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need coaching, how to run passive sub off powered mixer


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I have a EMX512s which is a 500 x 2 powered amp. After alot of testing, I have decided that my low budget setup just won't quite cut it with only 2 mains so I am going to go with a simple 2 mains + 1 sub setup.

 

My current thought is to use:

2 yamaha S112v on poles for my mains

(originally wanted S115v but these take less power and had bit better mids + cheaper)

1 yamaha peavey or JBL passive sub

 

My thought is to hook up the 2 yamaha speakers into my main channel. My understanding is since each speaker is 8ohm, I would have a 4 ohm load and my main channel power amp sends 500 watts at 4 ohms so that would mean 250watts to each speaker.

 

Then I was planning to use the monitor channel to feed the single sub. My power amp sends 500 watts at 4 ohms or 350 watts at 8 ohms so I as assuming that means I would get 350 watts to my passive sub if it is an 8 ohm box. Looking at the smaller passive subs out there, they all seem to be in that ballpark power wise.

 

Later I plan to buy a couple powered monitors and connect them to the monitor line out on my amp.

 

Main question is can I do this? I realize it probably is not the ideal setup but just wondering if it would work for someone on a budget? I am trying to get a startup classic rock band ready to do some small gigs as soon as school lets out which is in about a month.

 

thanks for any input you are willing to share. I did the band thing back in the 80s but it was a long time ago and I mainly did adjustment, not setup or config so just trying to learn as I go here.

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i do not think this will work effectively for you.

 

you need a crossover for both the tops and subs as well as external amplifiers to fully pull this off.

 

you CAN route and power the speakers like you describe, but you will not like the result. your sub will likely act as a near-full range driver with out a crossover - depending on actual sub of course. this will ultimately result in comb filtering due to multiple sources of similar signal.

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As I see it, you should be able to execute this, but I'm fishing a bit here - I'm really not sure of routing on that thing. So I'll throw out some theory...

 

Set the mixer to "stereo", or Main L/R. You are still going to run in mono, but this will allow you to use the "monitor out" to run a line to some powered monitors (or monitor amp/passive monitors) later. Pan all instruments to left

 

Plug mains into amp a, sub into amp b. Run a line level cable out of "L Main out" on front of mixer into a crossover (Check out a product called the Rolls "Tiny" Crossover (sx21). Great little $60 active unit for crossing over with a powered mixer.) Crossover "high out" into "L Main Amp Input" of Yamaha Mixer. Crossover "Low Out" into "R Main Amp Input".

 

I would think that would work (depending on whether the Yamaha has all these routing options) and still leave you a line out for monitors...

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thanks for the comments guys. I am probably not doing a great job of explaining what I am thinking about doing and without a picture, it is hard but the yamaha powered mixer I use sends 500 watts to the main speaker channel (marked A) and 500 watts to the monitor speaker channel (marked B).

 

I was thinking I could power both yamaha SM112V speakers thru channel A by just daisy chaining them. Ie. the channal A output goes into one speaker which is then connected to the second speaker so they share that 500 watts.

 

Then I would use channel B to power a single subwoofer by just connecting the channel B output to the single passive sub.

 

When I buy 2 small powered monitors, I connect them to the 2 Main out jacks which the instructions in my owners manual say can be used to send unpowered signals to a set of powered speakers.

 

I guess the main part I am unclear about is using the channel B for a single sub. Will the sub use that powered signal and automatically filter out the high frequency or can I manually filter it out with 7 band EQ for the monitor channel or would I have to have an external crossover. Some subs say they have built in crossovers. Oh confusing stuff.

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thanks for the comments guys. I am probably not doing a great job of explaining what I am thinking about doing and without a picture, it is hard but the yamaha powered mixer I use sends 500 watts to the main speaker channel (marked A) and 500 watts to the monitor speaker channel (marked B).


I was thinking I could power both yamaha SM112V speakers thru channel A by just daisy chaining them. Ie. the channal A output goes into one speaker which is then connected to the second speaker so they share that 500 watts.


Then I would use channel B to power a single subwoofer by just connecting the channel B output to the single passive sub.


When I buy 2 small powered monitors, I connect them to the 2 Main out jacks which the instructions in my owners manual say can be used to send unpowered signals to a set of powered speakers.


I guess the main part I am unclear about is using the channel B for a single sub. Will the sub use that powered signal and automatically filter out the high frequency or can I manually filter it out with 7 band EQ for the monitor channel or would I have to have an external crossover. Some subs say they have built in crossovers. Oh confusing stuff.

 

the Yamaha EMX512 has two built in amps, which can be run as:

Main left/right or

Main "mono" and Monitor

 

 

May I humbly suggest you run the Yamaha in "Main L/R" mode with the tops on one side and the sub on the other. Then when you get powered monitors run them off the "monitor out" jack. This will allow you to run a seperate monitor mix for the monitors. The small challenge with this setup is plugging in break music, as channels 7 and 8 (or 9/10 and 11/12 as labled on the EMX) accept stereo RCAs, and you probably don't want to run your break music with the left side coming out the sub and the right coming out the top :rolleyes: but you can solve this with a simple stereo to mono rca adapter.

 

As others have pointed out, you will get comb filtering where the sub and tops frequencies overlap (probably 80-1000hz or so), this may or maynot be a big deal. You'd have to listen and see how bad it is.

 

Best is to use a crossover to send the appropriate frequencies to the top and sub, but the EMX has no amp I/O jacks (I think the Mackies do) so if you want to use a crossover, it will have to be passive.

 

You suggested using the 7 band EQ to roll off the high freqs sent to the sub, and this could be done if you run the sub off the monitor send as you originally stated you intended to do. Using the EQ as a substitute for a crossover may help, but this is a poor substitute. It will only reduce the higher freqs by 10-12 db, and running extreme eq like that introduces it's own problems.

 

Better is using a passive crossover for the sub (as discussed on a different thread you were involved in). I poked around and found a few passive crossovers at parts-express, but they are only rated to 200 watts and cost $50+. I understand the parts get expensive building a high wattage low pass crossover.

 

Best would be using a powered sub with a built in active crossover. Plug it into one of the main outs on the front of the EMX and away you go.

 

Bottom line to all this though, is try it out yourself. If it sounds good to you, go for it!

 

good luck!!!

:thu:

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t

I guess the main part I am unclear about is using the channel B for a single sub. Will the sub use that powered signal and automatically filter out the high frequency or can I manually filter it out with 7 band EQ for the monitor channel or would I have to have an external crossover. Some subs say they have built in crossovers. Oh confusing stuff.

 

 

most quality subs do NOT have passive crossovers built into them.

 

A well designed passive crossover can work well in a quality top box, but pro audio systems almost ALWAYS use active crossovers for the sub/top box frequency split.

 

Some lower quality subs do have passive corssovers, and you might be satisfied with one of them (but probably not).

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Plug mains into amp a, sub into amp b. Run a line level cable out of "L Main out" on front of mixer into a crossover (Check out a product called the Rolls "Tiny" Crossover (sx21). Great little $60 active unit for crossing over with a powered mixer.) Crossover "high out" into "L Main Amp Input" of Yamaha Mixer. Crossover "Low Out" into "R Main Amp Input".

 

 

this would be a fine solution, but the EMX512 does not have amp I/O jacks.

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Plug mains into amp a, sub into amp b. Run a line level cable out of "L Main out" on front of mixer into a crossover (Check out a product called the Rolls "Tiny" Crossover (sx21). Great little $60 active unit for crossing over with a powered mixer.) Crossover "high out" into "L Main Amp Input" of Yamaha Mixer. Crossover "Low Out" into "R Main Amp Input".

 

Heres the output section from the block diagram. Isuppose an ambitious DIYer with no concern for the warranty could easily add I/O jacks to do this

 

:thu:

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Looks like it has Main and Monitor outs, but no lines back into the external amp to use it as a slave. hmmmm - that's not very good design IMO.

 

not arguing here, just pointing out the reality of hardware design.

 

I am a software architect at a fortune 50 company. The company is best know for it's hardware, and while I work in a software group, I know a lot of guys who work in hardware, where alot of decisions are made based on sub-penny savings on a $200 retail product.

 

False economy? Maybe, maybe not. I would bet that 95% of the buyers of the EMX512 wouldn't know what to do with amp I/O jacks. And if you need them, there are more expensive mixers that provide them. I'll also point out that while the EMX512 is "stereo" there is not a single balance knob on the box :) I own one of these mixers, and think it is a mighty fine for it's intended purpose.

 

Its all good!

:thu:

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thanks guys and I am picking up alot of good info by reading this forum. I'm not prepared to tackle modding my PA at this point (afraid I would screw it up) so looks like either getting an active crossover with a passive sub or going for an active sub is the way to go. With the cost of the crossover, might be smarter to shop around for a reasonable active sub so then I could at least use the monitor channel on the amp to power passive monitor speakers which i already have.

 

Haven't even shopped for powered subs but expect they will be quite a bit more $$$. Guess I better keep saving up.

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I've been thinking about adding a main in L and R to my PA and wanted to run something by the experts. Since I don't really want to drill extra holes in my box, I was thinking about taking the effect out and foot switch jacks that are already in the box and just rewiring them to be the main in jacks. That way I could always restore the box to original specs if I needed to later. The part I don't know is what would be the best spot to tie them in.

 

Oh wanted to add, i would not be doing the actual soldering job but would be taking it to my Dad who is a retired Engineer from the aviation industry. He would have no problem doing the physical soldering job but would need to know where to tie the lines in.

 

Any thoughts?

 

Here is a pic of the PA http://www.sweetwater.com/store/closeup/EMX512SC--Main

 

I was going to just disconnect the wires to the effects out and footswitch so I could use those jacks and avoid drilling holes. I could just as easily use two 1/4" jacks from one of the channels say 7/8 if that ended up being easier.

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I've been thinking about adding a main in L and R to my PA and wanted to run something by the experts. Since I don't really want to drill extra holes in my box, I was thinking about taking the effect out and foot switch jacks that are already in the box and just rewiring them to be the main in jacks. That way I could always restore the box to original specs if I needed to later. The part I don't know is what would be the best spot to tie them in.


Oh wanted to add, i would not be doing the actual soldering job but would be taking it to my Dad who is a retired Engineer from the aviation industry. He would have no problem doing the physical soldering job but would need to know where to tie the lines in.


Any thoughts?



I was going to just disconnect the wires to the effects out and footswitch so I could use those jacks and avoid drilling holes. I could just as easily use two 1/4" jacks from one of the channels say 7/8 if that ended up being easier.

 

 

No expert here, but a few thoughts...

 

Lets get the warnings out of the way... You will void your warranty, you might kill yourself, etc etc...

 

Assuming you will run channel A as your mains and B for your sub out...

I would convert the Yamaha "Main out A" jack into a TRS jack, thus being able to send/receive on this one jack, and convert your Yamaha "Main out B" into a "Main IN B" for channel B.

 

Run a Y cord from the Yamaha to a Rolls SX21 plugging the "Main OUT A" into the SX21 "input", and the "Main IN A" into the SX21 "high output". Run a cable from the SX21 "low output" into "Main IN B".

 

Done...

 

Or - if you really want to get adventurous, consider buying a Rolls SX21, gut it from it's case, and mount the whole thing INSIDE the Yamaha. This would of course, "commit" you to a certain application, but if your setup is consistent, this would be fine. I've seen DIYers do much more extreme mods than this!

 

good luck!!!

:thu:

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