Absorption, Diffusion or a combination of it all?

Might depend on what your goal is.  Rooms and acoustic problems are so varied.

In my experience, the most valuable place for absorption is in the first reflection points on the side walls and ceiling, and the wall behind my listening chair.  I focus on diffusion on the front wall and behind my speakers.  Took my room to another level.  Bass traps are also valuable.

Others may go with another recipe.  

Diffusion properly placed adds fullness and depth to the imaging.  Usually listeners like diffusion directly between the speakers and directly to the sides, and behind the listening location.

A 100% absorptive room sounds terrible. :)

All of it ! alternate absorption and diffusion , use absorption at the first reflection points.

From what I’ve read, which may or may not be accurate in all instances, is that you want absorption behind the speakers (front wall), and diffusion behind the listening chair (back wall).  Based on experience, I can vouch that the aforementioned holds true for electrostatic (dipole) speakers, but I'm not sure that it carries over so definitively for regular speakers. 

OP. Anthony Grimaldi has an "acoustic recipe" based on thousands of rooms he has tuned. You may want to tweak it a bit but it gets you extremely pleasing results as a starting point. It starts at the :49 min mark in this video:

https://www.youtube.com/live/G0ekssXX7rE?feature=share

Both, is typically the answer.

Diffusion - and even deflection - has been the greatest help for my system, once the bass was tamed (with absorption).

According to the pro's pros, without a proper analysis of the room, you are guessing, and may make the acoustics worse.

I have experimented a lot over the years with acoustic panels, mostly from GIK. I have used both ears and REW measurements to accomplish what I like. I am currently all GIK. What worked for me best is:

Side walls: Combination of 242s and Alpha 4As

Ceiling: 242s

Front wall (behind the speakers): Alpha 4A and 6A

Bass traps: Alpha 6As (my corners are scaled, with multiple outings, so I can only “tuck them in” with overlapping Alpha 6As)

Back wall (behind my listening chair, about 10’ behind): Alpha 6As

I like the Alpha series a lot. Very versatile, as they are a combination of absorber, diffuser, and bass trap: https://www.gikacoustics.com/product-category/alpha-series/

All…thanks for your thoughts! 
I watched the video and it makes sense but isn’t easy to implement, no room is ideal as far as wall space, ceiling, windows, doors, etc. Good as a guideline though.

So since I’m already using the GIK 242 and 244 bass traps in the corners, I’m thinking to add a set of A2 Alpha Pro, exactly the same design pattern @thyname has in his room. Decent amount of absorption and enough diffusion. I don’t want to completely deaden the room. Still researching. Keep the thoughts and suggestions coming. 

OP

If you look at my virtual system you can see how I implemented the video. Interleaf diffusors and absorbers, pretty simple. 2D diffusors in front half of the room and 3D diffusors in back. Absorption on the back wall directly behind MLP with diffusors to each side. 

I initially started with 2 GIK quadratic diffusers on a shelf in front of my tv screen between my speakers. I liked the results so much that I purchased two more and put them atop the original pair.

I’d definitely recommend either quadratic diffusers or something like GIK Alpha panels. The latter have the advantage of providing both scattering and some bass trapping, if you get thicker ones.

For what it’s worth, Paul McGowan prefers diffusers to absorbers; the former mix reflections of all frequencies equally, while the latter absorb different frequencies to different degrees. McGowan also explains that the reason “first reflections” cause problems for imaging and soundstage is that they arrive at the ear “too quick for the brain to sort them out as delayed copies,” so they muddle the spatial effects of the perception of the direct sound.

It's easy to make a diffuser. Go to Home Depot and buy a long, square wood pole. Using a skill saw, cut it into lots of small cubes with angled cuts. The angles don't need to be precise or the same, nor do the cubes need to be the same height. In fact, the diffusion pattern is actually enhanced by irregularly sized and shaped pieces. Softer woods absorb more than harder woods, but either will work. Then glue them, flat side down, onto a board of the size you need. If you want to absorb some lower frequencies, glue them onto an acoustic ceiling panel (also available at places like Home Depot). Works well and looks good, too.

This very absorbing conversation may confuse you on diffusion.

Most say behind speakers you diffuse.

If you build Snifle's diffuser keep in mind it will be heavy!!!

IDK who Paul McGowan is, but does he have any science to back up his claims about sounds arriving "too quickly" for your brain to sort them out?  

Also, do you have any evidence that can be replicated that softer wood absorbs more sound than harder does? If that's accurate (and it's not) what happens to the softer wood after is absorbs all the sound it can hold? Does it explode? Does sound start leaking out? And if it's saturated with sound, wouldn't it then be unable to absorb more sound and revert to the hardest wood ever grown? 🙄

Or, don't bother with either and simply enjoy music with a bit of room sound.

Thanks Kota1. That was a great video. It's over an hour and I watched the full thing while picking out pearls of wisdom that may improve my own setup. Thanks Anthony and Audiohaulics for the video too.

@wolf_garcia 👍

@leggs 

After watching that video I moved the treatments I already had to the suggested locations, wow! I previously had absorption on the front wall in addition to those bass traps in the corners (pics in my  profile). I replaced the absorption panels with two combo panels and big difference. 
Then I followed the rest of the "recipe" interleafing absorbers and diffusors, etc. I bought most of my treatments through auralex and found great results at reasonbale prices, especially the diffusors. If I were starting from scratch I would just get a room kit from anthony's company, www.sonitususa.com.

In acoustical terms 99% of our rooms are small - 30x20x12 or 15x13x8 both are small acoustically speaking. However those two room sizes will require different approaches. Small room acoustics are very challenging.

The challenge is to get the most out of your space and spkr placement / listening position and addressing room acoustics are the single biggest influence on a system, more than any piece or gear IMHO. I’m not into HT, only 2-chnl, but generally speaking many of the same principles apply

• Addressing bass is prob first priority along with first reflections. Putting pillows and or thin 2-4" panels in corners will do nothing to the lower bass region.
• Using only absorption (a lot of it) wont give you a balanced / linear response, so a balance of absorption and diffusion is needed.
  • Unless you are building a room from scratch and designing true corner trapping via a acoustician, floor to ceiling bass traps in corners (tube traps, tri-traps etc) are a good starting point.
  • 4-6" broadband at first reflections AND ceiling. Treating the ceiling is very overlooked. Its actually "free" real-estate
  • Diffusion > this is tricky as this can be applied to various areas, but can also create a lot of problems if not done correctly. I would get advice on how to implement this, but on ceiling and front wall are good spots. The back wall (behind you) is also good, but req minimum distances to listening position
  • Multi subs give tremendous value and impact for the bass/sub bass region.

These are just some basic ideas, but get a mic and REW and measure your room is where I’d start. Also, I think its a matter of priorities as well. If you are fine with "whatever" and it sounds fine, that’s cool. If you want the very most from your system and are willing to put in the time, you must deal with spkr positioning and room acoustics, no way around it.

DSP and the like are also no substitution / fix. Get the above right first, then if one wants to dabble with DSP, that comes last IMHO.

@mrskeptic: Paul McGowan is the founder of PS Audio. Is he a "scientist"? Certainly not. Is he a blow-hard? Yes. His "books" are full of dubious and self-serving claims, as are many of his too many Youtube videos. I also know people in the business who have expressed skepticism about him for various troubling reasons. However, many regard PS Audio as a serious audiophile manufacturer, and McGowan’s videos as sources of well-informed advice ("well-informed" meaning: lots of industry experience in high-end audio; that cuts several ways, of course). I own one of his earlier DACs, and love it. Make of his advice what you will.

Now, I’m not an acoustician. But I do have a lot of education (make of that what you will as well), and I’ve published on issues in contemporary physics. As I understand it, sound absorption works by converting the energy of sound waves into heat energy. So, no, wood does not absorb sound until it "can hold no more" at which point the sound either "leaks out" or the wood "explodes." Anyone with the tag "mrskeptic" should be ashamed at such silliness. The way sound absorption works, in terms of physics, is well understood and explained in many available places.

As for whether or not softer woods would absorb more than harder woods—I admit my ignorance on this, but it does make physical sense. In general, softer materials (pillows, heavy carpets, foam, acoustic panels, etc.) do, in fact, absorb more than harder, "reflective" materials (dry wall, plaster, glass).

As for @jeffseight’s caution that the DIY diffusion panels I described "will be heavy"—well, they can be (with hard, heavier woods like walnut attached to heavy acoustic panels that are large). But smaller panels made from lighter (softer) woods, like pine, attached to lighter boards, are not prohibitively heavy. Too heavy to mount with double-stick tape, but not at all too heavy for other sorts of methods (such as are used for hanging even large and very heavy framed pictures).

Finally, yeah, all this is tweaking, and usually unnecessary. Or...it can make a bigger difference than an expensive new component. FWIW, I totally agree with @redlenses03: room acoustics is one of the very most important elements in getting good sound. I’ve posted about this at length elsewhere on this forum (regarding concert halls, in particular, with respect to the recent renovation of Avery Fisher/Geffen Hall in NYC). The Number One element in good sound, however, is the quality of the original recording. There are plenty of "experts" who will second that opinion. Speakers are No. 3. After that, it’s all tweaks. Even amplification, so long as it’s sufficiently powerful not to be driven into clipping, has been empirically shown to be of relative unimportance. As for cables and power cords.... Of course, many on this forum don’t believe in empirical demonstrations. I hope, when you get sick, you don’t avoid empirically minded physicians, or disregard "measurements" when it comes to "high performance" vehicles. Science works. It’s not the endpoint of audiophilia, but it is certainly not irrelevant.

@drbond - Have you tried diffusion behind your electrostatics? I started out with GIK Alpha Absorber/Diffusors behind my dipole speakers and was not happy with the soundstage and liveliness of the music. I switched to ATS Quadratic Residue Diffusors and really like the change (as did my audiophile friends). 

Of course, every room is different, and not everyone has the same preferences in sound presentation. But I've generally found manufacturers of dipole and open baffle speakers to recommend diffusion behind the speakers. I had thought that the GIK panels would have worked ok but they were sucking too much of the life out of the music.

Perhaps I'm a purist. I want to hear the recording the way it was produced and intended to be heard.

So for clarity, I prefer my sound to be direct. I group diffusion with diffraction and reflection as unwanted complexities that were never intended.

It's a bit like the harmonic distortion added by tubes. Some love it and some hate it.

pedroeb

... So for clarity, I prefer my sound to be direct. I group diffusion with diffraction and reflection as unwanted complexities that were never intended ...

Reflections, diffusion and diffraction are all part of sound in the natural world. Music isn’t designed to be played or heard in an anechoic chamber.

I recommend every audiophile spend a few minutes in an anechoic chamber, if given the chance. It is a very eerie experience. Most unpleasant.

If you want to hear a recording in the most ideal conditions

go outside when it is quiet-for some impossible- and set up

your speakers and required gear. 

Your eyes will pop out !!!

You may move to a warmer climate too!!

@redlenses03 I spent quiet a bit of time dialing in speaker placement. I’m sure I can squeeze some more out of it when the room acoustics are dealt with. 
Need to look into REW. Haven’t had the time yet. 

@jaytor

Yes, I tried many combinations, including nothing at all. I found that absorption (and bass traps) behind the speakers along the full length of the front wall presented a most realistic presentation: most detail and clarity with realism. Without as much absorption, the sound was more robust, but unrealistically robust, and slightly muddled. Depending on your amplifiers, etc, less absorption may be better in your system.

@erik_squires 

i beg to differ on an all absorptive room sounding terrible. I think it depends on the room. My room was designed by an acoustician and I built it. I would love to have you over for a listen. I think it will really surprise you. If you are ever in Colorado and would like to check it out let me know. 
 

Ron 

@audphile1 

I would suggest a consultation from an acoustician. Jeff at hdacoustics is very good. Duke LeJeune recommend him to me. He can analyze your room for you. He designed my room and it turned out amazing. Good luck !

Perhaps I'm a purist. I want to hear the recording the way it was produced and intended to be heard.

Compressed and with a sizzling treble for ear buds/car radio playback? I think a lot of recordings are engineered with the lowest common denominator in mind.

i beg to differ on an all absorptive room sounding terrible.

Really?  You have a room that has no reflections, and is 100% covered in absorption materials?  @ronboco 

@erik_squires 

Hi Erik. That is mostly correct. My room is right on the edge of small to medium so my acoustician designed it to sound bigger than it is. There is no drywall in the room. The walls behind the speakers have Rockwool in between the studs and 1/4 inch pegboard over the studs so there is probably some reflection there. All the other walls have Rockwool then pegboard then a layer of 2 inch rigid fiberglass over the pegboard. The ceiling has Rockwool in the joists and two layers of pegboard and 2 inch rigid fiberglass. The outside of the room is 1/2 inch drywall then a layer of mass loaded vinyl then  another layer of 5/8 inch drywall. All cracks have been caulked. I put some pictures on my systems page. I have been very happy with the result. I enjoy having people over with more listening experience than I do to critique my system. 

You will need absorbers and diffusers for certain. Just look at my house of stereo. Too much work involved to put it in a post and it's all room dependent anyway. Keep at it, you will make mistakes, persevere and you will be glad you did.

All or nothing, all the time.  Twas' always thus.

One finds the balance one wants, some luckier than others. *S*

Enjoying the hunt is what counts....

....meanwhile...  may as well dance....

The peg board proves my point.  😀

You can reach out to GIK directly and they will do an assessment of your listening environment. GIK has an online form that you fill out and you can include photos of your room. I had tried doing it on my own, by tackling first reflection points. But when the analysis came back one of their techs came back with a detailed analysis and set of recommendations that included some of the things I had and then went further, like a pair of 4A Alphas Series Bass Trap Diffusor/Absorber -- which are amazing! -- that go "on" the front wall, behind the speakers (though not directly behind.)

Anyhow, to me, that is the way to go. Reach out to them and see what an expert says.

Does GIK really do an assessment of your listening environment?  I modeled my room on their site, uploaded photos of my room, and uploaded REW measurements.  All I got was a generic response that did not include anything related to the specifics of my room.

@Gordon

Yes, that was my experience. Mike Major was the guy that helped me. I submitted all my stuff. He replied right away that he was stacked up and would need some time to review. (I liked that b/c he set the expectation up front.) He wrote a fairly lengthy set of recommendations and comments. I was impressed.

I wouldn't have posted if I wasn't so pleased.

Maybe you could try again and/or call them.

As with everything else in this hobby, it takes a lot of experimentation to get the best results. You can get a head start by hiring an experienced acoustician to come an evaluate your room and provide recommendations, but your personal tastes need to dictate the final solution. 

It's relatively easy and inexpensive to experiment with absorption since low cost fiberglass or rock wool panels can be purchased from your local home-improvement store (Lowes, Home Depot, etc.), or you can just use spare blankets, pillows, quilts, etc. 

Diffusion is a bit more challenging since good diffusors are somewhat costly. I haven't found the cheap diffusor panels to be that effective.

But once you get it reasonably dialed in, acoustic treatments provide a LOT of bang for the buck. 

I got an email chain going with Mike Major of GIK. His recommendation based on information and pictures I provided is to fill the side walls up with at least 5” thick absorption panels all the way to the level of listening chair and go as thick as possible with bass traps on the front wall. 
 

I’m evaluating all suggestions at this point as I continue the researching. 

@jpan , @audphile1 Thanks for your feedback.

Floyd Toole did listening tests to determine if listeners preferred absorption, diffusion, or bare wall at the first sidewall reflection point. 

Diffusion and bare wall were the most preferred....with absorption by far the least preferred for sidewall first reflection. Going off memory only like 14% preferred to absorb sidewall. 

Why do so many people recommend absorbing sidewall first reflections? It has to do with pro-audio rules of thumb and advice given by acoustic product companies such as GIK.

Pro-audio wants as much direct sound as possible, to take the room out of the equation....basically a headphone type experience with speakers so their mixes with translate. 

Hi-fi uses the room to enhance the experience. That's why we don't listen at a desk or shove our speakers up against the wall. 

Having said that, very close sidewall or close behind our head reflections can be very destructive and smear the sound...as long as we have some space though, our genius brains can sort out the direct sound from the indirect sound and we get this really nice ambiance or reverb without the smearing.  

Experimented today with all the panels (GIK 242) except bass traps leaned against side wall at first reflection points. It helped with better focus, imaging was more precise and the soundstage deeper and wider. Front wall was bare. 
I think it depends on the room size. Diffusion may work combined with absorption in my small room. If the room was larger it’s possible the diffusion alone would be fine. Not sure. I’ll need to try. So far I think Mike Major is on point with absorption. 

I see advice all over the map here yet nobody condsiders the size of the room? It's not one size fits all!

OP, diffusion is great but unfortunately not of much use in a small room simply because you need to be seated a minimum distance away for the effect. Situated close to your ear will just not do.

My suggestion is to at least heed the advice to measure the room yourself. That way you can ignore the noise being made about creating a room that is dead.  It has been mentioned to get GIK to 'analyse your room' and then buy their products. Well they are in business to sell stuff and will, as has happened to some I know, oversell if you keep buying. 

To measure: Install REW, it's free

Buy a microphone: for the cost of a dinner.

This will provide the tools to achieve the ideal response in your particular room. Tables online will supply the target time required for the sound to decay, across the spectrum by a certain amount, this amount also found in the tables.

What I can assure you is that with the confidence you gain with understanding the requirements for treatment, and can measure any changes from adding traps or panels, will be the biggest step towards an immersive and realistic sound. Ideally the treatment will essentially largely remove your room's sonic imprint and transport you to the venue.

No electronic component exists that could correct the acoustics of a room regardless of cost. The recommendation to 'just get DSP" to sort out the problems can not sort out the damage that strong early reflections cause. How can any electronic gizmo know how much decay to apply and at which frequencies to apply it?

Should you hire 'professionals' to do an installation you can of course measure the results to ensure they do not reduce the decay time beyond the recommended time, which is generally 300 to 400ms. Overdoing the absorption is what renders the room being too dead. You newfound skills will allow you to prevent this.  It will also help you find the best position for the speakers and a sub or three.    😀

The subject is fascinating, understandable and most importantly, essential for great sound. I repeat:  No $5000 cable nor $10000 amp can do anything to tame the elephant.   But you can  😎

Love this topic as it’s not as common but extremely important.  Working with the folks at GIK (or other acoustic expert) is key.  REW has been a very helpful tool along with my ears, and the USB mic was a worthwhile investment as I’ve used it multiple times over my three year journey in treating my room.  I cannot recommend it enough. And the GIK folks will use those REW measurements to help diagnose your room and suggest treatments.  My listening chair is only 2’ off the back wall so pure diffusion wasn’t recommended.  I’ve read elsewhere that pure diffusion on the back wall isn’t beneficial unless your listening chair is 6’ or more away from it.  GIK  instead suggested their combination diffusion/absorption Alpha series panels, as I had low frequencies that needed to be tamed along with me trying to make my room sound bigger,  My last and final addition was adding 3 x Q7D diffusers to the front wall and a pair of wall hung monster bass traps directly behind the speakers.  My small square room has never sounded better.

Having a good mix of absorption and diffusion is certainly essential. Also consider DSP based room correction technologies which operate in the time domain. Dirac Live helps listeners correct for one of the weakest components in the audio chain, the listening room. Dirac Live not only corrects the frequency response, but also the impulse response of the loudspeakers in a room, yielding improved imaging and timbre, better clarity, tighter bass, and less early reflections, as well as reduced resonances and room modes.

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If most listening is below, say 85 db, are room treatments still as important?

85 decibels is a sound level equivalent to that of a food blender. Uncomfortable and only tolerable for a short time. Most listening levels might not even be that loud.

Having said that, peaks can still get fairly high above the general listening level, so treatment is still wise.

Maybe not as important, but crucial.

Taking time to research. I’m using the panels that I already have to experiment. I’ll play with REW soon. We’ll see what it does.