Five feet from the front wall

@james633 

 You will want to be no more than 39” or more than 7’ for smooth bass due to 1/4th wave rear wall cancelation.

I found this to be true for my Harbeth 40.3XDs, although I read somewhere 24" from the rear of the speaker so 39" from the front is a coincidence. The furthest I could get the front baffles from the rear wall was about 5ft - bass response was poor. 39" tightened up the bass nicely. I don't have side walls to content with.

You have a lot going on behind your speakers - which may be detrimental. 

desper,

for box speakers. For bipolars I have no idea as the back wave is out of phase. I will have to think about the math on it. 
 

Macg19,

good to hear it worked out. those distances are based on wave lengths and the speed of sound. What ever the distance is from the wall times 4 it will cancel at that frequency. So 5’ is 1/4th of 20’ and that works out to 57hz (57hz has a 20’ wave peak to peak) right at where kick drums get their weight. Keep in mind it is the center point of the bass so if you have rear ports that center point is the sum of the port and driver… at least at the port tuning point. 
 

I use active crossovers so my speakers are highpassed so it it a bit more complicated as both sub and speaker distances matters. Those pictures of my system the speaker is 43” from the speaker face and 24” for the subs when using an 80hz crossover. I am using a 60hz now and have them out 4.8’ to accommodate that (I should update picture I guess). 
 

the room clutter might hurt a bit. The screen between my speakers is “acoustically transparent” screen from Screen Innovations. It is said to drop 6db starting at 2khz though audioholics measured it at closer to 10db. Regardless I have A/Bed it up and down and it is really hard to tell a difference. The JBLs are very directional at 2k so it might be moot. My real issue is the low ceiling which causes problems at 40hz. I turned my whole ceiling into a bass trap (cost $3k and about a month of work), I also have 9 bass traps in the room. It helped but still not great without room correction which I try to avoid these days. I am +/- 6db now… sounds ok. 

Genelec explains it better than I ever could.  
 

https://www.genelec.com/monitor-placement

At least for my Apogee ribbon dipoles the sweet spot seems to be 4’ off the back wall, but always experiment with your speakers in the listening space. There are too many unique factors in any listening space.

@dsper 

When I measure, it’s from the front of the speakers to the front wall and when I do toe in, it’s in relation to the front wall as well. So I have two systems. The first has the front of the speakers four feet from the wall and no toe in and the other has the speakers 42” from the front walls and about 10° toe in.

All the best.