Speaker Ohm ratings

[tot_Ou_tard]

Following Tone's lead I am starting a new thread about impedance.

Spud suggested having a 2x12 cab wired in stereo to allow the flexibility to use one head per speaker. Sounds mondo cool to me!

I wrote to Avatar and asked about this, but I am confused about impedance. It seem that an 8 Ohm 2x12 stero cab is wired in parallel so that one gets 8 Ohms at each input and 4 Ohms if using it as a mono cab.

What am I supposed to do if I want the flexibility to do *both*??

[Plank_Spanker]

That makes sense - each speaker is 8 ohms and paralleled together for a 4 ohm load in mono - "Ohm's Law" in action . What's the rated output impedance of your amp(s)?

What do you mean by "doing both"? Having the capability of running mono if you want, stereo if you want?

Just about any amp can live with a 50 percent impedance mismatch, as long as you don't exceed minimum impedance ratings for a SS amp.

[Tone2TheBone]

A pair of 16 ohm speakers wired parallel becomes an 8 ohm load. (duh) whilst 4 - 16 ohm speakers in a 4x12 cabinet are wired series/parallel which end up again at 16ohms. Why I said this I dunno...

You're asking how you can make 2 - 12 inch speakers both stereo and mono? Maybe jumpers with jacks wired to the speakers so that all you have to do is select which way you want to run the cab? Is that what youz is askin'?

[Plank_Spanker]

A pair of 16 ohm speakers wired parallel becomes an 8 ohm load. (duh) whilst 4 - 16 ohm speakers in a 4x12 cabinet are wired series/parallel which end up again at 16ohms. Why I said this I dunno...

You're asking how you can make 2 - 12 inch speakers both stereo and mono? Maybe jumpers with jacks wired to the speakers so that all you have to do is select which way you want to run the cab? Is that what youz is askin'?

You're either going to run the cab stereo or mono in one sitting. You won't be at the back of the cab switching jacks between songs - unless..........

[Tone2TheBone]

Plank - Isn't there a slick way he could already have say a 2x12 cab hardwired with female jacks that would allow plugging in for stereo operation or mono operation? Sure he'd have to stop playing and physically plug in...but it would be cool to have a cab that lets you do this. Don't they already make some like this that he could copy or even buy?

[Plank_Spanker]

Plank - Isn't there a slick way he could already have say a 2x12 cab hardwired with female jacks that would allow plugging in for stereo operation or mono operation? Sure he'd have to stop playing and physically plug in...but it would be cool to have a cab that lets you do this. Don't they already make some like this that he could copy or even buy?

My Mesa 4x12 is wired for that. It has four jacks -two stereo at 4 ohms, one mono at 8 ohms, and one to daisy chain to another cab. I can plug in 4 ohms stereo, switch plugs for 8 ohms mono, or daisy chain another cab. It just involves wiring separate input jacks.

[Tone2TheBone]

My Mesa 4x12 is wired for that. It has four jacks -two stereo at 4 ohms, one mono at 8 ohms, and one to daisy chain to another cab. I can plug in 4 ohms stereo, switch plugs for 8 ohms mono, or daisy chain another cab. It just involves wiring separate input jacks.

There you go ToT. Something like this would be pretty cool I think.

[tot_Ou_tard]

That makes sense - each speaker is 8 ohms and paralleled together for a 4 ohm load in mono - "Ohm's Law" in action . What's the rated output impedance of your amp(s)?

The AD30VT has an 8 Ohm output. My "future" Valve Junior head has 4, 8, & 16 Ohm outs.

What do you mean by "doing both"? Having the capability of running mono if you want, stereo if you want?

'xactly that.

Just about any amp can live with a 50 percent impedance mismatch, as long as you don't exceed minimum impedance ratings for a SS amp.

That phrase has got me boggled.

Don't exceed minimum?

Shouldn't one not go below the minimum, nor *exceed the maximum*. You know, kind'a like as a definition?

[tot_Ou_tard]

There you go ToT. Something like this would be pretty cool I think.

It'd certainly be cool. It'd require extra wiring on my part.


I'm still a little confused about what I should order to have the maximum flexibility.

[Plank_Spanker]

Tot,

I haven't figured out how to work multiple quotes in one reply here, but.................

Your AD30VT has an 8 ohm output.

Your future Valve Junior is selectable to 8 ohms.

You're golden for a cab rated at 8 ohms - stereo.

As far as the impedance mismatch goes, I should have said "never go below the rated minimum impedance of a SS amp" - too many years talking tech to tech. It's bad juju that can fry the amp.

[tot_Ou_tard]

Tot,

I haven't figured out how to work multiple quotes in one reply here, but.................

Your AD30VT has an 8 ohm output.

Your future Valve Junior is selectable to 8 ohms.

You're golden for a cab rated at 8 ohms - stereo.

As far as the impedance mismatch goes, I should have said "never go below the rated minimum impedance of a SS amp" - too many years talking tech to tech. It's bad juju that can fry the amp.

Thanks Spanky!

Just so I have it clear. You are saying that if I run the 8 Ohm stereo as mono (ie at 4 Ohms) it'll be alright? That sounds t'me me like entering bad jujuville. Or have I twisted it all around again?

I guess that my question is:

For my AD30VT I know that 8 Ohms is OK (that is its output rating).

Is 4 Ohms fine or bad jujitzu?
Is 16 Ohm bad cahones or fine n' dandy?

Sorry for being so dense.

[Plank_Spanker]

Thanks Spanky!

Just so I have it clear. You are saying that if I run the 8 Ohm stereo as mono (ie at 4 Ohms) it'll be alright? That sounds t'me me like entering bad jujuville. Or have I twisted it all around again?

You should be quite safe running mono at 4 ohms. You can select it on the Valve Junior, and the Vox shouldn't have a problem with it.

[tot_Ou_tard]

You should be quite safe running mono at 4 ohms. You can select it on the Valve Junior, and the Vox shouldn't have a problem with it.

Wow! Thanks Planky.

So what kind of tonal differences do you get running an 8 Ohm amp into 4 Ohm versus an 8 Ohm cab?

[Plank_Spanker]

Wow! Thanks Planky.

So what kind of tonal differences do you get running an 8 Ohm amp into 4 Ohm versus an 8 Ohm cab?

You probably won't hear much of a difference in tone.

[tot_Ou_tard]

You probably won't hear much of a difference in tone.

Fantastic. Thanks again.

[Plank_Spanker]

So,

What cab is going to be?