Speaker Placement - Frequent Placement Changes?

This setup closely follows the Golden Ratio rule. I have almost the same room dimensions as yours and have tried that configuration. You can certainly start with it and fine-tune from there.

However, I can tell you that the rule is not guaranteed to eliminate what it’s designed to address—namely, standing waves and room modes caused by reflections. It also doesn’t necessarily provide the optimal placement for soundstage and imaging. The results depend heavily on the speaker’s horizontal and vertical dispersion patterns.

In my case, I ended up positioning the speakers 28" from the side walls, 4’ from the front wall, 35" in height, and with approximately 10° of toe-in (all measured relative to the tweeter). Note that 28" is the minimum distance needed to prevent sidewall reflections from blending with the direct sound, which can otherwise blur imaging and reduce clarity.  I place the speakers that way to maximize the soundstage.  Note also that the 4’ distance from the front wall was set due to a practical constraint I had. If you don’t have such a limitation, try increasing that distance to achieve a deeper soundstage.

Yes, inch matters.

After you’ve settled on the main speaker placement, you can start fine-tuning the subwoofer position. I eventually placed mine next to the speakers on the inner side.

Whenever I’ve made significant changes to the system, I’ll readdress speaker placement. I was using the Cardas Golden Ratio for Rectangular Rooms but recently changed back to the Odd Order Placement, advocated by Vandersteen. Better tonal balance and focus.

My speakers are on wheels so I can move them as I like.

My extended experience with speaker placement taught me that finding the perfect speaker placement in any given room requires getting two things perfect: #1 seating position, #2 speaker placement relative to seating position (and this includes toe-in, etc.).  In any current oddly shaped room, I found myself constantly adjusting both my seating position and speaker positioning simultaneously.  In my oddly shaped room, it took quite some time, with me making constant adjustments before I was able to  finally sync my seating and speaker positions together to where I was receiving the desired results.  It simply takes trial an error, and more trial and error, and eventually you’ll achieve perfection.  Or, as close to perfection that can possibly be achieved in that particular room.  Happy listening.   

@tcutter 

tilted back and toed in equivalently

This is good information and something I didn't know - will have to try. 

@lanx0003 really excellent post - thank you for the details. The image in the OP was  just an example - I couldn't accommodate Cardas' speaker placement, which if I remember correctly, was about 5' into the room for me. 

I've been following Jim Smith's formula which is essentially 83-84% of the distance from each speaker to the MLP - I'm currently at 82%. Speakers are 36" from the front wall, 100" between speakers, 82" to MLP, and 40" from closest sidewall. Dual subs; asymmetrical positioning to help reduce nulls and a smoother (perceived) bass response - I haven't gotten to measurements with the addition of the second sub. Compromise appears to be the phase, but subs and speakers sound coherent for the most part.