I'll chime in on this one>>>.
Look, we use equalateral triangle as a "Golden Rule" of sorts.. In other words, all of our designs start with what equalateral triangle (or 5.1 setup in a circle with ITTU speaker angle placements which include 30/0/30 for L/C/R) speaker layout.
Why?? Because that's what puts us on axis with a speaker that we assume we like, and that sounds most accurate on axis. It also is one of the precepts that the center "phantom image" in stereo reproduction is based upon.. If the triangle gets too wide than you feel as if you are in a hole in the middle of the image, and panning is exagerated.. If the triangle is too narrow, than you will exagerate all of your panning in an effort to setup a wide enough stereo field.
Rules: Yep, the mans right... there are now rules in Rock N Roll.. so, experiment at will and find what works for you... but I'm telling you that ALL of our in-wall monitor system are based on equalateral triangles that focus somewhere between 12" and 24" behind the armrest of the console.. why? because at around 12" of "overshoot" your ears are just about in the direct path of the speakers.. further back, widens the sweetspot (for larger triangles 9-11 feet) without putting you in the hole I described above. This is all based on our experience doing this several hundred times in good rooms, bad rooms and everything in between!! I will tell you in no uncertain terms that the SINGLE BIGGEST THING YOU CAN DO TO TUNE YOUR SYSTEM, is experiment with speaker placement:
1. Start with positioning the pair for "optimal" bass response (that's a big statement right?).. what sounds best and/or measures best for YOU..
2. tweek speaker toe-in angle and fine position adjustments to tighten up the stereo image.. when your mono is rock solid and the speakers "dissappear" and your sound stage opens up, that's when you've got it right! we're talking critical listening hear guys..
3. finalize toe in to control HF response to taste.. totally on axis should give the most and flattest HF response, all other variables being equal..
Yes, I'm ignoring the room for this discusssion because as I've said, this is what we do in room after, room, after room and it works.... at least for Lars and I...
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