best biggest baddest sub driver out there? (1 Viewer)

[Mark gas]

What about the co drive sub?

www.codrive.com

 

[Bill Fagal]

Someone want to do the math on how much air needs to be moved to produce the kind of levels Dan is talking about?

Ok, I'll take a shot. (I seem to be making a habit of reverse-engineering Dan's goodies. :b) (Please note that the following is nothing more than the sum of my best guesses based on reasonable numbers and doesn't account for all unknowns, such as corn-pup technolgy! )

The tools I used were Brian Steele's handy dipole response spreadsheet (Dipole.xls) and WinISD Pro. Since Dan hasn't told us much, I had to create an imaginary driver, but I made a point to tilt the parameters a decent amount toward good open-baffle response at 20Hz, just to give the benefit of the doubt:

Qes: 0.6
Qms: 20
Vas: 800 liters
Fs: 20Hz
Xmax: 99mm
Sd: 4sq. ft.
Re: 5.8 ohms

I let WinISD infer the rest of the parameters.
Here is the predicted response in a sealed box of about 20,000 liters--essentially an infinite baffle. It's about 5 dB down at 20Hz, or a little better than 87dB/W.

Next, I simulated this driver in Dipole.xls. Here is the predicted free-space response of the 24"x24" raw driver, along with the predicted IB response. It is about 21dB down at 20Hz, or about 17dB below the IB response.

Now here comes the rub. I went back to WinISD to figure out how many watts it would take to get this naked driver up to reference level at 20Hz (I forget the number, but I chose 112dB). Of course, since the dipole cancellation shaves off 17dB at 20Hz, I had to raise the IB SPL at 20Hz to 112+17=129. As you can see, WinISD predicts it will take about 15kW to get this naked driver up to 112dB on-axis at 20Hz (nearly 150mm of P-P excursion). Got half a dozen K2s?

 

[Mike SJ]

So Dan, is he close?....

 

[Bill Fagal]

In the Latin: "Qui tacet consentit." :wink:

just jerkin' the chain...

Bill

 

[DanWiggins]

I'm not saying until CES, but then again Bill is a smart guy... Let's just say it takes a lot less power than calculated - we'll have plenty of easy to get power for it.

Dan Wiggins
Adire Audio

 

[Bill Fagal]

I'm not saying until CES...

Ladies and gentlemen, the unflusterable Dan Wiggins!

Dang, I'd hoped my unbridled surmising would at least serve to pry loose a few more details...

Bill

PS. Dan, with the raw excursion you're talking about here, I'm wondering if we've been on parallel tracks and you're rolling out a variation of my top-secret high-zoot suspension! Is there any way I could sign an NDA and have a peek? It sounds like your R&D is mostly finished, but I might yet be able to contribute some valuable ideas. Transducer design is my passion, and among other things, I've given extreme-excursion suspensions a good deal of thought. Email me if you're interested.

 

[Bill Fagal]

And while all you bass adicts are imagining and wondering what type of subwoofer motor could possibly generate the type of excursion Dan is hinting at, here's a pic from a certain recent U.S. patent application for you to ponder...

Merry Christmas,

Bill

 

[Mike SJ]

drooooooollllll

 

[dave alan]

It looks like a version of the XBL2 motor. LARGE, grooved top plate, grooved T yoke...

I wonder...

If that isn't an underhung voice coil, what is?? Is it because the gap varies that you call it something else, or do you call it something else to distinguish it from standard-gap underhung coils?

How is the XBL2 gap different from other multi-gap motors?

 

[Bill Fagal]

I like to call the topology "Innerhung."

I don't know what Adire calls it...

 

[Brian Tatnall]

Wiggins posted this all over Here .

Well, all our original design notes - and the patent application itself - reference split gap. You see, our approach can do more than just 2 gaps, and there are benefits to going to more than 2... But XBL^2 is a descriptor of what it does, not how it does it. Split Gap is the topology, XBL^2 is the technology/benefit.

As far as the TC Sounds unit shown, it is a very long overhung voice coil, with extra windings out on the end. In other words, in the center of the VC it's a 2 layer unit. Then you go out towards the end, and it's a 4 layer. Then go out to the very ends, and it's a 6 layer (or effectively like that). It does give you a flat BL curve, however there are LOTS of drawbacks (enumerated above). And of course, you need to make your gap wide enough to account for the widest part of the voice coil, too...

That is why the BL is so low with so much magnet and voice coil out there - wide gap, and probably some copper shorting rings (a la the MASS units) to lower the inductance to an acceptable level, but again that widens the gap and lowers the BL...

For comparison, the Brahma has 25% MORE BL with less than 1/3rd as long of a voice coil (Estimating the displayed unit has a VC that is 3.25" long). The XXX has 50% more BL, with less than half the voice coil length.

Extreme overhung designs are inherently BL inefficient. To get decent BL you sacrifice a LOT of moving mass (added) and inductance (added). JL addressed the problems with extreme overhungs in their own way, but they still have low BLs as well (2 layer voice coil to keep inductance and moving mass in check).

Now as far as stroke goes, what about this graph (measured on our BL jig):



Yes, I truncated the measurements at 3" each way (6" peak to peak - I don't want to give the true limits out yet), and yes the BL is over 32 N/A over that entire range. It's just one of the medium throw units we have kicking around here (yes, at this point, 6" is medium throw - 2" is short throw).

Dan Wiggins
Adire Audio

I can imagine why they might not need so much power.

 

[Mike SJ]

!!!

 

[Scott Simonian]

 

[Nick Hallett]

Sheesh...my shiva was already obsolete, now this...

I bet Adire could make some money at their CES booth by selling changes of underwear when people see this thing...

 

[DanWiggins]

Bill,

We call it Split Gap topology, for obvious reasons... The whole technology, where all aspects of motor linearity are addressed, yield XBL^2 - eXtreme BL Linearity.

Dan Wiggins
Adire Audio

 

[Mike SJ]

When can I buy one?

 

[John E Janowitz]

Now thinking about the BADDEST subwoofer driver I know of leads me away from the conventional driver types.

I do know of one driver out there that is 8" in diameter and moves 18" peak to peak. It will displace a total of 15L of air peak to peak. I know Dan has also talked with the inventor in the past.

Once the technology catches up a little more, this may be the wave of the future. It is run off of linear acceleartors. The same technology that can take the huge bullet train and move it from stop to 100 miles per hour in a few seconds. Linear accelerators have been tested in guns in the military. They can move a bullet fast enough to nearly melt the metal.

The system has no BL curves, no suspension, no distortion, and takes no amplifer to run it. Whatever signal goes in comes out directly. The force is exactly the same along the entire 18" motion. It is all based on computer positioning. The diaphram can be positioned anywhere along the track instantly.

The computer technology is not yet advanced enough to fully take advantage of the possibilities. Also the material technology is not advanced enough to play at higher frequencies. Imagine the force on a diaphram trying to move it 18" peak to peak 80 times per second for an 80hz tone.

The 8" driver does exist but can only play very low frequencies with the current technology. Talk was of an 18" version in the future as technology catches up. Figure an 18" driver capable of 18" peak to peak would displace about 76L of air. I have a feeling 5-10yrs from now we will be seeing something like this completely shake up the subwoofer world.

John

 

[Brett DiMichele]

John,

You sure about no BL curve and all that?

The reason I ask is because the guns the military is fooling
around with use copper wound coils to eletromagnetize and
propel the steel slug out of the barrel "Coil Guns" as they
are named. I have a friend who did some work on the barrels
for such guns (he's a machinist and they were doing the
gov't contact work) buzz was that they could shoot 9mi per
second....

Bullet trains are driven by huge electric motors.. Not real
much there in the way of ground breaking technology. Mono
Rails on the other hand that use Mag Lev are fairly techie
in nature

 

[DanWiggins]

John,

I'm familiar with linear accelerators, having been severely chastized for building rail guns in the EE lab back in my college days, and being hired at a military R&D facility partly because I did build rail guns in the lab (my interviewer loved talking about that).

They definitely have BL curves, definitely have distortion, and definitely require amplifiers. The big power has to come from somewhere. And to control the variable position, you need to vary the force. Which means you need to control the current in the system which sets the force. It can be analog or computer controlled, but in either case it is controlled, and has an amplifier (a variable power supply is essentially an amplifier).

The need for a suspension is also there. You can't get away from a suspension - all actuators have them, for the basic issue of damping (remember, spiders/suspensions were originally called dampers, because that is their function in a moving system). Without a suspension the system really breaks down for AC operation. The suspension may not be a traditional speaker suspension, but there is still a damper in the system somewhere. Ask a mechanical engineer about the tradeoffs of a damper/no-damper oscillating system, and you'll quickly see that you need a damper.

Brett,

Rail guns use the projectile as part of the conductive path; gauss guns use magnetic fields inside coils to propel the projectile. Both rely upon magnetic forces for acceleration, and as such both will have BL curves as you state. Even a rotational servo motor like the ServoDrive units have a BL curve - it's flat for essentially ever, because it's rotational force is flat over the entire turn, but it still has a BL curve. So you are correct - it will have a BL curve.

The only drivers that don't have BL curves are electrostats, but they have EA curves (electric field times area of the stator). Same things apply to both, because in either case the force in the system is BLi/EAv, and are analogous in the rest of the equations.

Dan Wiggins
Adire Audio

 

[John E Janowitz]

Brett,

This is a little different. If you look up trains and linear accelerators you'll find a bunch of information. Or look up patents associated with linear acceleartors. A version of the system used as a woofer actually propels a silent submarine. The only difference is that in the submarine the diaphram moves one direction, collapses like a squid, returns to the start, expands and then moves again. In the woofer it just moves both directions. He calls the system Deep Drive, I assume because it propels the submarine. It also works good as a name for a woofer. There were also tests using the system as a weapon. The human chest resonates somewhere around 7hz. Create enough SPL and people either die or fall to the ground helpless. He said you basically drop this thing down from above, have it knock everyone down to the ground, then turn it off and before people can recover and get up you come and zip tie up their arms and legs. There are lots of things our military has in the works that many will never know about.

Regarding suspension, yes there is something there to damp the system, but not a typical suspension at all. No spiders to stretch or surround. The diaphram basically sits inside a tube. The accelerators are placed at 3 points equally around the tube. There is some kind of slick component on the inside of the tube and the diaphram. They literally touch but have a nearly air tight seal. As long as the computer can position the diaphram exactly where it should be, there won't be any distortion. The problem is that the computer technology can't do this accurately enough yet.

I wish i knew a little more of the details of how it works. I am just going by what he has explained. Maybe I can get him to stop by.

John