So if power is a consideration, shouldn't things be overbuilt? Why rate a very short 4 layer coil at a point where it is about to fail, instead of including wiggle room for the end user to be foolish?
If you would like to come and see how we power test our MAGs, you're more than welcome. I know many who can attest that they will take what we rate.
So why not over-build drivers to take 2x the power as targeted? You lose the efficiency / goals of your subwoofer for one. Adding extra turns, height, extra “wiggle room”, etc, for user abuse is fine if you don’t mind compromising the goal of the speaker system unless that
is one of the goals. I don’t like cutting corners on a design just so the speaker holds up with twice the amount of power as the speaker is rated for. My market isn’t your market.
4ohm coil, Inductance at 6, 4, and 2 millihenries respectively. Note the red arrow where your inductance is starting to become an issue and causing your impedance rise starting to cause your response roll off. According to your math that is not possible, but according to that plot you are still out of the frequency range that it matters in a subwoofer.
Then you don't follow, maybe I wasn't clear. You typically want your frequency response to be flat for 1 octave beyond the crossover point, so that the crossover - and not the speaker - dictates the rate at which the response attenuates.
Now, simple first year college physics tells us that the impedance of an inductor in Ohms is 2 times pi times frequency times the inductance in Henries. Or, Z = 2 * pi * f * L.
We also know from basic physics that Ohm's law (V=IR) and Kirchkoff's Voltage Law (the sum of all voltages around a loop must be zero) that we can do a voltage divider with the Re of the voice coil and the Z(Le) (that is, the impedance from the inductive portion) of the voice coil; when these two values are the same, then we will have a 3 dB attenuation in output - we are at the corner.
Now, solve the above equation for F, in terms of Z (which will be Re) and L:
F = Z / (2 * pi * L)
Plug in 3.5 Ohms for Z, and then vary L to get your f! I'll leave it to the reader to determine the value of L that give an F of 160 Hz...
Anyway, let's look at some outputs of frequency for a typical driver, in a typical box, with a variety of inductance values (this was done with a copy of LspCAD Pro 5.10 with nonlinear modeling turned on):
We see that - as inductance increases, the output really starts to change. The F3 of 1 mH is 550 Hz; the F3 of 3 mH is 160 Hz; the F3 of 5 mH is 130 Hz! Meaning that depending upon the crossover point we could have an issue with frequency response.
Note too the big peaking you get; all are in the EXACT same box, with the exact same (save Le) T/S parameters! Clearly the FR of the driver is seriously impacted by the inductance.
FURTHERMORE, as anyone who understands Fourier Theory (that time and frequency domains are dualities of the same data set), take a look at the impulse response for two of the drivers (Le = 1 mH and Le = 5 mH):
Now, the ONLY thing changed was inductance; which driver settles down faster, which one has the better transient response? This is the transient response IN BOX; it includes the effect of the low end filter created by the box. I'll leave it for the reader to conclude which one settles faster, but the answer is clear.
Right, but there is a huge following of people who do not like a woofer that is 'flat', for extenuating circumstances that are outside of what may or may not be 'right' according to laws of perceived 'SQ' and that quest for a 'ruler flat response'.
Great - and for them (and you) - DO NOT BUY THE MAG!! It's that simple! Not everyone wants the same driver; find the driver that matters for you! Would you tell people who do want flat to only buy high inductance, long settle time drivers?
But I don't think that anyone who is concerned with high SQ value will discount the value of a low inductance driver. In fact, that's one of the things most of the high end home audio drivers shoot for - a low and linear inductance.
As far as a woofer, my personal tastes are not with xbl^2.
XBL^2 isn't the only way to get low inductance. It's just one of the side effects of the motor design, but it's not the only way to get there! Shorting rings, shorting coils, sleeves, and just plain small underhung coils work too...
If you want to debate the merits of XBL^2 versus other drivers - IN A GIVEN CONTEXT - I'm more than willing. If you want to debate the merits of lower inductance - IN A GIVEN CONTEXT - I'm more than willing. But you can't peanut-butter every driver like you’re doing here.
Many people (on here as well as other places) agree as well, as it is like putting ketchup on an Oreo to them.
OK, and many people disagree. See, that's what makes car audio fun – there are differences of preference. NO WHERE have I stated that you must – no matter what - buy a low inductance, XBL^2 driver. Yet you seem to want to state that a low inductance, XBL^2 driver will never work as a car audio subwoofer! It may not work for you, but it works for me. And we'll both find plenty of people to agree with us.
Leave the holy wars out of it; understand and accept that your solution is not the valid solution for everybody, and I'll do the same.
Not talking about non-linearity's, just inductance right now. That's what the spectral vibrometry machine is for.
Except that inductance IS a non-linear value! Please see Klippel at al; inductance VARIES with position AND power. It's a 4 dimensional function (magnitude, position, frequency, power). You CANNOT talk about inductance without talking about it being a non-linear value, unless you want to keep this at a grossly inaccurate and first grade level (also, how does a spectral vibrometry machine determine inductance versus position and power?)
You can't expect to attempt to tailor to a group of people (mainly the internet market) and pray to whatever god you pray to and hope that know what they are doing.
Isn't that what marketing is? Isn't that what EVERY SINGLE COMPANY tries to do? Tailor a product that will be acceptable and useful for a segment of the market that they are interested in? Are you saying that products are designed simply at random, and whatever sticks to the market is the winner?
If so, that's a very interesting viewpoint of product design and development.
But what are the drawbacks for getting hung up on it? Less thermal mass, less room for wiggle, and FAR less room for 'oops' on a volume knob, gain, or subsonic filter.
Sometimes yes, sometimes no... And it means - what I have said a dozen times (PLEASE try to get it this time): no driver is suitable for everybody! If you have to have the loudest, biggest power handling thing out there, then screw the inductance! It doesn't matter.
BUT, if you want accurate and flat output, you are fine with 130-135 dB SPL, you care about extreme sound quality, then low and linear inductance becomes a definite issue.
Again, you're trying to take your set of criteria and apply it to the entire marketplace; that is completely invalid. You can’t do that, and I can’t do that! There are different segments within the market who have different needs, and will either value or ignore high power handling, just like they value or ignore inductance. If you cannot agree to this then this thread might as well be locked - there will never be any agreement.
Regardless, at 60Hz and 7mm of excursion you must be at 28mm of excursion at 30Hz to have the same level of output.which only makes the discussion stronger.
You're making excursion statements in the absence of output! As I showed earlier, you only need 7mm one way from a 12" driver to reach 110 dB SPL at 20 Hz in a car. For a vast segment of the car audio market, that's a LOT of output. So if my driver can do 14mm at 20 Hz (113 dB SPL), then it's plenty for quite a good chunk of the market.
7" mid-woofer sitting beside me that does 12mm linear.within 2.2dBa +/- from 70-2500Hz.the days of no excursion are far over. Doesn't seem to have an inductance issue either.
Yep, they've been around for 5 years. I believe Wiggins was selling things like that back in 2004. ScanSpeak's been selling 7-8mm one way, low inductance drivers for about 20 years (the old 8545 for example).
What about Infinite Baffle? Is that not an "SQ" application? Where excursion reigns supreme?
How loud do you need for SQ? Seriously, give me a number. And then we can talk about what's needed for excursion. Give me the number first, and we'll go from there. The results will really surprise you...
Who said it has to be 10" deep and weigh 60+ pounds?
OK, name a driver that can handle 3 kW in an SPL competition and that is less than 4.5" deep and weighs under 18 pounds.
See, not everyone has the exact same needs and desires as you. And I can tell you (and I'm sure many other manufacturers can tell you) that with a certain segment of the market, if it's NOT 10" deep and it DOESN'T weigh 60 pounds, then it's crap. For a segment (unfortunately, fairly large) of the market, weight means "it'll quad and give great Hz and mad DeeBeez" (everyone reading this has seen the threads). Lightweight and shallow is a negative for them. Big heavy drivers are where it’s at.
I understand that. I recognize there are lots of needs and desires in the market, and I try to work on a smaller market niche. That niche is concerned with size, weight, and inductance.
