Can I run two different cabs off the same power amp?

[Jamie Snell]

Hi all

i have a Behringer power amp which outputs:

280w @ 8 ohms per channel

450w @ 4 ohms per channel

700w @ 2 ohms per channel

i have a Trace Elliott 1015H cab which features 2x10 and 1x15. It’s rated 800w @ 4 ohms.

I am considering a matching TE 2x10 extension cab which is rated 400w @ 8 ohms.

My question is: Can I send the output of channel one of my amp to the 4 ohm cab and the output of channel two to the 8 ohm cab?

And assuming this is ok, will I get the full 450w going into the 4 ohm cab and the full 280w going into the 8 ohm cab? Or will the overall impedance have changed therefore changing the wattages?

Any advice welcome! Thanks.

[BassmanPaul]

You are correct. The 4Ω cabinet will get 450W from one channel and the 8Ω cabinet will get 280W from the other. You could also run both from one channel for 2.66Ω  should you need to and leave the other channel for some other use.

[Jamie Snell]

7 minutes ago, BassmanPaul said:

You are correct. The 4Ω cabinet will get 450W from one channel and the 8Ω cabinet will get 280W from the other. You could also run both from one channel for 2.66Ω  should you need to and leave the other channel for some other use.

Thanks for confirming my thoughts, but just one point - running both off one channel @ 2.66ohms wouldn’t be a good option as that is below both cabs respective minimum ohms?

[warwickhunt]

Just now, Jamie Snell said:

Thanks for confirming my thoughts, but just one point - running both off one channel @ 2.66ohms wouldn’t be a good option as that is below both cabs respective minimum ohms?

You're clouding/confusing the matter.  IF each channel of your power amp is separate and can operate at 2 ohms then your 4 AND 8 ohm cab are within its parameters and both can run off 1 channel.  However each cab will get a bit more/less power, not the end of the world BUT why not just run 1 cab off 1 channel (ie 4 ohm on #1 8 ohm on #2)?  

[warwickhunt]

I should have said that your cab ohmage can not / will not change, it is fixed.  The only thing that changes dependent upon ohmage / load is your amp.  The higher the number your amp 'sees' (has attached) the lower the power output.  Putting 2 cabs on as you are talking lowers the ohms and draws more power from the amp.  

This is all phrased in layman's terms. 

 

[Jamie Snell]

3 minutes ago, warwickhunt said:

You're clouding/confusing the matter.  IF each channel of your power amp is separate and can operate at 2 ohms then your 4 AND 8 ohm cab are within its parameters and both can run off 1 channel.  However each cab will get a bit more/less power, not the end of the world BUT why not just run 1 cab off 1 channel (ie 4 ohm on #1 8 ohm on #2)?  

Impedance always confuses me!

and yes I think my preference would be to run the 4 ohm cab off one channel and the 8 ohm cab off the other. In fact thinking about it, that’s the only way I can do it as neither cab has an output/link.

[Jamie Snell]

Ignore me, the 2x10 has an output link so could send one output to that and then the output link to the 4 ohm cab. So next question is what impact would this have on the ohms and wattage?

[warwickhunt]

Just now, Jamie Snell said:

Ignore me, the 2x10 has an output link so could send one output to that and then the output link to the 4 ohm cab. So next question is what impact would this have on the ohms and wattage?

Cans - None.

Amp - 2.6 ohms if you connect to single channel.  

[Jamie Snell]

18 minutes ago, warwickhunt said:

Cans - None.

Amp - 2.6 ohms if you connect to single channel.  

Ok thanks. I think I was getting ohms and watts mixed up. If I ran the cabs off one channel then wouldn’t the amount of wattage be too high for the 8 ohm cab which is only rated at 400w?

[warwickhunt]

13 minutes ago, Jamie Snell said:

Ok thanks. I think I was getting ohms and watts mixed up. If I ran the cabs off one channel then wouldn’t the amount of wattage be too high for the 8 ohm cab which is only rated at 400w?

The wattage is shared BUT you need to research and appreciate that quoted figures are bragging figures, so are nominal/vague.

[Jamie Snell]

9 minutes ago, warwickhunt said:

The wattage is shared BUT you need to research and appreciate that quoted figures are bragging figures, so are nominal/vague.

Thanks again and sorry I did know the wattage gets shared. And yes all amp manufacturers are guilty of promoting wattage levels which are ultimately bragging figures! 
 

Linking the cabs would give a better volume balance whereas running each cab off separate channels would require some manual volume balancing using the channel volume pots I guess.

[warwickhunt]

Way easier to balance what each cab gets using vol knob, if you have both on one channel how do 'you' give each one more/less power?  

[pete.young]

5 minutes ago, warwickhunt said:

Way easier to balance what each cab gets using vol knob, if you have both on one channel how do 'you' give each one more/less power?  

You dont. Assuming that the 2 sockets in the 2x10 are wired in parallel, the 4Ohm load will draw twice as much current as the 8Ohm load, so 2/3 of the total power will go to the 4Ohm speaker and 1/3 to the 8Ohm speaker.

[adamg67]

I've done similar things to this with stereo power amps in the past. If the power amp does bridge mode (mine did) then you could run the cabs in parallel off it like a big mono power amp...

BUT

As people have already said above you will get a better more flexible setup running each cab separately off one side of the stereo - it's safer (harder to get wrong), it's not different if you decide to just take one cab, and it's nice and flexible as you can balance what you hear with the volume controls. Plus, there are people who say you will get a better sound from each can separately rather than in the same circuit in parallel, and people who say it makes no difference, but if they're separate you're safe that way as well.

[warwickhunt]

4 minutes ago, pete.young said:

You dont. Assuming that the 2 sockets in the 2x10 are wired in parallel, the 4Ohm load will draw twice as much current as the 8Ohm load, so 2/3 of the total power will go to the 4Ohm speaker and 1/3 to the 8Ohm speaker.

Agreed but we don't know that the cabs/drivers are totally comparable and not been messed with, if you have 2 cabs and 2 channels you gain nothing from running both off one channel!  

[BassmanPaul]

35 minutes ago, adamg67 said:

I've done similar things to this with stereo power amps in the past. If the power amp does bridge mode (mine did) then you could run the cabs in parallel off it like a big mono power amp...

*********************************

If the amp does bridge then it would be limited to a 4Ω minimum load. Running both cabinets in Bridge will destroy the amp!

Lets say that one channel of the amp into a 2..67 Ω load puts out 600W. The 8Ω cab will get 200W and the 4Ω cab 400W.

The idea of just running on one channel means that say the PA goes down, you could sub the second channel to get through the gig.

 

Edited June 22, 2021 by BassmanPaul

[Jamie Snell]

Hi all, thanks for your advice and comments so far.

Using an online Speaker Ohm Calculator it tells me that connecting both speakers in parallel at 2.67 ohms will distribute  the power 33.3% to the 8 ohm cab and 66.7% to the 4 ohm cab. Given the amp outputs 700w @ 2 ohms then this would equate to 175w to the 8 ohm cab and 350w to the 4 ohm cab.

Given the 8 ohm cab can handle 400w and the 4 ohm cab 800w I think it would be best to output to each cab from each channel as that would give me 280w to the 8 ohm cab and 450w to the 4 ohm cab. That’s 730w in total rather than 525w. Plus using this method means that if one of the amp channels went down, or one of the cabs for that matter, then it’s less hassle.

Hopefully my conclusion makes sense, but if I’ve got anything wrong do let me know.

Thanks again, Jamie

[BassmanPaul]

I believe that several of us have told you that already!!

[warwickhunt]

Honestly, you are overthinking it.  

I have ran 4 / 8 / 16 ohm cabs rated from 100 to 1200 watts (in LOADS of combinations) with 100 - 1600w amps and I've never destroyed one yet.  So long as you don't connect a cab that is lower rated in OHMS than the amps minimum load, then you just need to proceed with caution and start turning the volume up listening to what your speaker is telling you.  

[Jamie Snell]

59 minutes ago, BassmanPaul said:

I believe that several of us have told you that already!!

Just wanted to be sure I had understood correctly. Thanks for your help.

[Jamie Snell]

16 minutes ago, warwickhunt said:

Honestly, you are overthinking it.  

I have ran 4 / 8 / 16 ohm cabs rated from 100 to 1200 watts (in LOADS of combinations) with 100 - 1600w amps and I've never destroyed one yet.  So long as you don't connect a cab that is lower rated in OHMS than the amps minimum load, then you just need to proceed with caution and start turning the volume up listening to what your speaker is telling you.  

I’m a bit anal! Thanks for your help.

[agedhorse]

On 22/06/2021 at 15:10, adamg67 said:

I've done similar things to this with stereo power amps in the past. If the power amp does bridge mode (mine did) then you could run the cabs in parallel off it like a big mono power amp...

 

No, the amp is rated for a 4 ohm minimum load in bridged mode. 

[agedhorse]

On 22/06/2021 at 14:58, Jamie Snell said:

Thanks again and sorry I did know the wattage gets shared. And yes all amp manufacturers are guilty of promoting wattage levels which are ultimately bragging figures!

No, not all amp manufacturers are more guilty of this. 

Don’t accuse others of something you don’t yet understand.
 

 

[Jamie Snell]

19 hours ago, agedhorse said:

No, not all amp manufacturers are more guilty of this. 

Don’t accuse others of something you don’t yet understand.
 

 

Give over mate.

[BassmanPaul]

@Jamie Snell a word of kindly advice if I may: @agedhorse designs amplifiers for Mesa. Before that Genz Benz.  When he opines on a subject it's advisable for you to listen to what he has to say!!!  He knows what he is talking about!