Originally Posted by CherylJosie
Also, maybe true dipole radiators with thick absorption behind them would perform better at lower frequencies because they a have directional radiation pattern with a strong off-axis null. No specific info on this, but it seems that dipoles might be superior for projecting a controlled reflection on the ceiling at lower frequencies.
Whether such exist for Atmos applications is beyond my knowledge. I suspect such would be of limited LFE and fairly large. Dunno. The upward-firing Atmos speakers I have seen online all seem to be sealed boxes with dynamic drivers and a minimal wave guide that is probably not effective at controlling the dispersion of lower frequencies.
I've been generating additional DELAYED, DISPERSE "Room Reverberation" in my various Surround systems all the way back since the Mid-70's....playing back Vinyl LP's and Quad 8-Tracks. And in the past 12-years using DIY Bi-Directional "BIPOLAR" Planar-Magnetic Front Speakers....but ONLY for Mid-Range/Tweeter:
There are very few FULL-RANGE Dipole Speakers on the market anymore [e.g.Magnaplanar, Martin-Logan CLX/CLS Electrostatic and various old Electrostatics, e.g. KLH 9, Infinity, Carver]....and they are HUGE [such as the first example shown in link above].....and EXPENSIVE. As you surmised, the REFLECTED Rear Bass Signals tend to CANCEL out the Front Radiated Bass Signals. For these THREE reasons, most modern Dipole Speakers use a CONVENTIONAL Sealed or Ported Woofer and only the Mid-Range/Tweeter Freqs generate a Dipole Pattern to enhance the Delayed, Diffuse Room Reverberation Sound Field [such as second Martin-Logan example shown in link above].
Low-Frequencies generated by Woofer & esp. Sub-Woofer convey little if ANY directional information primarily due to the distance between your ears being LESS than a Wavelength on Low Freqs, so it is impossible to discern direction for 200+ Hz and below....and very difficult for 200-400+ Hz due to the Room Modes....your ears hearing a confused mixture of ROOM REFLECTIONS coming from multiple directions [with very little attenuation at each Reflection]...including the Ceiling.:
ALL Directional Information is coming from Mid-Range/Tweeters. However since they are quite DIFFERENT, I suspect that they would NOT be all that great for ATMOS. I'm currently helping my Son-In-Law set up his first 5.1.2 ATMOS (actually HALF-MOS, cuz 5.1.2 AVR can only do FRONT or REAR Height) System....and I am NOT interested in spending upwards of $2,000-2,500 for a new 5.1.4 AVR...and MORE for 7.1.4 AVR.....plus even MORE expensive Speakers that my wife is going to object to adding to the Living Room....
You might want to read my fol. posts re ATMOS Speaker Selection and Layout. Stacking an ATMOS Height Speaker pointing directly UP, on top of the L/R FRONT Speakers is NOT compatible with ATMOS....it needs to Reflect off the Ceiling about 1/2 the distance to MLP in order to be received by your ears...THAT may require a 30-60 deg UP angle: