Room Treatment? How important is it to treat the wall behind/between the speakers?

A couple of corner bass traps and some diffusion in the area between the speakers are what I would recommend. You want to avoid parallel walls front and rear so diffusion behind the speakers will help break up standing waves. 

@mashif thanks - note there is no rear wall per se, the area opens up to an open floor plan so the actual rear wall is 50ft from the speakers. 

That's good! If the low end sounds okay you might be set. Otherwise bass traps in the corners behind the speakers should help. 

I would try some acoustic panels, 2' x 4' mid wall behind the speakers.  It's a trial and error game.  My understanding is you want to prevent reflection off the front wall.  

“How important is it to treat the wall behind/between the speakers”

@macg19 

Back wall, along with front wall and side reflections are equally important for an acoustically well treated room. 

Ultimately, the character of your room—how live or dead it is—will be the deciding factor in whether absorption or diffusion works best.

Absorption panels behind and between the speakers can tighten up imaging and help tame those early reflections that smear detail. Diffusion panels, on the other hand preserve a sense of openness and depth, preventing the room from becoming over-damped.

A mix of the two strikes the right balance, but the room itself will be your ultimate guide, thus requires some experimentation on your part. 

In my own room I’ve found a combination works best (see my virtual system) …diffusion on the front wall to keep depth and openness, and absorption on the back wall and side walls to tighten imaging and control reflections. That balance really helped me achieve a more natural and engaging presentation.

@OP - as with the post above, quadratic type diffusers on the wall between the speakers will open up the soundstage. Bass trapping in the corners behind the speakers can be beneficial too - not just in the bass but also in removing frequency masking that obscures midrange detail. 

2 or 3 of these on the front wall would help, but again it depends on if the room is too reflective. Usually this works best. https://www.gikacoustics.com/product/q7d-diffuser/?tw_source=google&tw_adid=649245158855&tw_campaign=19732823023&tw_kwdid=aud-1960089553334:pla-293946777986&gad_source=1&gad_campaignid=19732823023&gbraid=0AAAAAD-4A3F6gAISH72YM8xitFwA92Cxa&gclid=CjwKCAjwlOrFBhBaEiwAw4bYDZk2xlwzmWaT1Na8GDPm5bucLMq9R8Y4X4U1S3FVhkGfH8u-somATRoCPzgQAvD_BwE

The recommendations from both GIK and ATS were consistent when I requested assistance.  Diffusive panels directly behind the speakers.  Bass absorbers in the corners.  Both companies reviewed my room and setup.   Both indicated I did not need diffusive panels because my wall unit was sufficiently textured.  I recommend you contact both and send pictures of your room and set up and follow their recommendations.  

@macg19,

Your equipment is very nice and room seems to have good capability. First thing I would do is to move your speaker at least 3 more feet into the room (if possible). Adjust the seat position to close to an equilateral triangle, keeping all vertices between the speakers and speakers and you the same. That will also improve direct sound from them vs room reflections. I use lots of diffusion in my room (all walls and ceiling). You can check the pictures of my room in my profile. They are not updated after my latest diffusers and bass traps inside the closet were added, but you'll have an idea. Best of luck, 

Thank you all for the advice. I could move the diffusers on the left side wall to the front wall and use an absorption panel instead. The right wall (bay window) already has an absorption panel + drapes. 

@kellerjr01 Thanks! I have tried the speakers 5ft from the front wall but the bass gets boomy + it puts the listening position too far into the living room.

I plan to add something like the GIK Soffit Bass Traps floor-to-ceiling eventually but there are other priorities for $$$ atm. 

My understanding re: diffusion panels is that  their effectiveness depends upon the size of one's room since they're not helpful in small ones. As to what constitutes a small room...GIK and other experts can guide you. Good luck!

@fthompson251 I sent pics and dims to GIK and that is exactly what they recommended.

@kellerjr01 I took your advice and tried moving the speakers out again - front baffles are now 5 ft from the wall now. I could go another foot.

So far I like it.

I realized I had added more treatments since I last tried them that far out in the room and the listing position is fine - speakers are 7ft apart and listing position is 8-9ft now without moving the chairs.

@macg19,

Glad to hear that :). Give them space to breath. You can always keep tweaking and also adjusting the toe-in to find the best compromise between the phantom center and lateral front soundstage.

For reference, the front plane of my speakers are now 77in from surface of the front wall, with 84in between tweeters and also 84in from the listening position, in a perfect triangle. Toe-in less than 10 degrees I cannot ever tell the sound is coming from the speakers, but will come from behind their plane all times and "extending" several feet behind the front diffuser as some of the recordings were made. Soundstage to left and right of speakers is more dependent on the mixing but sometimes extend up to 3 feet beyond their physical positions, like coming from outside the side walls of the room. 

Check out this room calculator to find your first reflections. Those in the horizontal plane and from the ceiling are more consequential than the floor. Good luck!

@macg19 in my profile's virtual system photo you can see my approach - two bass absorbers (8" thick) behind the speakers and a (home made) skyline-type diffuser between the speakers. 
 

I also have three 2by4 foot diffusers on the back wall behind my listening position. 
 

Vigorous thumbs up to the positive impact of sound treatments behind and between my speakers in a 20 x 26 x 12 ft. dedicated room. The sound stage deepened greatly to the point of an illusion of being able to step into it. I’ve sound treated the ceiling, too that further enhances the illusion. I use bass traps, absorption and diffusion panels. My speakers are floor standing Tannoys paired with Tannoy supertweeters and Hsu subwoofers in an analogue system, 

@bimmerlover 

Congratulations on putting together a wonderful system and equally complimentary room! 

@macg19 Congrats on a nice looking rig and room.  If you're open minded to a few suggestions for better sound, here goes . . .  these are not criticisms just ideas to try out.
> Early Reflection Symmetry: (1) I'd pull your speakers forward so that your soundstage depth may improve but also the carpet now catches the speaker's 1st order floor reflections. (2) Is the ceiling treated? Might you consider white colored Skyline diffusers made from Styrofoam at the 1st order reflection points so that they blend into the ceiling color wise and so that you aren't impaled should they fall? (3) Sidewalls are different construction materials and may cause havoc with tonal balance and imaging - try a stand alone 6" thick GIK Monster bass trap for each speaker's closest sidewall.  The right stand alone trap should be the same distance from the right speaker as the left stand alone panel is from the left speaker.  The farthest speaker's sidewall 1st order reflection (R_speaker -> L_sidewall and vice versa) may require asymmetrical treatment as pulling the speakers forward may now place the right speaker firing into the left doorway (essentially an absorber) so you may need to experiment with just a right sidewall treatment of another stand alone absorbing panel by the bay window for the left speaker's 1st order reflection or a reflective 3/4" thick reflective board to redirect away from you to acoustically mimic what the left doorway is to the right speaker.  (4) Place 1D QRD panels centered on the front wall and front wall corner bass traps
> have you access to acoustic measurement software (REW / OmniMic)? If so, then Energy Time Curve data for early reflections will help with trying to achieve acoustical L/R symmetry for 0-10ms.  I'd suggest frequency limiting the ETC data to 3 one-octave ranges centered at 500 / 1 / 2kHz as their reflection energy differs based on wavelength, speaker directivity, toe-in angle etc.  Focus on the 500Hz and 2kHz octaves for L/R cross-channel symmetry for tonal balance and imaging respectively.  You should also try to achieve cross-octave symmetry across the 3 octaves (500<->2kHz) for each channel separately for tonal balance purposes.

@ntpc4 Thanks, I haven't seen that calculator before, it confirmed I've got the side wall treatments in the correct spots after moving my speakers out to 5ft.

@bimmerlover I've check out your VS before - very nice!

@kevinzoe Thanks for the comments and suggestions. I have moved the speakers out to 5ft which is much better. The calculator confirmed the left wall panel is in a good spot & I do have the bay windows treated as well. I tried the sound blocks next to the speakers it sounds better when they are behind them. I have REW (but I dont know how to use it) and a calibrated mic (but no way to connect the output from my PC) but I also have DIRAC Live so I can run some test tones through the BS NODE again and see what has changed. 

Right now it sounds really good with the speakers pulled out. Soundstage is much deeper and coherent.

I put a couple of adsorption panels up against the painting as a quick test and even that helps, so I have no doubt I need to #1 replace the painting with a diffuser #2 see if I can figure something out for the ceiling  - perhaps something like this might work?  and #3 add some corner bass treatments like the GIK Soffits.

Thanks to everyone that contributed so far.

@kellerjr01 VERY nice system! How do deal with the big window?

@kevinzoe I took some measurements with DIRAC and a MiniDSP calibrated mic and posted a screen shot in my virtual system. Symmetry doesn't look terrible but I have no idea how bad the peaks and nulls really are.

I can apply the filter to the NODE but obviously not the analogue source. 

If anyone cares to take look and provide an opinion it would be much appreciated. 

Thank you.

@macg19  Thanks for taking the time/effort to take measurements with DIRAC. 

It appears that DIRAC is working as it's expected matching L and R speaker decibels levels as best it can based on whatever parameter limits you set.  But you're on step 4 when steps 1-3 aren't quite finished.  There is a sequence to treating a room and it generally goes like this: (1) begin with Early Reflections and L/R speaker's reflection symmetry within 0-10ms which usually involves 1st order reflections in most domestic sized rooms.  Energy Time Curve data is used for this step which REW provides but I don't know if DIRAC provides.  (2) Bass Decay time should be dealt with next to reduce masking of midrange details when bass decay times are excessive compared to those of mids/highs.  A T30 metric is found within REW and you can get pretty granular by using 1/3rd octave intervals to see where problems lie and what the best type of bass trap is to use (velocity or pressure). Again, not sure DIRAC measures this as it was designed more for frequency response and not the time domain (i.e. early reflections and decay times). (3) Mid/High decay times come next with the use of diffusion and reflection and appropriate T30 decay times suitable for your room size. (4) last comes frequency response and gentle EQ which is where DIRAC lives as I understand it. (I use Audiolense XO for FIR convolution filter creation myself.)  While Frequency Response is usually the default go-to chart to use, it is impacted by the sound bouncing off reflective surfaces between the speaker plane and your listening position.  Because the frequency response's informational content includes the effects of early reflections, it's important to get those locked down first otherwise you're chasing your tail.  Looking at your system picture I am not convinced that the wooden slats on the left sidewall and curtains on the right side are giving you symmetrical early reflected energy especially in the 1 and 2kHz octave regions where our hearing is most sensitive - the wooden slats would preserve the 1 / 2kHz octave energy while the drapes would attenuate it, and I hazard to guess that only through the use of DIRAC are the L/R frequency response curves very similar.  I'd encourage you to try the same type and thickness of absorption panel on each sidewall as a common denominator to different construction materials used for each sidewall which impacts tonal balance.  Play with absorption panel angles and distances from the wall behind it to achieve L/R Early Reflection symmetry before turning on DIRAC.

Reading your DIRAC graph:
> first off, the chart looks like it might be at 1/24th smoothing which shows all the nasty bits, so don't be surprised or discouraged. 
> the curves track each other nicely which is DIRAC's sweet spot but range from about -2 to +8dB for a +-5dB range which should ideally be at +-3dB or better.  Getting the sidewall's 1st order reflections symmetrical should help DIRAC out so that it doesn't boost/cut EQ as much.
> The large "U" shape in the 30 - 80Hz range is trouble as a kick drum lives in the 40-70Hz range as does bass guitar, and other instruments.  The R speaker at 45Hz is about 6dB louder than the L channel - not good. This could be caused by the R speaker being near an external wall with brick/concrete behind the drywall which reinforces these low frequency's energy whereas the L speaker is near an inside wall that is less stiff and flexes. Pressure traps can help here like GIK Scopus T40 / T70 traps as can multiple subwoofers.  Experiment further with speaker / chair positioning to see if that "U" hole can be remedied as it is beyond DIRAC's boosting limits.

@macg19   https://pmamagazine.org/early-reflections-101-the-first-10-milliseconds-that-make-or-break-stereo-imaging/

@kevinzoe - excellent article. Thanks for posting.

I have not used available Software to create the management of Sound within my room, it is carried out using different configurations for absorbent and reflective materials.

The placement of materials used is now concluded and having Triangle Shaped Absorbent Materials in all Room Corners is a must have in my room.

This set up has a Absorbent used behind each Speaker.

Rockwool with a Mass of 35Kg / m3 and used at 100mm (4") Depth is an affective  absorbent and a very cost effective method. It is good practice to create a small dimension cavity between inner face of Rockwool and the Rooms Wall. 

@macg19,

You can see updated pictures of my room in my profile now.

Long story on how to deal with the window... First thing I did was to use REW real time analyzer data/graphs (using the MiniDSP calibrated mic) to see where the resonant points of the room were when I played  low frequencies that I would hear the clear "booms" from the listening position. Just play the tones you want and walk through the room with the mic and find them while you are using the RTA or a SPL meter calibrated with C curve (A curve will not tell you true response for bass). Room bass nodes were partially located in the 4 room corners walls, from floor to ceiling, but they were much more concentrated inside the back sides of the closet - almost up to15db higher than in the listening position. So, I started to investigate what type of bass absorber was the best for the buck and ended using the Acoustic Fields designs. Worked like a charm... I made them as big as I could to fit the available space of the closet without tearing it apart. To make it happen, I had to repurpose the fractal diffuser that was inside the closet and moved it to the right-side wall and the small one from the right wall I originally had I moved to the window side. I did not want to remove the window, so what I did was to use a technique they use in mixing studios where they use portable treatment to control their recordings. I build a pair of sawhorses and created a support for my small fractal diffuser.

The bass traps significantly improved the entire bass response of the room because I could better integrate the subs with the main speakers using crossover & volume adjustments while maintaining a better response of the bass. With the 4 bass absorbers in place, I was able to lower the response of the room around ~35Hz by about 6db. Repurposing the two fractals, I also eliminated the problem of the window, since I eliminated the first reflection problems from both speakers adjusting the position of the middle of the diffuser height to the listening position. Soundstage got more precise and expanded to the sides of both speakers.

You can use a mirror to find first reflection points. Just ask someone to hold it in the wall and move it until you see the mid driver/tweeter – just pay attention to which speaker you are seeing... That is the area where you need to treat for first reflections. Same is true for ceiling and floor.

Hope this helps answers your question.

@kellerjr01 Thanks for posting the pic - you put a lot of time and effort into the room.

A couple of quick points. The DIRAC graph is the measured (uncorrected) response. 

Also I used the room calculator posted above to check the location of the side wall first reflections. I had originally used a mirror. The calculator and the mirror are in agreement. 

I’ll found the cable I need to connect my laptop to the system to generate test tones from REW and I have a MiniDSP mic. I'll work on figuring out how to use REW next. 

My take:  This is an are which benefits strongly from a mix of diffusion and absorption depending on the speakers.  

Diffusors between the speakers and to the sides both enhance imaging and sense of acoustic space.   If not possible, then treat with a light touch. 

The ceiling between the listener and speakers however is a real good candidate that is often overlooked. 

I have a 13x23 ft purpose built room with rockwool behind all walls and acoustimat "rubber" on all walls and ceiling too (under the sheetrock of course). The room is acoustically tight and relatively sound proof so even listening loud it doesn't transmit to other parts of the house. I have GIK treatment too- diffusors for first and second reflections on the sidewalls and bass traps in each front (behind the main speakers) corners as well as in the rear. I'd add them to the front corners, bass "pools" up there and can add boom or muddy sounds. 

I've got REW working and I've taken some measurements, but I dont know how to interpret the results.

Is anyone able / willing to analyze the file or know of someone that can for a fee? 

@macg19   Sure, I can do the analysis for you.  Let's communicate via PM so that you can tell me what you're after and I can advise you on which measurements to take, how to take them, what file format to send to me and I can return a custom Report with additional charts and analysis that REW doesn't provide, including type and placement of treatment recommendations.  Send me a PM if interested.

@kevinzoe 

Thank you Kevin for the very kind offer. I will send a PM when ready. I have a few things to get done before taking measurements and looking at next steps.

I experimented a lot over the weekend and Monday moving around speakers, acoustic panels/blocks as well as the listening position.

NOTE: I know a single frequency response measurement form DIRAC doesn’t tell the whole story but my goal at the moment is to try and get some L/R symmetry and get rid of extreme peaks and nulls.

I took down the RockWool-stuffed painting and the room sounded terrible, harsh, so it was doing something positive albeit likely not ideal.

So I decided to order another pair of 24x46 GIK Wood Slat panels for the side wall as an interim (cheap) solution and moved the existing ones to the front wall behind and between the speakers and I installed a 24x48x2 absorption panel at the first reflection point on the left wall in their place until the wood slats arrive.

This made a big difference – the harsh glare went away and the sound stage was better, for example in terms of vocals being deeper in the stage and instruments arranged in various locations on the sound stage. 

I also moved the 4 Sound Blocks around in every configuration imaginable, and they made almost no difference to the DIRAC frequency response measurements except when I stacked all 4 (2x2) on the right wall about 8ft from the front wall. This helped the 59-60Hz null but they look ridiculous.

Ultimately, I was able to get almost the same effect by moving the primary listing/measuring position forward a foot or so, so that it is under the 8ft ceiling rather than under the vaulted ceiling behind the listening position and moved the speakers back a bit as well.

Here is what I learned:

1. The answer to my original question is YES!!!
2. Installing additional acoustic treatments to treat low lower frequencies without a plan based on measurements is a crap shoot.  

So next step is install the slat diffusers on the left side wall and then take some REW measurements.