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ohm changing before amp?


ziggydolphinboy
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Hi all,

 are there any deivices , units that can change the ohm rating before you come out of the amp..or in?

 

bassically i have two 4 ohm cabs and the amp only goes to 4 ohms meaning i can only run one cab from the amp?

 

im a complete mindblock with ohms i just dont get it.

i have a ebs head that goes down to 2 ohms so may just use that , but wanna use my new head as it sounds sweet.

 

any thoughts ?

 

kindest regards

ziggy

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You may possibly be able to rewire your 4 ohm cabs to 16 ohm each. Then you can plug one @16 or both into your new amp @8ohms. They would have to be multiple driver cabs. If the amp is hefty it won't have a problem with one 16 ohm cab.

 

Other option is a series cable, for running the two 4 ohm cabs in series = 8 ohms.

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Connecting two cabs in series isn’t advised unless they’re identical though, I thought? Otherwise (if you find ohms confusing, look away now) the interaction of the varying impedances at each frequency can give you undesired behaviour. 
 

@ziggydolphinboy if you can’t rewire both cabs, another option could be to run the aux out or post-fx DI out from your amp to a power amp that would drive the second cab?

 

 

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there are a number of advantages of running two cabs at 8ohms

 

The increase in radiating area increases the efficiency so you'll get an extra 3db of sound, this is greater than the roughly 2db you'll lose because your amp will produce less power into 8ohms.

 

You'll double the power handling.

 

The excursion of each speaker will be reduced this is usually the ultimate determinant of how loud the system will go and instead of the peaks taking the speaker into distortion using two will bring them back into their designed operating area.

 

The halving of the power to each speaker will reduce the temperature and resistance of the voice coils at high levels reducing thermal power loss.

 

stacking one speaker on the top of the other will bring the speaker nearer to ear level so you will hear the crucial mids and highs and be hearing more of what the audience will hear

 

It looks cool

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There is no real way to mess with impedance. Yes you could use a transformer but it will be both heavy and expensive. The unit mentioned above will change 4Ω to 8Ω so you would need two - one for each cabinet. All four of my Acme B2 2x10 cabinets are 4Ω. Then again all of my amplifiers are happy into a 2Ω load. My power amps will drive 2Ω per channel so they can push all four of my boxes at once.

 

In your case I would pick up a stereo / two channel power amp and drive it from your existing amplifier. These are pretty cheap for what they bring to the table.

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6 hours ago, chris_b said:

Where is the benefit?

 

My untechnical guess is that 2 4 ohm cabs running at 8 ohms, with a series cable, would sound like 1 4 ohm cab running at 4 ohms.

 

8 hours ago, nekomatic said:

Connecting two cabs in series isn’t advised unless they’re identical though, I thought? Otherwise (if you find ohms confusing, look away now) the interaction of the varying impedances at each frequency can give you undesired behaviour. 

 

 

That's correct.

 

It blew me away when I found out that cab impedance varies widely with the frequency.

 

I have no idea how series funk happens, despite Agedhorse's best efforts.

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1 hour ago, ziggydolphinboy said:

Thank you all ever so much,

 Plan is use my new ats stuff for one band and main baand at smaller gigs.

bigger gigs use my ebs to run both cabs or epifani head with the new stuff

 

sorted

thank u all

 kindest regards

ziggy

Not sure what that means.

 

Ultimate caution warning. Do not connect two amps to one set of connected cabs, not even by mistake, or you will get two smoking ruined amps almost instantly.

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15 hours ago, nekomatic said:

Connecting two cabs in series isn’t advised unless they’re identical though, I thought? Otherwise (if you find ohms confusing, look away now) the interaction of the varying impedances at each frequency can give you undesired behaviour. 
 

 

 

 

Correct, when cabinets are different the reactive loads can interact in less predictable ways. When this is done with identical drivers, like in a 210 cabinet using 2 x 4 ohm drivers in series, there is no problem.

14 hours ago, chris_b said:

Where is the benefit?

 

My untechnical guess is that 2 4 ohm cabs running at 8 ohms, with a series cable, would sound like 1 4 ohm cab running at 4 ohms.

Not really. Even though the power to the two cabinets would be less, the gain due to coupling as well as at high output levels the reduction in power compression might make the two end up being quite close in practice (depending on the sensitivity of the cabinets of course).

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On 17/11/2021 at 01:23, Downunderwonder said:

Not sure what that means.

 

Ultimate caution warning. Do not connect two amps to one set of connected cabs, not even by mistake, or you will get two smoking ruined amps almost instantly.

its kool, ill use my new rig for smaller gigs,

big gigs ebs head running 2 4 ohm cabs .

 or one head to one cab and just rub a stereo out from my pedal board 🙂

 

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