Does the first reflection point actually matter??

@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.

Of course quantity trumps.

If you have 6 or 40 panels. 40 is 6.66 times more area than only 6 panels.
And when a reflection is more than reflecting one time. Let say it bounces 3 times before it is so week that it is -60 dB.

Then we have 6.66 times x 3 bounces gives us 20 time more treatment... 

So that is why we do not react or find any big difference on if you treated the first reflection points or not when I'm comparison to a room that have 20 times more treatment than the other!

I still say not all have of different reasons (time, founds or ascetics) not willing to get 40 pieces of treatment all over the room.

In most cases maybe you only buy 2/4/6 panels maybe bigger and thicker 1m x 0.5m each.

And we known for each reflection sound does it get weaker and weaker. So if/when you only got a few panels (less of a coverage area) then we start to treat the strongest reflection that is the first one. Of course absorbers will not take all reflection away. And of course the few panels will not contribute as much as if you had 6.66 times more panels and coverage area.

But it is for most of us a starting point and we can always add more panels along the way.

Maybe the only real problem is how I interpreted this information early on.  Maybe it was never meant to be a point thing but a starting place?

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. 

@erik_squires wrote:

"I believe most audiophiles would be unable to tell if those treatments were at the reflection points or not, and that in many cases 4 panels of 2’x2’, no matter how well placed, would be unable to effect an audible improvement."

and

"By ["treat"] I mean to alter the [room] surfaces by increasing the absorption and decreasing the ability of those surfaces to throw a coherent reflection by both absorption and diffusion."

Thank you Erik.

My reservations about using absorption on the entire surface, rather than just on the places where it has the most beneficial effect, are twofold.

First, to the extent that absorption is more effective at short wavelengths than at long ones, it will change (darken) the spectral balance of those first reflections. That may still be a worthwhile net improvement if the room is overly reflective, but in general it is desirable for the reflections to have approximately the same spectral balance as the direct sound.

Second, absorption continues to be effective long after the first reflections... ALL subsequent reflections which strike the absorptive material have their spectrum and overall loudness altered accordingly. So treating entire room surfaces can result in an overly dead room.

Reverberation time is seldom an issue in small rooms unless they have a slap-echo issue, and even then treating the entire wall with absorption is probably unnecessary. (Some argue that the term “reverberation” is actually inappropriate for small rooms because discrete reflections dominate, but I think it conveys a useful concept.)

As has been mentioned, loudspeakers are not true point sources, nor do we normally sit with our heads sufficiently in a vice that a 1 foot square treatment panel is what anybody is advocating. So I think "first reflection zones" is a more useful concept than "first reflection points."

I think you and I disagree on whether the timing and magnitude of reflections matters. If not, then neither does it matter where your absorptive panels go. If it does, then where they go also matters.

As I stated before, imo your assumptions are valid for large rooms (wherein the reverberant field is uniform enough that the reflections average identically at any given location) but not for small ones (wherein we have discrete reflections at any given location).

It sounds to me like you want to use enough absorptive acoustic treatment panels to make a significant difference throughout the room. Imo that would make sense ONLY if the speaker’s off-axis response is so bad that the reflections are generally detrimental. If the reflections are beneficial, weakening all of them and degrading their tonal balance with absorption would be detrimental. I’m not saying absorption has no place in home audio, but I am saying that the less of it we "need", the better.

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.

Duke