Curious what folks/Axiom think about opposed subwoofer design in general. Where you have two drivers in a single box on opposite sides of each other.
Ah...a topic near and dear to my heart. If I am not mistaken, Mirage produced the first commercial subwoofer with an opposed woofer design with the drivers operated in phase with one another. This first model was the BPSS-210 and was originally designed for use in systems with the first Mirage bipolar speakers, the M-1 and M-3. This was in the very early days of home theatre and most of the original subs were sold with 2-channel systems. The design benefits behind opposed driver subwoofers are improved room loading from the multiple drivers and an almost complete cancellation of cabinet vibration. These designs are not gimmicks, they most certainly result in improved performance when well designed. I believe the main reason that we don't see more of them on the market is that the second (or third) driver(s) add significantly to the cost. One thing to watch are designs claiming to have force cancelling drivers where one driver is actually a passive radiator. In this case there will be no benefit in terms of reducing cabinet vibration. Interestingly enough, as Ian and I have been working on design ideas for the "v4" series of subwoofers we have been discussing the possibility of one or two models incorporating a balanced or force cancelling driver configuration. As with everything we do the designs would be evaluated strictly based on their performance versus the current models. Now is as good a time as any to throw the question out there: Is this type of design something that would interest you?
Andrew, you beat me to the punch on this one in stating that Mirage was probably the first to incorporate this type of design, a natural in their case working hand in hand with their enormous bipolar models you mentioned and they did sound very good. One thing you didn't mentioned when HT started to come in to vogue, Mirage designed and built an excellent crossover unit that worked beautifully in conjunction with any sub, an item somewhat ahead of its time.
The only passive radiators I have seen and heard in a few models were incorporated in to small powerful subwoofers to attempt to reinforce the bass in ultra small cabinets. Despite the claims of deep, powerful bass in a small package, I was never impressed with any of these overpriced designs and I think the marketplace has shown it.
When it comes to subwoofers, I have always believed that you can't really defy the laws of physics, the bigger the cabinet, the better, deeper AND louder the bass with less distortion. Since it will give somewhat more flexibility in placement and provided it is competitively priced, the bipolar design is one that Axiom should strongly consider for the future, forget the passive radiators.