The NHT Recommendation is 1.5x(Speaker to Speaker) from the front of the speakers. Due to the room/use, they will be about 11' apart, so I will have to be back by 15.5' from the front of the speakers, which puts me in the 2nd row of seats. I am curious if others have experimented with a closer distance and the results. I need to go find Ken Kantor, and make sure I do this right!
I think the most critical distance or measurement is that the 2.5's .. 2.9's and 3.3's ( which I have ) must be placed at 3 inches from the back wall
In this placement the side firing woofers on those models create a corner with the back wall and are aided in bass reinforcement ... NHT has taken this placement into consideration and adjusted the crossover so the top to bottom balance is correct with no frequencies sticking out if you correctly place the speaker 3 inches from the wall behind them
If you pull any of those speakers into the room 2 to 5 feet as you might do with a normal speaker ... they lose the bass coupling and reinforcement that NHT designed into them and become thin and rather bright sounding because of the lack of bass
I suspect your 11 foot speaker spread is to accommodate a very large screen and that you wish to place the left and right speaker at the outer edges of the screen
My space is a bit smaller and to maintain the dimensions where I like to place the speaker and seating placement in my room ... I've set up my 3.3's and seating at 1.25 with no ill effects or losses
I like to keep my tweeters and mids about 20 to 25% off the wall behind them and my seating at 25 to 30% off the wall behind the listening position ... this places both the speakers and seating position to be in the least excited and effected room modes
Your 11 foot speaker spread and 15.5 seating distance creates an Isosceles triangle with the two sides being equal and longer than the base spread of 11 feet
You could try going back to a equilateral triangle set up with all sides being 11 feet then the height from the base to the seating position would be 9.52 feet
You can juggle the numbers around with this easy to use calculator ... http://www.calculatorsoup.com/calculators/geometry-plane/triangles-equilateral.php
With sides "a" .. "b" .. and "c" all being equal in a equilateral triangle ... plug in your 11 foot dimension into "a" and you will see that the height from the base to the seating position ... "h" is equal to 9.52 feet
Now this is pure speculation on my part but an equilateral triangle set up may put you more in a "Near Field" location and that a spread of 1.5 may place you in a "Far Field " location ... but again that is "pure speculation" on my part
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