@deep_333 wrote:
Paul’s vid describes the free lunch that he got with initial use of crappy drivers. How about this....Get the low distortion high excursion bells and whistles driver. Now, stack/integrate several of them so they don’t have to move as much for said spl level. Now, add servo control on top of it...it is incremental. It could all be overkill at normal listening levels, but, maybe not, because it is still the highest distortion component in the chain, relatively speaking.
It’s interesting to note that, with the knowledge and experience of being a servo-feedback designer himself (for the bass system of the IRS V’s), Paul is expressing how "everything is a compromise," and that - it follows - includes the servo-feedback circuit itself. What’s entailed in this specifically isn’t made clear, but it touches upon the aspect of a more purist oriented approach where, with a physically more all-out sub system, one can avoid "compensating measures" like servo-feedback, EQ-boosting and other. With the scenario you’re suggesting (i.e.: low distortion high excursion bells and whistles driver in stacks) the need for servo-feedback circuit will by all accounts be lessened, and so when will the insertion of such a circuit itself be deemed a larger, negative influence than the positive ditto it’s supposed to create? From my chair it appears that what Paul implies is that this is the very reason for them having omitted servo-feedback in their driver and amp upgraded sub towers, because servo-feedback wouldn’t have the desired, positive effect here when all is said and done.
As to the negatives of larger subs and the compromises that may or may not be involved here, structural integrity/enclosure resonances is the one area that is usually addressed. The important question to ask then, to me at least, would be to which degree subwoofer enclosure resonances of a certain magnitude would be an actual impediment in the reproduction of music, not least compared to the contribution of mechanical noise/distortion coming from smaller, direct radiating and inefficient woofers working much harder; would you rather have a capacity strained* small sub setup with more or less inert enclosures, or a capacity unlimited, larger ditto with what is still structurally sound cabs (i.e.: built with interlocked, CNC-machined and Baltic Birch multi-layer plywood, and heavily braced)?
From experience I can say with absolute certainty that, in each and every case, I would choose (and have chosen) the latter option. It’s no contest, period. How many have actually made an informed decision based on experience with both options? Close to none, because the by far most common scenario is that few even considers large, efficient subs for reasons we know all too well, and thus the only frame of reference to go by for most is that of smaller, inefficient subs.
On a related note, I have some coupled cavity speakers, i.e. the physical bass drivers sit inside and are cavity coupled to external radiators (Acoustic filter/ clean bass). One might argue that it is a unnecessarily complicated design. But, the free-er lunch there was that you didn’t need very expensive drivers trying to hit a price point (the expensive driver that may or may not hit a performance requirement just because you kept spending up the wrong tree). I know because i also owned a cost no object conventional speaker design from that same designer...a few different ways to do these things/clean it up, i suppose.
My quip would be: there’s no free lunch with smaller sub designs.
The good thing working with large, efficient sub designs is that of being dictated design appropriate woofers. Either you use them, or performance will be severely impacted (and who’d want that?) - that’s the deal. With tapped horns, like I use, there are very specific woofer requirements and a relative small specs-"window" to accommodate, or else the design won’t perform as intended. Like, too little motor/magnet force and the horn isn’t properly resonated; too much and the air pressure will be too compressed at the throat section and thus also not resonate the horn properly. Too light and non-rigid a cone is an issue as well, also because a cone too flimsy would simply be ripped to pieces with the uneven pressure built-up at the front side of the cone in the throat of such a design.
Build and board material quality is also important here. When the woofer cone really starts moving in tapped horns (and it takes a lot in domestic milieus) the pressure built-up inside the horn path can be so severe that the enclosure cracks open due to the immenses air pressure forces created inside (remember: the single 15" woofer per cab of my tapped horns is force multiplied at the mouth into the equivalent of two 18" direct radiating woofers). In reality such sub designs are built to withstand SPL’s at full tilt, why they’re rigidly built for that very reason - i.e.: design dictated.
*When are subs capacity strained? When there’s not enough if any notable headroom to speak of at the max. SPL one desires. What’s sufficient headroom? From my chair, no less than 10-15dB’s, preferably +20dB’s.
