Two cabs = less tone?

[amiller]

I've got two 4X12 (16 ohm) cabs set up in my studio. One of the cabs is in the ISO room and another is in the control room. I only mic the cab in the ISO room and use the cab in the control room so that I can interact with it and the guitar (hate headphones.) Unless I'm recording, I only have the cab in the control room hooked up...for writing and just jam'n.

I was jam'n last night and noticed that my tone sounded thin and small. I did some tweaking on the amp but couldn't get things happening. Then I remembered that I had both cabs still hooked up. I unplugged the ISO cab and WOW my tone came back big time.

What's up with dat? How do I use two cabs like this and keep the tone the same?

 

[blackba]

What amp are you using?

Are you sure you are matching the impedance on the head with the load? I know I like my bassman better with a 4ohm load as it was intended than through an 8ohm load....

 

[amiller]

The amp is an XTC. It has two speaker outs set at 16 ohms.

 

[Jordon]

If you have 2 16 ohm cabs running together, then the impedance selector (rotary switch on the XTC, just like the Uber, right?) should be set at 8 ohms. You're definitely gonna have some odd results if you're running 2 16 ohm cabs into an amp set to 16 ohms.

Remeber this:
1 16ohm cab = set the amp to 16ohms
2 16ohm cabs = set the amp to 8ohms
1 8ohm cab = set the amp to 8ohms
2 8ohm cabs = set the amp to 4ohms
1 4ohm cab = set the amp to 4ohms

Don't run 4 16ohm cabs or 2 4ohm cabs!

 

[degenaro]

What Ziel said, that's because you have an impedance mismatch...with 2 cabs you're running 16 into 8, with one it's matched...16 into 16.

 

[Jordon]

What Ziel said, that's because you have an impedance mismatch...with 2 cabs you're running 16 into 8, with one it's matched...16 into 16.

Ha, glad I got that right, Ed!

-Jordon

 

[D-Rock]

Yeah, I run my two 8 ohm cabs together at 4 ohms and it sounds great.

I would say you might be having an ohm discrepancy.

 

[amiller]

Hmmm...I'll switch the ohms tonight...seems odd that it would be that big of a difference.

 

[Jordon]

Hmmm...I'll switch the ohms tonight...seems odd that it would be that big of a difference.

You're putting an improper load on the transformer, there's gonna be all sorts of odd effects...not to mention a possible transformer blowout.

 

[degenaro]

Could the two cabs be out of phase with each other?

They always could, but it's unlikely. Especially seeing that he's running an unsafe impedance mismatch.

 

[degenaro]

Hmmm...I'll switch the ohms tonight...seems odd that it would be that big of a difference.

Oy-vey...dude, it may seem odd to you, but running a 8 ohm load (2 16 ohm cabs) with the head at 16 ohm is a big no-no.

 

[messenger]

Can you run an 8 and a 16 together? If so what would you set it to?

 

[degenaro]

Can you run an 8 and a 16 together? If so what would you set it to?

Yes, it'll be a 5.33 impedance, set the amp to 4 ohm, the 8 ohm load will get 2/3 of the signal.

 

[amiller]

Hmmm...I'll switch the ohms tonight...seems odd that it would be that big of a difference.

Oy-vey...dude, it may seem odd to you, but running a 8 ohm load (2 16 ohm cabs) with the head at 16 ohm is a big no-no.

Yeah, I know you can't run a head at 16 ohms into speakers combined to 8 ohms. But, these are two seperate speaker outs on the XTC...so, are the XTC's speaker outs wired in parallel, series or is there something on the speakers outs that matches the ohms...I really don't know that's where my confusion comes from.

 

[degenaro]

Hmmm...I'll switch the ohms tonight...seems odd that it would be that big of a difference.

Oy-vey...dude, it may seem odd to you, but running a 8 ohm load (2 16 ohm cabs) with the head at 16 ohm is a big no-no.

Yeah, I know you can't run a head at 16 ohms into speakers combined to 8 ohms. But, these are two seperate speaker outs on the XTC...so, are the XTC's speaker outs wired in parallel, series or is there something on the speakers outs that matches the ohms...I really don't know that's where my confusion comes from.

To my knowledge ALL speaker jacks on amps out there are in parallel. You have an impedance selector like this, right?

 

[amiller]

To my knowledge ALL speaker jacks on amps out there are in parallel. You have an impedance selector like this, right?
quote]

Yes, and the manual tells me to set it to 8 ohms if I set the amp to 1/2 power. However, the manual doesn't mention anything about the ohm selector if I add a second cab via the second speaker out. Having said that, I will definitely err on the side of caution and set the amp to 8 ohms when I connect the second cab.

 

[blackba]

To my knowledge ALL speaker jacks on amps out there are in parallel. You have an impedance selector like this, right?
quote]

Yes, and the manual tells me to set it to 8 ohms if I set the amp to 1/2 power. However, the manual doesn't mention anything about the ohm selector if I add a second cab via the second speaker out. Having said that, I will definitely err on the side of caution and set the amp to 8 ohms when I connect the second cab.

All the amps I have seen with a impedance selector knob or switch have the outputs in parallel. So yes set the impedance to 8ohms when using the 2 cabs and 16ohms when using one. Report back if this fixes the issue.....

 

[degenaro]

To my knowledge ALL speaker jacks on amps out there are in parallel. You have an impedance selector like this, right?
quote]

Yes, and the manual tells me to set it to 8 ohms if I set the amp to 1/2 power. However, the manual doesn't mention anything about the ohm selector if I add a second cab via the second speaker out. Having said that, I will definitely err on the side of caution and set the amp to 8 ohms when I connect the second cab.

Well two speaker jacks and one impedance selector mosdef wants to be set to 8 ohm for 2 16 ohm cabs.
I rememember an XTC that had two impedance selectors, one for each jack or somthing like that. Wanted to make sure that isn't what you had going on.

 

['63-Strat]

Amiller,

Definitely set it to 8ohms if you have 2 16ohm cabs plugged in man.

 

[amiller]

OK, I experimented a little with the ohm settings tonight. You guys are SPOT on!!! The tone is much better when the ohms are matched correctly...safer too!!!

I still notice a difference in the tone when using two cabs vs one and I ensure that the ohms are set properly. One cab with ohms set to 16 sounds brighter and more urgent. Two cabs with ohms set at 8 sound smoother and a little more musical. 'Nice to know when looking for a certain tone.

Anyway, BIG thanks everyone...better tone and maybe I won't blow my amp up...at least not because of an ohm mismatch.