Acoustic Sound Treatment

I have installed 4 DIY 4'x 30'' Jon Risch's sound panels.

Three went on the back wall covering four French doors.
The other went on a side wall at the first reflection point. The other side is a open wall.

The result I got is almost unbelievable. I never dreamed that these panels would change the sound so much for the better!

The music was all over the place before the panels. Now the soundstage is where it belongs and the sound is more focused. LP's that I thought were not recorded well are indeed right sounding.

This audio hobby done right must hit on all cylinders to reach the ultimate end. One of them is sound treatment. We can disagree on cables etc. but you have to be BD&D not to hear a difference in a properly treated room.

The back wall ceiling starts on a upward climb to 22'.

Would two ceiling corner panels help out to further treat my room?
Would two ceiling corner panels help out to further treat my room?

Yes. Undoubtedly...two large corner panels will likely give an audible improvement in bass and lower mid.
Glad they worked so well for you, my experience with the same DIY project was equally revelatory. It is likely that a couple of panels at the corners of the 22' wall and ceiling juncture would further improve the sound. In my room I found the first two panels improved the sound the most, further panels have yielded smaller incremental performance boosts. If one doesn't avail themselves of professional room analysis, there's going to be elements of guesswork and luck whose results amateurs can't anticipate.
Amen--you are preaching to choir, but I am glad to hear it. Couldn't tell you about your last question without knowing a lot more about the room and speakers. However, in general some type of bass trapping in the corners is beneficial.

If you click on my system you can see the Audio Note speakers and the open area of the right speaker.
Above the left speaker the ceiling is 22' high. The back ceiling starts at 9' and goes up 22'.

If these members, who don't have panels, only know what these DIY panels have done to my system they would all be builing or buying some ASAP.

I can only imagine what you can do in a professional manner. It is like finding audio gold. Sometimes you can read reports on acoustic sound treatments and it goes over one's head. But to hear it first hand has made a firm beleiver out of me.
If I ever build another house you will be first on my list for my dedicated sound room.

I would dare to say that one's system can not reach it highest peak without the room being properly condition.
Congrats to you. I agree with the other recommendations for some bass traps. After checking your system I'd like to see some pics of the DIY panels.
Another believer. Congrats and welcome to the club.
As for the corners. I am not sure if you meant corner bass traps or small corner peaces called " corner-busters ", which are triangular panels that mount into the ceiling corners of a listening room to trap the sound that would otherwise echo back into the room. These are important treatment areas since sound eventually finds it’s way into the corners of a room. Yes they help, especially improving speech clarity and in most cases eliminate megaphone effect. If you are not sure if they are right for you, get it from the place with generous return policy.
Good luck & happy listening
Mariusz Stark.
Its true the sonics from my Realistic reciever and un-named speakers that came attached, sounded just like the best high end- price no object system, I was hearing at the best retailers and shows after I used acoustic treatments. It gives me pause to wonder why buy all this expensive gear, when the room, properly treated, will be the finest "component" you own.
I never dreamed that my room is a "component" and a bad one at that. I would say it is one of the best upgrades I have done to my system.

Can someone explain to me why such a huge difference in sound?
Acoustical design must take into consideration that in addition to physiological peculiarities of the ear, hearing is complicated by psychological peculiarities. For example, sounds that are unfamiliar seem unnatural. Sound produced in an ordinary room is somewhat modified by reverberations due to reflections from walls and furniture; for this reason, a broadcasting studio should have a normal degree of reverberation to ensure natural reproduction of sound. For best acoustic qualities, rooms are designed to produce sufficient reflections for naturalness, without introducing excessive reverberation at any frequency, without echoing certain frequencies unnaturally, and without producing undesirable interference effects or distortion.
The time required for a sound to diminish to one-millionth of its original intensity is called reverberation time. An appreciable reverberation time improves acoustical effect, especially for music; a loud sound should still be barely audible for one to two seconds after the sound has stopped in an auditorium. In a private home a shorter but still discernible reverberation time is desirable.
For modifying the reverberations, you have a choice of two types of materials, sound-absorbent and sound-reflecting, to coat the surfaces of ceilings, walls, and floors. Soft materials such as cork and felt absorb most of the sound that strikes them, although they may reflect some of the low-frequency sounds. Hard materials such as stone and metals reflect most of the sound that strikes them.
In most cases, the acoustics of a room will be satisfactory if a proper balance between sound-absorbing and sound-reflecting materials is created. Troublesome echoes may frequently occur in a room that otherwise has a proper overall reverberation time if the ceiling or a wall is concave in shape and is highly reflecting; in such cases, sound may be focused at a particular point, making the acoustics bad at that point in the room. Similarly, a narrow corridor between parallel reflecting walls may trap sound by repeated reflection and cause troublesome echoes, even though the overall absorption is sufficient. Attention must also be given to the elimination of interference. Such interference arises from the difference in the distances traversed by the direct and the reflected sound and produces so-called dead spots, in which certain ranges of frequency are canceled out.
Another aspect of room acoustics is insulation from unwanted sound.

The Funk & Wagnalls New Encyclopedia are licensed from K-III Reference Corporation. ©1994-96 K-III Reference Corporation. Posted without permission for educational purposes only.
50% of the sound you hear is indirect, bouncing off walls, ceiling, floor etc. So it is often said that the room is 50% of the sound. You also have major issues with alteration of sound based on room gain at various frequencies, most often bass, but in a room with a lot of hard flat surfaces it can occur in the higher frequencies as well. Having an untreated room is kind of like having a graphic equalizer with random settings on it thrown into your signal path (sort of--but you get the point). How many audiophiles do you know that would say "hey let's add a graphic equalizer with random settings in my signal path", but in a sense that's what's happening with their room.
so should one put panels behind listening position or behind speakers first?
so should one put panels behind listening position or behind speakers first?

I'd go for behind the listener for bass trapping first but generally more broadband bass traps is better and you can't ever really do enough in bass trapping...although you can over do it in the mid and treble frequencies if you have way too much surface area of panels =>an acoustically dead room = yuk!
First - proper speakers placement. You should start there.
First reflection points next.
Now... there are 2 schools of "live end - dead end".
1.Live front end - dead back end.
2.Dead front end - live back end.
It is hard for me to recommend which road should you choose, since everybody have a different opinion on this subject. Second I don't want somebody to think that I am an expert on that matter, because I am NOT. What I do have is a lot off experience in set-ups in problematic rooms and my own experimentation and measurements. And NO, I am not a dealer or installer. What I do , I do for my friends and fellow audiophiles. I never charge a stinking penny and I do it for pure satisfaction.
In my own room I implemented treatments according to my rooms particular problems. All room are more or less different from each other and that makes it more difficult to recommend one solution over the other.
My own preferences is semi-dead front end and live- diffused back end with just a little absorbing.
Trick is to not to over treat you listening room. Believe it or not but some reflections are beneficial and you don't want to kill all of them. Ceiling treatment and bass tweaking is another matter maybe for another thread.
Mariusz Stark
The principles of LEDE were begun in the 60s for recording studios. These were dead behind the speakers and live behind the listener. Mimicking an inversion of the recording process (i.e. performers on a live stage and microphones that were dead behind them). In our listening environment we are recreating the performance--not working as a studio engineer. In this case, live on the speaker end and dead behind the listener works best.

Here is an article that may help:
On the Soundstage
Rives, where does diffusion fit in? Does one consider a wall treated with diffusors as dead or live?

Reason I am asking, I have had some very unsatisfactory result when treating my back wall with diffusors. The same diffusors on the front wall (behind my speakers) seems to create a deeper soundstage and quite pleasant to my ear.

Interesting article. It appears that LEDE enjoyed a very brief craze and is now dead. Interesting that a studio had to remodel because it sounded so bad.

I am often puzzled why most Audiogon virtual rooms have extensive acoustic treatment on the wall behind the speakers and first reflection points and yet most have no treatment at all on the wall behind the listener. Perhaps it is just that on the whole more rooms are small and few are large.

Perhaps visual cues also have a lot to do with sound perception. The logic being that if you can't see the acoustic panels (behind the listener) then they are not effective.

My experience has been that a dead end behind the listener and a bright end around the speakers is able to create a very exciting soundstage which mimicks a live performance. The only caveat is that no side wall should fall within 4 feet or less of a speaker mid/treble driver as it starts to collapse or confuse precise imaging. I would include the floor in this minimum distance too - so speaker stands are essential to get the mid/treble away from the floor.

In small or narrow rooms I would support the idea that first reflection points must be treated with acoustic panels. In a large room I think you can get away without treating first reflection points as long as you have carpet and not tile floor and you obey the 4 foot minimum rule.

Just two cents as always and bearing in mind that I like a live energetic sound and that I have a largish listening room, which means that long reverb times/room modes are my main issues.
Diffision is live. It does not deaden the sound but rather diffuses or redirects it. Diffusion or passive resonance behind the main speakers is most effective in most rooms. I absorption or a combination of absorption and diffusion behind the listener works well. Diffision alon behind the listener can lead to odd spectral patterns--it can be done, you just have to do it judiciously.