OK, so this whole OHM thing just rattles my already jiggling gray matter.  
 
I have a vintage 2x15 guitar cabinet that I am putting two brand new Eminance speakers into.  The speakers are 8 ohms each.
 
The settings on my guitar amplifier are 4 or 8 ohms.
 
Which setting do I use on my amplifier so I don't blow the darn thing?!  My guess would be 8, and if you tell me I'm wrong, I'm glad I asked!!!
 
I think the wiring (series vs. parallel) have to do with it as well?  I will tell you right now, that there is a single plug with two cables coming from it that each wire into a respective speaker.  So I don't think it is wired in series?
 
OK, that's all I have!  Let the education begin, and thanks in advance! 

spindlebox

 
...I have a vintage 2x15 guitar cabinet that I am putting two brand new Eminance speakers into.  The speakers are 8 ohms each.
 
The settings on my guitar amplifier are 4 or 8 ohms.
 
Which setting do I use on my amplifier so I don't blow the darn thing?!  My guess would be 8, and if you tell me I'm wrong, I'm glad I asked!!!
 
I think the wiring (series vs. parallel) have to do with it as well?  I will tell you right now, that there is a single plug with two cables coming from it that each wire into a respective speaker.  So I don't think it is wired in series?
 
OK, that's all I have!  Let the education begin, and thanks in advance! 

1. If you had only one speaker, you would use the 8 ohm setting to match the impedance of the speaker.
2. If you use two 8 Ohm speakers in parallel (one connection from the amplifier goes to the + terminal and the other goes to the - terminal of both speakers), the resultant impedance would be 4 ohms, so set it for 4 ohms.
3. If the speakers were connected in series one wire from the amp would connect to the + terminal, a seperate wire from the - terminal of that speaker connected to the + terminal of the second speaker, and the last wire from the amplifier would go to the - terminal of the 2nd speaker. This would result in an impedance of 16 ohms.
 
Doesn't sound like "3" is the case, and most likely "2", in which case use 4 ohms. I assume this is a tube amplifier since transistor amps don't require impedance matching as long as you don't exceed the power handling of the amplifer.
 
Hope this helps,
 
Walt

There are 2 ways to wire those speakers. 4 ohms or 16 ohms are your only options. You want to wire them for 4 ohms so the cab will match the impedance of your amp output. To wire them for 4 ohms you connect the positive terminal of speaker 1 to the positive terminal of speaker 2. Connect the negative terminal of speaker 1 to the negative terminal of speaker 2. They are now wired in parallel. Connect the positive terminal from either of the speakers to the positive connection of the cab. Do the same with the negative terminal of either speaker.
 
That's all there is to it. Polarity is very important. You should see a + or - clearly marked on the connector tab of each speaker. If you mix the polarities, there will be phase cancellation and the cab will sound thin and nasty as one speaker goes in while the other goes out. If you can't see the polarity just connect the left terminal of 1 to the left terminal of 2 and so on.

SOOOOOOO glad I asked!  Thanks to both of you.  Once I dig into that cabinet with the speakers, I may get on again.  Probably tomorrow as I have to work in the studio today for a few hours.
 
Thank you!

spindlebox
SOOOOOOO glad I asked!  Thanks to both of you.  Once I dig into that cabinet with the speakers, I may get on again.  Probably tomorrow as I have to work in the studio today for a few hours.
 
Thank you!

Glad we could help. Ask away!
 
Walt

OK, here's a question before I dig in.  It is obvious I am going to have to add a bit of wire to do the Parallel wiring, what type of wire would you suggest?  I have a Radio Shack nearby.  Thank you!

Cheap lamp cord, #18 braided will work just fine. You should solder your connections or use some type of crimp connector for best results. If you simply twist the wires together it will work but you want to be sure vibration won't cause the connection to fall apart. I solder the connections on the speaker but some like to use the crimp on spade connectors. 

spindlebox
OK, here's a question before I dig in.  It is obvious I am going to have to add a bit of wire to do the Parallel wiring, what type of wire would you suggest?  I have a Radio Shack nearby.  Thank you!

Like everything, it depends. Assuming it's a low power amp (<100 Watts) and the wiring length is short (inside the speaker cabinet) than 18 GA should be sufficient. I have a 65 Reissue Fender Twin Reverb that I use and it is rated at 85 W RMS. It uses 18 GA wiring. 
 
What was the original wiring gauge?
 
Walt
 
 

WallyG

spindlebox
OK, here's a question before I dig in.  It is obvious I am going to have to add a bit of wire to do the Parallel wiring, what type of wire would you suggest?  I have a Radio Shack nearby.  Thank you!

Like everything, it depends. Assuming it's a low power amp (<100 Watts) and the wiring length is short (inside the speaker cabinet) than 18 GA should be sufficient. I have a 65 Reissue Fender Twin Reverb that I use and it is rated at 85 W RMS. It uses 18 GA wiring. 
 
What was the original wiring gauge?
 
Walt
 
 
 
 
 

Hey Walt, unknown on the original gauge wire for the cabinet.  It's all been torn out.  I will be putting up to 100 watt amps through this thing though, so it's gotta be able to take it.

spindlebox

WallyG

spindlebox
OK, here's a question before I dig in.  It is obvious I am going to have to add a bit of wire to do the Parallel wiring, what type of wire would you suggest?  I have a Radio Shack nearby.  Thank you!

Like everything, it depends. Assuming it's a low power amp (<100 Watts) and the wiring length is short (inside the speaker cabinet) than 18 GA should be sufficient. I have a 65 Reissue Fender Twin Reverb that I use and it is rated at 85 W RMS. It uses 18 GA wiring. 
 
What was the original wiring gauge?
 
Walt
 

Hey Walt, unknown on the original gauge wire for the cabinet.  It's all been torn out.  I will be putting up to 100 watt amps through this thing though, so it's gotta be able to take it.

The current going through each speaker wire is 3.54 A rms. (I = square root of Power/Impedance or I = square root of 100W/8 or 3.54A. This assumes you run seperate wires to each speaker.
 
For short lengths of wire, 18 GA wire can handle 16A, or for power transmission (i.e. Line Cords) is rated at 2.3A. 16 GA can handle 22A for chassis wiring, or 3.7A for power transmission. 
 
For 100 W of power,  I would recommend the 16 GA to be on the conservative side. Since wire is cheap I would also run seperate wires from your amplifier output to each speaker. Amplifier output plus to Speaker Terminal plus and Amplifier Output minus to Speaker Terminal minus for each speaker. 
 
Walt
 
PS: Look at the size of the wire in the speaker that is going to the voice coil. Much lower GA since it's considered "chassis wiring" category.