Hi,
If you examine the maximum linear displacement (+/-3.5mm), it is lower than small mid range/woofer equivalents. If the lower crossover frequency is quite low, then it will distort the sound at higher SPL.

The Volt BM220.8 has +/-4mm, and the SB Acoustics SB17NBAC35-4 has +/-5.5mm. If you look at the Purifi driver - they only sell one (not sure of the price or availability) then it has an Xmax = +/-10mm. Not sure if this is a typo, as it is nearly 2x more than the same size unit from SB.

EDIT : The volt BM165.1, 6.5inch bass/midrange, has an Xmax of +/-6.3mm.

Regards,
Shadders.

Edited by user 23 August 2019 17:49:44(UTC)  | Reason: Additional info

This is a most ambitious project where the investment justifies exceptional mid and treble

HF could well be a Mundforf AMT 'ribbbon'

The mid, on a classic basis, could be a high power pulp cone Scan unit with neo magnet and an open frame, probably not the cut cone type as here the better damping may dilute dynamic expression.

A high order L-R Xover at 2kHz is eminently possible

Martin

Not a fan of Isobarik. Yes, it means that you can reduce the cabinet volume to a half for any particular performance for that driver, but at the expense of halving the load impedance, and no change in voltage sensitivity. And of course the implication that the trapped volume between the drivers experiences no change of pressure is not true, i.e. it's not isobaric.

All the speakers I have professionally designed have been active - and this was over 40 years ago! But I have been designing amplifiers and matching for underwater applications for the best part of 30 years and just take it for granted that the transducers will be designed for the best coupling to the environment, and that any changes in system Q for best response can be controlled not only by the matching circuits (the equivalent of passive crossover designs) but by changing the output impedance of the amplifier itself. And this impedance can be negative when one wants to lower the system Q in some part of the spectrum - but of course you can only do this when you know that the amplifier will always see the load it is designed for. At the bottom of the spectrum the lowest frequency band I have been involved in is 25Hz - 250Hz, 1 x 60kW, and the highest 5MHz-10MHz, 32 x 5W. I've been tempted to get back into speaker design but I really don't have the time, but if I did it would definitely be active with one amp per band and all band limiting/shaping, sensitivity matching, etc being carried out before the amps.
The real problem would how I would test/develope such a design: when I was doing loudspeaker design I had a pretty good semi-anechoic studio plus decent measuring equipment for most of the work, and for extreme bass responses I used real-world "free-field" - a large grassy field outside the studio with the speaker facing straight up to a microphone on a very long pole above. It was a bit weather-dependant though!