"Maybe yes, maybe no! What's in the bag, Danger?"
anyway, I want to know for the two "4&8ohm parallel jacks", do I have to use both at the same time. Im just curious because the word "parallel" is there, and parallel usually means like running 2 cabs, at least I think so. I want to just plug one of the 4/8 ohm jacks into a 2x12 amp and leave the other 4/8 ohm jack unused. Is this safe?
btw, the other jack on the far left that is partly obscured is a dedicated 16ohm only jack.
The two jacks are in parallel. This means that they are strapped together internally and it doesn't matter which one you insert the speaker cord plug. It's like plugging 2 lamps into the same outlet. The receptacle inside the box has just strapped them together. Everything is still a load on the same line.
So you can plug in one cab or two. Just make the load right if you have 2! Speaker loads add up in series by simple math (8 + 4 + 4 = 16) but in parallel it's a bit more complicated.
If the speakers are all the same load you take the original load and divide by the number of speakers in parallel. So with two 8 ohm cabs you have 8/2 = 4 ohms. Another example would be with four 16 ohm speakers in a 4-12 cab. 16/4 = 4 ohms. You could also wire each pair of 16 ohm speakers in parallel to make 8 ohms, then put the pairs in series and get a total load of 16 ohms! That's how some cabs can put a 16/4 ohm switch on the back.
If you play with the numbers you'll see why you can only match up speakers of the same load into certain outcomes. Those four 16 ohm speakers can never give you a total of 8 ohms.
You can put an 8 ohm speaker and a 4 ohm speaker in parallel but it doesn't work out nice and clean. It will be around 3 ohms. In series it would be 12 ohms. This is usually not a good idea because the power no longer shares equally. The 4 ohm speaker will hog twice the power. If you had 100 watts driving them and both speakers were rated at 50 watts the 8 ohm speaker would see 33.3 watts and the 4 ohm would see 66.6! The 4 ohm running over its rating might burn out. That's why it's easier to stick with speakers of all the same impedance.
The 4/8 switch means you set both jacks to 4 ohms or both jacks to 8 ohms.
If you have them set to 8 ohms you plug in an 8 ohm cab. If you plug in an extra cab then you've put two 8 ohm cabs in parallel, making a total speaker load of 4 ohms. So you should set the switch to 4 ohms.
If you plug two 4 ohm cabs into the jacks you've put two 4 ohm loads in parallel to make 2 ohms. This is too low - you don't have a 2 ohm switch setting.
If you had two 16 ohm cabs you're ok. Plug 'em both into the paralleled jacks. You'll have a load of 16/2=8 ohms. Set the switch to 8 ohms and rock on!
The dedicated 16 ohm jack is just that, dedicated! If you have only one 16 ohm cab you plug it in there.
Hope this helps.:rockon2: