Teach me about ext cabs

  • Thread starter Thread starter WhiteStrat
  • Start date Start date
WhiteStrat

WhiteStrat

Don't stare at the eye.
Please teach me, that is.

I have a 100 watt combo with 2 12's. It can be run at 4, 8 or 16 ohms. I'd like to try it with another cab (maybe even one I'd build) but I've never done so before, and I don't fully comprehend the "matching" science. Put simply, what do I have to pair up with in order not to blow something (either the amp or the speakers)?

BONUS LIGHTNING ROUND: I also have a Blues Jr--15 watts at 8 ohms into a single 12. Again since I don't understand matching completely, I'm wondering if there'd be a cab that could work on both amps (not at the same time!), so I can see how either of 'em with different speakers.

(BTW, In each case I'm not talking about using the external cab in addition to the existing speaker. I don't need more volume. I'd be unplugging the internal and just using the external--one at a time.)

Thanks for your time!
 
What are the speakers in your combo rated at, and how are they wired?

Daisy chaining a second cab would be series, therefore cutting the ohm rating in half of what the 2 speakers together are currently running.

If your 100 watt is switchable, then get a cab that would suit the ohm rating you need for the blues junior, so you have a cab that works for both.
 
Wow...quick reply, thanks! The speakers in the combo are each 120 watts and 16 ohms. They're wired in parallel.
 
Guitarer said:
What are the speakers in your combo rated at, and how are they wired?

Daisy chaining a second cab would be series, therefore cutting the ohm rating in half of what the 2 speakers together are currently running.

If your 100 watt is switchable, then get a cab that would suit the ohm rating you need for the blues junior, so you have a cab that works for both.
Click to expand...

But if I'm not daisy chaining, but rather just putting the new cab in place of the internal speakers, I just need the same (2 x 120 @ 16ohm) in the external cab?
 
Correct...But don't feel the need to limit speaker choices with such a high wattage. 120 watts between both speakers would be enough, let alone each. Most speaker companies also rate their speakers pretty conservatively, meaning there's a good chance you'd be fine with speakers that are rated to the same exact wattage of your amp...But whether or not you're that much of a risktaker is up to you. I have a friend running 2 Greenbacks (25 each) in a 50 watt, and has dimed it many times with no problems.
 
Guitarer said:
Correct...But don't feel the need to limit speaker choices with such a high wattage. 120 watts between both speakers would be enough, let alone each. Most speaker companies also rate their speakers pretty conservatively, meaning there's a good chance you'd be fine with speakers that are rated to the same exact wattage of your amp...But whether or not you're that much of a risktaker is up to you. I have a friend running 2 Greenbacks (25 each) in a 50 watt, and has dimed it many times with no problems.
Click to expand...

Y'know that's what I was thinking. I don't see any 120 watt 12" speakers out there. I really wanted to try some greenbacks or 30s and they're all much lower wattage.
 
v30s are 60 watts each, you would have no problems at all running those.
 
WhiteStrat said:
Please teach me, that is.

I have a 100 watt combo with 2 12's. It can be run at 4, 8 or 16 ohms. I'd like to try it with another cab (maybe even one I'd build) but I've never done so before, and I don't fully comprehend the "matching" science. Put simply, what do I have to pair up with in order not to blow something (either the amp or the speakers)?

BONUS LIGHTNING ROUND: I also have a Blues Jr--15 watts at 8 ohms into a single 12. Again since I don't understand matching completely, I'm wondering if there'd be a cab that could work on both amps (not at the same time!), so I can see how either of 'em with different speakers.

(BTW, In each case I'm not talking about using the external cab in addition to the existing speaker. I don't need more volume. I'd be unplugging the internal and just using the external--one at a time.)

Thanks for your time!
Click to expand...

Make sure you wire the new speakers in phase with each other as well-if the polarity isn't marked you can use a battery to do so, a 9 volt battery shouldn't harm the speaker. The battery will cause the speaker cone to either thrust forward or backwards-when it thrusts forward the positive pole on the battery will be the positive on the speaker's connector.
When wiring 2 speakers phase is very important so there isn't phase cancellation with the speakers.
 
Yep.... getting an 8 ohm cab would be about the only thing to do if you want to get a cab that works with both amps. You could get a single 8 ohm speaker, or two 16 ohm speakers, or two 4 ohm speakers.... or four 8 ohm speakers... I think those are your options, and then you would have to wire accordingly... The two 16 ohm speakers would have to be wired in parallel to make 8 ohms, the two 4 ohm speakers would have to be wired in series, and then the four 8 ohm speakers get a little strange, because you would have to wire them first in pairs, in series, to make each pair equal 16 ohms. Then you would wire those pairs in parallel to make them a total of 8 ohms.

Fun!

~Shawn
 
eyema_believer said:
and then the four 8 ohm speakers get a little strange, because you would have to wire them first in pairs, in series, to make each pair equal 16 ohms. Then you would wire those pairs in parallel to make them a total of 8 ohms.

Fun!

~Shawn
Click to expand...

Or vise versa.
 
Guitarer, mikemorgan, anfontan, eyema_believer:

Thanks for all your replies guys! And thanks for the docs, Mike! It all makes much more sense to me now. Hard to believe I'm just figuring this out--I've always just plugged into what ever I own. But now with a couple different amps with really different sounds, I'm stoked to broaden their horizons. :)

Thanks again!
 
Anfontan said:
When wiring 2 speakers phase is very important so there isn't phase cancellation with the speakers.
Click to expand...
Wow, thanks - I have a 2x12 slant Sovtek cabinet that I put some new speakers in, and the volume and punch dropped significantly. I think I'll try just swapping the leads on one of the speakers.

Whitestrat - you must be getting like zero speaker overdrive with those 120 watts - I've never seen speakers like that.
 
antichef said:
Whitestrat - you must be getting like zero speaker overdrive with those 120 watts - I've never seen speakers like that.
Click to expand...

Yep--zero! It's a three channel amp: clean, nasty & nastier (the 2 nasty's sound the same to me :confused: I leave one set w/less gain for crunch, one really saturated for lead). Anyway, there is so much headroom in those speakers that I have never, nor will I ever--at 100 watts--get any natural speaker distress out of it.

I'm not complaining, 'casue there's plenty of tones I can dial in, but yeah, 120's up there, huh?
 
antichef said:
Wow, thanks - I have a 2x12 slant Sovtek cabinet that I put some new speakers in, and the volume and punch dropped significantly. I think I'll try just swapping the leads on one of the speakers.

Whitestrat - you must be getting like zero speaker overdrive with those 120 watts - I've never seen speakers like that.
Click to expand...

sovteks are sexy. :cool:
 
Guitarer said:
What are the speakers in your combo rated at, and how are they wired?

Daisy chaining a second cab would be series, therefore cutting the ohm rating in half of what the 2 speakers together are currently running.

If your 100 watt is switchable, then get a cab that would suit the ohm rating you need for the blues junior, so you have a cab that works for both.
Click to expand...

Plugging a second cab into the external jack puts the cab in parallel, not series, but it does halve the impedance, as you say, provided the ext cab is the same impedance as the internal speaker. Connecting spkrs in series doubles the impedance, parallel halves it (again, assuming the same impedance for both).

I have a Blues Jr, and I don't remember it having an ext spkr jack. IIRC the internal spkr is hard wired to the amp with no jacks at all.
 
ggunn said:
Plugging a second cab into the external jack puts the cab in parallel, not series, but it does halve the impedance, as you say, provided the ext cab is the same impedance as the internal speaker. Connecting spkrs in series doubles the impedance, parallel halves it (again, assuming the same impedance for both).

I have a Blues Jr, and I don't remember it having an ext spkr jack. IIRC the internal spkr is hard wired to the amp with no jacks at all.
Click to expand...

Yeah I was confused about Guitarer's comment too. I assume that by "daisy chaining," he meant plugging the 2nd cab into the 1st cab, but then I remembered that this was a combo amp we were talking about.

But yeah, as ggunn said, putting speakers in series will double the resistance, not half it.

Regardless, the OP said that he doesn't want to use both the internal speaker and the ext cab together.
 
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