'Sorry I've been rather absent lately- the baby keeps momma and I quite busy (well that, and that little CEDIA thing...)
Anyway, I've been reading this thread (although admittedly didn't look at the link to Rives website) and I wonder; is the subparc a truley class D design or is it a hybrid like a class G? It's interesting to me that Richard would be so adamant about the analog-only nature of the parc; and then follow that up with a parc mated to a class D amp..
And to answer who uses passive subs anymore: well me, and every single one of my clients (CAT doesn't make a powered sub, but they do make a 600W x2 fully differential amp that will kick the snot out of a very heavy 22" aluminum woofer). So active vs passive designs is merely semantics anyway, Jeff has been pounding away with his BDEAPs and bitchin crown amps for a couple years now. Before that a little company called BagEnd made some pretty serious passive designs using 18" woofers, and then there was the Whise Profunder-a 21" design right?
Technically speaking, all subwoofers are inherently passive, it's just that most speaker companies include a plate amp with them (mounted inside the enclosure) because most people can't decide on what shoes to wear, much less which amps out there can properly handle the loads presented by the more serious woofer designs...and rightly so, that's the job for engineers (MG) not laypeople or even installers for that matter- how many do you know went to school for electrical engineering?
And in relation to Michael's last post: the A/D - D/A conversions that happen down low ARE much less obvious, but what IS obvious is when you start taxing the processor(s) inside a DSP. For instance: Symmetrix makes 2 8x8 DSPs; one of them uses 4 processing chips ( I think they're Sharc processors ), the other uses 1. Now let's say we have a very basic system that uses 1 woofer (wrong)- well, that single processing chip works just great, because all the computational power is going to only one channel- really light load.
______BUT__________ If we use 4 or 8 or say for argument's sake 32 woofers in one room, that one lonely processor really isn't going to be a tremendous help, because we'll only be able to effectively use one or two filters per woofer if we're lucky, before the thing just runs out of steam. Would that necessarily make the room sound bad? Probably not, but if we could replicate that situation of one processor per-woofer, well then we can make all the amplitude, frequency, time and phase adustments we want to get all of those 32 motors as perfectly in-sync as possible, therefore pressurizing the room more evenly throughout.
Rives operates at a level, and in a realm far beyond the world of Denon receivers and Audessey outboard boxes- just look at Mike Lavigne's room as an example. So too does Symmetrix- a company used in the pro world to make sub stacks work together at your local concert venue.
Neither analog nor digital hold the answer solely; the two must be used together properly in order to maximise each of their strengths, and to minimize their weaknesses.
I mean,I certainly wouldn't use digital correction on anything above say 140 hz- and I really don't think that an analog solution can take on the kinds of projects like concert venues because of the lack of filters available, and the ability ( or lack thereof ) to use multiple filters on multiple woofers without using several of those devices.
And here's my final .02 on this: a purely class D amp in most cases will work quite fine considering that most subs have a relatively flat impedance curve, but if you throw in a woofer that drops close to about 1 ohm at times, well- you're probably going to have an issue: since most class D amps will shut down as the load approaches what the amp sees as a dead-short ( this was the reason for my original question, because lass G acts like a voltage-source switch-mode amp most of the time, but when impedance drops- it acts more like a good-'ol class AB ).
For those of you who are obviously smarter than I am, feel free to politely correct any misinformation I may have just spread.