Advice: cabs, ohms, power?
 

I have an 810 1200 watt rms that runs at 4 or 8 ohms, a 215 1200 rms that runs at 4 ohms, and a bass head that runs at 2, 4, or 8 ohms at 2000, 1300, and 700 watts.

Right now I'm running both cabs from the head and not getting nearly as much power as I expected without peaking. My questions are...

How many ohms am I running at?

Am I pushing too much or too little power into my cabs?

How could I have been getting more power from a stand alone 810 than a combo of 810 and 215?

I'm also running a compressor and a DI pedal.

Any help would be much appreciated!!!!

What amp? If you are running a dual amp unit bridged at 2 ohms (your total load with both cabs) you are overloading the amp. Each amp unit may handle a 2 ohm load individually but will not handle the 2 ohm load in bridged (in bridged mode each amp will see a 1 ohm load).

really? which brand?

Well, there's also the little matter of physics. Do some reading in the sticky threads under amps. This may or may not be the case, but your different speakers could actually be somewhat "canceling each other out" in some frequencies. It's much more complicated than that, thus the suggestion to read some on the subject of mixing drivers. Again, it might not be the case for you, but it's a possibility for sure.

Yes also possible one cab is out of phase with the other.

Dang it B! You always manage to say the same thing I do with about 1/10 the words!

It's a gift :D

Let's just say my "gift" is in the other direction. I could write a term paper using the topic "Describe the result of adding 2+2".

Hey OP, yer cabs might be out of phase, which is what I said too, only mine was longer.

Excellent catch anyway! I should have thought about the cabs canceling each other by the one cab is louder than two combined. Too many irons in the fire sometimes? :)

Check for out of phase, run both cabs @ 4 and the amp should be 2 Ohms... theoretically that should be most efficient... theoretically.

i still wanna hear about this magic 8x10 that switches between 4 and 8 ohms!

i suspect we're confusing the stereo and mono options on the back panel.

Summing up:

The first question is what amp?

The 8x10 will be two 8 ohm halves or one 4 ohm. Both cabs together on a mono amp channel is 2 ohms.

Phasing can be completely off by miswiring, check 9v battery with linked cabs and 1/4" lead. All cones should move in or out together.

Or simply a lousy cab combination not working well, search "why are mixed cabs bad?" Phase response of the cabs may be unmatched.

But even if they were matched for phase they can't make a coherent bass sound. Get a PA.

+1 to all this.

as for the 9V test, to be specific you should touch the tip of the cable to the + of the 9V, and when you do all the speakers involved should pop forward.

I'm running a carvin b2000, a peavy 215 with both speakers replaced with carvin neo 15s, and an ampeg pr-810h. The ampeg is where it gets a little messy...

It IS 2 410s put on top of each other and I have read it can be run stereo, the top and bottom halves playing separately, however I've never been able to figure out how. It being an older cab, most of the inputs are faulty so I've had one repaired (the one I use) and assumed it's been at 4 ohms since all 8 speakers are working together.

I'm getting a bit lost on what you mean by phasing.

For the 9v test, do you literally touch a 1/4 cable to the + of the battery? That's it? Just look to see if ALL the speakers move outward?

Thanks again for bearing with me folks, this is extremely helpful.

Also, here is a link to the head, speakers, and ampeg.

http://www.carvinguitars.com/products/B2000
http://www.carvinguitars.com/products/NE15-8
http://www.ampeg.com/manuals/PR-810H.PDF

Take your speaker cable and plug it into your cab.

Take the end that would go to your amp, and touch the Neg (-) pole to the sleeve part of the 1/4.

Now gently place the Pos (+) on the tip.

When it makes connection, you should hear a thump and ALL the speakers should move OUT

Test both cabs the same way.

If BOTH cabs have the speakers moving out - your fine. If one cab moves IN, or not all the speakers move the same direction, then you will need tp fix the wiring.

No where on that Carvin 15" speaker does it say "RMS" in the power input specs! If you run 600 watts amplifier "RMS" power into it you might have a very bad surprise.

The other possibility is a drastic mismatch in cabinet sensitivity between the 810 and the 215.

Here's my thinking: with just the 810 at 4 ohms, it got 1300 watts. Combine both 4 ohm cabinets and while there are 2000 total watts, each cabinet only gets 1000.

So if the 215 was significantly less sensitive than the 810, maybe that's why you're not feeling an increase in output? Don't know, going from 1300 to 1000 watts in the 810 alone would not be that much of an output drop, maybe one decibel, so it seems unlikely this is the issue.

I would check for phase issues between the two cabinets, or between drivers within a cabinet.

WorldCarver,
I'm not the most knowledgeable person on this but my understanding is:
Multiply the ohms of the cabs together divided by the sum of the ohms of the cabs. The sum is the amount of load your amp needs to be able to handle, rounding down.
For example, a 4 ohm cabinet + an 8 ohm cabinet would be (4x8)/(4+8) = 32/12=2.666 ohm load. So, your amp would have to be able to function at a 2 ohm load.
8 ohm cab + 8 ohm cab gives you 4 ohms which is how much your amp would need to handle.
BTW, if mixing ohm cabinets, the lower ohm cab receives more power from the amp. Anyone, please correct me if I'm wrong.

Sorry for the delayed response.

I did the 9v test. The 810 moved OUT in unison and the 215 moved IN in unison. Does that mean the 215 is out of phase? If so, is the fix as easy as switching how the wires are attached to the speakers?