Looking for clarification on ohms...

[Magyar_Music]

Hey guys,
I know this has likely been discussed at length, but whenever I search for new threads on the topic I get bogged down in technical details.
Here's my question...

Amp (4 ohm) + cab (4 ohm) = OK
Amp (4 ohm) + cab (8 ohm) = OK (but decreased pushing power)
Amp (4 ohm) + 2 cabs (4 ohms each) = 2 ohm = bad?
Amp (4 ohm) + 2 cabs (8 ohms each) = 4 ohm = OK?

Thanks in advance! I'm downsizing my rig, but I don't want to limit it should I need to add a cab in the future.

Essentially, I have a 500W 4 ohm amp, and am looking at a 210, but might want to add a 115 or another 210 or 212 in the future, should I get an 8 ohm cab?

MANY, MANY THANKS!

 

[KJung]

You are correct, except that your 'bad' comment for the 2ohm situation depends on the minimum safe operating impedance of the solid state head (some are fine with 2 4ohm cabs or a 4ohm and 8ohm, which result in a nominal impedance of approximately 2.67 ohms). However, in your case, with your 4ohm minimum head, you are right.

In most cases, a small cab (like a 112 or 210 or most 115's) can't make use of that much power (even if it has a high thermal power rating), so 8ohm would be the smart choice with your amp. You won't notice much difference between the 4ohm and 8ohm version, and it will allow you to safely add a second cab in the future.

If, on the other hand, you have a moderately powered head (300-500 watts at 4ohms) and are considering one large cab like a 410 or 212, 4ohm is probably the best bet, assuming you will only use a single cab. You will, with most large cabs, notice a slight increase in volume, but more importantly, less compression from the head and a more even, open low end.

 

[Magyar_Music]

You are correct, except that your 'bad' comment for the 2ohm situation depends on the minimum safe operating impedance of the solid state head (some are fine with 2 4ohm cabs or a 4ohm and 8ohm, which result in a nominal impedance of approximately 2.67 ohms). However, in your case, with your 4ohm minimum head, you are right.

In most cases, a small cab (like a 112 or 210 or most 115's) can't make use of that much power (even if it has a high thermal power rating), so 8ohm would be the smart choice with your amp. You won't notice much difference between the 4ohm and 8ohm version, and it will allow you to safely add a second cab in the future.

If, on the other hand, you have a moderately powered head (300-500 watts at 4ohms) and are considering one large cab like a 410 or 212, 4ohm is probably the best bet, assuming you will only use a single cab. You will, with most large cabs, notice a slight increase in volume, but more importantly, less compression from the head and a more even, open low end.

Thanks KJung!
So, if I end up wanting to hook up two cabs in a "daisy chain" to my 4 ohm amp, they should be 2 8 ohm cabs?
Cheers!

 

[KJung]

Thanks KJung!
So, if I end up wanting to hook up two cabs in a "daisy chain" to my 4 ohm amp, they should be 2 8 ohm cabs?
Cheers!

Correct. And, hooking them up using two outputs from the amp, or one output from the amp and then connecting one cab to the other results in the same exact thing.

Another thing to think about is that it is usually the safest bet to add a second cab that is identical to the first. By 'safest bet' I mean that you will get 'more of what you are used to with the single cab', more meaning deeper low end and a lot more volume (since you are almost doubling the power AND doubling the cone area).

So, if you buy an 8ohm 210, the 'simple' choice would be to eventually buy a second identical cab, giving you a modular 4ohm 410!

 

[okcrum]

Word, KJung. I increasingly use one or two 8 ohm 2x10s stacked on end with a PF-500 Ampeg, and the rig kills. Modular is the way to go, and 8 ohm cabs fit that best. I also have a pair of 8 ohm 1x15s so I have a lot of combinations possible.

Out of curiosity, Magyar, what head are you using?

 

[Magyar_Music]

Correct. And, hooking them up using two outputs from the amp, or one output from the amp and then connecting one cab to the other results in the same exact thing.

Another thing to think about is that it is usually the safest bet to add a second cab that is identical to the first. By 'safest bet' I mean that you will get 'more of what you are used to with the single cab', more meaning deeper low end and a lot more volume (since you are almost doubling the power AND doubling the cone area).

So, if you buy an 8ohm 210, the 'simple' choice would be to eventually buy a second identical cab, giving you a modular 4ohm 410!

THANKS SO MUCH! Cheers!