That is right. I await the measurements with interest.
I can't believe that the design concept of this speaker has much merit. Worse I think your open air measurements will be totally misleading in terms of how this speaker would actually behave in a room.
First of all this speaker may be a sealed box, but it will not behave anything like a sealed box speaker as we have come to know them.
Since the speakers are out of phase, sure there will be a coupling. However both positive and negative pressures in the box will be cancelled apart from any non linearity between the divers. So the closed box model would not apply in any meaningful sense whatsoever. So essentially there will be NO restoring force from the box on the drivers. So the restoring force has to be provided almost entirely by the suspension of the drivers. So this is much more akin to the infinite baffle model and not the sealed model.
However there is a significant difference. In the classic IB model there is only forward radiation. The rear radiation is lost in the huge space behind the driver which should not connect with the room. So there is no cancellation. The system Q in these systems closely follows driver Q and restoring force is from the driver suspension entirely.
Now this speaker is a Dipole as the speakers are out of phase, and so side radiation will be cancelled. This has to be the radiation pattern.
View attachment 49619
Note the nulls either side of the speaker. However unlike a Quad ESL for instance, a sub is dealing with very large wave lengths, greater than the width of the cabinet by far. So front back cancellations will be far more significant I suspect. So no wonder they need such an enormous xmax. This I fear is likely to lead to deterioration over time, due to increased laxity of the suspension, having to provide the restoring force. This has long proved to be the achilles heel of IB designs.
I have the strong suspicion that free air measurements of this speaker may differ greatly from in room performance.
This seems to me an inherently highly inefficient design due to cancellations from the out of phase speaker design. I am highly sceptical that the non linearity of backward and forward motion, is going to be improved by the inherent coupling of the drivers in this design. My intuition is that the huge driver excursions required will negate that advantage and actually be worse, especially over time.
There is no way that this can be an efficient design, and has to be very much in the brute force category, which as I think you know, I abhor.
Good design always works with nature's forces, to create synergy and mechanical advantage, which enhances efficiency and reducing stress on mechanical parts.
I would actually wager pretty good money, that my TLs which do not require sub drivers, would outperform that design concept. The Proms started a week ago and there was a really good performance of the Poulenc organ concerto. Daniel Hyde let the voice of Jupiter really rip and the whole room really shook, with the drivers barely moving. The was like in the RAH, where the expert panel said after, all their chairs were vibrating, and so were mine. This work also has a large part for percussion, and they were totally tight and life like. That is what I am after, and essentially reject inefficient brute force approaches.
I fail to see how this design moves us forward in the least. To me it sounds like a real dead end. I would take a lot of persuasion to put out any hadr cash for it.
I would say because of the nature of the design, only reliable conclusions can come from free air measurement as well as in room ones. I say this, as I think your open air measurements could be satisfactory and in room responses exceedingly lumpy.
I await your measurements with interest as above.
