Does the first reflection point actually matter??

@erik_squires, It has been my experience that treating the first reflection points from the sidewalls in a narrow (14') room makes an enormous difference in imaging.   But I didn't get this using "normal" absorbing panels such as GIK monster traps.  What actually worked really well was a pair of 5' tall CD racks, positioned so that the front edge of the rack is angled out from the wall.  The front edge of the rack is positioned slightly to the rear of the first reflection point.  Apparently, the front edge of the racks are reflecting the higher frequencies from the tweeter and midrange back towards the front of the room.  Thus, reflected frequencies higher than 1500 Hz are blocked from a direct path to the listening position.  They are either directed behind the rack or directed back to the front of the room, thus delaying their arrival at the listening position enough that they do not compromise imaging.  

When the CD racks are removed from the room and I attempt to treat that same sidewall area with GIK products, the image collapses.  If I move the speakers enough to change the sidewall first reflection point, the image collapses unless the CD racks are removed a similar amount.  I've also noticed that depth and width of image is somewhat eroded by using GIK 242 or 244 type panels on the side walls forward of the CD racks.    

Note that this is not another ill advised attempt to use a partially filled CD rack as some sort of diffusor. 

My son did something similar in his room using bookcases, and he reported a huge improvement in imaging. 

Folks who have wider rooms will probably benefit less than those of use who listen in narrow rooms. 

@tony1954, we are more sensitive to localization clues in the horizontal plane.  Most of us have our ears mounted on the side of our head, not the tops and bottoms.  :)   So early reflection points on the side wall tends to be most impactful,  Back walls that are close to the main listening position can also be more impactful in terms of confusing localization clues.  In certain cases where a room is very wide or where the main listening position is well removed from the rear wall, floor and ceiling can be more impactful.  Conventional wisdom is that you would like to have all reflections arriving at the ear with a delay of 5 to 20 milliseconds down 20 dB relative to the direct signal.  Reflections arriving at the ear within that window tend to smear the localization clues provided by the direct signal.  Reflections earlier than 5 ms tend to merge well with the direct signal, and those reflections arriving later than 20 milliseconds tend to be perceived as separate echos adding to the spaciousness of the room. 

@jacksky, your summary of the relative importance of the various surfaces that may provide early reflections is dead on, as is your recommendation regarding angling side wall first reflection treatments.  If you look at my post above, that is exactly the approach I used in my room.  The difference is that I used a solid oak 5' tall fully loaded CD rack instead of an acoustic panel or diffusor.  The side of the rack closest to the speaker is about 8" wide, and that side is spaced about 3" away from the wall.  The front edge of the rack is located a few inches behind the center of the 1st reflection point.  Some of the first reflection is directed behind the CD rack, some of it is reflected back to the front of the room, and some of it has its reflection trajectory changed so that it no longer is aimed at the main listening position.  I figure that wavelengths longer than 1500 Hz are probably impacted by this arrangement.  I have an identical CD rack located in the same position on the right and left walls.  These racks are much more effective than full range GIK monster or soffit traps for this purpose.   My room is 14' wide, so dealing with FRP from the side walls is imperative.  This gives superb imaging in my room.  Great depth and width, great center fill, nice life size vocal and instrumental size.  Best imaging by far I have ever heard in a narrow room. 

optimize, some of your points have been addressed in previous responses.

That side point will act as a muted bass shy speaker that is delayed as it were placed further away..

Can this side walls reflection points contribute to a wider sound stage? 
Or some other benefits that can be a argument to not treat side walls reflections?

Because of how our brain processes reflections, how we perceive reflected sound depends on how long those reflections are delayed compared to the direct path from source to ear.  If the path of the reflected sound is longer than about 6 meters longer than the direct path from the source to the ear, the reflection will add to the spaciousness of the room.  Any reflection that is shorter than that will generally not be distinguished as a separate sound and will result in a spacial smear.  Another consideration is that the dB level of sound decreases as the distance increases, and the dB level further decreases every time it bounces off of another surface.  It has been my experience that reflections that have a path about 2-4 meters longer than the direct path are especially detrimental to precise localization of instruments and voices if those reflected signals are not at least -20 dB compared to the direct sound.  

So the answer is that some reflections off of side walls are beneficial, and some are detrimental.  I have left the sidewalls of my room untreated from about 0.5 meters forward from the first reflection point to the front corners.  Doing so gives me better sound stage width at the expense of increased slap echo.  I've devised a way to deflect the first reflection point away from the ear, which results in superb imaging in my rather narrow (~4.5 meter wide) room.  My approach is different than traditional absorption or diffusion.  It is more consistent with the approach described by Duke LeJuene above. 

The first sidewall reflection point matters in the design of a recording studio control room. Those I have been involved in used angles which direct the reflections away from the normal listening position.

If I read your post right, your room is less than 2 M wide.   I don't know how your room is laid out otherwise, but it seems likely to me that your side wall first reflection points have a delay of less than 5 milliseconds compared to the direct signal.  Some say that those very short delays don't compromise imaging as much as those having a delay of 5-20 milliseconds.  So you may not get much benefit from trying to treat your sidewall first reflections as others.  

@hilde45, my pleasure.  As for your ceilings, don't fix it if it ain't broken.  If you are getting good imaging and vocal articulation, and you are not being troubled by slap echo, count yourself lucky and focus on things that will make a difference.   We are much more sensitive to early reflections in the horizontal dimension than in the vertical dimension.

Your room is so atypical in its dimensions that general rules of thumb may not apply, as long as you stick with the long wall orientation.  In your room I would still worry about front and back walls first.  Treating those surfaces is likely to do more than even treating the corners in your room. 

I got into room acoustics because my system sounded lousy despite the fact that I had superb gear. Treating the room was the right approach in my room, but It may well not afford you that same level of improvement. Your room and system positioning eliminates some typical problems, but affords you less opportunity for further improvement on those problems that remain.   It really could be a non-productive rabbit hole for you.  Cheers!

hsw, I'm only going to answer for myself here.  My understanding is that humans are naturally more adept at localizing sources in the horizontal plane.  Our outer ears are mounted on the sides of our heads and aren't especially well designed to pick up vertical clues.  Presumably, our brains are similarly well suited for localization of sources in the horizontal plane.   What I can tell you is that in my room, which is 14 ft wide with 8 ft ceilings, effective "treatment" of the side wall 1st reflection point is orders of magnitude more important than "treating" the ceiling and floor 1st reflection points in providing a deep and wide image with good localization of instruments and voices.  My floor is not carpeted, and my ceiling is typical texture over drywall.   I'm not going to say that rugs and room furniture don't matter, just that in most rooms, treating the floor and ceiling don't matter nearly as much as treating the side walls with respect to imaging.  If you have a room that is atypically wide, or speakers that don't have wide dispersion, you may see something different.  Also, what you do with the floor and ceiling can certainly impact other aspects of room performance.  Floor to ceiling bounce can be a big contributor to slap echo, as example. 

@erik_squires, have you tried what Duke is suggesting on the sidewalls?  I stumbled onto this idea of redirecting the sidewall 1st reflections to the front of the room several years ago quite by accident.  Every attempt on my part to reproduce the benefit of redirecting by using absorbance has failed.  The image just collapses.  Had I not experienced just what this technique can do myself, I might be arguing as you are.  

@erik_squires , 

Floors are a different thing, but we don't spot treat floors. We treat the entire area in front of a speaker. I've never seen anyone put down a 2'x2' carpet exactly in the first reflection point, and this is kind of what i mean. 

Eric, I have a dedicated room.  I made 2'x4'x4" OC 703 panels that cover first reflection points on both the floor and ceiling.  The rest of my floor is untreated.  I realize this is not common, but I have a dedicated room and I am the only listener, so I can do what I want.   Both ceiling and floor "treatments" have very little influence on imaging in comparison to my side wall "treatment."    They certainly offer other benefits. which more than justify their use.  I have considered modifying my ceiling panels in order to add forward facing reflection to the existing absorption, but have not done so yet. 

As I recall, my measurements show that the floor and ceiling reflections are delayed about 4-8 ms, whereas the side wall reflections are more in the 6-12 ms range.   Without treatment, the ceiling and floor reflections are louder than those from the side walls.   With treatment, the side wall reflections are substantially reduced, whereas the ceiling and floor reflections remain relatively high.  To a certain extent, I think this is indicative of how much more effective reflection is compared to absorption.  

From my perspective, sidewall 1st reflection point treatment is conceptually sound, and in my room, theory has been supported empirically.  Imaging and localization in my room is superb.  It is the best by far that I have ever heard in a narrow room.  If you have experienced something different, perhaps that is because you are attempting to "treat" your sidewalls using panels that are not up to the task.  Again, I'm going to suggest that before you discount the concept, you evaluate the approach articulated at least twice by Duke and several times by me.   Rip a 4x8 sheet of half inch plywood into 2 x 8 sheets and place them along the side wall behind the first reflection points angled so as to reflect sound back to the front of the room and away from the MLP.  This is enough to reflect the wavelengths that are important to localization clues, and it turns early reflections into late ones.  It is a cheap and easy experiment.  Keep in mind that the first reflection "point" is far from a point, because the sound coming from your tweeter and midrange will spread out as it travels rather than proceed as a laser like ray.  So you will need to experiment with placement and angle.

Erik, first reflection "point" is probably an unfortunate term, which probably derives from conventional techniques used to determine the area in question.   First reflection zone would probably be much more accurate. Look at your REW impulse graphs.  You don't see a single intense reflection at, as example, 9.6 ms.  That is what you would see if the side wall early reflection came from a single point.  Instead, you see a cluster of reflections in a band that may be 3 ms wide or more.   All of those early reflections, or at least the higher frequency component of those reflections, are going to compromise image. 

An interesting experiment is to look at REW impulse graphs before and after adding conventional absorbing panels to those first reflection zones.  Even a GIK 6" full range Monster trap won't attenuate side wall first reflections anywhere close to the -20dB (compared to impulse) level necessary to mitigate 1st reflection erosion of spacial clues in most rooms.   An angled barrier that reflects sound back to the front of the room is a much better approach.  Depending upon the size of the barrier, some of the sound (low frequencies) will just wrap around the barrier as if it weren't there.  But the shorter wavelength (higher frequency) sound that is responsible for localization, won't wrap around the barrier but instead is reflected back towards the source.  The sound isn't turned into heat by absorption, it is just turned from an early reflection into a later reflection that adds to the perception of spaciousness. 

Imo there is an alternative approach which starts out with the design of the loudspeakers themselves, and which does not call for anything remotely approaching treatment of entire room surfaces in order to get good results. Briefly, the loudspeaker sends spectrally-correct energy in directions which minimize early sidewall reflections, and the reverberant energy is allowed to decay more or less naturally, perhaps using diffusion, as opposed to being rapidly absorbed. If anyone is interested I’ll go into detail.

@audiokinesis , I’m very interested in what you have to say on this, so if you are so inclined, please elaborate. Not that I want to distract you from completing my Swarm! ;>)