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Currently I'm using Yamaha EMX512 powered Mixer to power 2- 15" speakers in a MONO setting. 2 speakers are run out of 1 side of the AMP.

What do I need if I want to add a 18" PASSIVE sub into this set up (besides the sub itself )
Do I need an additional power amp ? or can the other side of the EMX suffice?
I assume I'll need some type of crossover ???


If I go POWERED SUB .... do I still need a crossover --I can't tell if the EMX has any internal crossover ??

Apprecaite any advice.

If you buy a passive sub you will need a power amp. Your powered mixer will not have enought power for a sub and it will not have a crossover.

Some amps have built in crossovers, along with most powered subs have crossovers.

For best sound if you buy active or passive you should use a crossover.

Okay, here's the deal. Right now you are using the amp in mono+monitor mode. If you do not have a monitor connected, you have a free amp channel that could be used to drive a sub. You would hook the sub up to the second amp output and dial in the amount of sub power you want with the monitor knob on the channels.

This shouldn't have a significant impact on the power available to your amp ch1 connector, which is currently running your FoH speakers. It will add heat to the unit, of course; so that might be a limiting factor if you really drive it hard.

What you should not do is run your two 15" speakers plus a sub with a passive cross-over off one amp channel. The EMX512 is for 4 or 8 ohm loads, and if you use three 8 ohm speakers on it, you are going well below 4 ohms, and it will not work for very long at a reasonable power level before it over-heats.

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Jeff Wheeler, moonlight DJ/KJ

So I "CAN" use the 2nd amp to power a sub ?

The one channel would be pushing 4ohms ( 2 8ohm spkrs) and the 2nd channel will be pusshing 500watts @ 4ohms.

But without a crossover --I would be sending a FULL signal to the SUB ?
Is that OKAY ? or will it defeat the purpose of the SUB??

Check the manual for your sub if you have it. There are some sub cabinets that do have a passive cross-over in them. If it doesn't, I wouldn't recommend sending it a full range signal. At minimum it would affect audio quality, in the rare worst of cases it could actually cause some damage. I would then instead recommend you get a separate power amp and crossover.

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DJ Tony
Let It Rip Karaoke

I have not heard of high-frequency content causing damage to a sub. If the sub does not have a cross-over network it will contribute heat, but it shouldn't hurt anything.

Yes, the configuration I suggested will send a full-range signal to both your tops and your sub. That will make them work against each-other, but I don't think the EMX512 has a power amp insert jack, so the only way to avoid this would be an out-board cross-over and some creative signal routing, or just buy an out-board amp.

A powered sub might be a good choice for you, though I loathe powered speakers.

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Jeff Wheeler, moonlight DJ/KJ

I haven't actually purchased a sub yet --so I should look for one with a built in crosssover ?

Would this sub - do the trick ???
http://pro-audio.musiciansfriend.com/pr ... sku=601342

That sub should be fine, has an internal low pass filter built in so it won't be trying to reporduce the entire frequency range. Only possible problem is the tops will not be crossed over at the subs frequency so they will still be trying to reproduce the frequencies as low as possible, possibly causing some phase cancellation in the sub frequencies actually reducing the subs effectiveness. It is an 8 ohm sub & the Yamaha amp pushes 350 watts into 8 ohms - pretty close match.

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LIKE Lonman on Facebook - Lonman Productions Karaoke & my main site via my profile!

"IF" I went this route and used 1 side of the amp for mains and the other side for the SUB. Would you suggest any special EQ settings on the mains to remove some of the bass or it wouldn't matter ?

Since each would have their own eq, i'd probably cut a little of the low end to the main cabs - the 125hz would be really all that would need to be cut to sort of compensate for the subs crossover point of 125 (I think that's where it is internally set). On the sub eq you won't really need to adjust anything over the 250hz range as the sub is already cutting out everything above 125 anyway.

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LIKE Lonman on Facebook - Lonman Productions Karaoke & my main site via my profile!

A graphic equalizer is no substitute for a high-pass filter, so bear that in mind. I do not agree with Lonman's suggestion that a 125 cut will be beneficial. It will reduce interaction with the subwoofer in the cross-over region but you will end up creating a gap in frequency response between where the sub is rolling off and the top is picking up. You will save amp power and top speaker heat, though there is no guarantee it will sound better.

"If it sounds good, it is good," so I am not saying don't try it; but it's not the kind of result you would have if you were able to use a proper cross-over device.

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Jeff Wheeler, moonlight DJ/KJ

Oh, and you *can* EQ out everything on the sub about one octave above the cross-over point, or two if the subwoofer's passive low-pass filter is not very steep. Ordinarily, this would create peaks and dips in frequency response; but since the sub is going to roll the signal off at probably 12 - 18 dB/octave, once you get a couple octaves above that point, no useful sound will be produced anyway. What will happen is the amp will still produce signal, so if you cut those higher frequencies out of the sub before they reach the amp, it will increase amp headroom and decrease heat.

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Jeff Wheeler, moonlight DJ/KJ

No it isn't a substitue, but can help & the gap will be minimal. All I was getting at is the tops are going to be trying to reproduce those same low frequencies that the sub is now going to be picking so cutting that low frequencey on the top will help a bit in that the tops won't be pushing those lower frequencies as hard.


I agree, but since his amp has no way to properly connect an external crossover - without adding new external amps - this bandaid method will help.

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LIKE Lonman on Facebook - Lonman Productions Karaoke & my main site via my profile!

Wouldn't it be easier to just use an active sub that has an active crossover This way he could use his tops in stereo and use it's eq to reduce the low frequencies

Micky has a good point. Since he's using a powered mixer, he might be better off using a powered subwooofer and just sending it a signal. I have the same powered mixer and I use the passive EV Sb122 subwoofer with my tops. The Sb122 sub has a filter built in so one top and one sub per side can be connected in parallel so no crossover is needed. The Sb122 is very light and portable, but it's almost $400 each and really performs best with a lot more power that the EMX512 puts out IMO.

For it's size, weight and price I don't think there is anything else out there that compares to the Sb122. If he's using a pair of 8 ohm speakers on poles, he can add one Sb122 sub per side without the need for a crossover or an additional amp. I use one EV Zx1 and one EV Sb122 per side with a small amp or with my Yamaha EMX 512 and it sounds great. I can also run my EV Sx100 speakers with the EV Sb122 subs off the Yamaha EMX512 if I need more/louder sound.

It still wouldn't help the fact that even if his sub had an active crossover that the tops would still be trying to reproduce the same frequenices because THEY still souldn't be crossed over at the subs low pass filter. Same situation - just different amps!
In which using the eq to adjust the low frequency would still be the same method I said a few posts agw using the internal amp of the Yamaha - yes it's a bandaid method, but will help. Not be great - NO!

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LIKE Lonman on Facebook - Lonman Productions Karaoke & my main site via my profile!

It *might* help, but it might not; as a 125Hz cut is going to produce a curve that stretches up to 250Hz before it becomes flat again. My concern was it may cause a frequency response gap that might be worse than letting the tops fight the subs a little bit. OTOH most people will probably never hear the difference either way; as I have my monitors cut -18dB all over the place and singers never complain, but if I didn't and there was a bunch of feedback, you bet they would complain about that!

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Jeff Wheeler, moonlight DJ/KJ