Sorry this has strayed off topic, but hopefully this can wrap this up. If there is further discussion on the topic of the BMF, let's take it to another thread here, the AV123 threads on it, or even my forum.
Originally Posted by Lindahl
Yes, but the passive radiator is being driven by the excursion of the 15" driver. When the 15" driver starts to give up, the movement of the passive radiator is affected, as well, no? The same way a driver's performance can be limited by it's voice coil capability, no?
You can't just ignore the excursion of the 15" driver. Sure, it'll exert less, given that two passive radiators alleviate the low and high end, but you're still limited by the excursion of the 15" driver in the mid-low end of the passband (25hz?), and it's 2nd and 3rd order distortion products will also drive those passive radiators (higher order is limited by the upper Hemholtz resonator), along with movement limitation of the passive radiators when the 15" driver starts to compress.
I've done a good bit of research and comparison on the designs as to why so many sounded horrid, and what their strengths and weaknesses are. Sure, the driver needs to remain linear. The reality is that even at the point of maximum excursion above low frequency tuning, the output is still greater per driver excursion than would be observed from the driver directly radiating. Above this frequency range, the loading of the front PR
gives it a huge advantage in required excursion per output.
Low-end performance in a reflex system is limited by the performance a bit above tuning. The bass reflex 18" driver's low-end limitation also lies around these mid-low frequencies. Since both subwoofers are limited by the driver's excursion in the same region, the 18" driver, having more displacement, will also have more low-end performance, since it's limited less than a 15" driver.
Am I wrong here? Maybe I was misunderstood, before?
It would be presumptive of me to assume what Chad's driver is capable of. The reality is that the resulting output capability of the bandpass system is closer to that of a conventional design with a larger or higher excursion driver than used.
Oh, and Mark, do you mind sharing the upper-end limitation of the BMF? Where it begins to roll off?
The response is pretty well flat to 80Hz, maybe 1-3dB down from the response maximum. More than enough to deliver strong attack and impact in a common home theater use.
And now back to your regularly scheduled programming...