calling all SPL monsters, again

No don't do it, it is NOT a good idea to wire the two voice coils of a DVC sub to different amps.  You will very easily destroy the woofers doing this. 

I'll try to explain it simply.  DVC woofers have two seperate electrical windings that are physically mounted on the speaker cone.  The coil is a motor.  It converts electrical energy from the amplifier into a physical force, and this force moves the speaker cone back and forth.  If the two coils receive different signals, the forces they place on the cone will also be different.  In the worst case, one coil will puch "out" while the other pushes "in" and the cone stays still.  This leads to fried coils.

It is impossible for two seperate amplfiers to generate the exact same signal (without some sophisticated feedback circuitry called "slaving" one off another.  And even then the amps will not produce the 100% exact same signal.)

The only wiring configuration for your subs (I assume they are DVC @ 4-ohms per coil?) is all six voice coils in parallel for a net 0.66 ohm load) or series-parallel (each sub wired in series for 8-ohms per sub, then these three 8-ohm loads paralleled) for a net 2.66 ohm load.

There is no easy way to wire two amps to three subs and balance the load.  You can wire two to one and one to the other or something like that if you want to...

Someone correct me if I've missed something.

well, my 2 cents for right now: you are totally contradicting yourself. You want TOTAL SPL, yet you only want 12's..... if you wanted TOTAL SPL, sound quality wouldnt matter a bit to you. TOTAL SPL requires BIIIIG woofers, and even BIIIIGERRR boxes. I dont think i'll be the only person to say this either.

Hey Dyon, I think this is the first time I have disagreed with you.  But you are partially right.  Here's an exerpt on DVC wiring from one of our tech papers:

"Copyright Ó Adire AudioÒ All Rights Reserved. Visit Adire Audio at http://www.adireaudio.com

There's one thing that often comes up about wiring DVC subs, and that is the mistaken conclusion that running different signals to each voice coil will "ruin" the driver. Let's recall how a dual voice coil driver is built. Basically, a dual voice coil driver consists of two motors (the voice coils) co-axially mounted (that is, wound together on the former) to a single diaphragm. The net force on the diaphragm is the sum of the inputs of the two motors.

Now, when you feed disparate signals to the motors, they do try to counteract each other. However, this will NOT result in mechanical stress in the system!

Why? Well, remember how a dynamic cone driver works. You have a static magnetic field from the permanent magnet. Then you have a dynamic magnetic field from the voice coils. It's the interaction of these two fields that generates the force that moves the voice coils/former that are attached to the diaphragm. Thus when the voice coil dynamic fields push against the magnet's static field, you generate a force on the former, which pushes on the diaphragm, and that pushes on the air, generating your acoustical wave.

Now, when you feed the same signal to both voice coils of the driver, the dynamic fields of each coil are the same. They add together, and generate one single force (equal to the sum of the two individual forces) against the static field. Presto, cone motion.

Take the "worst case" situation. You wire the two voice coils out of phase. At first, you think one coil is trying to push forward, the other backward, and suddenly the system tears itself apart, right?

Nope. What happens is that one coil sets up a dynamic field. Let's say, for clarification, that coil 1 generates a signal to push the diaphragm forward. Since coil 2 is wired in opposite phase, it sets up a dynamic field to push the diaphragm backward. Net result is that the two magnetic fields CANCEL themselves out! That is, the dynamic field that's pushing on the static field from the magnets is ZERO. The field from coil 2 adds to the field of coil 1 in such a way that the net field is zero. Much like adding a two sine waves of the same frequency that are shifted by 180 degrees.

This is the SAME basic principle with shielded drivers that use bucking magnets. Use a field of the opposite polarity to cancel the original field out. If the driver's motor magnet has a given polarity, use the bucking magnet to introduce a field of opposite polarity, so that the two fields cancel themselves out. Net result is no field.

So, when we run two different signals to the voice coils, what we find is that the magnetic fields of the two combine to generate a net TOTAL field that interacts with the static field of the magnets. The two voice coils NEVER fight each other in a physical way; it's all in the magnetic field.

Dual Voice Coil Drivers 3

Now, you might say, what about the increase in heat? After all, most subwoofers rely on the conversion of electrical power to acoustic power to lower the dissipation in the driver, right?

Again, wrong. Look at the parameters of a typical subwoofer. Look specifically at N0 (eta naught). This is the parameter that gives the electrical-to-acoustical power conversion efficiency of the driver.

This number, for most dynamic cone subwoofers, is less than 0.5%. In a FEW cases, it may be as high as 3%. But, for the most part, you'll see N0 well below 1%. What N0 represents is the percentage of electrical power that's transformed into acoustical power. For example, let's take a driver with an N0 of 1%. Apply 100W to the driver. Of the 100W electrical power delivered, 1%, or 1W, is converted to acoustic power (1%). The other 99%, or 99W, is converted to heat.

Look at a typical dual voice coil sub, such as Shiva. It's N0 is ~0.4%. This number is VERY comparable to other 12" DIY high-end subs out there, and represents a driver with an 88 dB SPL rating.

Now, apply 300W electrical power. Wire the voice coils in parallel, in the same electrical phase. We'll get our acoustical output, or (300 * 0.004) 1.2 acoustical Watts of power out. The other 298.8W of electrical power is dissipated as heat.

Now wire the two voice coils out of phase. What will happen? Well, we know from the above that the two magnetic fields from the voice coils cancel each other out, so there's no net cone motion. Thus our acoustic power output is zero (can't have any, if the cone doesn't move).

That means ALL the power is dissipated as heat within the driver. How much? 300W. Compare this to the situation where the two voice coils are connected in the same polarity: 298.8W. Net difference? 1.2W of dissipation. In essence, you will cause exactly 1.2W of extra power dissipation in the system by crosswiring the voice coils.

Now, is that 1.2W extra heat going to be a problem? Most likely, no. If a driver is rated to handle 300W, chances are it's not going to have a problem with 301.2W. 400W, sure, but a 0.4% increase in power dissipated? Well, the temperature of the voice coils may raise another 0.1 degree C, but that's about it.

Anyway, the net result is that the increase in heat from dissipation is essentially zero. The one area of consideration is that self-cooling of a driver is reduced when motion is reduced. So the driver can handle the out-of-phase situation for a little while, but because of the reduced cooling, heat will build up faster."

Here's a link to the tech paper this was taken from: http://www.adireaudio.com/Files/TechPapers/DualVoiceCoilDrivers.pdf

Steven Kephart

Adire Audio

Actually that's more from frequency response than driver size.  If you have a boost of the higher bass frequencies, then it will sound tighter.  But you will be missing out on a lot of the lower stuff.  Having the lower frequencies boosted will make it sound more boomy.  But you can have 15" subs that don't do well down low, or 10" subs that have more low  end depending on the install.  It's all a matter of frequency response.

Steven Kephart

Adire Audio

Very good info, Mr. Kephart.  Thanks.  I agree completely with the mecahnical stress portion of the description, but have to say that the thermal portion is not complete.  In SOME CASES, of course your paper is correct, the additional thermal load from the VC being forced into a zero momentum condition will not result in dangerous heat loads, but in others it can almost instantly cause damage.  I guess it depends on the driver design and the amps and how close to thermal maximum the power loading is to begin with, but I've seen it happen (specifically with Infinity Beta series woofers.)  I've even seen damage occur when different frequency bands are applied to the VCs through crossover design (this was on a MTX woofer as I recall.)  Other undesireable effects include loss of net output whenever VC signals cancel each other, increased audible distortion from cross-talk and other magnetic and physical non-linearities created inside the motor structure, and changes in the T/S electrical parameters of the driver.

On the other hand, I have also gang-amped SPL systems for people and never given it much thought since I knew the life expectancy of true SPL competition cars is a moot point as long as they make it through the meet!  Unless someone states otherwise, I try to generalize my answers on the forum for all applications, and I maintain that it is safer and better for the drivers to ensure unity amplifier signal on DVC drivers.

Thanks, and please feel free to disagree any time!

That I don't know.  I will have to ask Dan about that as he is the one who wrote the paper, and is the real expert (at least in my case).  But I feel the paper proved that except in this worse case senario, there shouldn't be any damage because there really isn't any more power.  The damage only comes when there is no movement (less cooling), which only happens when the coils are wired out of phase from eachother.

My friend runs those.  In fact I would have if they weren't out and I hadn't gotten my a/d/s/ subs instead.  Those Beta drivers were very nice.

And that's where I was agreeing that it isn't a good idea.  Especially for a daily driver.  Although I don't think it would hurt anything, it sure wouldn't sound very good.

I'll definitely feel free, but I don't see it happening very often.  I have been VERY impressed with your knowledge and experience.  I was rather surprised when you said you have used our products, especially the Tumult.  Sorry to bring this off topic, but I am very curious to hear what you thought about it.

Steven Kephart

Adire Audio

Yeah . What ever you guys said i agree.

Well what ever you guys are doing. Good Luck in meeting your goal.