#1
Ive got a peavey valveking 100. I want to run to a crate g412sl (with the dual input jacks) and a seismic 2x12 cab in parallel. Is that safe after ohms have been taking into account?
#2
After ohms have been taken into account, yes. That is the tricky part, though. I am not sure how exactly the VK has its outputs set up. It says paralleled, so I think using both outputs would give you the ohm rating you have the selector at, and using just one would give you double the rating. Parallel halves the rated impedance of two loads the same rating (two 8 ohms is total 4 ohm load). Series doubles (two 8 ohms is 16 total load).

So if you run the 4 ohm output of the amp, one jack to the Crate (at 8 ohms?), and the other to the Seismic (at 8 ohms?), it should be fine (two 8 ohms parallel = 4 ohms?). I am not entirely sure if that is right, though, so someone should check behind me before you blow your amp.

Another concern is if your Crate cab operates in mono if only one side is used. Or even if it is 8 ohms either side, or 4 ohms one side. And the same concerns for your Seismic cab as well- what model is it exactly? It might would be easier to just use one cab but that is just me.
Last edited by Will Lane at Nov 11, 2016,
#3
Will Lane thanks for your reply. See the vk does run parallel so i swithed it to 4 ohms. The crate cab im using doesnt have any stereo or mono switches. Just 2 ouputs. Im find no information on wheather it is stwreo or mono with using just one jack. My seismic cab i know for sure that the second jack is for a daisy chain (running in series?).
#4
Quote by randall.goodson
Will Lane thanks for your reply. See the vk does run parallel so i swithed it to 4 ohms. The crate cab im using doesnt have any stereo or mono switches. Just 2 ouputs. Im find no information on wheather it is stwreo or mono with using just one jack. My seismic cab i know for sure that the second jack is for a daisy chain (running in series?).
Yes, this is where it gets complicated. The Seismic cab's daisy chaining could be series or parallel, it depends. Mismatching imps can lead to broken equipment so I try to be very sure of what the equipment is rated at and how it is wired, no guessing. What model exactly is the Seismic cab?

I cannot find any info on the Crate unit either. If your Seismic cab can take the full brunt of the VK (100w+), I would hold off on using the Crate until you can open up the back and see exactly how it is run. Should be just use one side of the VK's output, impedance switch at the same rating of what your Seismic cab is rated at. From the VK manual:
If two enclosures of equal impedance are used, the switch should be set to half the individual value. For example, two 16 Ω enclosures necessitate an 8 Ω setting, while two 8 Ω enclosures would require a 4 Ω setting. Minimum speaker impedance is 4 Ω.
Last edited by Will Lane at Nov 11, 2016,
#6
the output jacks on amplifiers are almost always set up in parallel. there is a reason for this, but i don't feel like getting into it in detail, just know that setting up a series connection is a pita when dealing with amplifier speaker outputs.

the jacks on cabs are generally set up in parallel as well, it is for daisy chaining another cabinet in parallel. there can be stereo jacks, but if there is no switches to change between the mono and stereo setting on the cab then once again it gets to be a pita to use all 4 speakers in a 4x12 if the cab is stereo. it is generally a safe bet to conclude a plain, two connector jack plate is set up for mono and the jacks are wired in parallel with each other.

now, the cabinets.

f two enclosures of equal impedance are used, the switch should be set to half the individual value. For example, two 16 Ω enclosures necessitate an 8 Ω setting, while two 8 Ω enclosures would require a 4 Ω setting. Minimum speaker impedance is 4 Ω.


for the most part this is accurate enough to follow, this concept does assume the cabinets will use the same number of speakers and the same wiring. you can run into some issues though if don't consider some of the more complicated aspects that arise from using cabinets that use speakers with different impedance.

for example, your 4x12 most likely uses four 8 ohms speakers wired in series-parallel, your 2x12 most likely uses two 16 ohm speakers wired in parallel. normally, if all speakers are the same impedance, then they will all see the same amount of current and therefore do the same amount of work. but if you use two different impedance speakers then the lower impedance speakers will see more current and will end up doing more work.

so as an extreme example of this suppose you have a 150 watt head running at it's nominal output. you have two cabinets, a 4x12 wired with 8 ohms speakers and a 2x12 wired with 16 ohms speaker and all the speakers are rated for 25 watts. if all the speakers were 8 ohms then all six speakers would get (150/6) 25 watts of output from the amp, but since this setup has two 16 ohm and four 8 ohm speakers then the 8 ohm speakers would see more than 25 watts and the 16 ohms speakers will see less than 25 watts.

in that example this is bad because it means the 25 watt speakers will be handling more power than it's rated for, which could cause a speaker blowout. this isn't a big deal if you are running 100 watt speakers instead, then all you are left with is a volume difference. those 8 ohm speakers will be quite a bit louder than your 16 ohm speakers will be and that can be frustrating.

this is often the reason you don't see people running different impedance speakers in the same setup, it has complicated results that cause an uneven distribution of signal to speakers. cabinets with a different number of speakers often run speakers of different impedance and that is why you don't often find people running different sized speakers cabs together either.

i should mention that there is nothing dangerous about running speakers of different impedance as long as you are sure they won't have too much power sent to them. so i am not saying you shouldn't do this, i am just making you aware of what is happening if you hook this up together.
punk isn't dead, it's always smelled that way.

"A perfection of means, and confusion of aims, seems to be our main problem."
-ae
Last edited by gumbilicious at Nov 12, 2016,