Two 8ohm cabs with one 4ohm cab?

[thedudebrah]

I've searched and read the FAQ and have found mixed information on this, so I'm here starting my own thread. Plus, my brain hurts when I even look at the equation, so I need my hand held.

The amp in question is an SVT-VR, capable of handling 2ohm, which is how I use it now with two 8x10s.

I have a single ported 4ohm Carvin 2x10 that I've paired with the SVT at 4ohm in the past. Great success.

I recently bought two 8ohm SVT-AV 2x10 cabs to pair with the SVT and make my rig a little lighter and more modular. This combination also sounds great.

I'd like to use all 3 cabs with the SVT if possible. If I understand my findings correctly, the 4ohm cab will be getting a little more "power" than the two 8ohm cabs. The part I'm not certain about is what the total load will actually be. I recall reading a number of 2.6-something, which the SVT should be able to handle?

I'm also unsure if speaker cable routing makes a difference here. Should it be:
Amp speaker output 1>4ohm 210>8ohm 210>8ohm 210

-or-
Speaker output 1>4ohm 210
Speaker output 2>8ohm 210>8ohm210

My reasoning here is based on the modularity of the 2x10s since the fridge doesn't fit in my car and I don't want to drive my truck JUST to take a fridge out. If it's a horrible idea, I'll just stick with one pair or the single Carvin cab.

 

[rickdog]

With the three cabinets wired in parallel, the load will be 2 ohms. Figure it like this: two 8 ohm cabinets in parallel make a 4 ohm load. Putting that in parallel with another 4 ohm load makes 2 ohms. Easy.

The 4 ohm cab will get half of the power. The two 8 ohm cabs will split the other half of the power, so each will get a quarter of the power. Since you didn't blow up the 4 ohm cab by itself, you probably won't hurt it when it gets only half the power. Same thing for the two 8 ohm cabs.

The Carvin cab and the two Ampeg cabs are probably voiced quite differently. They may or may not work well together. Test them to make sure they have the same polarity, or they may cancel out the low end.

 

[thedudebrah]

With the three cabinets wired in parallel, the load will be 2 ohms. Figure it like this: two 8 ohm cabinets in parallel make a 4 ohm load. Putting that in parallel with another 4 ohm load makes 2 ohms. Easy.

The 4 ohm cab will get half of the power. The two 8 ohm cabs will split the other half of the power, so each will get a quarter of the power. Since you didn't blow up the 4 ohm cab by itself, you probably won't hurt it when it gets only half the power. Same thing for the two 8 ohm cabs.

The Carvin cab and the two Ampeg cabs are probably voiced quite differently. They may or may not work well together. Test them to make sure they have the same polarity, or they may cancel out the low end.

Perfect, thank you for explaining it in simple terms for me lol. It'll get the basement test before I bring it out to a gig!

 

[jeff62]

Does your SVT-VR support a 2 ohm load? Unless it’s different that a regular SVT, which support a 4 ohm load, it does not. Playing at 2 ohms will fry your SVT-VR unless a 2 ohm load is supported.

 

[Mark Reccord]

Does your SVT-VR support a 2 ohm load? Unless it’s different that a regular SVT, which support a 4 ohm load, it does not. Playing at 2 ohms will fry your SVT-VR unless a 2 ohm load is supported.

Every all tube SVT has a 2 Ohm tap on the output transformer, so 2 Ohms isn't a problem for any of them. Some of the solid state ones are limited to 4 Ohms minimum (like the 3-Pro and 4-Pro) but all of the tube ones are good for 2 Ohms.

On the VR, it doesn't matter how you wire the cabinets as long as the impedance switch is set at 2 Ohms (it's electrically equivalent), but I'd be inclined to run one cable out to the 2 8 Ohm boxes and jump them and one out to the 4 Ohm one.

 

[thedudebrah]

Does your SVT-VR support a 2 ohm load? Unless it’s different that a regular SVT, which support a 4 ohm load, it does not. Playing at 2 ohms will fry your SVT-VR unless a 2 ohm load is supported.

Yes it does, as stated in the original post. There's a 2/4ohm switch on the back and I use it appropriately when I'm playing with cab setups.