Exactly how much of that inductance shift/change can you hear?Science is science, but if you can't hear it and it is not audible...wouldn't it be smoke and mirrors?
It depends on a lot of things, not just the bandwidth, but the power and the amount of change in the system.
In terms of bandwidth, classical/traditional crossover filter theory suggests a self-inductance F3 at least one octave above your bandwidth of interest. For a 3.5 Ohm DCR at 100 Hz, that would be 2.75 mH. Ideally you should have an inductance lower than that, and many long voice coil drivers are considerably higher (see our old Mag’s, Q’s, etc).
In terms of linearity versus stroke and power (both of which need to be considered, as inductance changes with both variables), Klippel suggests that inductance changes of more than 50% are audible issue, for any bandwidth system. Is it necessarily a
bad sounding effect? Depends upon how accurate you like your audio reproduction. I used to think our v3 Mag’s sounded pretty darned good. But then I started using a Brahma instead of our Mag’s for HT duty and then I couldn’t get the v4 prototype out of my car for some odd reason.
I see very few people advocating greater nonlinearity and higher levels of distortion as the best way to achieve sound quality. If you are only looking for maximum output or power handling, then I agree concerns of inductance are moot. But then again, my drivers aren't intended for maximum output or power handling, but rather sound quality.
drop an octave excursion has to double to have the same amount of output
That's actually wrong; a drop of an octave requires FOUR times the stroke to maintain the same output. *edit* I now see this has been addressed already on the previous page.
But to the larger concern of stroke... Is your hypothetical 14mm suitable? For the vast majority of people, it is. Think about just 12 years ago - the highest stroke subwoofers on the market were lucky to reach 10mm, and there was no shortage of great sounding vehicles back then. Some vehicles which are still considered high-water marks used drivers with less than 10mm of stroke, let alone 14mm.
But again, it depends upon what you want to accomplish; if you just want the loudest thump-bucket out there, then go ahead and buy the biggest magnet, the biggest diameter, longest wind length voice coil and hit it with 3 kW and enjoy your 145+ dB.
If you're looking for quality sound at a more realistic listening level, then 14-20mm is more than adequate for your situation.
And realize that for many people, a 60 pound driver that is 10" deep is un-usable for their application. Smaller, shallower, lower weight drivers that sound very accurate and work great to generate 125-130 dB SPL (which is what you can get with a 12" woofer moving about 13-14mm one way). Albeit, this isn’t for everyone, but neither is a 27+mm monster that weighs 60+ lbs.
but it plays flat from 35-300Hz..what good is that in a Subwoofer when you are playing organist music that is in the >35Hz range?
I assume you mean
To generate an audible signal at 20 Hz, the Fletcher Munson curve and info tells us we need around 110 dB SPL to be perceived as "equally loud" as 85 dB at 1k Hz (which is quite loud – the 85 dB at 1k Hz, that is). Given the 25-28 dB boost a typical car has at 20 Hz, we need a transducer that can generate 85 dB SPL at 20 Hz. A 12" piston only needs to move less than 10mm one way to do so. So how would a 14-16mm driver result in "inaudible" bass at 20 Hz? How would it not be capable of reproducing less than 35 Hz? It doesn't. It may not win you SPL competitions, but for a wide section of the market, it's more than useful. Be careful to not project your own desires upon the entire car audio crowd; it may not work for your situation, but I bet that there is little that Scott Buwalda and Alan Dante would agree on in what a subwoofer needs, but both would be 100% correct
for their own applications.
Yes you are hitting low-inductance straight on the head, but that is only one pepperoni to the whole pizza pie.
As is stroke, which you are hitting. Here's the deal, though - if you're going after sound quality, then inductance is ALL the pepperoni. Stroke is just one piece of onion, and power handling is a small piece of sausage.
If you're after SPL, then inductance becomes that piece of onion, power handling is the crust and pepperoni, and stroke is the cheese and everything else.
But, your mids should be picking up the pace after 56Hz or so anyhow...but you are a true God of Sound Quality...why am I even telling you that?
That depends upon your application. In my car, it actually blends and sounds best with a crossover above 80 Hz (my x-over is set at 95 Hz now), and every install is different. Not everyone has capable 6.5’s that are able to reach down to 50/60 Hz at the levels they desire. That's why making a blanket statement like "inductance doesn't matter for subwoofers" is dangerous; in fact, it can matter a LOT.
At the same time, making a statement like "lower inductance is usually a good thing in terms of linearity and THD" is always valid; you have to decide if linearity and low THD are important to YOU, but a low inductance will always help with that. It isn’t for everyone because everyone’s goals, applications, and desires are different.
