20ms between the direct sound and the first reflected sound arrivals, this helps reinforce the direct sound and where it originated. For music you typically then want strong, diffuse and well distributed reflections, with a strong lateral component, for a certain time period with the levels of the reflections then decreasing over time. This gives the room warmth and spaciousness and is where the good halls really excel. The specific time periods may vary, but 50-80ms is typical. You almost always want to avoid and discrete, higher
level late reflections as these are perceived as discrete echoes. Some of the same type of factors enter into churches and other spaces where audience interaction is desired, except in that case you are looking at reflections among the audience. And sometimes determining the goals for reflections is based simply perception, for example the
lobby that people want to have perceived as being larger and grander than it really is may even want many late reflections and echoes.
Early reflections off surfaces can also affect the sound from the speakers. A
speaker reproducing low frequency sounds located a few feet from a surface may result in reflections that cancel with the direct sound at some frequencies and sum at others.
Designing a sound
system gets into first considering factors such as the intended use, the environment (the room),
practical considerations such as where you can or cannot locate speakers and in the real world budget is almost always a factor. Only then can you start determining the appropriate performance requirements including
frequency response, coverage, levels and so on. For spoken word you have to consider intelligibility. The requirements for a sound
system to support rap or hip/hop may differ from those required for live acoustic performances even for the same room. A
system that has to
cover both as well as speech may need to have capabilities that exceed any single application. And this has just gotten you to where you are ready to start laying out the
system and selecting devices.
Someone with experience may be able to look at a space and know what will or won't work, but it takes many good and bad experiences to get to that
point. In fact, one of the biggest problems with all the
acoustics and audio design tools out there is that while they are very powerful, many people using them have no idea what they really are doing and do not recognize when they get questionable results.
As long as this post is, it is just touching on a few of the basics. This is not in any way meant to scare anyone off, but simply to show just how complex it really can be.