Studying the measurements from the Klippel and combining it with what I'm hearing, it's getting clear that this speaker doesn't completely follow normal conventions, and you can't just tune it flat on-axis and assume it will sound balanced.
For instance around 500hz the Manta is 3dB down at 40 degrees, while a typical speaker is maybe 1dB down. So the directivity is more narrow than usual in the front as well. At 60 degrees a regular speaker is perhaps 2dB down at 400hz, the Manta is 4dB down. At 90 degrees the Manta is 8dB down at 400hz. More common would be around 4dB. On a smaller speaker perhaps just 3dB.
Since the cardioid effect is unusually wideband, it also falls off pretty hard in the higher frequencies.
So the Manta is freaking awesome at +/-40 degrees, which covers any natural listening area. If you go more off-axis than that you may experience some imbalance in the sound. Not so much that you'd react at a party, but enough that it's interesting to observe. In my living room they're placed at a wall that ends on one side, so you can basically walk around the speaker towards the kitchen area. As you pass the speaker at around 90 degrees, the bass seemingly disappears. Very interesting experience.
The preliminary "official" measurements from the Klippel is +/-2.5dB, but this is 1-2dB down in the 120-350hz area compared to how they were originally tuned based on listening sessions. I suspect at least some of that lift will sneak back in to get it balanced.
They're now situated in my somewhat larger living room (as opposed to my dedicated listening room), the area is open to both sides and maybe 50-60m^2. Similar to the smaller room, there's more ambient / immersive sound and wider soundstage than normal, and also an addictive almost visceral punch / feel in the midbass even at moderate volume.
Aaaaaaaaaanyway, the conclusion from the Klippel session is that the Caridioid systems are definitely operational.
After studying 90-120-150-180 degrees we can define a .."dispersion characteristics specification" as follows:
Cardioid dispersion characteristics (120-180°):
~100-500hz: 10-12dB attentuation
~500hz-1khz: 16-20dB attentuation
~1-5khz: 25dB attentuation
This is a more wide-band cardioid effect than I'm aware of in any other speaker.
Here's on-axis vs 180 degrees. The 180 degrees curve is now more even in the 100-500hz area than earlier, and the effect is good in the entire band. With the "entire band" I'm referring to ~50-5,000hz. Above that the dispersion is very narrow even in regular speakers.
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What does this mean in terms of energy into the room? In the previous iteration I claimed a 30% reduction in energy at 90 degrees, and 50% at 180 degrees compared to a traditional speaker. This is now increased to >40% at 90 degrees and >60%(!) at 180 degrees. The comparison speaker is the average dispersion of three different speakers with similar baffle size.
In summary: 40-60% of the reflected energy in the 90-180 degrees area on both sides of the speakers are removed at the root.
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