Power Amps and Live Applications

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jndietz

The Way It Moves
So, this Behringer power amp I was looking at advertises the following:

Capable of parallel and bridged mono operation.

2x1,200W @ 2 ohms; 2,400W @ 4 ohms bridged.

And I don't exactly know what that means... could someone elaborate?
 
The power amp has two amps in it. One powereing the left channel and one powering the rihht channel. there should be a switch to link them together to double the power for mono operation.
 
So, wow, so it'd have enough power for two 1200W montiors, some floor monitors, and maybe even a subwoofer?
 
jndietz said:
So, wow, so it'd have enough power for two 1200W montiors, some floor monitors, and maybe even a subwoofer?
Click to expand...

Well...the thing is first it only has two channels, so you could pick any two of those...some tops and monitors, tops and sub, monitors and sub...

The second is that though it is capable of 1,200W per channel, that's at 2ohms impedance. Most speaker boxes are 8ohms. The higher the impedance of the box, the less power the amp can put into it. An 8ohm box vs. a 2ohm box means the amp would put out about 1/4 of it's 2ohm rating, or about 300W. The good news is that stringing together boxes drops the total impedance, letting the amp generate more power. The other good news is that speakers don't "need" a certain amount of power. Your 1,200W speakers will run fine with 300W, just with 6db less maximum volume.
 
You need to work on your mathematics skills before you plug things in though.
 
My math is fine, I'm just not entirely familiar with how watts and ohms work, thats all...

I guess what I'm wondering is, can you have more watts in amps than you have in speakers or vice versa?
 
A quick answer... yes. But, as previously stated you have to be very careful with the watts in relation to ohms of both the amp and speakers. Check online for the user's manual for this power amp and it should have some various diagrams showing different ways to hook up speakers with the correct ohms.
 
Not really sure how, but the 4ohm and 2ohm ratings up there got switched around. The amp would have a HIGHER power rating at 2ohms than at 4ohms.

Boingoman was right, you can "daisychain" speaker cabinets to drop the impedance. Let's say you have two 8ohm cabs that you hook INTO the first one, then from that one you use the OUTPUT to go into the next cab. This halves the impedance of the cabs, making a single 4ohm load. This way you can get better efficiency out of more cabs, but you have to pay close attention to what you're doing.

To answer your second question: You can have more power in an amp than you have wattage on your speakers, and you can have more wattage on your speakers than you have power in your amp. The problem with that is this: First, if you're not careful it's easy to blow your speakers with an amp that pumps out a lot more power than they can handle. Secondly, if you're not running a speaker around where it was made to run wattage-wise, it won't perform as efficiently.

From my experience RMS ratings in cheap-o amps like this tend to be VERY conservative, and sometimes even outright lie. 1,200w at 2ohms, okay, but I've never run a 2ohm setup in my life and probably won't ever.
 
Air Duster:

So, is this what you are saying?

<img src="http://jndietz.toastednet.org/pasetup.JPG"</img>

The cabinets that I have are 8 ohms each. What you were talking about, with regarding splitting the ohms in half with two cabs -- is that picture #1?

Well, I guess, is this picture correct in general?
 
Air Duster said:
Not really sure how, but the 4ohm and 2ohm ratings up there got switched around. The amp would have a HIGHER power rating at 2ohms than at 4ohms.
Click to expand...

The 4ohm rating of 2400W is for bridged mono operation. It's right. :)
 
jndietz said:
The cabinets that I have are 8 ohms each. What you were talking about, with regarding splitting the ohms in half with two cabs -- is that picture #1?
Click to expand...

In picture A, if both cabs are 4ohms as labelled, the total load on that channel would be 2ohms. Both cabs would receive 600W at full output, which is 1/2 the 2ohm power rating for one channel . If they were 8ohms, the total would be 4ohms, and both cabs would receive 1/2 of the 4ohm rating for one channel, probably 300W each.
 
jndietz said:
My math is fine, I'm just not entirely familiar with how watts and ohms work, thats all...

I guess what I'm wondering is, can you have more watts in amps than you have in speakers or vice versa?
Click to expand...

Research Ohm's Law. :D
 
boingoman said:
In picture A, if both cabs are 4ohms as labelled, the total load on that channel would be 2ohms. Both cabs would receive 600W at full output, which is 1/2 the 2ohm power rating for one channel . If they were 8ohms, the total would be 4ohms, and both cabs would receive 1/2 of the 4ohm rating for one channel, probably 300W each.
Click to expand...
this is basically right except thatmost amps don't really double power output when the ohms halve.
very good power amps with robust power supplies will but less expensive amps (read Behringer) won't.
For example .... the power amps in a Mackie 808 arerated at 500watts each into 4 ohms and only increase to 600 watts at 2 ohms.
 
Lt. Bob said:
this is basically right except thatmost amps don't really double power output when the ohms halve.
very good power amps with robust power supplies will but less expensive amps (read Behringer) won't.
For example .... the power amps in a Mackie 808 arerated at 500watts each into 4 ohms and only increase to 600 watts at 2 ohms.
Click to expand...



Also keeping in mind that the crappier amps won't tolerate 2 ohms
 
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