The problem with absorption panels- it kills the fine details

I think the consensus is that most rooms don’t need much acoustical treatment as long as there is a furnished room.

All the listening rooms we see with all the really really fancy gear only have all the really really fancy gear in them. It’s ridiculous it’s not normal.

I also think the consensus is diffusers make more sense than absorption panels because they scatter the waves and reduce lots of the reverberation affect. But they don’t diminish and absorb all the detail. So if only the world would create better looking diffuser panels then the crap they have now. Some look nice but many of the so-called absorption diffuser combo panels which are ridiculous look horrifying, with a few exceptions here and there.

I would buy diffuser panels in a minute if they looked nicer, but frankly they are a pain in the ass to buy because the marketing and the availability and the design and the size is so difficult to deal with with on all those damn websites that do a terrible job marketing this product. And the ease at which you can mount them on the wall is absolutely horrifying, it could be a lot easier.

The consensus SHOULD BE, if we are honest with ourselves, is that most audiophiles slap some stuff on the walls without knowing what they are doing, why they are doing it and without a desired outcome in advance.

In other words, we apply acoustical treatment like we test cables, we A-B a bit, experiment a bit and then proclaim it "done". If we want a professional outcome, hire a professional. Most professionals though don't get called in until its a clusterph&*% of homemade, DIY or ordered off the internet random "solutions". Talk to a few pros and you will find they are most often in the business of trying to fix a bad haircut.

Random outcomes and hope are rarely the best strategy.

My impression is that over-deadened rooms are extremely detail revealing. It sounds dead, not my cup of tea, but you can actually hear more detail in the recording. "Air" and "detail" are not the same thing to me. I like some "air" in the room and to my ears it always comes at the expense of some detail, but it’s a worthy trade because it’s just more enjoyable. Now if it’s unevenly deadened, which is typically the case, you might end up with reduced apparent level in the upper treble with the lower midrange and upper bass still reverberating like crazy, so in that case you can end up with a muffled sound. But if you over-deaden a room broadband it sounds exquisitely detailed, perhaps painfully detailed. Diffusion can have differing effects, depending on how it’s done. Diffusers that have long wells or cavities will absolutely smear detail if they are too close to speakers.

The thing is, somebody might still find that to their liking, and the word "detail" can mean different things to different people. Generally it has been found that listening rooms are preferred with an RT 60 of around 0.3 seconds. The RT60 should be shorter in in the mid range and longer in the highs and lower bass. A lot of home listening environments end up just the opposite. The walls and various room openings often leak the lower bass pretty quickly, and the carpet and furniture sop up the upper treble very quickly, leaving a lingering midbass and lower midrange. Typically the absorption should be focused there, where it’s most needed and not where it’s not needed. A midbass to lower midrange absorber with a treble reflector/diffuser ends up making a lot of people happy. I’ve had people tell me,( and I’ve experienced it myself), that if you put a TubeTrap too close to a speaker with the treble reflector pointing toward you it can actually make the sound in the room too bright.

Sigh. 

Just sigh.

OK, it's clear a little clarification on acoustics is needed here. Not trying to mansplain, but just to provide some context.

1) Speakers provide input into the listening space. What you hear is the direct sound from the speakers plus the reverberant output of the room. This is why equalization, graphic or automated DSP is a mixed bag - it can only change the input to the room, not the output of the room.

2) In every room there is a point where the direct sound level equals the reverberant field level. This is called 'the critical distance'. Listening inside the critical distance is listening in the nearfield. Beyond the critical distance you hear mostly reflected 'far field' sound - mostly the room output. In a 2000 ft3 room, depending furnishings, the critical distance will typically be 3 to 5 feet (!). Extending that distance to hear more of the speaker and less of the room is a function of speaker angular coverage and acoustical treatment. This is why you see directional horns in recording studios and live sound, and why nearfield monitors like KEF LS-50s and venerable LS3/5a designs get lost in larger rooms - they are tuned for nearfield listening.

3) Acoustical panels (2" thick) absorb sound, mostly from 200 Hz and above. Diffusers, well, diffuse the reflected / reverberant field, normalizing the level and reducing 'hot spots. Placing either to reduce first reflections is the first objective of any acoustical treatment plan.

4) Below 200Hz is the province of bass traps. Since the fundamental frequencies of most musical instruments and the human voice are under 200Hz,the importance of bass traps cannot be overstated.

5) The acoustical requirements for a listening room, home theatre, and recording studio are all quite different, as are the requirements for recording a large symphonic work versus a small jazz quartet versus a multi-tracked pop or rock track. Home theaters in particular benefit from being the most damped, as you are replacing the entire reverberant field with the surround sound mix.

Overdamped 2-channel listening rooms, as noted, can sound 'dead', but left untreated they too often suffer from mid and upper mid-range 'glare' and lack of definition as well as boomy, uneven bass because the listening area is well beyond the critical distance, leaving your ears at the mercy of the sum of all room reflections and anomalies.

6) There are lots of online acoustical calculators to help begin the process of tuning a room for your specific requirements and listening taste. These are a starting point, not an end point. Also, there are numerous online advisors on the subject, some are quite skilled and others quite arrogant, most with a product or service to sell. Hey, gotta pay the rent. 

Furniture is far too vague a term to generalize. Suffice to say a sleek italian leather sectional is at best a diffuser while an overstuffed Victorian fabric sofa is quite an effective, if not optimally placed absorber. 

More than an other component, your room and it's acoustics will return more on your investment than any other changes you can make. A modest rig in a well controlled room will be more enjoyable than a mega-buck system in a poor room.