Hi,
I'd like some advice from people on this great forum that have built rooms from scratch.
We did do just that back in 2002: adding a living room (28x15x8ft) to our house, where the main stereo system would also reside.
Room dimensions: Back then I was convinced of the usefulness of "optimized" dimension ratios so I had a look at the different approaches and decided to go for the Bonello criterion, because it spliced oh so nicely to the concept of the Schroeder Frequency. On both accounts I now know better. The builder made the room wider than was planned, so the criterion was no longer fulfilled, but that had no negative impact at all. I all those years I’m listening to music in that room I could find only 3 or 4 tracks where a mode is audibly excited.
Room treatment: being built from brick ‘n mortar with tiled floor reverberation time was going to be way to high, so we had installed a ceiling made from stretched synthetic fabric with 10 inch space above the fabric loosely filled with rock wool. The whole works as a huge membrane absorber and the effects are very convincing. No other acoustic treatment. The directivity of my loudspeakers in combination with placement on the longer room wall gets the level of the lateral reflections close to the perception threshold, should there ever be evidence that first reflections have detrimental effects.
My opinion on this issue:
1. Don’t bother with optimized room dimension ratios, build the room as large as possible. The benefits of optimized ratios can only be experienced when sound source and listener are in corners of the room.
2. Since there is no scientific evidence for first reflections having detrimental effects, forget about those, unless your speakers are placed such that there is substantial right-left asymmetry. For that reason I would place the records at the back, one never knows. Reflections from the front are masked by the direct sound so perception thresholds are quite high. No problem there.
3. Lower reverberation time such that the room is pleasing to your ears. Measurements are not necessary, let your ears be the judge. Normal furnishing such as curtains, upholstered sofas, carpets/rugs should do the job. If all room surfaces are acoustically hard, you might need additional acoustic treatment.
4. Vaulted ceilings: are said to lead to sound concentration, the effect of which appears to depend on where the focal points are located. Such ceilings might be tricky, try to get more technical/scientific information how they behave acoustically. Should such a ceiling be problematic, then apply treatment.
Klaus