4ohms on one side and 8 ohms on the other

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The Wizard Of OZ

Well-Known DJ
Dec 13, 2007
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Tampa Bay Area
So, can this be done? This is a theoretical question.

Let's say you have (2) 8ohm passive full range speakers on one channel and one 8 ohm passive sub on the other channel. Is this bad for your amp? Does the amp even care?

More specifically,I have the Yamaha EMX512 powered mixer with 500w+500w.

What about a regular amp with a non powered mixer? Do you have to have the same load on both channels? If so, why?
 
Likely it is no issue. Most mixer amps are designed to run mains/monitors or dual mains. It is understood that they may be loaded with different impedences.

Any modern power amp worth it's salt will handle this with NO issue.

Ben
 
Ben's right. With pro power amps, you actually have two amplifiers in one package. Most DJs use 'em for stereo sound but you don't have to. Amp channels are independent of each other.

One nice option is to use a single amp in mono for bi-amping. Channel 1 can feed your mid-highs. Channel 2 can feed your lows. If you don't need stereo sound, this scenario can save you quite a bit of money in the amp department. :)
 
Giving thirds to Ben and Fred,

It won't hurt a thing, how are you doing the crossover for the sub?
 
The sub I currently have has a crossover built in. It's the EV SB122. From my understanding it doesn't need an external crossover. However, in my pursuit of optimal sound I may get an EQ/crossover so my mains aren't trying to reproduce the same low frequencies as the sub. That should give me a little better sound from what I've read.

What prompted the thread is I was looking at a Yamaha 15" passive sub. If it doesn't have a crossover built in I'll have to get one. I was thinking of getting a combo EQ and crossover unit or a DBX driverack or similar type unit because I want to put together a rack with an amp, an EQ/crossover and a non powered mixer. If I don't go that way I'll get a couple of dual 15" powered speakers and a non powered mixer and a powered sub.
 
if you are running a powered board it will need sub inserts
(send and returns) for the gear to work properly.

For some of my smaller bar shows I use a mixer and then a single 3500 watt amp with a crossover a pair of 10" mains and a single 18" sub. It works well plenty of bass, coverage and volume.
 
Sub inserts? never heard of that. I have run my speakers with one sub connected to a main. Seems to work just fine. These subs were designed by EV to work without a crossover. They pass a full range signal to the mains when connected together. "The Electro-Voice Sb122 is a compact, lightweight subwoofer system that is designed to add bass enhancement to Sx and Zx Series speaker systems". I have a pair of the Sx100.

Here is the description:
The Sb122 combines the advantages of a long-throw 12 in. woofer with a strong, lightweight composite enclosure. The large vent is designed to move more air for increased low frequency output. The EVS12SB cast frame transducer created for the Sb122 uses the same motor and suspension design as the EVS18SB used in EV's acclaimed Gladiator Sub. With nearly two inches of peak-to-peak excursion capability, this is literally a twelve-inch with the heart of an eighteen-inch. An integral low-pass filter allows the Sb122 to be directly connected in parallel with a full-range speaker for truly impressive low-end output without the need for an additional amplifier and processor. Additionally, the filter is transparent below 160Hz, allowing the Sb122 to be used as an independent subwoofer in biamp applications without the need to disable the internal filter. The Sb122 features a convenient pole mount socket on top of the enclosure to allow a small full-range speaker such as the Zx1 or Sx80 to be mounted on the optional ASP-1 accessory pole, resulting in a compact system that sounds much bigger than it looks.
 
Here goes your problem.

Your powered mixer is 500 watts at 4 ohms and 350 watts at 8 ohms.

Your sub is 800 watts program, you are underpowering your sub by 450 watts!

I don't know the make and model of your main speakers, but feeding them 250 watts I am sure you are underpowering them also.

Looks like it's time to get a bigger amp.
 
I need MORE POWER. :sqeek:

I think that's the way I'm leaning. Either add an amp for the subs and run the mains from the powered mixer or start over completely and just keep the powered mixer as a backup. The powered mixer has enough to run the mains, I know that for sure, they're rated at 200w continuous. the subs are rated at 400w continuous.

EMX 512
Maximum Output Power @ 0.5 % THD at 1 kHz:
500 x 2 @ 4 ohms
350 x 2 @ 8 ohms (UA)
320 x 2 @ 8 ohms (H)

I don't know what UA or H designate?
 
You should power your subs with the program power.

They are 400 watts RMS 800 watts Program and 1600 peak.

In all honesty you should power them with about 900 watts.

A QSC RMX 1450 in bridge mono will do nicely.


I you would remind me of your mains I'd be happy to look up the specs on them.
 
I already looked them up and posted their specs up above. EV Sx100, 200w continuous. My powered mixer has plenty of power to push a pair. If I add a second amp for the subs pushing around 600w per channel at 8ohms I should be good with plenty of power. I have (2) of those Sb122 subs. I want the subs to be tight and punchy. The subs are rated at 400w continuous.
 
Wiz,

Why not plan for a bi-amped system? You can use your powerhead to feed your mid-tops in stereo and it's got your processing built in. Just add an active crossover, sub cab and power amp.

Thoughts?
 
Again 200 watts continuous is 400 watts program. You are slightly under powering your tops.

600 watts in under-powering your subs. The most cost effective way to power your subs is Bridge Mono - This makes a 4 Ohm Load.

A QSC RMX 1850 HD is a very good match and will provide both of your subs with 900 watts. If you run the amp in bridge mono.

If you would like a lighter sub amp a PLX 1802 will do the trick.

A QSC GX-5 Is a perfect match for your tops.


I have spent many years using passive speakers and I found out the wrong way to do things, it was quite costly. I don't want to see you making the mistakes I have in the past. It's very important to properly power speakers, when you do they will last a long long time.
 
Thanks, Cam.

The amps will fare better, too because they're not being pushed to their limits. A cool running amp is a happy amp. :)

System headroom is especially critical with subs. If you're doing a wedding reception, it may not matter. But ya never know what you'll be facing. Brother Cam can tell you about those Pennsyltucky shows where you've got a dancefloor that suddenly wants MJ's Billie Jean rattling the rafters. ;)
 
Cam I appreciate your help. I thought the 200 continuous was well within the power range of the powered mixer. If it's underpowering them, then I don't want that. I want clean, crisp sound.

Ok Fred, how about a little primer on bi amp and tri amp cuz maybe I'm not on the same page here. My main speakers are two way with a 1" tweeter and a 12" woofer. I have (2) passive subs. If I ran the mains with the powered mixer and added an amp for the subs, is that considered bi amped? If I do something like this I am going to add an external EQ/crossover. If I put the powered mixer in reserve and use two power amps, one for the mains and one for the subs and a crossover/EQ then this is biamping?
 
The Wizard Of OZ said:
Cam I appreciate your help. I thought the 200 continuous was well within the power range of the powered mixer. If it's underpowering them, then I don't want that. I want clean, crisp sound.

Ok Fred, how about a little primer on bi amp and tri amp cuz maybe I'm not on the same page here. My main speakers are two way with a 1" tweeter and a 12" woofer. I have (2) passive subs. If I ran the mains with the powered mixer and added an amp for the subs, is that considered bi amped? If I do something like this I am going to add an external EQ/crossover. If I put the powered mixer in reserve and use two power amps, one for the mains and one for the subs and a crossover/EQ then this is biamping?
Click to expand...
Indeed it is, my friend. :)

Since your tops are bi-ampable, you can tri-amp your system if you wish. But let's look at bi-amping for now. Set your tops for full range (non bi-amped). Set the electronic or active crossover to two-way. Feed the mid-high or tops output to the amp that's driving them. Then feed the summed sub output to the amp that's driving them.

Your powerhead will be great for driving the top cabinets because the mid to upper frequencies don't require a lot of amp headroom. I'm just sayin' this to save you having to buy another amp. But you could buy two amps and keep the powerhead in reserve... or use it for smaller engagements that don't need a lot of sound.

Thoughts?
 
Fred,

Except that here again we get into needing sub inserts on the powered board to be able to run the outboard signal back through the board amp. Or for Wizard we can call the sub inserts (main inserts or main send/returns). Or hope that the board he is using allows a main out from the board without passing through the amp and an amp insert for left and right, all this could be accomplished internally if the board is capable of that. I am too lazy to try to find the board he is using and what it's specs and features are.
 
Sub outs are send and return for the main output on a board. It allows the signal to be sent out of the board through external processing gear and returned to the board to go out through the main output. For you to use a crossover with a powered board and still use the boards amps you would need to be able to send the entire signal out through the crossover and then return the highs in a bi-amp system back to the boards amp.
 
Thanks, Steve. I'd forgotten about that. :)
 
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