Halcro,
This
link will help you understand. Just watch the animation and bear in mind that the reflections cause "comb filtering" making some frequencies disappear altogether. Notice the rear wall "purple wave" has a stonger arrival at the listener nearly as big as the primary green acoustic wave - in fact it is teh biggest and messiest secondary arrival as it has lots of coherence. The best sound is achieved when secondary reflections arriving at the listener are separated from the primary arrival by about a minimum of 7 Msec with 10 to 15 msec generally regarded as optimal. Reduction in their amplitude helps but fundamentally it is best to avoid any early reflections (you need to drop a reflected signal by more than 10 db before it begins to less destectable to the ear as a source of sound directionally). Fatiguing or claustrophobic is the impression you get from a lot of very early and large amplitude reflections as the brain is bombarded with sound from all directions. Rememember that as you move the listener towards the back wall it will reduce the primary engery and increase the reflected energy - at about 2 feet the rear wall reflections may actually become LOUDER than the primary sound and a mere 4 msecs behind it (confusing the soundstage).
Likewise Ethan Winner explains room acoustics and the importance of creating a
Reflection Free Zone at the listening position.
Another helpful tip is to look at the recommended place to position bass traps. Invariably the best spot for maximum bass absorption is a foot or two out from the wall - this is where the modal acoustic energy from room modal standing waves is often the highest (with corners being the very strongest) - obviously this also happens to be a bad place to have your listening position.
Another useful tip is to google studios and take a look at their designs from photos -
for example. Search as much as you like but you will NEVER find a setup in a prestigious studio (where they can afford the best) with the listening position close to a side wall or a rear wall, as everyone knows how bad and cluttered this will sound. Generally distance to rear wall will EXCEED distance to side walls and rear walls will often be treated/damped because the strongest most coherent reflection in a room is
1) The bass reflection off the wall behind your speakers ( this is why studios build their main speakers into a wall or use very close small near-field monitors for critical listening - just as you see in the photo - you can find hundreds more and more or less they will be the very similar)
2) The bass reflection off the wall from behind the listener (long hall like rooms with treated rear walls behind listeners are preferred).
I hope this helps. I understand it is not that obvious and that too much literature concentrates on side walls and neglects the wall behind the listener. This subject is probably the most important but least advertised aspect of teh audiophile hobby. However, remember that manufacturers want rather you spend more on their cables, amps, and speakers than acoustics. Besides, if you are sturggling with acoustics then you are more likely to be disatisfied with your system compared to others and therefore keep spending money on upgrades...
I would suggest that Rives would be an excellent resource too you can find god articles they have written also. Of course these companies (like Ethan Winner's Realtraps) make a living from selling designs and acoustic products but they are not above giving common sense advice for free. Perhaps Rives will chime in - they will know an awful lot more about this than my rduimentary and superficial treatment of this subject.
