I have a 2-12 cab running at 4 ohms and a 1-15 cab running at 8 ohms and want to use them both at once from a amp rated for 4 ohms. Is this a problem?
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Using 4and 8ohm cabs from same amp
- Thread starter rberry7777
- Start date
+1
Running a 4 and 8 Ohm cab presents an impedance below what is save for a 4 Ohm stable amp. 2.66 Ohms.
Hi,
It's not recommended but I've done it a lot with my rig. I have Carvin Red Line series speakers (2x10 and 1x15) with a GK 800RB. That speaker combination puts the total load at something like 2.67 ohms. Some amps will NOT like this but mine has never been a problem.
Thank you for your indulgence,
BassCliff
It's not recommended but I've done it a lot with my rig. I have Carvin Red Line series speakers (2x10 and 1x15) with a GK 800RB. That speaker combination puts the total load at something like 2.67 ohms. Some amps will NOT like this but mine has never been a problem.
Thank you for your indulgence,
BassCliff
Horrible anecdotal advice! Do not run your amp below what it is rated for.
There is no way to "re-wire" a 4 Ohm 212 into an 8 Ohm 212, with out replacing the drivers. That would probably be pretty cost prohibitive.
You could, but that would require building a special cable, or a series box. Also need to make sure that the cabs are wired in phase.
Then you would have a 16 ohm 2X12, and a 8 ohm 1X15.
The 1X15 will get 2/3 the power from the amp, while the 2X12 only gets 1/3 - counter-productive.
Thanks guys. I did try it and it sounds great
Not sure how my gk. Mb200 would like it as a sustained diet. Not talking bout a need for huge volume here. It is a great sound though.
Not sure how my gk. Mb200 would like it as a sustained diet. Not talking bout a need for huge volume here. It is a great sound though.
Correct. In fact, there is no feasible way to use these 2 cabs with your current amp, including with a series cable. Just not a good plan at all. Something would have to change, either the amp, or one or both cabs. Just run the amp with the 4 ohm 212, and call it good., If that's not enough volume, something's gotta give. Do NOT run that amp below 4 ohms, unless you don't care if it fries, which it will.
BurningSkies
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- Feb 20, 2005
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As a sustained diet!
Also, if you do more damage than just blowing fuses or the amp-auto-shutdown, you'll be out of luck for warranty work for the amp.
While I will not recommend running an amp into a lower load than it is rated for, I think most modern amps will go into protection mode before frying. Unless you are really cranking the volume right from the get-go, in which case you may be able to fry a few output transistors before the protection circuit reacts, but I still think it's a long shot.
Nevertheless, I don't like to have my amps go into protection mode either, especially at a gig! I would say don't run below rated load.
Nevertheless, I don't like to have my amps go into protection mode either, especially at a gig! I would say don't run below rated load.
Are you using both speakers through your "lo" output?
An 800 rb can easily run that load with the 4 ohm cab on the 300w "lo" output, and the 8 ohm cab on the "hi" output.
You still wouldn't have 2.66 ohms though as you have two separate power amps being dual mono or biamp.
Either way not really relevant.
This post is so wrong on so many levels. Running an amp below its minimum impedance is abuse pure and simple. Relying on the protection circuit, if the amp even has one in the first place, is faulty thinking. It's like driving dangerously 'cos you "know" the airbags will save you if you have a crash!!
Protection circuits are there to HELP prevent accidental damage or occasional stupidity. Intentional stupidity is not a realistic design possibility.
That's right. It can be done and it is definitely NOT recommended. I have read in threads here that amplifier company reps have said the same thing.
The thing is that amplifiers are limited in the amount of voltage and current that they can produce. It is excessive current that will cause overheating and damage to components. Lower impedance results in higher current. At a less than maximum volume level the amp will not be putting out its maximum current.
Then there is the issue of the variability of a speaker's impedance. Some speakers have an impedance LOWER than their rated nominal value at certain frequencies so with them it happens ANYWAY. [Invalid or Expired Link Removed] is one example, the Legend CA154. It drops below 3Ω at about 150Hz and it is rated at 4Ω. Outside of about 100Hz to 400Hz it is actually quite a bit higher. At 100Hz it is 5Ω and it rises as the frequency goes lower. At 500Hz it is also 5Ω and it rises as the frequency goes higher. The Kappa 3015 behaves practically the same way. It is rated at 8Ω and gets to about 6.5Ω at 200Hz and rises on both sides of that. This means that with two of those you have about a 3.2Ω load on your amp at 200Hz and you don't see people writing not to use them with a 4Ω amp. When loaded in a cabinet the same thing goes on. Link Removed. That cabinet goes below its nominal 8Ω at several frequencies so, of course, two of them will be below 4Ω at those frequencies. It should be mention that with two cabinets having a nominal 2.7Ω impedance it is highly likely that they will go below that at certain frequencies.
My point is it is not as dire as some seem to be making it. It CAN be done but one can not expect the maximum volume level from your amp and it is taking a risk that could prove hazardous to the amp's health.
The fact that you MIGHT get away with it will not help if in set two your rig goes silent and you turn around to see smoke. Yes impedance is not a fixed value, but exceeding the minimum load intentionally on an amp is just tempting fate.
<sigh> There's none so blind as those who chose not to see!
When you abuse your amplification it WILL fail. It just depends when!
