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Pros and Cons of a 4 Ohm Sub


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As most of you know I have been looking to buy a pair of passive subs.

 

I was tempted for a while by the MRX518S which curiously has a 4ohm driver.

 

Got me wondering why JBL would do that? :confused:

 

Is it mainly because power amps produce more power into a 4 ohm loads? I guess thats fine if you only want to run one per side.

 

Is there more to it?

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I prefere 8 ohm subs as i often on small gigs use one power amp with tops one side and subs on the other. This keeps the amp happy running at 4 ohms.

 

 

Same.

 

I could never understand it which is why i never got a pair.

 

I guess jbl might think that people at this level are only likely to use one sub a side??

 

I think it was the same with their previous mpro model.

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They probably blew the original driver and replaced it with the 4? driver, which they probably drove the piss out of too.

 

 

Nah. The JBL Mrx518, mpro 418 and SR4718x boxes are all 4 ohm boxes.

 

It's a practice that dates back to a time in the not so distant past when 4 ohm subs may have been preferred (especially at the small rig level) because common amplifiers were in the 400 watts at 4 ohms range. Something like a MA2400 that could provide 800w at 4 ohms cost thousands.

 

You'll see that other are other similar single driver subs like previous versions of a SP118s that are also 4 ohms.

 

But now with the widespread availability of big amps for cheap, I think you're probably not gonna see it anymore.

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Nah. The JBL Mrx518, mpro 418 and SR4718x boxes are all 4 ohm boxes.


It's a practice that kind of dates back to a time in the not so distant past when 4 ohm subs may have been preferred (especially at the M.I.) because common amplifiers were in the 400 watts at 4 ohms range.


Something like a MA2400 that could provide 800w at 4 ohms cost thousands.


You'll see that othere are other similar single driver subs like previous versions of a SP118s that are also 4 ohms.


But now with the widespread availability of big amps for cheap, I think you're probably not gonna see it anymore.

 

 

Exactly, and as amps got larger, these companies have found themselves with the delimma of increased warranty claims due to overpowering... as many of these users could not grasp the concept that you must use the 4 ohm amplifier rated power measurement compared with the speaker's power handling (at 4 ohm) rating.

 

4 ohm is just fine IF you know what you are doing. In fact, there are some nice 4 channel amps (like the QSC CX series) that deliver about 500 watts per channel into 4 ohms... that gives stereo tops and subs all in one compact amp. Also, something like the RMX-1450 or 1850 is ideal with these boxes. The 1850 can drive 4 boxes, the 1450 can drive 2.

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I also think JBL put 4 ohm drivers in those boxes to make them sound a little louder on the showroom floor than the competition. I always felt there was a sneaky reason behind that decision, but the main one was probably that they thought most users would just use one per side. Scalability is a more common concept now than it was a few years ago.

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