• From: Detroit
  • Registered: 2006-06-02
  • Posts: 5,807

Topic: wiring an amp cabinet

I need some input on wiring speakers into a 4x12 cabinet...

1.The amp driving it is a 55 watt Rivera amp with two 8 ohm outputs.
2.The speakers I'm using are Celestion Vintage 30 16 ohm

SHOULD I:

A)
Use 2 Speaker jacks = Parallel Wiring; In Phase where
2x12 16 ohm loads - total load = 8 ohms
2x12 16 ohm loads - total load = 8 ohms

or

B)
Use 1 Speaker jack = 4 Speakers - Series/Parallel Wiring; In Phase where
4x12 16 ohm loads - total load = 16 ohms

From what I hear, an amp that outputs at 8 ohms can drive a 16 ohm cabinet... but I'm looking for a best situation.

- Nic from Detroit... posting on JB's Forum since 6-2-2006
Ask me about my handwound Great Lakes Guitar Pickups
Since 2010, Bonamassa fans have taken advantage of my JB friend discount = my cost + shipping. cool

2 Reply by Sonicboom (edited by Sonicboom 2010-09-24 02:22:53)

  • Registered: 2010-07-09
  • Posts: 122

Re: wiring an amp cabinet

First, what does Rivera say about the output impedance of the amp when running two cabs in parallel?  Normally, they will act like speakers in parallel.  So, with two 2x12s at 8 ohms in parallel, your amp will see 4 ohms - not 8.  This means in that config. you'd need to set the impedance selector on the amp (assuming it has one) to 4 ohms to get max. efficiency and power out.

Ideally, you want to match the speaker load with the output transformer impedance on the amp - this delivers the most power and is the easiest on the amp.  However, you can run them mismatched with a slight reduction in output.  I would not run them mismatched by more than one step - don't run the amp at 4 ohms when the speakers are 16 ohms or vice versa.  The reason is that mismatched impedance causes power to be reflected back to the amp - it is not all delivered to the speakers.  The reflected power creates heat and is hard on the tubes and output transformer.  In extreme cases, it can lead to early failure of either.

Being a Joe B. forum, I would run them as two 2x12s.  This gives you the option of running a second amp into the other pair.  Again, in either case that you mention you are only mismatched by one step, so you should be fine.

EDIT: An assumption I'm making is that the amp does not have two 8 ohm taps on the output transformer which would mean that it could drive two 8 ohm cabinets independently without a change in the amp's output impedance.

Guitars: '79 LP Custom, '01 Dickey Betts Goldie - 80 of 114, '00 Chandler Lectraslide
Amps: '00 Marshall 1987x, '70 Marshall 1959 SL, 4x12 JBL D120s
'64 Vibroverb - JBL D130, '66 Super Reverb - CTS Alnicos
'77 Peavey Deuce (great for melting stubborn ear wax)
  • From: York, PA
  • Registered: 2010-08-27
  • Posts: 1,749

Re: wiring an amp cabinet

I would go with the 2 2x12 approach based on versatility.  I wired one of my 4X12 cabs that way so I could use a second head or sometimes I just use both jacks and 1 head.

And not to insult your intelligence!, maybe you already know this, but I would also recommend putting some newspaper over the back of the speaker BEFORE you solder to avoid any bits of solder from falling down into the speaker.  Or if you're using wire end connectors disreguard!
-Seth

  • From: Detroit
  • Registered: 2006-06-02
  • Posts: 5,807

Re: wiring an amp cabinet

Great insight there!

Yeah, each speaker output on the back is 8 ohms each...
I'm thinking of going the two 2x12's myself.

- Nic from Detroit... posting on JB's Forum since 6-2-2006
Ask me about my handwound Great Lakes Guitar Pickups
Since 2010, Bonamassa fans have taken advantage of my JB friend discount = my cost + shipping. cool
  • RickB
  • RickB
  • BONAMEGAMETAL
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  • From: San Diego
  • Registered: 2009-10-30
  • Posts: 12,198

Re: wiring an amp cabinet

2X12 would be the best.
If rewiring, make sure that all speakers are matched as to power sharing.
Electronically as a rule, it is always better to mismatch high than low. That will eliminate possible overload damage to the output stage of the amps.
Rick

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  • From: Detroit
  • Registered: 2006-06-02
  • Posts: 5,807

Re: wiring an amp cabinet

RickB wrote:

2X12 would be the best.
make sure that all speakers are matched as to power sharing.

Rick

what do you mean by this?

- Nic from Detroit... posting on JB's Forum since 6-2-2006
Ask me about my handwound Great Lakes Guitar Pickups
Since 2010, Bonamassa fans have taken advantage of my JB friend discount = my cost + shipping. cool
  • RickB
  • RickB
  • BONAMEGAMETAL
  • Offline
  • From: San Diego
  • Registered: 2009-10-30
  • Posts: 12,198

Re: wiring an amp cabinet

NPB_EST.1979 wrote:
RickB wrote:

2X12 would be the best.
make sure that all speakers are matched as to power sharing.

Rick

what do you mean by this?

If you wire series parallel to achieve the match, all speakers must have the same rating so the sound pressure is evenly distributed. Sorry for the confusion.

Free download from Vienna! http://mbsy.co/bNLR
Lots of unique videos of Joe http://www.youtube.com/watch?v=cwd5vL8fXTw
Buy Joe's merchandise here. http://www.jbonamassa.com/affiliates/id … hp?id=1381

RickB's Website

  • Registered: 2010-07-09
  • Posts: 122

Re: wiring an amp cabinet

Good point.  In this case he should be clear since he is using all the same speakers with the same impedance.  Which brings up an idea - mix the speaker pairs.  One 2x12 could be for the British sound and the other could be alnicos.

Guitars: '79 LP Custom, '01 Dickey Betts Goldie - 80 of 114, '00 Chandler Lectraslide
Amps: '00 Marshall 1987x, '70 Marshall 1959 SL, 4x12 JBL D120s
'64 Vibroverb - JBL D130, '66 Super Reverb - CTS Alnicos
'77 Peavey Deuce (great for melting stubborn ear wax)