I can’t help yapping a lot about this.
Being 74, I’ve messed with lots of spaces and lots of speakers, various toe-in’s ..., better equipment and more experiences progressively along the way. I’ve also worked with AV consultants for the Boardrooms, Training Rooms, Conference Centers I designed for my clients for 46 years before retiring. A space can be gorgeous, but if the AC ain’t right, if the sound ain’t right, I have failed.
Yes, tweeters aimed at your ears when seated. Published frequency graphs of speakers ’smoothness’ measurements are taken with direct dispersion, and then some reviews show fall off graphs of off center dispersion.
If you look at individual driver Polar response graphs,
you see how directional various drivers are. 3/4" domes; 1-1/2" domes are omni-directional, diminished volume distribution to all sides. Variations like drivers with diffraction lenses widen the distribution, perhaps limit too strong direct radiation so sides are stronger, perhaps limiting vertical dispersion.
My main system, 4 way, 3 horns, 15" woofer, they have horn shapes designed to achieve wide horizontal dispersion and purposely narrow vertical dispersion to avoid both floor and ceiling diffraction mixing slightly time delayed and improper direction from the primary direct waves. Thus believing horns are ’wide’ in all directions is erroneous. There are phase issues also. My horn tweeter’s orientation is visually opposite to the distribution, an uninformed person might mount them incorrectly horizontally
Some horns, i.e. JBL’s, Altecs: their shapes are tailored for wide/limited vertically when mounted horizontally
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Yes, time aligned, i.e. tilted back, as high frequencies travel faster than mids and mids faster than lows. Listening distance involves very slight or slightly more time differences, they might be very small differences, but everything we do is to eliminate very small differences.
Some speakers have driver height and time alignment ’generally’ solved by their sloped front faces, like my JSE Infinite Slope Model 2’s.
My current flat boxes. wanting to keep the enclosures shorter than the JSE’s: I put a 2x4 flat in the front of the base, thus raising the front 1-1/2", projecting my horn tweeters directly at my seated ear height and effecting some time alignment which is a guess at best.
see 9th photo here, shows guts and under the base
One of the reasons I am such a fan of L-Pads for individual drivers is to achieve the best/flattest frequency distribution, in any space, at ____ toe in. I use a mic and cd with 29 1/3 octave test tones to get them ’right’ in any specific location. If conditions restrict/prevent ideaal toe-in; an L-Pad can boost the highs when measured at your listening position. Just restored a pair of AR-2ax’s, working on a second pair. I had forgotten they came with two level controls. Mine are flat in bookcases, toe-in not possible, so level controls help adjust dispersion for my center position in my office, and will help in my garage workspace when 2nd pair done.
When I have two listeners and the small table in the middle, I alter the toe-in, narrower, so that each is closer to the speaker on their side, but the opposite speaker is aimed directly at their chair. Wider center imaging is created, very enjoyable on either side.
My front home theater speakers were designed specifically to do that. Main face aimed at opposite side, and two tweeters on the back sides.
http://www.hifi-classic.net/review/dbx-soundfield-100-135.html
Some recordings are weirdly mixed, i.e. Bill Evans at the Village Vanguard, considered one of the all time great performances.
Very wide separation, big hole in the middle. I’ve been there many times, it’s a small room and a small stage. I toe my speakers in more to narrow imaging/reduce the hole in the middle.
Thus I like speakers easily re-positioned for various placements/toe-ins. Luckily my wood floor’s grid helps me re-position my main speakers 1 listener/2 listeners/wide/narrow.