continued:
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.
Now, about wiring both channels of an amp to each coil of the driver. If you create a direct electrical connection between the two channels of an amp that are generating different signals, you'll have one of two results:
1. The amp will shut down
2. The amp will self-destruct
NEVER wire channels of an amp directly together if they're carrying different signals. And, I would
strongly caution never to do it, unless the amp is specifically designed to operate in that mode. Small interchannel differences in operation, even when fed the same signal, will result in the two channels essentially shorting each other out. Bad things happen!
So, if you have a two-channel amp, and wish to use a DVC driver, connect one channel to one voice coil, and the other channel to the other voice coil.
Two channel amp with two DVC drivers? Wire the voice coils of each driver in parallel. Then connect one DVC driver to one channel, and the other DVC driver to the other channel. But NEVER connect the two amp channels together!
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