Diffuser or absorber behind listening position....and is it worth doing??


I am a relatively new to serious two channel listening so I don't have a lot of experience to rely on. However, from what I have read on this site I do feel pretty confident that improving my room acoustics via absorber and defusers panels will be the best way to improve SQ at this point. Unfortunately, because my listening room doubles as my living room the only place I can only use panels ( no base traps) and only behind my listening position.... hence my title question. What say you.....will I benefit from adding diffusers? Or should it be absorbers? or forget it and be happy with what I have. (which I am.... )

Here are some room and placement specifics:
Room 12 ft by 18ft 
Speakers (ribbon tweeter) on Long wall with large window with wood blinds on right and drywall on the left
Speakers baffle are 32 inches off front wall and 48 inches off both side wall and are 10 ft apart with a 6x9 rug.
Sitting position can be either against the wall or 2ft off the wall (just slide couch forward....which I do because sound stage and imaging is better).

My main goal is to improve imaging and stage. If it is worth doing, would there be any other benefits? Also,
could you recommend how large a space should the panels cover..... how thick panels should be?

Thanks in advance



 
mrpsync
In my experience, that would do little, glass windows are no good, even with the blinds drawn.  I found putting rug in front of the speakers helpful.
My main goal is to improve imaging and stage.
There's much more effective ways to do this than room treatments.

Do you already have your speakers on Townshend Podiums? Are all your components on Pods? Are your components treated with Synergistic Research ECT? Are the speakers treated with HFT? Are you using any HFT room treatment? Orange Fuses? FEQ?

All these will improve imaging and stage far more than any room treatments you will be able to get WAF for. Deservedly so. No one should put up with tube traps when putting the speakers on Podiums will clean up the bass just as much and improve imaging and detail more than any acoustic treatment you could do in your room.

Actually any one of these will be about as good as all the panels, while being essentially invisible in terms of decor. 
Owens Corning 703 make it yourself  see( hear ) You already know what 2’ got you.....the anti science crowd does not understand the attenuation those 2’ provided AND how to get more....

can you post a few pictures in the virtual systems page also please.
do you have an ipad ? You might want to run an app inside Studio Six digital tools, PM for free help. Pretty much every recording studio has glass...and of course there are excellent acoustic curtain companies.in your room.the issue is balance w drywall opposite. Carpet good but not a broadband absorber, it will help.

Don't dismay many a dedicated audio room lags far behind the natural diffraction, diffusion , etc in a well lived in room.
MC
Appreciate the respond and I probably should have mentioned I have bookshelf monitors and that they are on isolation stands. So I think I got that covered. Unfortunately I don't recognize the acronyms ....so pretty sure I haven't tried them. I have some homework to do.


601 -  sounds like you think absorption is the way to go. Do you have dimension to recommend?

I'll try and post images tomorrow.

thanks
2’ above and below ear and if possible 3-4’ outside of each ear. A 4-6” deep panel. i hide 2” deep  behind framed art canvas. make them yourself, not an expensive experiment....

have fun, doubt you break anything......
Absolutely benefit.  :)

While first reflection points and bass traps are important, controlling the overall energy in a room is as well. Don't forget your ceiling.  Also, consider some of the super-thick panels from GIK. 4" and 7" thick panels can make up for limited numbers.
Have you thought of Synergistic UEF panels withe the UEF dots? I have found them very effective in my listening room. Smaller panels that work magic. And you can demo them - 
601 - Pics and description posted if that helps. Also thanks for the dimensions. Those work for my needs as the panels will be hidden behind couch when not in use and hung up when listening. thx
Eric - it's my understanding that first reflection points (and bass traps) carry the greatest impact. But unfortunately ceiling, side wall, and traps are a no go. But if I understand you correctly even simply addressing the the wall behind me (and only the wall behind me) is worth while, and I think you are suggesting absorption over diffusion like tomic601...please correct me if I'm wrong.
much appreciated!

Also thicker would also affect a greater range of frequency correct?
@OP, 
Nice looking room. I love having a fireplace-though mine is gas. Something about a mantle seems so warm and cozy...

In any case, I see two arched entryways near the speakers. They seem to be somewhat at different angles from the speakers. This, in my opinion, would result in differing sound reflections. If you could put up a couple of room dividers behind them, I think you might be surprised at the change.
Also, take any advice from Tomic601, he knows his stuff.
Bob
love the groove.The openings are bass mode killers, so you are ahead there.... Bob is right about back wall asymmetric reflection...let me ponder that. I would recommend a lightweight diffuser to hang over TV screen. A RT 60 after you do the behind couch absorber would be fun,put studio six on your ipad.
fun.....
Bob- thanks for the compliment;  my fireplace is gas as well and enjoy it for the same reasons. 

You are correct that the wall and openings angles behind the speakers are different (though not as much as the Pano image suggests). With that said the baffle plane of the speakers intersects with the walls/blinds and not the opening....so I suspected it's  mostly low frequency from the speakers (rear ported) that is lost into the openings. But that is only my speculation,  you're probably right and will experiment with room dividers. Thanks you

Oh, and I appreciate the vote of confidence with Tomic601. I've read his posts in the past and concur.

Tomic601

It's reassuring the opening in the room are conducive to eliminating room nodes (one less thing to worry about). Sometimes I only hear issues after reading they exist on this forum.... It can be a curse :)

I like the idea of using lightweight diffuser panel over the TV, once the absorber is behind the couch. And I'll check out studio six and try to get familiar with it.

Also, if I may, does the information I provided to Bob regarding speaker plane and angles help with asymmetrical reflection quandry? or is my speculation misguided?

Thanks
If all you can do is the wall behind you then do that.

If the wall behind you is close, like immediately behind your listening position go with 100% absorption and as much as you can.

If it’s 6’ or more away, a mix of absorption and diffusion.

Another thing to do is consider speakers with more controlled dispersion. Klipsch Heresy’s for instance, line or ESLs are going to be better for you, as would open baffle.

If you can do the left wall, along with thick curtains on the right then do that too.

Keep in mind a lot of room treatment looks really good now, GIK art panels for instance let you pick any art at all. 
Area high-shag rugs are very useful. Home Depot DIY insulation fiberglass with foam wall panels work well behind the speakers and side walls help dampen brightness. Acoustic foam or pillows near your ear-level and ceilings are a plus. Additional foam behind your listening chair rounds-off the bounce-back. 
Don't be flummoxed into falling into a hole of improvements. GIK acoustics do picture panels so you can combine art with diffusers / absorbers. I have 3 art absorbers back wall with 2 corner tritraps. I have 2 diffusers on stands I move into place for serious music time for the side walls. I also have 2 thick pile rugs on top of each other in centre of room.

These all help.... I then went further and placed speakers on isoacoustics feet(massive differance but £500) and got a good mains stabiliser. 
Erik, you nailed it; said what I was going to say and others had missed.

OP, for the same reason you know not to put the speakers too near boundary walls, you really don't want to sit right against the back wall, or even 2 or 3 feet forward.  You will hear mis-timed reflections of everything.  To a significant extent you will be listening to the back-wall as well as the direct signal from the speakers.

I agree with Erik, if you really must sit there then pad the back wall out all you can so it absorbs rather than reflects.

That is the only solution, but a crude one.  Unfortunately, 12x18 feet is not ideal for hi-fi, especially a big system. Whichever way you set it up, you are compromised beyond full salvation.

I have a similar shape room to yours, fortunately a few feet wider and I am set up the other way.  So along the long axis the (dipole) speakers can be 5 feet from the wall behind and I sit somewhere in the middle of the room, well away from reflections.  I have to compromise a little as the outside of the speakers are a little less than 3 feet from the side walls.  But for dipoles it's better to have a bigger space behind than to the side, as they face nearly straight down the room so most of the rear signal beams backwards.


MC has no clue on acoustics, to treat a room properly will require both absorption and diffusers. Glass is the worst for acoustics, no pods/springs will fix that. Go to the experts like GIK, ASC, or Acoustic Fields (as examples) to get their opinions. Once you treat your room, then you can apply tweaks to your system to get the best out of it, but you won’t be putting $1 springs on components to accomplish this. If you have a terrible sounding room, a $100,000 audio system will sound like a $500 system. 
Regarding the wall behind listening position. I support the use of absorption via self made panel.  One place to look for DIY material is ATS Acoustics. They are located in Piper City Illinois. Have a nice web site. They can place any photo you wish on to acoustic material for the panel. 

Good luck with this project.
OK, first off thank you all for contributing your insight and suggestions. Especially those that were considerate enough to circle back and answer additional questions!

So, I'm definitely ordering some absorption panels for behind the listening position to cover a 4x6 ft space and 4 inches thick. Main objective achieved!

In addition, I'll be researching a light weight diffuser that's practical to implement covering the T.V. located between the speaker on the front wall when listening (any recommendations?)

Lastly, I'm also strongly considering setting up temporary free standing acoustic panels ( I have photo lighting stands I could repurpose) for managing the side wall's first reflection pionts when listening as an experiment. I just need to determine if all the set up is going to be more of a determent or a benefit to simply enjoying music.....which is the really the point and don't want to lose sight of that.

Thanks Again
I have a room almost exactly the same size (11 feet by 17.5 feet).  Diffusers can be beneficial.  However, be aware that QRD type diffusers (quadratic) need very careful implementation.  QRD diffusers can do weird things to the sound if they are placed very close to your listening position (like within 6 feet).  In this situation, the QRD diffusers can boost some midrange frequencies while cancelling out other midrange frequencies.  This creates a very bad and unbalanced sound. (this was from testing QRD diffusers on the side walls).

I was successful in placing two 2' x 2' QRD diffusers in the middle of the back wall.  That was the only place these QRD diffusers really worked.

I also have two 703FRK panels in the rear corners and another two 703FRK panels mounted at an angle on the front wall / ceiling edge.  These panels are actually "reflectors" for mids/highs due to the foil on the front surface. 

The rest of the panels are absorbers or tuned membrane bass traps.

The variety of "diffusers" that GIK applies onto their panels are not really true diffusers.  They are primarily "reflectors" to prevent much of the sound from being absorbed, but still keeping the panel useful for bass frequencie absorption.

The GIK "gridfuser" is sort of a QRD diffuser but without the channel slots.  Their PolyFuser is like a broadband reflector that reflects all angles (sort of works like a diffuser but more forgiving).

Be careful with how much absorption you add.  You can definitely over damp a room and suck the life out of the high frequencies (thereby removing excitement).
As an option to consider, Jeff Hedback is a designer who has created several hundred studios and also a large number of high end personal listening space designs. I've used several of his studio designs myself. Jeff basically works from his home, employs remote techniques to read your room acoustics, and works with you to create a custom design. The design comes to you in the form of architectural drawings and specifics as to materials and techniques. He then monitors the progress and results with more remote measuring methods. Award winning work and a nice guy to talk with. http://www.hdacoustics.net/
https://ua-acoustics.com Way less $ than GIK but not as pretty.

Or buy a 12 pack of  2' x 4' x 2" Owens Corning #703 rigid panels and experiment. $130.

Try 2 front, 2 back and one each side per Eric's instruction.

I don't know if treatments will provide the sound staging improvement you are looking. It will clean up the
"Smearing" effect you get when the same sound is reaching
your ears to close together in time.

In my mind this comes well before any other considerations.

You are at a very great/exciting/rewarding stage of Audiophilia
as the improvements in front of you now will make make the
biggest SQ improvement you are likely to achieve.

Please let us know your results!


Blankets and pillows can be your friend when experimenting.  Cover your TV, and put up a make shift absorber on the sides. 

If you do put something on the sides, again, due to lack of materials, go for a thick panel, but now you should consider diffusion as well. Look at the GIK impression series.  They can come with feet, so you could for instance put a diffusor in front of your TV while listening and move it out of the way when you need to.
Hi @chorus,

 I was just looking at the OC 703 panels yesterday.  How are you using the panels? I   Was thinking of making a frame out of 2x2 and hanging them on the walls.  If they work, I can replace the 2x with nicer frames and my wife can pretty them up.

Thanks

JD
Chorus recommended ua-acoustics for a really cheap solution.  Be aware that these are just foam panels.  They are NOT the same thing as GIK panels which use fiber material similar to Owens 703 and the like.  I have tried foam panels before and they really don't do what you want them to do.  They don't absorb all frequencies and I actually had worse results with foam panels.

GIK Acoustics really is the cheapest "GOOD" solution here.  There is a company called ATS Acoustics that has panels slightly cheaper than GIK, but they use a hard-back panel frame (essentially a 1/4" piece of plywood on the back).  This is not the design you want because I have found the hard-back will resonate with the material and create more echo/vibration.

The 3lb 703 is excellent choice to work with because it is super light and it also does not sag.  I wouldn't recommend the 6lb 703 because it's a lot heavier and doesn't really do much different.  For my room, I just took a 703 2x4 panel and wrapped with with Guilford of Maine black fabric.  I just used spray glue on the back side to hole the fabric closed.  I don't made frames for my panels, but I also don't hang them (I just sit them on the floor/wall or on top of a bass trap agains the wall).  You can make frames if you want.  It's really not difficult.  Just get some light weight pine 1x2 from Home Depot and cut them.  Then glue/nail/screw the frames together and inset the 703 into the middle.  Then wrap with fabric of your choice.
Good info keeps coming.

Auxinput - thanks for the more in-depth explanation and panel types,....the rundown helped a lot.

Eric - you answer preempted my question about side panels function and type. got another one though. The GIK panels are only 5 ft tall and my tweeters are 42 inches off the floor. I'm thinking I need at least 6 ft of panel height... yes?

Chorus - with all the variables and unknowns the panels will have on the room's acoustics,  much less my interpretation of better. I think going with the DIY approach and getting 12 panels is the right path to get started for this experiment. This way I can customize sizes and depth to better fit the room and my storage requirements. I think I can build what I need for a little less than $200 (probably won't be pretty though). GIK was becoming a lot of money for an experiment.

Mark
@mrpsync, 
Thanks for initiating this thread as it has generated well informed and educational contributions from knowledgeable Gon members who know their stuff and willing to share their experience.  .

Besides you,  certainly others have gained iuseful nformation on how to systematically approach the first steps of applying acoustic treatments in one's home. This is an example when this forum really shines.
Charles 
Auxinput - appreciate the insight on the 3lbs vs 6lbs. However I can't discriminate between the two on the site I'm using to order. Is the 2 inch thick 3lb and 4in thick 6lb?
No, it's the density of the material.  I think it is lbs per cubic foot of material.  So a 6lbs version of the 2" panel is going to be twice as heavy as the 3 lbs.  ATS Acoustics sells the 3 lbs version here:

https://www.atsacoustics.com/item--Owens-Corning-703-Case-of-6--1004.html

A box of 6 of the 703 2" thick 3 lbs version is $72.  Add about $50 for shipping gets you a total of $122.
Okay, hold the presses.  I was talking on assumptions.  The 703 has a density of 3 lbs.   It is the 705 that has a 6 lbs density.  So if you order the 703 from your website you should be good.

There is absolutely no difference in acoustics between the 3lb 703 and the 6lb 705.  The 705 is just going to be a heavier object to mount on the wall.  In most cases, you actually want the lighter 3lb density.

It isn't until you get to the Roxul Rockboard stiff/heavy panels that you will find any differences.  Their 2" panel will absorb more midbass frequencies (around 125 hz), but they are extremely heavy at 6lbs or 8lbs and they tend to sag.

No worries....didn't pull the trigger yet!

thanks
nice thread......

run your RT60 before, listen, and after ya hang 50%, again...all the while listening to music...

fun
Tomic - crazy helpful to me :)

If your referring to Studio Six I may need to take you up on your PM offer if it still stands.

Thx
From my reading, acoustic experts state that the listener needs to be a minimum distance from diffusers for them to work correctly. Any less than that distance is not advised, absorption is recommended instead. So what is that distance? I'm not positive, but I believe it is in the neighborhood of 5-6 feet. I may be mistaken.

I have to sit very close to the rear wall, so made a 4' X 4', 6" deep frame into which I installed a 6-pack of Owens Corning 703 (each 2' X 4' X 2"). Works pretty good, and in any event will have to suffice until and if I ever have a larger room, which appears at this point unlikely.
Synco de- I made 12  2' x 4' fabric wrapped panels using 1 x 3 cheap wood with inlaid corner bracing on the back. I I could ever figure how to post pictures of my system on this site I would show you.

Bottom line I was about $300 all in for wood, 703, fabric and stapler.
(buy/borrow a pneumatic) Sold six at $25 each and kept the other
6. My cost into the ones I kept was $150. Can beat that. 




Lined drapes on the windows and a large fiber art piece behind the listening position will help. Both can enhance the living room feel and fiber art piece, large handmade rug or handmade quilt can be an investment as well. If a TV is involved, a quilted cover for that will work wonders.

Good luck.
Change the wood blinds to heavy drapes and you do not mention the floor but that can have a detrimental effect on the sound especially if it is hardwood, ceramic, or some other hard surface. If it is a hard surface floor try a heavy area rug in front of the speakers. With just these small tweaks you will have a much better sounding room.
I have been at this in my room for 7 months. I started off just trying things here and there and listening. The number of places to put things seemed infinite. I had blankets and towels everywhere, bought some panels, moved them around. It was time consuming and crazy making. Then I took some advice I had been resisting -- buy a $100 mic and download REW, Room EQ Wizard. Learn the basics. Measure, treat, listen. Repeat. Learn where your room’s reflection points, peaks, and nulls are -- for real. In some cases, theoretical predictions were correct, in other cases, they were way off -- because I have an odd room.

I bought OC 703 panels and wrapped them in fabric. With 6 of them I made two 2" panels and 2 4" panels (doubled up in side a fabric pillowcase). These proved to be very effective tools to test out various effects in the room, especially when doubling them up and leaving space between them and a wall. They were excellent preliminaries -- in conjunction with REW and listening -- and gave me confidence about how much treatment to invest in later. Throwing money at the room acoustic problem is more wasteful than throwing it at gear because it's much harder to recoup by selling. And it's hard to integrate into an existing domestic arrangement.

Set some goals, get the right tools, work patiently and incrementally. My two cents.
Hilde45 - I have read several of your posts regarding your journey to manipulate your room's acoustics and they were a good source of motivation. Our reasoning and approach to improving acoustics seem to run parallel, including cost and resistance to use EQ technology (for now anyway) . Although I believe I have the added challenge of storage and convenient repeatable implementation.....uhhhhg:) 

Anyway I pulled the trigger on 12 panels of 703 and other materials, it's about $275 all in. So If it doesn't work....well, it's wouldn't be a big financial hit. Plus I have a consumer HT system in another room that SQ would definitely benefit from, and it would be easier to implemented without the added hurdle of portability and aesthetic restraints.

Speakermaster; 53B - unfortunately the addition of rugs and drapes aren't an option. But a quilted throw is an option.Thanks

By the way, if all goes well I plan to post images of room with panels implemented vs stored in "my virtual room". 

Thanks again


The advice to acquire a mic and download REW or HolmImpulse, as used by Earl Geddes and also free, is solid. Playing with this allows you to see the results of added treatment.

The basic problem all rooms have is the sound taking too long to decay and the use of EQ simply can not reduce the decay time, it needs to be absorbed and the OC703 you bought is great for the job.

tomic601 mentioned RT60. This is the time it takes for the sound bouncing chaotically around your room to decay by 60dB. and without looking up the figure for your size room would, I guess, be about 400ms. So if you see some frequencies with a T60 of 1 sec. these are the ones to be tamed. Then after introducing and/or moving some more treatment take another shot until you achieve an even smooth response across the full spectrum. Great fun.

By doing it this way you avoid any guesswork and will come to realise that the suggestions to hang a drape or install a thicker carpet is like trying to win the jackpot.

The thicker the absorber panel the greater the range of absorption. So 6" will be more broad-band than 4"  Move away from the back wall and use absorbers. You would be too close to a diffuser on the back wall.

Have a good read of this: https://ethanwiner.com/acoustics.html#bass%20traps
@mrpsync  I'm glad my diary of attempts was helpful. I really fumbled a lot in the beginning, but earnestly. You did well buying 12 panels, by the way. That gives you sufficient quantity to actually do some very real experiments, especially, as Lemonhaze points out, using 6" panels. You can really affect bass peaks with that thickness if it's also some distance from the wall.

The other thing I'd add is that you should not get too hung up on building frames for these panels; fabric that is adequately transparent (burlap, muslin, etc.) will protect you and enable you to move things around. 

One other helpful hint I got early on was that if you're trying to troubleshoot a ceiling first reflection point and it's a pain to get a pad up there, try one on a spot below on the floor. That should help show some difference without all the ladders, staple guns, and cursing.
Yeah, I think Tomic also mentioned that he did find a need to frame panels either. I definitely welcomed that bit of info. Actually not having a frame will probably have other benefits too. For example not dinking furniture and scratching walls due to regular movement when setting up and storing.

Ceiling reflections are a concern since I won't be able to address it with panels. So I'm hoping  that it won't be to significant since my tweeters are ribbon, which have a more limited vertical dispersion than a typical dome tweeter..(so I've been told). And the fact my ceiling is 10 ft, and my listening position is about about 6 1/2 feet from speaker plane. So between the tweeters angle of dispersion, ceiling height and the "somewhat" near field listening I keeping my fingers crossed that first reflection points won't be an issue. maybe, just wishful thinking:) 

Lemonhaze - Appreciate the link and explanation about how delay is an issue. Your position on measurement, along with others; is driving home the point that I will need to do this as some point. I'll cross that bridge when I get there. I'm sure that it will my second thread:)

Thanks
My room is about the same size as yours, and due to the location of a fireplace there is no choice but to put the speakers on the long wall.

This is a long thread, so maybe I missed a relevant comment. If so, please excuse the repetition.

I wasn't sure whether to use absorption or diffusion behind the listening position. GIK recommended diffusion, but just in case, I ordered three large 4A Alpha panels, with the backs optionally covered with fabric ($12.00 per panel) instead of the default white muslin. That way they could be used for diffusion + absorption or turned around for absorption alone.

After experimenting, I ended up mounting them on the wall with the diffusion side out. That may or may not be the best approach for your room, but at least the reversible panels allow you to easily find out.
My sister, who manages some bands, and owns one she put together, suggested experimenting with comforters on the wall behind me, but since it is 25' away, I did not bother.  My stereo listening room is literally 3/4 of my house and has high ceilings,  but this might be good for you to try.
Oh,I forgot to mention that the band members did this in their listening rooms.
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