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16ohm load on a Momark 600w head?


SimonH
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Hi chaps - help! I have an empty GK 2x10 cab I would like bring back to life.

I currently use a 15in MB cab rated 400w at 8ohm and a 4x10 MB rated 800w at 8ohm. The head is a MB Momark 600w frame, runs down to 4ohms.

I want the option to run my refreshed 2x10 either on its own, or in tandem with either of the other two cabs.

If I have a pair of 10in cones rated at 8ohm 500w each, what config can I use to run the cab solo, or as a pair with either of the other two?

Or is that simply not safe/possible?

If I wire the new cones in parallel as 4ohm total, that will give 1000w at 4ohms and will handle the Momark head. But then I can't run them as a pair with, say, the 15in.

If I wire them in series as a 16ohm load, that will be 1000w at 16ohm - will the Momark be ok running that, what will it sound like, and can I then match the new cab with either of the MB cabs?

Thanks, and sorry if I'm being thick.

Simon H

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Now here's a can of worms....

[b]Short answer:[/b]
Personally I wouldn't use them together - so make your 2x10 4 ohms, and use it alone or not at all.

[b]Long answer:[/b]

OK first off, examples below are heavily simplified (before everyone chimes in) to get the point across briefly:

If you have an 8 ohm 4x10 and a 16 ohm 2x10, and you use them together, in theory each cone will be sharing an equal amount of power. i.e. the 2x10 will get half the power the 4x10 does from the amp - as it's got half the speakers that's OK.

If the 2x10 is 4 ohm it will get twice as much power into it as the 8 ohm 4x10 from the amp. So the power-per-cone will be far from equal - the cones in the 2x10 will be working 4 times as hard as the ones in the 4x10! - Not a good option.

But you also have an 8 ohm 1x15. So if you use that with the 2x10 at 16 ohm, the 15" will do twice as much work as the 2x10, or 4 times as much as each cone in the 2x10. Again not ideal, but personally I don't believe in mixing speaker sizes anyway.

So going 16 ohm with the 2x10 and only using it with the 4x10.

The 4x10 + 1x15 setup you already have suffers the same problem - the 15" is handling 4 times the power of each of the 4 10" drivers. So at 4 ohms, (max power), the 15 gets 50% (400W), each of the 10"s get 12.5% (100W) x4 = 50% (400W).

HOWEVER>>>

Mixing different cabs that were not designed to go together is a risky business. e.g. if one cab has a pronounced mid hump at 800Hz and you roll off 800Hz on the amp, it will also take 800Hz out of the other cab that does not have the hump. So then most of the 800Hz region you can hear will be coming from one cab. That's a really simple example, its a bit more complex than that. Basically it can be quite unpredictable. Same with mixing a 15" with either the 4x10 or the 2x10.

So my advice is... make your 2x10 4 ohms, and use it alone or not at all.

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I hear your point, and understand - I would only ever use the 2x10 with the 15, and I was thinking along the lines of copying a MB 2x10 combo and 15in cab set-up... that seems to be a popular combination.

And in my head, using a 2x10 4ohm cab pulling the full 600w from the head seems 'harder work' for the speakers than a pair of 2x10s running at 8ohms pulling 320w...

But I take your point. If you think a 2x10 running a pair of 500w 8ohm drivers to a total of 4ohms will work, I'll do that! Thanks for your help!

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I think it'll work as a standalone 2x10 (If the speakers can take the watts and frequencies in that cab) - but the 4ohm 2x10 together with the 8 ohm 1x15 will take your total impedance down too far in parallel (if the amp does 4 ohms min.) So if you wanted to combine it you'd have to wire the speakers in series. The end result may be quieter than using just the 2x10 though because you'll be up to 12 ohms.

You could go all fancy and have a switch on the back of your cab to go between series / parallel wiring internally so you can choose 4 or 16 ohms to suit your needs. However all of the above still applies - the MB 2x10 combo and 1x15 extension set-up may well have been designed to be used like that. I can't say.

Your 2x10 is going to be a bit unpredictable because the drivers (speakers) may not be well matched to the cabinet to start with, and the end result may well be a poor (or amazingly good) match to your 1x15 or 4x10 or both.

Hence I suggest you should aim to use it alone or not at all, so you have a compact setup for not too loud gigs, and a big stack like you've always had.

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