OPSODIS
This is not a true OPSODIS system I setup, but it's the closest I could create. No passive crossovers, all done digitally with FIR implentation, 600 Hz low, 600-4000 Hz mid, 4000+ Hz high. HRTF and phase processing done through AudioMulch with Waves Panorama 5.1 demo VST plugin. I've done two setups with this system:
Setup 1. Speakers split at around 6 degrees (highs), 32 degrees (mids), and 180 degrees (woofers).
Setup 2. Speakers split at around 6 degrees (highs), 32 degrees (mids), and about 90 degrees (woofers).
I've found OSPODIS requires a *very* precise setup in regard to horizontal and vertical speaker distances for the mids and highs. Being just a half-inch off can have a dramatic impact on sound quality, shifting the soundstage.
In both setups, regardless of HRTF or phase modeling, you get a sense of 180 degree soundfield (I would say over 120 degrees with setup 2). This image from ISVR visualizes the sound:
http://www.isvr.soton.ac.uk/FDAG/VAP...s/osd_prin.jpg
OPSODIS is unlike any other loudspeaker setup I've tested, and it's the setup I've spent the most time with (over 1 year of tweaking). Here's my rundown of the system:
When both the left and right speakers are kept in phase, it sounds somewhat similar to stereo. The in-phase system has upper-mids and highs that stay within the 30 degree boundary across the horizontal plane, but do extend vertically upward. Mid and low frequencies can extend anywhere from the center to 180 degrees both horizontally and vertically. Reverb effects in some songs are eerily in focus, and actually is detrimental as it makes some music sound overly-processed (or these songs could just be overly processed). When sitting out of the sweet spot, you tend to hear whichever speaker you are closest to, but this is less noteable in setup 2. Plus, when sitting out of the sweet spot, there is a loss in bass depending on where you move. Highs and upper mids are localizable to the speakers.
OPSODIS is interesting in that you can have some cross-talk cancellation by simply keeping the L/R channels out of phase (discussed in the patent:
http://www.freepatentsonline.com/6950524.html). I believe the effectiveness of this crosstalk method depends on the crossover, so I maxed out the FIR implementation to the point where I could almost hear ringing artifacts. When the Left and Right channels are 180 degrees out of phase, setup 1 becomes out of the question for any real application. When you're sitting perfectly in the sweet spot it sounds better than the in-phase system. However, move just an inch and you're ears are bombarded with bass phase pressure.
With setup 2 L/R out of phase, highs still stay within the 30 degree horizontal plane, but become much less localized to the speaker. Overall, there is a widened image when compared to the in-phase setup. Left and right mid-bass notes stay left/right vs. the in-phase system. What's more interesting is that when you sit outside of the sweet spot, the image still stays in the center and your ears don't focus on the closest speaker like with the in-phase system. Plus, bass is much more consistent as you move outside the sweet spot. However, the out of phase part can mess with the overall sound and it's not always desirable.
Some notes on HRTF via Panorama 5.1. It uses direct, reflecting, and reverberation sound to try and simulate an environment. Overall, it can add ambience to the signal and help emphasize the spatial aspect. With most of the predefined settings, it makes you feel like you are in a far back venue seat, not up close, but it is a convincing effect. It's a bit of a burden using it because some recordings sound good after tweaking the settings, with other songs no amount of processing makes the HRTFs sound "right" with the song.
Conclusion
All-in-all, OPSODIS proved to be the most effective and convincing sound setup out of the whole group. It can provide fairly convincing ambience and realism to some music (depends on the recording style I guess) when using HRTF, and a unique listening experience. Plus, it's semi-suitable for multi-listener experience - sound always comes from the center but feels a little flat and 2D compared to the single sweet spot.
For music the FIR crossover implementation is fine, but movies you need an IIR crossover (reduced sound quality) to keep the sound in-sync with the image. Here's the problem with movies though - you need a TV right where the tweeters should be (eye level). With the whole system needing to stay on the horizontal plane, you need to either elevate the whole system below the listener (which doesn't sound good), or above the TV (which is near impossible with the outside woofers). If OPSODIS wasn't such a pain to get right for all material, and was easy to setup with a TV, I would be using it now. Even after a year it's still just a basement project, just a very good sounding one. However, I may consider buying a commercial OPSODIS solution, now that Marantz finally realeased their ES7001 to the US.
Hope you found these posts informative and realize that so far I've not heard a system that demonstrates 360 degrees of acoustic bliss.
