Ohms thread no questions just a rant. :)

[Red Planet]

Man what a pain. I have been trying to figure out how to get three 8 ohm monitor cabs off one side of a power amp with a 4 ohm minimum and make it easy to hook up with no special cables.

I must be getting old cause this darn near exploded my brain. I know I needed to run them series but it hurt figuring it out.

I ended up rewiring the jack plate on one monitor for series and basically I am series between one 8 ohm cab with the other two 8 ohm cabs run parallel. I was not sure if that would work but all cabs appear to have equal volume. I believe I'm running at 12 ohms though my Fluke says 10. Anyway it's a fix for now and man did this hurt my brain.

 

[tjh]

... that would mean you actually have an IMPEDANCE issue ...

... we are missing a couple components here ... what is the impedance of the cab that you re-wired in series?? .. (might not hurt to know the impedance of each and number of drivers in that cab also, just to double check things)

... do all three cabs have the same number/type of drivers??

... bottom line, its is probably not likely that all three cabs are getting equal power to them ... but, fill in the blanks and can better figure out your % split with the power and your final IMPEDANCE ...

 

[Red Planet]

Sorry I thought I spelled it out.

I have three 8 ohm cabs. Each cab has only one 12" driver in it as well as a horn. Two of the cabs are wired in parallel to each other (4 ohms). Those two are then wired in series with the third 8 ohm cab. I wired the jacks in the third cab so as to place the two other cabs and this one in series with each other. Basically the jacks are wired with the positive of the single 12 to the positive on jack A and the negative to the positive of jack B and then a jumper between the two negative terminals on both jacks. Then when I plug a cable from speakers 1&2 into the A jack and run a cable from the B jack to the PA then the two sets are in series.

I believe this was my best bet as parallel on all three is 2.67 and series on all three is 24 ohms correct? I believe this should yield me 12 ohms and it measure 10 ohms with my meter.

As far as the power goes, I just used my ears. They sound even to me. I heard no unusual discrepancies between any of the three. I just pumped in some tunes and cranked them.

Now all that being said this is not ideal but it will get me through for now for an extra vocalist at my Church gig until I can come up with a plan B. Luckily this gig is not loud so I would not be starving for wattage.

 

[Red Planet]

I found this gizmo on the net.

Clearly I could not tell that kind of difference between the three. Maybe it's just not enough to tell.

Anyway it works and that is all that matters. It did make me have to think to wire up the jacks on the cab. That was a brain teaser. Shows how old I'm getting I guess.




System Impedance Calculator

Amp Power:
245 Watts


Speaker A: 8Ω

Speaker B: 8Ω

Speaker C: 8Ω


Total Impedance = 12 Ω
Speaker A Power = 40.83 Watts
Speaker B Power = 40.83 Watts
Speaker C Power = 163.33 Watts

 

[Red Planet]

Well after looking at this (I was doing the math in my head) I found this.




System Impedance Calculator

2 Series +1 Parallel


Amp Power:
475 Watts

Speaker A: 8Ω

Speaker B: 8Ω

Speaker C: 8Ω

Total Impedance = 5.333 Ω
Speaker A Power = 79.16Watts
Speaker B Power = 79.16 Watts
Speaker C Power = 316.6 Watts

I measured 6.8 ohms with my meter.

I tried it out and I cant tell much difference. In theory I'm getting more juice this way so I'll go with that. I can not tell one speaker is louder than any of the others. Perhaps it has to do with the efficiency of the one "odd" speaker as it is different than the other two.

 

[Hactar]

There is no way to wire three 8Ω speakers and get both a nice impedance and an even power distribute

The above 5.33Ω seems to be the best, but it seems that you ought to be able to hear which speaker is receiving the 316W.

 

[Red Planet]

There is no way to wire three 8Ω speakers and get both a nice impedance and an even power distribute

The above 5.33Ω seems to be the best, but it seems that you ought to be able to hear which speaker is receiving the 316W.

I agree.

I had to do something and this works for now. For the life of me I can't tell that one is any louder than the other and no one else could either out of 6 people. I set the three monitors in a row across the front about 3 feet apart from each other and if you walk back and forth you can hear them all equally.

It worked gloriously so that is what matters. This will get us by until we can purchase more monitors.