Speakers with ohms mismatch in same 2x12?

[smogfalls]

Hi guys, I have a question...

I have a lovely old JCM800 4010 1x12 combo, and I picked up an older JMP 2x12 combo chassis, with the intention of mounting my JCM800 in there and wiring up 2 speakers rather than 1.
I have the following 2 speakers available for the job... Scumback M75-LHDC and the original Celestion G12T-75...

Problem is... Scumback is 8ohms, Celestion is 16ohms. Is there anyway I can still go ahead and use these 2 together? And if so, how should I wire them and also which setting do I turn the amps' ohms' selector switch to?

Thanks so much,
Xan

 

[Micky]

If it was me, I wouldn't do it.
I would NEVER risk the damage to my amp going over or under with impedance match.
Best to ALWAYS match impedance.

I would get rid of the Celestion, unless you are married to it...

 

[smogfalls]

If it was me, I wouldn't do it.
I would NEVER risk the damage to my amp going over or under with impedance match.
Best to ALWAYS match impedance.

I would get rid of the Celestion, unless you are married to it...

Thanks for the advice mate, yeah I don't want to risk any serious damage... I just wasn't entirely sure of the risks.

I'm actually quite fond of the celestion, but obviously I can pick one up rated at 8ohms also to match with the Scumback. In doing that, how would be best to wire them? Series or Parallel? And what would be the total ohms in each scenario?

Thanks again,
Xan

 

[poeman33]

Maybe try and trade one of them, so you can end up with two of the same ohms?

 

[Micky]

2x8 ohms in series/paralell = 8 ohms

2x8 ohms in paralell = 4 Ohms

In a 2 speaker layout there is no series/parallel wiring.
Only series - (8+8=16) or Parallel (8/2=4)
So it depends on the output of your amp.
What outputs does your amp have? 4&8? If so then Parallel into the 4-ohm output.
8&16? If so then series into the 16-ohm output. 4/8/16? Then either way you want, into the appropriate output.

 

[Micky]

Thanks for correcting me, Micky!

I'm still learning...

You will get there. No problem. I just hate when mis-information gets taken as gospel. This is why it is important to SHOW the calculations and EXPLAIN the differences when helping others.

I know I fall victim to just wanting to say 'Use the SEARCH feature fucknuts!' alot of the time, but many are new here and don't rely on the search function like they should. The search here is actually pretty good, but you need more than three letters to search effectively. A lot of times looking for ohms or JVM, or JMP will deliver far too many results.

Rather than scare a lot of people away, it is best just to help them then educate them.

 

[smogfalls]

Thanks for the help and quick replies dudes, tis' very helpful indeed. I did search around the interwebz, and didn't find anything that seemed to answer my specific questions.
Thanks again,
Xan

 

[Adwex]

In a 2 speaker layout there is no series/parallel wiring.
Only series - (8+8=16) or Parallel (8/2=4)
So it depends on the output of your amp.
What outputs does your amp have? 4&8? If so then Parallel into the 4-ohm output.
8&16? If so then series into the 16-ohm output. 4/8/16? Then either way you want, into the appropriate output.

Micky speaks wisely.

 

[JohnH]

Apart from impedance mismatch issues, the other practical problem is that if you combine 8 and 16, in parallel, the 8 Ohm driver will produce 2/3 of the power and the 16, only 1/3.

Much better to change one of them.

 

[Marshallhead]

Yes, and note also that Micky's formulae only work when both speakers are the same impedance.

To calculate overall impedance of any mixture of speakers, then:

For a series, it's simply R1 + R2 + R3 (etc) = Rtotal where R is the impedance of each speaker. You just add the total of all the speakers together.

For parallel linked speakers, it's 1/R1 + 1/R2 + 1/R3 (etc) = 1/Rtotal. For example a 16 and two 8's all in parallel would be 5/16, giving 3.2 ohms total, because you have 1/16 plus 1/8 (aka 2/16) x 2.

If you then apply V= I x R, (volts = current in amps times resistance in ohms) and watts = volts x amps, you can then figure out how the output power is distributed among the speakers in the array, and why mixing impedances causes the power to be distributed unevenly.

Once you've learned that, you can then learn that capacitor networks work the opposite way, i.e. Caps in parallel = sum their values, caps in series, do the 1/C1, +1/C2 etc calculation.

 

[GIBSON67]

Sell the Celestion and get another Scumback, or sell the Scumback and get another Celestion and probably some cash back, too.