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Sub as an extension cab?


Bob O'Brian

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This may not be the ideal rig but I'm considering it because it doesn't require me to buy any gear.
I currently gig with a Markbass 121p which I DI. In my first band this works just fine, but I've recently joined another band who are louder and who don't have as good a PA.
The subs that we use in my first band are owned jointly by me and the guitarist- i.e. one of them is mine. They are 4-ohm Peavey 15" subs with crossovers built in.
In the new band, I'm running out of volume and the PA is clipping like a bastage. My Markbass can put 500w through 4-ohms so I was thinking about hooking it up to the Peavey sub, and connecting the Markbass speaker as a satellite, taking the high frequencies only.
I can't see why this wouldn't work, but I'm not sure whether it's a good idea?

Bob

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Erm, no.

It would go Markbass head -> Sub -> Markbass speaker.


Because the sub contains a crossover, the Markbass head would only 'see' the 4-ohm load of the sub.

 

 

Bob, the crossover will change it's inpedance as well. So, the head still will see 2 Ohms.

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Well I know it works. When I got the subs, this was how I tested them- just to make sure they made a sound, and passed the high frequencies through the crossover to a second speaker. Trouble is I had to lay the subs face down because the lead coming out the back of the Markbass is so short!

 

I'm off to buy a jack-socket speaker lead...

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Bob, the crossover will change it's inpedance as well. So, the head still will see 2 Ohms.



I don't think so. Thanks to the crossover, the two speakers act like one big full range speaker cabinet would. And if it doesn;t work like that, then I've been running the PA at 2-ohms every weekend :eek:

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Well I know it works. When I got the subs, this was how I tested them- just to make sure they made a sound, and passed the high frequencies through the crossover to a second speaker. Trouble is I had to lay the subs face down because the lead coming out the back of the Markbass is so short!


I'm off to buy a jack-socket speaker lead...

 

 

Just to be sure... Measure it.

 

You don't want that magic smoke coming out of your Markbass....

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Haha, I do not intend to liberate the magic smoke.

 

The sub is 4-ohm... the combo's speaker is 8-ohm... if I am not safe doing this then everything I know about wiring up speakers is wrong.

I was just wondering if it would sound any good?

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Haha, I do not intend to liberate the magic smoke.


The sub is 4-ohm... the combo's speaker is 8-ohm... if I am not safe doing this then everything I know about wiring up speakers is wrong.

I was just wondering if it would sound any good?

 

 

With the specs you provided,

 

Actually, to be exact, you'll be running your rig at about 3.47 Ohms. Which is below the amp's recommended impedance.

 

You'll sound louder, yes.

You'll have mad low end and response, yes.

Sound better? What do you think?

Chances are, your amp will run hotter and eventually fail.

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unless the crossover consists of a choke and nothing else, a strictly low-pass filter, the amp will see 4 ohms. But except for possibly a little more depth on the bottom, you probably won't hear much difference as the crossover will suck up a bit of the added power by converting it to heat.
Try it and if you are happy with the results, have at it.

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