Servo does not care about physical Qts value as it will create a new Qts value with servo feedback design. The goal here is to create an identical frequency response so that the transfer function is literally cloned. So you can say our servo feedback will make they have the same Qts value. However, this Qts value is in the range of 0.2 to 0.25. It is very low and means it is very fast bass.
The volume calculation is primarily based on the power output from the power amplifier. We don't want the risk of bottoming out the drivers. It is first determined by simulation, and then adjusted/confirmed by actual enclosures. SW12-4 and SW-8 are identical drivers in terms of efficiency, although one is 4ohms and the other is 8ohms. For one SW12-4 and SW12-8, 1.6cu ft is about right. 1.8 cu ft can cause it to over excursion a bit, but is still acceptable. All of these is with assumption that it is driven by a 370WRMS amp. So for a dual kit, each driver only receive 185WRMS power if we stay with A370. That is 40% less in terms of amplitude (power is square of amplitude). Therefore theoretically we need to increase the volume by 40% to make up for it. But that can make it too big and therefore I compromise and proposed 2.0 cu ft. We have since come up with a H600PEQ model that can deliver 600WRMS power to dual kit and that is 300WRMS for each driver. If you use H600PEQ, you can stay with 1.6 cu ft for each driver. In this case, you pretty much fully utilize the excursion of drivers. For those already bought A370PEQ for their dual kit, there is an easy path to upgrade to H600PEQ as they have the same heatsink. H600 is based on class-H amplification and therefore more efficient. All of our components are mutli-purpose. I cannot stand the notion that a particualr component is purposely built for a particular application.
With servo, we can introduce the idea of software abstration into subwoofer. It is very similar to PC video cards. What makes them appear the same to PC, it is the video card driver. What makes all direct servo have similar frequency response? It is the servo feedback. If we can make all of amplifier have the same physical dimension so that they can be drop-in compatible, that will be even better.
