My 2 ohm head with an 8 ohm cabinet?

[samalope]

Hey everyone!
So i am playing a festival style show tomorrow with a lot of other bands and me and 2 other bassists have the same acoustic b410 cabinet. The cabinets have an impedance of 8 ohms a piece, and my b600h head runs 600 watts at 2 ohms. So...
If i attach all three cabs to my head does that mean my head is at 2.666666 ohms? Is that how it works? Also, how many watts would that be at 2.66 ohms? I know i need 4 cabinets to be 600 watts @ 2 ohms (right... i think?)

Thanks to any help you guys can give, you all help me so much all the time

 

[bongomania]

The wattage difference between the 2.67 ohm load you'd have, versus an "ideal" 2 ohms even, would not be audible.

 

[samalope]

How many watts would it be at 2.67 ohms?

 

[Korladis]

Probably 500 something.

 

[samalope]

Thats what i figured but do you know how to do the math for it? I wanna know for future reference

 

[slyjoe]

There is no math for it due to the output stage transistors having voltage/current limiting - it doesn't follow the power calculation with passive components:

Watts = I^2 * ohms, where I is the output current.

 

[samalope]

What unit is I and where can i find that number?

 

[HolmeBass]

You could get a good approximation by plotting your amps watts into 8 ohms, then 4 ohms, and then 2 ohms on a graph- it probably won't be a straight line, as noted- but where the curve crosses 2.7 ohms will be within 10% or so of the actual wattage. As noted already, probably not an audible difference. Also probably not a very big difference, audibly, from 2 Ohms. 2 Ohms would be louder mostly because of the extra speakers / surface area, not the extra wattage. I think you'll be OK with that rig.

 

[samalope]

And 3 cabinets wont damage my head?

 

[slyjoe]

You have 600 Watts at 2 ohms - calculate it. I is amps.

That said, Acoustic doesn't publish any other power ratings. You are out of luck getting a "real" number. However, I'm not sure you need a real number. 2.67 ohms is above the 2 ohm minimum for that amp.

 

[samalope]

Sorry if this is noobish, but are amps constant?

 

[slyjoe]

No - but think of voltage being constant in your case. Then,

Watts = V^2/ohms. This may make it clearer - as the ohms go up, the watts go down.

 

[Korladis]

What do you mean?

 

[samalope]

Yeah i get that general concept, but i just wanted to know how to get a more exact answer. Alright thanks a lot everyone!

 

[slyjoe]

For a first order calculation, use the published specs.

600W*2ohms = V^2. Therefore, the voltage is 34.64 volts.

Now, plug 34.64 volts into the above equation - multiply it by itself and divide by the ohms you are using (2.67).