Absorption, Diffusion or a combination of it all?

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.

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.

@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.

@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.

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.

@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.

@wolf_garcia 👍

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.

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

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? 🙄

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!!!

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.

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.

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.

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. 

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. 

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/

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

Both, is typically the answer.

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

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

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. 

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

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. :)

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.