Magical World of Ohms

[Conroyfootball]

So, does the Ohms of a cab make any difference? 4, 8, 16?

I need to wire my cabs to 8 ohm to fit my amps but I was just wondering if 4 or 16 would be any different.

Rock on.

 

[GuitarStv]

Re: Magical World of Ohms

Amplifiers need to "see" a certain ohm rating in the cab that they're connected to. Using the wrong resistance can lead to a blown amp.

 

[guitarded]

Re: Magical World of Ohms

Amplifiers need to "see" a certain ohm rating in the cab that they're connected to. Using the wrong resistance can lead to a blown amp.

It's OK to mismatch if the load (speaker) is a higher rating than the amp's output jack. You won't achieve maximum power to the load but it will safely work. Going to a lower rated load is a different story. Now you are overdrawing current from your output transformer and everything is going to run hotter, plus you also won't achieve maximum power.

 

[Rich_S]

Re: Magical World of Ohms

WARNING! WARNING! The above is only true for solid-state amplifiers. For tube amps, it's the opposite: if you have to mismatch, it's better to have the speaker impedance lower than the amp's output impedance. A mismatch of 2:1 is not terrible (for example running a 4 ohm speaker on an 8-ohm tube amp). It will probably sound different, but not hurt the amp.

Overall, it's best to just keep them matched.

 

[Pink Unicorn Horsey]

Re: Magical World of Ohms

WARNING! WARNING! The above is only true for solid-state amplifiers. For tube amps, it's the opposite: if you have to mismatch, it's better to have the speaker impedance lower than the amp's output impedance. A mismatch of 2:1 is not terrible (for example running a 4 ohm speaker on an 8-ohm tube amp). It will probably sound different, but not hurt the amp.

Overall, it's best to just keep them matched.

Hmmm...

I thought for tube amps you had to make sure the cab's impedance was at least as great as the amp's output impedance. In other words, you could hook up a 16-ohm cab to an 8-ohm amp output jack (although the sound wouldn't be ideal), but putting something like a 4-ohm cab into the 8-ohm amp output jack would damage the transformers.

Am I misinformed?

- Keith

 

[ErikH]

Re: Magical World of Ohms

See page 2 post #26

When possible, always match anyway.

 

[More-Gear-Than-Skill]

Re: Magical World of Ohms

Oh dear, best we clear this up. Trannies are gonna fry, yo.

 

[Pink Unicorn Horsey]

Re: Magical World of Ohms

No Keith, you're right. Rich has it backwards. You cannot run a lower cabinet load in to a tube amp. 8 or 16 in to an 8 ohm tap, 16 only to a 16 ohm tap. Never go lower. The output tranny will see too much coming back and fry prematurely.

Thought so. Thanks.

 

[YJM_Rocks]

Re: Magical World of Ohms

A good rule is to match amp impedance to cab impedance. If they mismatch, get it rewired or whatever you gotta do.

 

[guitarded]

Re: Magical World of Ohms

That's just soo wrong man........ Now I know who NOT to buy a tube amp from on ebay

Solid State is more robust, but the same principle is true for both. Safest thiing to do is NOT mismatch at all!

WARNING! WARNING! The above is only true for solid-state amplifiers. For tube amps, it's the opposite: if you have to mismatch, it's better to have the speaker impedance lower than the amp's output impedance. A mismatch of 2:1 is not terrible (for example running a 4 ohm speaker on an 8-ohm tube amp). It will probably sound different, but not hurt the amp.

Overall, it's best to just keep them matched.

 

[Conroyfootball]

Re: Magical World of Ohms

OK. Is there a TONE difference in 4, 8, or 16 ohm cabs in a perfect world where the amp matches the cab.

Rock on.

 

[MikeS]

Re: Magical World of Ohms

It doesn't matter the makeup (SS or tube/guitar or audio) if you have to mismatch impedance, go higher. Your output will suffer, but that sure beats frying an output transformer.

An amp should tell you somewhere on the chassis what minimum load it is stable at. If not on the chassis, check the owner's manual. It could even be imprinted on the output transformer.

If it's a 4x12 cabinet you can't change the wiring and go from 4 or 16 ohm to 8 ohm with the same speakers.

 

[Pink Unicorn Horsey]

Re: Magical World of Ohms

OK. Is there a TONE difference in 4, 8, or 16 ohm cabs in a perfect world where the amp matches the cab.

Rock on.

I think the tonal difference would be more a function of which make and model of speaker you're using, and that the impedance is just a result of whatever combination you decide upon.

What's the impetus driving your question?

- Keith

 

[guitarded]

Re: Magical World of Ohms

You can change the impedance up (series) or down (parallel) by adding an extension Cabinet in series or parallel.

If it's a 4x12 cabinet you can't change the wiring and go from 4 or 16 ohm to 8 ohm with the same speakers.

 

[Pink Unicorn Horsey]

Re: Magical World of Ohms

I'm guessing Mike S meant to type "can" rather than "can't."

 

[MikeS]

Re: Magical World of Ohms

True, but I'm talking about a single cabinet.

Why pull everything apart in an attempt to rewire if rewiring will accomplish nothing?

And I meant can't. The impedance of a cabinet can be changed, but (4) four ohm speakers cannot be wired to a total load of 8 ohms... 1, 4, and 16 would be your conventional wirings with (4) four ohm loads.

 

[guitarded]

Re: Magical World of Ohms

If you are not getting maximum power (impedance mismatch), you will lose some of your tone. Same goes for pedals or anything where there is a large mismatch. And a large mismatch means a ratio not just a large number. With the speaker conversation 2:1 is a major difference even though it is just 4 ohms in absolutes.

I think the tonal difference would be more a function of which make and model of speaker you're using, and that the impedance is just a result of whatever combination you decide upon.

What's the impetus driving your question?

- Keith

 

[guitarded]

Re: Magical World of Ohms

Not sure...... I thought he meant you can't without rewiring the cabinet or changing the speakers. That is the way I read it, but attention to written detail has never been one of my strong points either.

I'm guessing Mike S meant to type "can" rather than "can't."

 

[ErikH]

Re: Magical World of Ohms

No, Mike is right.

You cannot make a 4 ohm or 16 ohm 4x12 in to an 8 ohm 4x12 utilizing all 4 existing speakers. The best you'll get is 2 of them wired in series (2x4 ohms) or parallel (2x16 ohms) to get the 8 ohms, leaving 2 speakers not working.

You'd have to replace all 4 speakers to the proper impedence and wire up the cab as it was, which is series/parallel.

-OR-

Deal with having 2 speakers not working.

-OR-

Wire up to go from mono (4 or 16 ohms) to stereo (8 ohms per side) mode like the Marshall JCM 900 cabs. You still can only run one side at a time though with one amp from an 8 ohm tap.

Remember, two speaker outs are most often wired in parallel on an amp. So, you could set your amp to 4 ohms and run both speaker outs to a 4x12 wired like the mono/stereo option above and be fine, so long as each side of the cab is 8 ohms.

 

[Pink Unicorn Horsey]

Re: Magical World of Ohms

Not sure...... I thought he meant you can't without rewiring the cabinet or changing the speakers. That is the way I read it, but attention to written detail has never been one of my strong points either.

I guess I misinterpreted what he was saying, too.