Why does pulling out main speakers from wall improve sound?

From Physics I seem to remember that sound waves reverse phase every time they bounce off a hard surface. I've put on a signal generator for various frequencies and tracked results using a handheld sound pressure level meter to measure changes in volume as I've moved the speaker. My best guess is that the sound waves reenforce at some spots and frequencies and (try to) cancel at other frequencies at the same spot. how significant is this? Not very. All said and done, the direct radiation path is more significant than all other indirect paths in my small room. I don't argue; I just listen.

While responding to another post, I was reminded of the Dutch and Dutch 8C. They address the issue in a different way:

1) They use mainly acoustic methods to present an out-of-phase "midrange" signal at the sides, to cancel the midrange as it is "wrapping" around the cabinet. Quotes around midrange as it will be frequency controlled.  This would replace acoustic treatment with a traditional speaker.

2) They accept boundary reinforcement in bass frequencies and provide DSP correction, something that can be done with any speaker.

In my opinion, listeners should just listen and make up their own minds. I think the problem in audio and other subjects is that people have too many premeditated ideas based on things they just read rather than just listening. Who cares if it goes against things people say. I've been in many situations like that on all fronts. I'll give an example. Many audio buffs say not to place Klipsch Forte's against the wall. I have two videos in two different rooms. Yes, they are two different rooms but one is treated professionally at Upscale Audio, has the newer version of the speaker, which according to others,is supposed to sound better. 

Even though YouTube isn't going to produce all the fidelity, it still offers a "relative" difference between the two different rooms regarding placement and sound which is clearly audible with earbuds or headsets if one listens. You be the judge. 

The Upscale Audio Forte IV's are placed several feet away from the back wall while the Forte I's in the second video are about 1 foot from the wall. 

Skip to 4:00.

just an FYI - In order to remove ambiguity, we occasionaly need to clarify “front” vs “back” when describing walls. This has been discussed on many threads, and there has been an overall consensus, which is shown below from one of many different threads on the subject.

nsgarch

2,524 posts

01-07-2007 at 07:44pm

The convention is that the front wall is the wall in front of you when you are sitting in your listening chair (the wall behind the speakers).

Another way is to think of the speakers as at the "front of the hall" as in a theater. The ’rear’ wall is the one behind all the seats ;--)
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This has been an excellent thread; any and all newbies should take heed and probably read it twice.

To all these comments I would only add that listening is a skill, developed over time and learning to identify the small changes in sound that happen after repositioning speakers is a good way to train your ears.

It helps me to be relaxed and in the right frame of mind. Patience is essential here because depending on the room and speaker combination very, very small adjustments in placement and toe-in will yield a noticeable change in response.
In my room it took a long time to strike the right balance between imaging and bass response, but after weeks and months the end result was satisfying.