Originally Posted by LTD02
ds-21, that is where i am coming from. ;-) ours are shared thoughts on driver design. maybe you could spec out the common ground where we agree and the areas where we disagree?? then, i if i have anything to contribute, it may have some usefullness. otherwise, i feel like i am just pissing in the wind. not to you, but to everyone else.
I agree that our area of agreement is broad, and our area disagreements narrow. So posting the things we agree on would add a lot to what's going to be a very long post. The three main disagreements (assuming the third isn’t just semantics) I see are as follows:1) What is the predictive power of your power-to-weight calculation (BL^2/Re/Mms)?
I hadn’t figured it for many of the drivers I’ve mentioned, but here it is (I cheated and used your numbers for the W15GTi):
For reference, the BL^2/Re/Mms index for the other drivers I mentioned. (You already listed the W15GTi and TC LMS-Ultra)
NS10-794-4a: 0.46 g/Ω (Qes = .42, 80mm vc)
NS12-794-4a: 0.37 g/Ω (Qes = .43, 80mm vc)
NS15-992-4a: 0.31 g/Ω (Qes = .37, 100mm vc)
NS18-992-4a: 0.23 g/Ω (Qes = .5, 100mm vc)
JBL W15GTi: 0.31 g/Ω (Qes = .51, 2 vertically split 76mm vc’s)
TC2+ 15 (Oaudio OEM): .28 g/Ω (Qes = .4)
LMS-Ultra: .38 g/Ω (Qes .34, 100mm vc)
Exodus Maelstrom-X: 0.25 g/Ω (Qes = .43)
Peerless 830500: 0.53 g/Ω (Qes = .21, 51mm vc)
Dayton Reference 15HF: 0.23 g/Ω (Qes = .49, 64mm vc)
All that number really says to me, based on my experience with those drivers, is, “how much EQ am I going to need to extend the response down low?” Which makes it not so different from Qes.2) What is the predictive power of normalized inductance (Le/Re)?
I say that low normalized inductance (well below 1mH of inductance per ohm of resistance) seems to be from my experience to be a necessary, but not sufficient, condition for a great-sounding subwoofer driver. Others seem to disagree, or place less emphasis on it. I readily concede that low normalized Le could simply be an indicator of best practices design, and not something necessarily targeted in driver design.3, maybe) Can a “car audio” driver be considered “elite?”
I say yes, based on the same criteria used to judge other drivers. Those include first subjective performance; measured performance such as BL(x), Le(x), and Km(x); and thermal properties (ability to measure similarly after being slammed as when cool). As well as “paper racing” qualities such as “does this subwoofer incorporate some unique trick design in its motor?” I say the JBL W15GTi qualifies, primarily because of its outstanding thermal performance.
Frankly, for all we know JBL might not be using the W15GTi’s platform more widely for home use because of cost and packaging reasons. (They did use a very similar driver in the original Vertec-series sub, but I think it’s safe to assume they’re not using it more widely for pro use because it’s so heavy.) Certainly, it looks
like a more expensive driver to make than the old 15” JBL drivers in the ur-Revel Ultima sub. There’s a lot more metal there. It’s also considerably deeper. Also, I wonder if it’s somewhat snobbery-related. (“Oh, the car guys picked up that pro driver, so it must not be worth bothering with for real audio.) It could also be true, of course, that the drivers they make but won’t sell to us are legitimately better. In which case, I just have one thing to say: damn! The W15GTi is already such a great performer, that the other ones must be really, really, really special.