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Author Topic: 2 ohm loads on bottom end  (Read 19777 times)

Kevin Conlon

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2 ohm loads on bottom end
« on: August 23, 2016, 10:18:29 pm »

I have never been a fan of 2 ohm loads, so close to a dead short. I have been reading and people say 2 ohms on a "modern" amp is ok. What i have is a QSC 4050HD, discontinued for the A model i think. QSC gives an output rating for 2 ohms, like 1600 watts per side. I want to use it on 4 ev mtl2b cabs (dual 18 manifold design for the youngsters). each cab is 4 ohms and i have been driving them with 4 BGW 620a mono amps ( no one has been able to id this mono model yet) and they do very well. I have 3 bgw amps x2 racks, 2 in use and a spare on each side, running on 240v. As i said they sound great but before i use the QSC i just want some feedback on using it at 2 ohms on a all day event. Next big thing i need the subs for is bluegrass and accustic stuff leading up to wide open rock for the closer at an outdoor festival. Is this 4050 modern enough for the task? I have access to another one( one serial # apart) for one channel per cab if this would be better. Thanks for any input!
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John L Nobile

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Re: 2 ohm loads on bottom end
« Reply #1 on: August 23, 2016, 10:32:03 pm »

Good question. I for one never run my subs at 2 ohms. But I'm old and I don't even think that was possible with old amps.
I'm curious to see what others have to say about this.
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Kevin Conlon

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Re: 2 ohm loads on bottom end
« Reply #2 on: August 23, 2016, 10:57:21 pm »

Good question. I for one never run my subs at 2 ohms. But I'm old and I don't even think that was possible with old amps.
I'm curious to see what others have to say about this.
I have lost amps to 2 ohm loads in the past. Transformer out tube amps i had hooked up wrong, nice smoke, but repairable. That is why i am reluctant to use it that way. I can series the cabs for 8 ohms but i have to try an a/b with the bgw's for output.
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Luke Geis

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Re: 2 ohm loads on bottom end
« Reply #3 on: August 24, 2016, 02:53:59 am »

Modern amps don't really care that much. I have seen it done and have had to do it. I don't like to do it for a couple reasons. Those reasons are debated a bit and may be irrelevant to you?

First for me is damping factor. This is a highly debated subject, but if you can have a better designed system that gives the best possible odds for performance, then why not design it that way? Effectively a damping factor of anything better than 20 is considered good. Well at 2 ohms, a 50' 12ga. cable will yield a DF of 12.3 considering a typical amp capable of a DF of <500! So not as good as it can be. Bring the ohm's back up to 4 and you sit at about a DF of 24. The cable length is a large part of this problem. Double, or halve the length and you double or halve the DF. This particular amp in question has a DF of <250. With a 50' 12ga. cable at 2 ohms you would have a DF of 12 and with a 4 ohm load you would have a DF of 23.

The second reason I don't like running down to 2 ohms is that THD usually rises as well. Again not a huge deal, but if your going to go for the best you can get..... A THD of around 10% is no longer pleasant to most people. Most amps won't produce that much even when your trying to play bad with them. It is a concern though if your are designing your system that way because your already near the end of the line and trying to get a little more. Not all amps will double the amount of power available when halving the ohms rating. If it takes 2X's the power to see a 3db boost in SPL, then anything less than double the power is pretty much not helping you. If you're already at the limit, 3db isn't going to get you much further. The likelihood is your going to burn through that extra output and induce just that much more THD into the sound.

In your case you have two 4050hd's. They should produce realistically 1,600 watts at 2 ohm's per side. The 4 ohm rating is only 300 watts lower per side @ 1,300 watts. In other words, negligible. If it were me, I would use both RMX4050HD's and run 1 speaker per channel.

It is a trade off. Ideally you want to run the highest ohm rating you can on any given amp that will still properly power the speaker. Unfortunately most amps don't produce 1000+ watts into 8 ohm's. So most are relegated to 4 ohms which is pretty much the standard rating for most speakers. 2 ohms is the end of the line and again most all modern amps will do it, but at what cost?
« Last Edit: August 24, 2016, 02:59:39 am by Luke Geis »
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Steve M Smith

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Re: 2 ohm loads on bottom end
« Reply #4 on: August 24, 2016, 02:58:05 am »

I think the best option is to have amps capable of running to 2Ω but run them at 4Ω.  Then if an amp goes down, you can double up the outputs to finish a show.


Steve.
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Ivan Beaver

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Re: 2 ohm loads on bottom end
« Reply #5 on: August 24, 2016, 08:05:40 am »

The correct answer is "It depends".

I have run some amps with a 2 ohm load into clip doing EDM shows and it has been fine-the sound good etc.

It depends on the amp, the length of the cable etc.

Some modern amps handle 2 ohm loads better than others.

Just because it is "rated" at 2 ohms does not mean it can do it under all conditions.

Some amps "fizzle out" at 2 ohms.  Others are solid.

Also you have to consider your speakers.

Just because they are "rated" at a particular impedance DOES NOT mean the ARE that impedance.

That is simply the "nearest" standard number.

They could be higher or lower.

And of course the impedance varies QUITE A BIT depending on the actual freq.

What is the impedance at the kick drum tuning?  It might be 18 ohms or 3 ohms.  That is where the most stress would be-generally.  With many types of EDM around 53Hz is the most stressful.

So you often have to look a bit deeper to get the REAL answer.

But your question, I have used the older 4050 on subs in quite a few installs and they have worked well.  But these have not been in stressful situations and generally I only loaded them to 4 ohms.
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John Roberts {JR}

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Re: 2 ohm loads on bottom end
« Reply #6 on: August 24, 2016, 10:23:06 am »

I think the best option is to have amps capable of running to 2Ω but run them at 4Ω.  Then if an amp goes down, you can double up the outputs to finish a show.


Steve.
What he said....

JR
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John L Nobile

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Re: 2 ohm loads on bottom end
« Reply #7 on: August 24, 2016, 10:33:49 am »

I think the best option is to have amps capable of running to 2Ω but run them at 4Ω.  Then if an amp goes down, you can double up the outputs to finish a show.


Steve.

That's my backup plan.
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John Roberts {JR}

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Re: 2 ohm loads on bottom end
« Reply #8 on: August 24, 2016, 11:16:12 am »

The correct answer is "It depends".

I have run some amps with a 2 ohm load into clip doing EDM shows and it has been fine-the sound good etc.

It depends on the amp, the length of the cable etc.

Some modern amps handle 2 ohm loads better than others.

Just because it is "rated" at 2 ohms does not mean it can do it under all conditions.

Some amps "fizzle out" at 2 ohms.  Others are solid.

Also you have to consider your speakers.

Just because they are "rated" at a particular impedance DOES NOT mean the ARE that impedance.

That is simply the "nearest" standard number.

They could be higher or lower.

And of course the impedance varies QUITE A BIT depending on the actual freq.

What is the impedance at the kick drum tuning?  It might be 18 ohms or 3 ohms.  That is where the most stress would be-generally.  With many types of EDM around 53Hz is the most stressful.

So you often have to look a bit deeper to get the REAL answer.

But your question, I have used the older 4050 on subs in quite a few installs and they have worked well.  But these have not been in stressful situations and generally I only loaded them to 4 ohms.
If unwilling to investigate all of the "it depends" just run the 2 ohm amps at 4 ohms and be safe.

Amp designers generally try to make their amps customer proof, and speaker designers generally try to make speaker impedance that won't be too stressful on amps.

The 2 ohm and 4 ohm ratings are not precise static impedances but general guides to aid in system configuration.

KISS

JR
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Ivan Beaver

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Re: 2 ohm loads on bottom end
« Reply #9 on: August 24, 2016, 12:28:06 pm »



Amp designers generally try to make their amps customer proof
Like the old Peavey CS800 that people either love or hate.

You could drive it into a dead short on the outputs and the amp would not die.

In fact that was the final test after a repair.  Short out the output terminals and drive it into full clip until it shut down.  Then remove the short and if it still worked, the repair was good.
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Ivan Beaver
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ProSoundWeb Community

Re: 2 ohm loads on bottom end
« Reply #9 on: August 24, 2016, 12:28:06 pm »


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