It doesn't say in the manual from what I read.
Hi mate. Just to note, the SAM manual says almost the same as
@Lesmor said about the SCLs (page 4):
"they should be placed with the center of the speakers at about the same height on screen as the actors would be"
Note it refers to the centre of the speakers, not the HF or UHF drivers. Some say it's best to have a tweeter at ear height, others would say it's best for ear height to be at the acoustical axis of the speaker, which is typically the midpoint between the tweeter and woofers.
TBH, the question of whether to sit with ear height on-axis to the UHF or to the HF is fairly academic unless you're sitting ludicrously close to them. There's about 20cm difference between them, which over a normal seating distance would translate to a negligible angular difference. The dispersion characteristics of the two are:
- HF horn dispersion: 80° H x 80° V
- UHF horn dispersion: 60° H x 30° V
Look at the green frequency response of the speaker, measured +/- 10 degrees vertically and +/- 30 degrees horizontally:
As you can see, there's very little difference across the whole frequency band (which is superb). Above the xo for the UHF tweeter (9kHz) there is no meaningful difference.
So, within the audible range of the UHF tweeter, it doesn't matter whether you're sitting on-axis with that or the HF, provided you're not sitting over +/- 10 degrees vertically to it.
Conversely, you may lose a very, very slight amount from the HF tweeter if you sat on-axis to the UHF, because that HF tweeter would start to beam above 4.5kHz (speakers start beaming at a wavelength equal to the diameter of the radiating cone; the SAM's HF is 75mm, thus beaming starts= 4573Hz). But that beaming will be mitigated by the massive waveguide (hence the above dispersion characteristics).
So all that supports the view that sitting on-axis the HF
might be marginally, but pretty much certainly imperceptibly, better.
If you want to test the difference and you have a UMIK + REW, you could run a sweep with a mic at the MLP placed at the UHF height, then placed at the HF height, then placed at the acoustical centre of the speaker, and then note the dB difference between the three. Make sure you have some AT screen material in front of the speaker when testing too, as those UHF frequencies would be attenuated by AT material. Odds on there being no meaningful measurable difference.