[BD55]

This seems like something I should intuitively know, but I am having a hard time understanding the virtues of dual voice coil drivers. Does it have to do with multiple driver setups, versatility, or something completely different?

 

[pharoah]

the first dvc subs i seen.were actually made to take a stereo source.it was a passive subwoofer that went between the amp and main speakers.now a days it might be to have multiple amp channels.driving a single unit.which kinda defeats the purpose if its a low power handling unit.in the case of something like the tc sounds 18.that can soak up tons of power.multiple voice coils and multiple amp channels to drive it could be useful.

 

[robbo266317]

They also give you the option of wiring them for 2 Ω or 8 Ω (Assuming it is a dual 4 Ω driver)

 

[BD55]

So essentially it gives you the option for wiring possibilities depending on the amp. Most HT applications are 4 ohm loads though, right?

That makes a lot more sense now, pharoah. If amps weren't bridgeable or there weren't many mono amps, it makes sense to be able to use a regular 2 channel amp.

Thanks

 

[theJman]

So essentially it gives you the option for wiring possibilities depending on the amp. Most HT applications are 4 ohm loads though, right?

You can't really make such a broad assumption I'm afraid. There are definitely 4 ohm sub drivers -- as well as 2 ohm and 8 ohm -- but I'm not sure you can say "most" will be 4 ohm. Depends on the driver really.

 

[andy_c]

Some sub drivers, such as the Polk MM1540, are available in both single voice coil versions, which are 4 Ohms, and dual voice coil versions for which each voice coil is 4 Ohms. The voice coils of the latter can be wired in parallel for 2 Ohms. If two subs are used, and independent control of the delay and/or level of each sub is needed, two channels of amplification are required. In such a situation, cost savings in amplification can be obtained with the 2 Ohm configuration.

Here's an example of two Crown amps:

Crown XLS2500
Power = 775 Watts per channel into 4 Ohms
Street price = $600

Crown XLS1500
Power = 775 Watts per channel into 2 Ohms
Street price = $400

 

[ach81090]

AFAIK wiring options is the only reason.

 

[BD55]

You can't really make such a broad assumption I'm afraid. There are definitely 4 ohm sub drivers -- as well as 2 ohm and 8 ohm -- but I'm not sure you can say "most" will be 4 ohm. Depends on the driver really.

Sorry, what I was trying to ask here was what is the typical ohm load for HT amplification. Thinking about it more, obviously there needs to be that versatility in wiring, loads, etc. Thanks

 

[BD55]

Some sub drivers, such as the Polk MM1540, are available in both single voice coil versions, which are 4 Ohms, and dual voice coil versions for which each voice coil is 4 Ohms. The voice coils of the latter can be wired in parallel for 2 Ohms. If two subs are used, and independent control of the delay and/or level of each sub is needed, two channels of amplification are required. In such a situation, cost savings in amplification can be obtained with the 2 Ohm configuration.

Here's an example of two Crown amps:

Crown XLS2500
Power = 775 Watts per channel into 4 Ohms
Street price = $600

Crown XLS1500
Power = 775 Watts per channel into 2 Ohms
Street price = $400

Ok, but using my limited knowledge here, when you have a 2 ohm load, you will have a higher likelihood of overdriving the amp, right? Overheating, distortion, etc?

 

[andy_c]

Ok, but using my limited knowledge here, when you have a 2 ohm load, you will have a higher likelihood of overdriving the amp, right? Overheating, distortion, etc?

Yes, that's true. The amp must be designed to be capable of being used with a 2 Ohm load for this to work. Pro amps are commonly used in subwoofer applications, and these are often specified for operation into 2 Ohm loads. In the case of the Crown amps mentioned in my earlier post, the power ratings quoted are for 0.5 percent THD at 1kHz.

Consumer amps are a different story, and generally aren't specified for operation into 2 Ohm loads.

 

[lucasa.miller]

I've also heard because of there are 2 smaller voice coils instead of one, the inductance is lower (Le).

That's why some people love quad voice coil speakers, lower (usually) inductance.

 

[BD55]

Yes, that's true. The amp must be designed to be capable of being used with a 2 Ohm load for this to work. Pro amps are commonly used in subwoofer applications, and these are often specified for operation into 2 Ohm loads. In the case of the Crown amps mentioned in my earlier post, the power ratings quoted are for 0.5 percent THD at 1kHz.

Consumer amps are a different story, and generally aren't specified for operation into 2 Ohm loads.

Ok, that makes sense. I was really thinking in my mind all this time that pro amps were just a higher power handling sibling to consumer amps, but it makes total sense that a pro amp would be able to drive that load with lower distortion etc. Is it just a quality issue, or just designed that way?

 

[andy_c]

Ok, that makes sense. I was really thinking in my mind all this time that pro amps were just a higher power handling sibling to consumer amps, but it makes total sense that a pro amp would be able to drive that load with lower distortion etc. Is it just a quality issue, or just designed that way?

Some of the reasons seem to be a matter of the intended market. It's typically an expectation in the pro market for a two-channel amp to be specified for bridged-mono operation into 4 Ohms. In bridged-mono operation, the amp in effect "sees" an impedance of one-half the actual load. So specifying the amp for bridged-mono operation into 4 Ohms is the same as specifying it in two-channel mode, with each channel driving a 2 Ohm load at half the power of the bridged-mono scenario. So in the case of e.g. the Crown XLS 1000, it's rated for 1100W into 4 Ohms in bridged-mono operation, and 550W per channel into 2 Ohms stereo. You'll see this pattern in two-channel amps that are capable of bridged-mono operation (per-channel output power into R/2 Ohms is one-half the bridged-mono output power into R Ohms).

Another consideration in output power capability is how hot the output transistors get for a given power delivered to the load. Two major contributors to this are the capacity of the amp's cooling system and the efficiency of the amp. Pro amps usually have cooling fans, and it's often the case that a cooling fan with modest heat sinking and efficient design of a "wind tunnel" to exhaust the heat is more effective thermally than a monster heat sink with no fan. This is at the expense of fan noise of course. A modest heat sink with a fan is less expensive than a monster heat sink as well.

Regarding efficiency, there are amplifier topologies such as class H and class D, often used in pro amps, that give substantial improvements in efficiency over the class AB mode typically used in consumer amps, at the expense of a slight increase in distortion. Higher efficiency means less heat needs to be removed from the output devices from the outset. The slight distortion increase of class H and class D designs over class AB is mitigated by the use of lots of negative feedback in the amplifier. Negative feedback does a better job of reducing low-frequency distortion than it does distortion at high frequencies, because of a technique called frequency compensation which is necessary to keep the feedback amplifier from oscillating. But for a subwoofer amp, we only care about low-frequency distortion anyway, so if the fan noise can be kept low, using a pro amp for a subwoofer can be a big win, providing high power at low cost.

 

[BD55]

So in a nutshell: in a pro amp you get higher power handling and efficiency at the expense of a little more distortion, but for subwoofer use this little bit of added distortion doesn't really matter because negative feedback can control low-freq distortion better than high-freq distortion. So fan noise seems to be the only real issue with using a pro amp for powering subs. Thanks for the great info Andy; I'm sure I could've googled it, but your explanation was very straightforward.

 

[lucasa.miller]

I have a Crown Drivecore and can't tell if the fan is ever on. It's not audible in my setup.

I use a pro audio amp for my application because of the $ per watt ratio Pro Audio Amps offer. $500 for 2100 watts can't be beat.

 

[BD55]

Well, morphing from a discussion about DVC vs SVC to pro amps, I think when I have the chance to do a sub build, I will definitely be going the pro amp route vs plate amp.