| Hi Durv,
No, there is no "definitive shape" for a CR or a LR. If you build from the ground up, there are of course some basic schemes that can be applied, but there is no one-fit-all solution. Even if the building is being built from ground up, there will always be constraints about size (budget!), material used (budget!), etc...
Here are basics for both CRs and LRs:
To make the long story short, today in CR it's all about Front-To-Back rejection of the acoustic waves. A CR will be shaped so that there are as little reflections as possible in the 10ms time slot (i.e. around 3,3m distance) and diffraction, (not diffusion!) will be used so that the waves are directed towards the back of the room, hence reducing acoustic pressure around the sweet spot to the direct signal as much as possible.
Once the waves reach the rear part of the CR, one should try to absorb, diffuse and diffract so that the reverberated field (short RT in CR, longer in LR) will not color too much the direct field/sweet spot. In a way and up to a certain extent, I will try to reproduce what you would hear from your speakers if you were listening to them in the sweet spot, in a totally quiet desert. Of course, the aim is NOT to have an anechoic or semi-anechoic room, that is really not what you want either.
It happens a lot that when I upgrade a room it takes a while for the engineer to get used to the new acoustics. But then they realize their mixes translate much, much better.
In the case of a LR, there are many examples of what bad acoustics can do to your recordings. One people usually don't think about is EQ. Sometimes, on tracks that were recorded in bad LR (drums, piano, etc...) when using the consoles' EQ or any other EQ, it sounds really "phasy" at some frequencies. Some AE will say that it's the EQ itself, when it's actually the bad room you are hearing! On a good recording, you can push the EQ much further before it sounds "phasy"...
But then again, there is not one-fit-all solution for a LR. The aim there nowadays is to be able to control your RT and have systems to change the color of the room depending on the type of recording that is currently going on. A basic rule is to try to reach a point where the reverberated field in the room is rather neutral, try to limit flutter echo, resonances (modes), etc... It is first dealt with heavy room shaping as well, like in the CR. But in this case, more ambiance is desirable, which is achieved through modular panels - which are a lot of fun to create.
Cheers |