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Post subject: Extension cab help needed - ohms matching
Posted: Sat Mar 30, 2013 5:27 am
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I have a new Genz Benz Streamliner 900, and I am trying to build a flexible, modularized rig that is lightweight and easily portable. My first cab is the NX2-12 (4 ohms, 600w) which I thought would cover most in-door situations. However I also play outdoor gigs and feel like I want another cab (bass not supported by the PA in my band). I forgot about ohms matching and bought a 1-12 extension (350 w @ 8 ohms) and am now being told that I cannot run the two cabs together in parallel because it creates a 2.7 ohm load which will damage the Streamliner.

Due to the cost of the new 2-12 cab, I am committed to it... but my question is, what else can I pair with it, if anything? I now see lots of examples of rigs with two 8 ohm cabs run in parallel, but that is not an option for me.

Help! Any ideas?


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Post subject: Re: Extension cab help needed - ohms matching
Posted: Sat Mar 30, 2013 7:14 pm
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This is actually quite common for guys who buy a rig and then later want to build on it. They go for the 4 ohm cab first to get the extra volume and then they're stuck. If they know they want a scalable rig from the start then they should have gone for the 8 ohm cab first and then bought a second 8 ohm cab later. For you I have no advise except to either buy a third cab in 8 ohms or else trade in your 4 ohm cab for an 8 ohm one. Sorry. I do not recommend you run both together for the reason you already stated.

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Post subject: Re: Extension cab help needed - ohms matching
Posted: Sun Mar 31, 2013 5:52 am
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Thanks for your help & response - yeah, tough lesson learned.


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Post subject: Re: Extension cab help needed - ohms matching
Posted: Sun Mar 31, 2013 12:23 pm
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Firstly, that single 4 Ohm 600 watt cab is not perfectly matched to the head which does 900 watts at 4 Ohms. A full 1/3rd of the power capability is wasted plus you risk blowing one or both speakers if you push it past 600 watts. Used with that cab, you might as well have a 600 watt 4 Ohm amp.

Secondly, when using the same 900 watt 4 Ohm head that 1x12 8 Ohm 350 watt cab you bought is INSUFFICIENT to pair with another 8 Ohm cab for the same reason as the first thing. It just doesn't have the power capacity.

Third, never mix cabs with different Ohm ratings in a stack. Don't pair 8's and 4's. You can use a pair of 8 Ohm cabs with a 4 Ohm amp and a pair of 4 Ohm cabs with a 2 Ohm amp. You have a 4 Ohm amp, so you can use a pair of 8 Ohm cabs or a single 4 Ohm cab. A 4 Ohm cab that can handle 900 watts would be far better than the 600 watt one you have now.

Fourth, you are usually restricted in power capacity by the lowest wattage rating cab doubled. With the 350 Watt 8 Ohm 1x12 cab even if you add another 8 Ohm cab you won't get to use all 900 Watts that head has. You could use 700 of the 900 watts wasting about 22% instead of the 33% of the amp's capacity going to waste now. Neither one is a great solution.

In short, for maximum wattage and to insure you don't blow a speaker are going to have to sell/trade/buy some cabs.

If you don't want to sell/trade anything you have already, then there is only one thing you can do that will allow you to use both the cabs you have. That 900 watt GB head has an effects loop send that will double as a slave amp output. You can use it to patch to a "slave" power amp. It doesn't have to be a bass amp with a preamp, it just needs to be a power amp.

Without buying more speaker cabs, you can use a slave power amp to push the 8 Ohm 1x12 cab now. You'd want one that will only push 350 watts into the 8 Ohm 1x12 cab. So something like this power amp: QSC GX3 Stereo Power Amplifier. Street price is about $250. It does 350 watts into 8 Ohms. You could add one more 8 Ohm cab to this slave amp later and get about 500 watts from it. So with one cab fed by the slave amp combined with your 2x12 from the Genz Benz 900 that would give you about 950 watts of capacity. Add another 8 Ohm cab to the slave amp and you'll have 1,100 watts of capacity.

What I'd do is sell or trade the mismatched cabs you have now and re-cab with a pair of 8 Ohm cabs that will handle the 900 watts at 4 Ohms, meaning they each should handle 450 watts minimum, or with one 4 Ohm cab that handles at least 900 watts. Yes you can do the slave thing for $250, but you'd really gain almost as much volume with a cab or cabs that match up power wise and impedance wise with the head and then not have so much gear to tote.

12's and 15's or 18's sound fine indoors but outdoors I always want the punch of 10's to carry. The deeper tones from larger diameter speakers just don't carry as well outdoors as the more piercing tone of 10's. The fact I love the tone of 15's doesn't change the fact that they are less effective outdoors than indoors.

Here is one cab I know would work with that head and take all 900 watts and be fine. You could buy one in 4 Ohms or buy a pair of them in 8 Ohms. The Avatar B410. It takes up to 1400 watts with stock Delta speakers and 1000 watts with Neo speakers for an up-charge. I'd probably buy the 4 Ohm Delta version so I only had to move one cab. Simple and relatively cheap. They are only available direct from Avatar and the price varies based on cab covering and grill options. (I'll probably go for Line-X with metal grill next time I need new cabs. When I bought my current Avatars about 6 years ago there were no cover/grill upgrade options so I have rat fur and black metal grills.) Or you could go with the Avatar 2x10 8 Ohm cabs and stack them as they take 700 watts each with Deltas and 500 each with Neos. I guess it depends on your ability to haul a more bulky 4x10. I know some people have size restrictions due their vehicle and a pair of 2x10's might work better with a hatchback compact car, however that would cost more than a single 4x10.

One thing I know for sure is that you are never going to maximize your amp's substantial capability with either of the cabs you have right now. You can take 1 of 2 roads. You can add the slave amp for the 8 Ohm cab or re-cab with cabs matched to the power and impedance limitations of your head. I think re-cabbing is the far better, simpler, most efficient and compact of the 2 roads.


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Post subject: Re: Extension cab help needed - ohms matching
Posted: Mon Apr 01, 2013 3:46 am
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Thanks so much Brother Dave. I appreciate the thorough response. I need to re-do my strategy, and it'll cost $$.


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Post subject: Re: Extension cab help needed - ohms matching
Posted: Tue Apr 02, 2013 8:40 am
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How often do you play outside??? Just rent an 810 cab as needed. Cost effective.

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