hey all, I am going to be upgrading my gear from a 15w practice amp to a new 80w amp and cab, but I dont know exactly what I should be looking at in regards to things like ohms and that sort of stuff.

ok so what I would like to know is does the amp and cab need to have the same amount of ohms and what is the difference between 8 and 16 ohms?

oh and also do you have any tips on choosing the right amp and cab, and is there anything else I need to know about amp and cab compatability?

if you guys can help me, i'd be forever in your debt
The Cab and Head should have the same Ohmage. If you use two cabs then they half the wattage. As in two 16ohm cabs make 8ohms overall.

I think a 16ohm cab can work in a 8ohm head but you don't get the full power.
I am doing this in science, not sure how it affects amps though.

Ohms (Theta) is the resistance.
Voltage (V) is the potential difference.
Current (I) is the current size.
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Basic rule of thumb is to never go below the rated Ohm spec for the amp. As resistance(ohms) goes down, current(amps) goes up, and vice versa. If the head is rated for say 8 ohms, then don't go with a 4 ohm cab as you will overheat the amp due to the greater current flow through the circuitry. Either stick with the recommended ohm rating, or go up to a greater number, but never lower. Keep in mind tho that by going to a higher ohm value cab, say from 4 to 8, you'll be cutting back on the amount of overall power going to the cab, so you won't get the full range of sound out of it. In essence, stick with the rated value for the head and you're good to go.
And btw, Imafrog, it's called Ohms Law and works for everything electrical/electronic, from the basic light bulb to the space shuttle. In it's most basic form:
It takes 1 Volt to push 1 Amp through 1 Ohm of resistance.
Last edited by LeftyDave at Apr 27, 2008,
ok im a bit confused now(sorry!)

the amp head Im going for can switch between 4-8-16 ohms so thats alright,

there are are four different cabs I have been reccomended for though two can switch between 4-16 ohms, the others that I do like better are just 8, and just 16 ohms.

when you speak of the overall power, would that mean that 16 ohms would have more power than 4 ohms? or something. like for example if I had them both running on 4 ohms would I be able to crank it and overdrive and have the same volume as a clean soft setting on 16 ohms? i'm assuming 4 ohms is less power = less volume or am i completely wrong?

so in regards to the second two cabs I like which one would you say I go for, the 8 or the 16?
Quote by Imafrog
I am doing this in science, not sure how it affects amps though.

Ohms (Theta) is the resistance.
Voltage (V) is the potential difference.
Current (I) is the current size.

Ohms are represented by omega, not theta. But, yes, you're right.

Basically, you need to get speakers with the amount of resistance that's indicated on the back of the head. Some heads can switch between different ratings, like a lot of Mesas do.

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ok im a bit confused now(sorry!)

the amp head Im going for can switch between 4-8-16 ohms so thats alright,

there are are four different cabs I have been reccomended for though two can switch between 4-16 ohms, the others that I do like better are just 8, and just 16 ohms.

when you speak of the overall power, would that mean that 16 ohms would have more power than 4 ohms? or something. like for example if I had them both running on 4 ohms would I be able to crank it and overdrive and have the same volume as a clean soft setting on 16 ohms? i'm assuming 4 ohms is less power = less volume or am i completely wrong?

Completely wrong! lol. It's a teeter-totter effect. As resistance goes up, current goes down, and as resistance goes down, current goes up. If you use lower like 4, then the available current to the speakers will go up, higher power. Go up to 16 ohms, and then the amps go down, equalling less power to the speakers. Remember, ohms is resistance, not power. Current flow, or Amps, is the actual bit of electricity that is moving, and the higher it is, the more it can do. Got all that so far? lol

so in regards to the second two cabs I like which one would you say I go for, the 8 or the 16?

I'd go with the 8. It's the middle of the road, are pretty common and won't get you into any sort of trouble with the amp. If the amp is switchable between the three choices, no worries anyhow. If you were to go with a 4, then you could theoretically get the same volume level out of that cab at say 5 volume than the 8 would deliver at 10 volume. Although it really doesn't work that way. 4's would be louder at a lower volume. 16's would be softer at the same volume, so you'd have to crank it up to get the same results.

Replies in Red. Long story short, use which ever you like, since the amp is rated for all 3. 8's are your best bet tho. Pretty common like I said.