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I'm considering getting a pair of JBL MRX518s subs. I see where JBL specs these at 4 ohms each. I wanted to run the subs off one side of a Crown Xs1200, which would be 1600 watts ( 800 per speaker ) @ 2 ohms. The other side of the amp would be running the mains at 4 ohms. I see where Crown states the THD goes up when running at 2 ohms ( from .15% to .5% ). What are the problems/downside to doing this, if any?

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I think you'll be just fine considering the other amp channel is doing mid/high stuff at 4 ohms. Generally an amp works hardest at 2 ohms on both channels and low frequency program material. All the power going to a speaker comes back and is dissapated as heat, low end uses a lot of power. Since it's only 1 channel though I think you'll be just fine.

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I see where Crown states the THD goes up when running at 2 ohms ( from .15% to .5% ). What are the problems/downside to doing this, if any?

Most of the unwashed run their subs past xmax where their THD is much higher than the amp's anyways. Live you can get away with maybe 5-15% without any problem I think? In fact my theory is that the unwashed dislike properly powered, flat subs because they seem less loud since the low fundamentals are less loud to our ears than the harmonics. I believe this is the "comes alive above xxxx watts" phenomenom often spoken about in reference to certain subs. I cheat and us a fancy harmonics generator (MaxxBass) that simulates this at safe power levels :cool:.

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Thanks! I'd hoped it would be okay. We're not LOUD but we like to run the kick drum and perhaps a little bass guitar (4 string) through the PA at times. BTW, what does this mean?

 

 

I HPF the mrx subs pretty high btw..

 

 

And at around $600.00 each, do ya'll think the JBL MRX subs are decent/good/fair? We only play smaller events with our system. Larger events have their own sound system. Plus, we don't play LOUD, either onstage or in the FOH.

 

Also:

 

 

I cheat and us a fancy harmonics generator (MaxxBass) that simulates this at safe power levels

 

 

Could I replicate this, if needed, with a 31 band EQ to some extent?

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BTW, what does this mean?
I HPF the mrx subs pretty high btw.

 

HPF = High Pass Filter. Most smaller subs drop off below 50hz so it's a waste of power and excursion capability to feed them anything too low. I personally would HPF those at 40hz but if you wanted more "punch" and a more "classic" sound HPF at 50hz would get you more output at the "chest thump" frequencies (80-100hz) for a given wattage amp and make the subs last longer.

 

Also I've heard these are pretty good for a 52 lb cab:

http://www.loudspeakersplus.com/product/SL118S/LPI-CABSSL118S/

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HPF = High Pass Filter. Most smaller subs drop off below 50hz so it's a waste of power and excursion capability to feed them anything too low. I personally would HPF those at 40hz but if you wanted more "punch" and a more "classic" sound HPF at 50hz would get you more output at the "chest thump" frequencies (80-100hz) for a given wattage amp and make the subs last longer.

 

 

 

Okay, thanks. In the past, when using some older JBL subs, I did cut them off ( HPF) at 40hz. Since JBL states the MRX's only go down to 45hz, setting the cut off at 45 or 50 hz makes sense. How do they sound above 100hz? I'm using some 2 ways ( 15 and horn ) and I see crossover points from 90 to 120 recommended often. I'm not that fond of the mains and would like to upgrade those as well to a lighter in weight 12" and horn, maybe the MRX512M. However, I see the PRX612 is only a few more bucks. I like the idea of light weight powered mains with DSP.

 

Is it possible to have active, powered uppers like the PRX line and use passive subs, like the MRX line?

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