Questions about my live set-up

[BobOC]

My five piece band (pop/rock) has two new Peavey PR-15 speakers (8 ohms, 400 watts Program/800 watts Peak).

One of the band members just purchased a Yamaha EMX66M powered mixer...the Yamaha is advertised as having two, 300-watt amps. The specs say: "300W + 300W into 4 ohms; 205W + 205W into 8 ohms.

My two questions...

1. Is the Yamaha amp powerful enough for the Peaveys?

2. We'd like to use one of the amps on the Yamaha to power the main Peaveys, and the other amp to drive 3 monitor wedges, in series. I think the three wedges are all 8 ohms, although one might be 4 ohms. Will the Yamaha be able to handle the two Peaveys and the three monitor wedges?

Thanks very much for your help....!

- bob.

[apl]

Originally Posted by BobOC

1. Is the Yamaha amp powerful enough for the Peaveys?

2. We'd like to use one of the amps on the Yamaha to power the main Peaveys, and the other amp to drive 3 monitor wedges, in series.

1. Yes, as long as it can get loud enough for you, which it probably will. The two PVs will be 4 Ohm in parallel.

2. Normally when you chain monitors they're in parallel, and two 8 + one 4 Ohm would be 2 Ohm in parallel. That may not be enough of a load. If you put the two 8 in parallel, that pair will be 4 Ohm, then series that with the 4 Ohm, and you'll have 8 Ohm total.

[BobOC]

Thanks, apl.

So, in other words, hook up two monitors into the "B" outputs, just as I put the main speakers into the "A" outputs, and then series the third wedge with one of the first two monitors?

Also, you cleared something up for me...the "basic" output of a power amp is parallel, so two 8 ohm speakers = a 4 ohm load to the amp. I don't know why it's so hard for me to grasp all of this stuff. I should've paid more attention in math class, I suppose!

[apl]

Here's the manual. You should read up on it. If an amp has two outs labelled A, or a speaker has two inputs, those are all usually in parallel. To get one in series usually takes some rewiring of a jack.

[mshilarious]

Honestly, your amp is underpowered for your mains, and without rewiring your wedges, which you don't want to do, running three of them off a single channel is a bad idea.

Get a larger (1000W) power amp for your mains, and use the mixer's amp for the monitors, two on one channel, one on the other.

[BobOC]

Thanks, ms. But now I'm a bit confused again.

One of the websites (americanmusical.com) sells this PA Head as a "package" with Yamaha's BR-15 speakers. I believe that the BR-15's have the same specs as the Peavey PR-15s (8 ohms, 400 watts Program, 800 watts Peak).

Here's the link...

http://www.americanmusical.com/item-...MX66M-PAK.html


I would imagine that the store (or Yamaha) would not sell these products in combo if they weren't properly matched....or would they?!?

I'm not concerned about a lack of volume, as our gigs are small (100-150 people), and we won't be maxing-out the volume on the EMX66M. I do not, however, want to do damage to the speakers by under-powering them.

Thanks...

[mshilarious]

Originally Posted by BobOC

Thanks, ms. But now I'm a bit confused again.

One of the websites (americanmusical.com) sells this PA Head as a "package" with Yamaha's BR-15 speakers. I believe that the BR-15's have the same specs as the Peavey PR-15s (8 ohms, 400 watts Program, 800 watts Peak).

Yes, but they aren't anticipating that you'll only be using one side of the amp for two cabs, and the other side for three wedges.

[BobOC]

But don't most people use that type/size of powered mixer for two cabinets and a couple of wedges? It's advertised as being for combos or small bands. I'd imagine that a basic small club/coffeehouse setup would be two main speakers and two (or three) monitors.

Thanks again for the input...

[mshilarious]

Originally Posted by BobOC

But don't most people use that type/size of powered mixer for two cabinets and a couple of wedges? It's advertised as being for combos or small bands. I'd imagine that a basic small club/coffeehouse setup would be two main speakers and two (or three) monitors.

Thanks again for the input...

Sure, a basic setup is two mains and two monitors. But that doesn't mean with a grand total of 600W. 150W per main is not a lot of juice. That's fine for a monitor, where the musician is only about 8 feet from the wedge.

A coffeehouse gig ain't a five piece pop/rock band for 150 people. How loud is your drummer? You won't be able to get much more than vocals out of your mains, and you'll be driving those amps hard.

Go ahead and try it, but PLEASE do not run three wedges off one channel unless the mixer is rated for 2 ohms, which you didn't say it was.

[BobOC]

msh...

Thanks for the advice. Actually, with the kind of stuff we do (60s/70s rock covers, at private parties and such), we usually just need to have the vocals, keyboards, and amplified acoustic guitars through the PA. I can't foresee us micing up the electric guitar/bass amps, or the drums. We're not playing at nightclubs or anything like that. I also use the PA when I play in my bluegrass band.

I will definitely heed your word and avoid running three monitor wedges! Two will suffice.

One of these days, I will figure out Ohms' Law!

Regards...Bob.

[mshilarious]

Originally Posted by BobOC

One of these days, I will figure out Ohms' Law!

Ohm's Law: volts = amps * ohms.

so if your voltage is fixed (which it is at a particular gain setting), when you cut impedance in half (4 ohms vs. 8 ohms), then the amps must double, which also doubles wattage (watts = volts * amps)

Doesn't work out perfectly for amplifiers, something to do with efficiency that's beyond me. But the principle is right: your amplifier is more powerful when the impedance of the speakers is lower.

Anyway, what you were probably wondering was how to calculate parallel resistance, which is:

Rtotal = 1 / ( 1/R1 + 1/R2 + 1/R3 )

Such that three 8 ohm wedges in parallel is 2.67 ohms.

[wilkee]

Originally Posted by BobOC

msh...

Thanks for the advice. Actually, with the kind of stuff we do (60s/70s rock covers, at private parties and such), we usually just need to have the vocals, keyboards, and amplified acoustic guitars through the PA.

Regards...Bob.

Keyboards could be a problem, Depending upon what is playing they need a fair amount of PA power. With what you are using it may be preferable to get a backline Amp/Cab for the keyboard and keep the PA for Vocals and acoustic guitars.

Tony

[BobOC]

I have just TWO MORE question!

One point that I left out is that I'll be running everything through a non-powered 16-track mixing board first (it's a new Yamaha mixer, although I don't know the exact model offhand). I'll be using the pre-amps on the 16-track board for the vocal mics, acoustic guitar mics, etc. I'll then take the two main stereo outputs of the 16-track and feed it into Inputs #1 and #2 on Yamaha powered head (which is, I know, mono).

"Just get a power amp," you say. But I'll also be using the powered PA head for smaller, solo acoustic and acoustic duo gigs, when I don't want to lug the 16-track mixer around.

So, my FINAL questions are....by boosting the mic signals with the 16-track preamps, will this mean that the EMX66M will not have to work as hard? And finally, if volume is not an issue, what's the likelihood that the EMX66M will damage the Peavey PR-15 speakers (or vice versa). If there's little likelihood of damage, then I think I'll be ok, volume-wise.

Thanks again to everyone for the help...

[mshilarious]

Originally Posted by BobOC

So, my FINAL questions are....by boosting the mic signals with the 16-track preamps, will this mean that the EMX66M will not have to work as hard?

Nope, preamp is a separate gain stage from power amps. Makes no difference, and it should work fine.

And finally, if volume is not an issue, what's the likelihood that the EMX66M will damage the Peavey PR-15 speakers (or vice versa). If there's little likelihood of damage, then I think I'll be ok, volume-wise.

It's the other way around: if you're OK with the volume, there is little likelihood of damage. If you're not OK with volume, then you will be cranking that little amp to the max, which can have the result of blown tweeters:

http://www.rane.com/note128.html