Speaker Height / Tilt

Nope. The real issue is to align the tweeter or mid correctly relative to your head, and it's all subjective.

I find a lot of speakers sound better if I listen below the tweeter axis, and sometimes with the tweeters not pointed directly at me.


Now, to answer you more specifically, what you want to avoid is listening above the tweeter axis. That's where usually the phase and lobing issues you are thinking of occur.

Hi @B_limo

For whatever reason, Stereophile hates e-mailing web links via e-mail, so here you go:
https://www.stereophile.com/content/monitor-audio-silver-8-loudspeaker-measurements

In case anyone is wondering, here is my reply:

If you mean dome tweeters, nope, they are directional, eventually. Worse, some suffer from resonance on axis which is dealt with nicely off-axis.

Now, the issue next is lobing. That is, how the tweeter's response adds or subtracts from the next driver down (in frequency).

With traditional multi-way speakers with a tweeter on top, a mid or mid-woofer below it, the sound is pretty good to the sides and below, but not so good on top.

Take a look at figure five in this review. Notice that at 4 kHz or so there's a significant dip at 15 degrees above axis. It's a little hard to see, but the reviewer put the cross hairs right on it.

Now, compare that to the chart above it, figure 4. To the left and right the drop off is equal and smooth. Further, note how much the top octave drops off axis. This is normal, off center response for this type of tweeter.