Most rooms don’t need acoustical treatment.

I think it matters a lot. In 2017,  I reluctantly moved one piece of furniture and it made a big difference. I would say 100% difference. The system sounded twice as good. Moving my LP rack to the first reflection point on the left speaker was like finding the autofocus on a camera lens. And I simply rearranged the stuff that was already there.

That change alone made me chase optimum room configuration for 4 months.  I didn't use specialized products. This is how powerful a room can be.

I just never thought it could make that much difference all these 30 or so years...I would move the speakers around a bit and adjust a few things and if it sounded good, I thought that it was set. Didn't think to try a little harder. 

I agree with erik.  If this silliness is not kenjit then it must be his brother.  It's just dumb.

Ok, now I learn more.

absorption done by couch rug and curtains, yeah.

but seems that diffusers have great value,  ie.  They scatter and add clarity to sound waves, and make room seem bigger.  It’s mystical, no one knows why but this seems good.  A panel will do better than a bookcase, so I buy diffuser.

@jumia -- I think you misunderstand the general direction of this thread.   

The subject of room acoustics is well understood by those who have studied it extensively. However, it is not an issue where an amateur can do a five minute Google search and have any assurance that they've come up with the correct answer for their particular situation.   

There are lots of things like this in life.  You want your airline pilot, doctor, structural engineer, and so on, to have specialized knowledge and training for their job.  It is certainly easy enough to look up info about all of those subjects on the internet, but that hardly means that the person who does that is ready to fly a plane, operate on a person, calculate load bearing specifications, or do the many other things that people spend years training for.  

Acoustics, and all those other things, still may be mysterious to you, but that doesn't mean that others out there don't have a good handle on things.  

But, that's the nice thing about this hobby. You can experiment to your heart's content with no concerns about the plane crashing, the patient dying or the building collapsing. Who know, you may even end up improving the way your stereo sounds for you! 

Jim Smith in his excellent book "Get Better Sound" talks about the room, and how spending lots of money on your hi-fi without treating the room (and setting up the speakers properly too), at least on a basic level, means you’ll never hear the full potential of your system. A modest system in a well set up room will often sound better than a more expensive system in a room that is untreated, especially if the room has inherent problems ( dimensions, ceiling height/shape, large/many windows, too live or too dead a floor etc).

Right on the spot and my amazing experience after 2 years of listening experiments...

The truth is most people has never take the journey themselves and they are completely unconscious of the poweful impact of acoustic in 2 way:

Passive balanced materials treatment....

Active controls of the zone pressure of the room....The room can be activated, it is not only a set of passive walls waiting for the waves to be absorbed, reflected or diffused...The room is like a set of strings in a very tight compressive mechanism, a violin for example; because the waves cross the room 80 times a second in my room for example.... Zone pressure play a great part if we use them to balance the natural frequencies response of our room to compensate and balance well with our specific speakers...Helmholtz science...

No gear can beat the room at ANY price....EVEN in near listening in a small room....Unbeknownst to most....

This is my experience.... Those who contradict have never experience by themselves how cutting few inches from a straw can improve or destroy a room... I did...

The more important asset of an audio system is not the gear it is a dedicated room.....Most people upgrade gear trying to compensate for a bad room without even knowing it...They called their choices "tastes".... But in music only exist natural timbre perception first OR last, not taste first AND last....

It’s snake oil, voodoo science.
So why is accoustical panels gonna help?

It is not voodoo science at all... But we must read a little about acoustic science, comic book will not help here.... But the problem is that company sells costly ready made esthetical easy solutions... But it is not so simple , buying costly materials is not the solution at least nor for me.... And each room has specific problem because of his geometry, topology and content, which no company can take the time to solve in details at low cost...I made all my materials treatment with useless and discarded materials and i never bought anything costly at all.... It takes time and listening experiments tough... But it worked...