George (on Topic Only)

Actually, Xl (inductance limits) should be included... After all, inductance affects the dynamic performance of the driver, as well as nonlinearities of the motor, and it becomes more and more dominant as you move higher in frequency. For subs, you're right - Xmag and Xsus are the big ones. For mids, Xl becomes just as critical, and for tweeters, Xl and Xsus are everything (Xmag is irrelevant).

And of course, inductance also affects BL compression, too, so it will affect Xmag at higher powers...

So for some drivers/frequency ranges, inductance limitations are critical. Remember, Xmax is used for ALL drivers, and is relevant for all drivers... Now you can see why ALMA had an entire panel discussion about this seemingly simple parameter.

Dan Wiggins
Adire Audio

 

Absolutely..
That does make perfect sense.

But it almost seems as true that at the same rate that inductance becomes more and more of a factor actually limiting the driver's ability to reach excurison levels (as the frequencies increase)...
Xmax becomes less and less important, at least in the eyes of those shopping around for drivers.

I definitely was thinking in the context of subwoofers, however, in my rationale that Xsus and Xmag seemed to drive the raw "how far can it throw", while inductance being tied more to the finesse.

Interesting to illustrate the shift.. how Xmag progressively becomes less and less of a factor (I presume simply because of the lower excursion requirements, being that it's easier to design a low excursion motor), and how Xi becomes increasingly more of a factor, both in raw excurison and in sound quality.
Interesting dynamics.

 

To a large extent, yes. But again, Xmax is important for mids and tweeters, too... And in many cases, even woofers (not even high excursion units) can be severely hampered by inductance prior to BL or Cms. It's not common, quite rare actually, but does happen.

Dan Wiggins
Adire Audio

 

Well, in order for this to happen, that woofer would need to have a tremendously high inductance though, correct?

The part that I'm having difficulty picturing is a woofer that would have such a high inductance, that didn't have a tremendously long coil that would seem to inherently give it relatively high excursion.

Unless you just keep layering it up... 8 layer, 10 layer, 12 layer coil anyone?

 

Here's a file I found:


As you can see, as the coil moves into the motor the flux increases greatly. Can anyone explain why this is happening? I have a feeling it has to do with a coil of wire with current on it around a piece of steel. But it looks like the total flux in the system increases by quite a bit. In fact, I would almost expect a BL curve that wasn't curved, but sloped.

Any comments?

 

I learned something interesting about cars, and was wondering if it transfered back to subwoofers. I found out in vehicles that if you have a longer stroke, that increases torque. For horsepower, you want a shorter stroke but a larger piston diameter.

Now I'm wondering what differences in the sound of woofers comes from this. So let's say we have two drivers of the same displacement. One has a larger cone, but smaller stroke. I know that it will most likely take more power to push the higher stroke one to match the displacement. But does torque and horsepower apply in any way to subs? Also, we will assume both use XBL2 motors and the tests are taken at 70% of Xmax so the curve is completely flat.

 

actually, I think that analogy would interestingly work if you think of Horsepower as BL and torque as 1/inductance(lower inductance, increase ability to accellerate immediately)....

if you increase the coil diameter(assuming you keep the flux through the gap constant), and the amount of layers of coil, you put more wire length in the gap and thus you have more BL. But if you use the same amount of coil length in total (think same displacement in engines), but instead you use a single layer, longer coil config, you have reduced inductance(and thus quicker change in accelleration).

 

I believe I can explain what's going on here -

The gap:
You have a permanent magnet, that's setting up a magnetic field in "the gap"... between the pole piece and the top plate.
Essentially, one of the magnetic poles is touching the top plate, and the other magnetic pole is touching the back plate... so the pole piece is charged with that pole's energy.
Let's call the top plate "north" pole, and the back plate (and therefore the pole piece) "south" magnetic pole.
That's what establishes a magnetic field in the gap.

The coil:
And - you have an electromagnet - the voice coil.
The top of the voice coil winding represents one pole, while the bottom of the voice coil winding (the bottom of the former) represents the other.

The combination:
When the magnetic gap is sitting there, you have so much magnetic energy in that area.
But now, you are energizing the voice coil, so IT has magnetic energy...
When the coil enters the gap - now the gap has the magnetic flux of it's own magnet... AND the magnetic flux of the voice coil.

It's not going to combine and double... because the magnetic fields are at 90 degree angles from each other.... but it will still combine constructively.

Hopefully that makes sense...
And even better, is accurate (since I couldn't find anything official on the issue )!

 

The next big event will take plave on Dec 5, 2014. After that is February 25, 2014 at 3:00PM

For the mathematics behind it go to my blog on Astrotheology: the missing link Cusack's Model of the universe.