How do live venues power on-stage monitors and sub-woofers?

[Dolmetscher007]

I have been asked to source and buy a power amp for a PA system that will be used for a live-band venue. I'd say the venue is "mid-sized" maybe 40 ft. x 80 ft. Loud rock bands, as well as some hip-hop/DJ/EDM, are the genres of the venue.

I am no expert on power amps. Every PA system I have ever used was purchased as a pre-put-together system with powered speakers and a simple mixer. I went to Sweetwater.com and just started looking at power amps.

Since I know nothing about DSPs when it comes to Power Amps, I have no idea what to think about all that jazz. I gravitated to the most powerful amp that did not mention DSPs and things I don't understand, and I found the: Crown XTi 6002 Power Amplifier

While looking through them all, however... they all seem to only have two outputs. Makes sense; left-speaker... right-speaker. But I know that we will also need three stage monitors (1 for the drummer, and 2 for front of stage). We will also want to add a Sub-Woofer down the line... if we think we need it.

Since power amps only have a L and R output, how do live rigs power monitors? Come to think of it, Mixers only have L & R outputs. So... how do stage monitors get their signal?

I have played in bars myself, that had a whole separate, side-of-stage PA system just for monitors. That would be really nice, but out of our league. What do more modest venues do?

 

[rayma]

There are often "monitor" outputs that are mono.

 

[JonSnell Electronic]

The left and right are for front of house or the main PA. The chosen mixer must have at least four groups or monitor channels. These groups can produce, at your selectable level, a mix of what the drummer needs, so say his monitor is group 1, group 2 and three can have different outputs programmed.
Most drummers want kick drum, lead vocal and a general mix in the back ground yet a lead guitarist will want backing vocals, snare drum for rhythm and some lead vocals.
The variation is endless when you use groups or monitor outputs.
In professional systems a 'snake' or multi-way cable from the desk is the most efficient way to send signals to the stage.
Hope that helps.

 

[nigelwright7557]

There are two ways to do it.
1/ Buy a big powerful amp and match it to the speakers.
2/ Buy lots of smaller powered integrated amps/speakers and daisy chain the inputs.

 

[Enzo]

House PA systems likely have more amplifiers than a single left/right one. Usually we use a separate amp for subwoofers. I certainly would have separate amps for monitors. MAny subwoofers are powered speakers, in which case a line out feed from the mixer into the self-powered sub. But passive subs with separate power amp is certainly not rare.


Rather than look through Sweetwater, CALL them and talk to a sales engineer. He will know all the equipment, and will be able to ask you things to determine your needs. Don't shop by eliminating any amp with DSP, just because you don't know DSP. Geez, I know nothing about automotive computers, but I sure don't want a car without one. DSP means many things, but if your amp has say an anti-clipping feature in DSP, you really don't need to know anything to turn it on.

 

[dmills]

Most decent rigs will use at least two or three channels of amp per side, and possibly more for subs as well.
Then the monitors are generally two channels each (Line level active crossovers are very much a thing these days). I would expect 6 amps (of various sizes) or the equivalent in powered speakers (Not a bad way to go).

Ideally you have a separate monitor board, but failing that mons are what the pre fade aux outputs on the FOH console are for, not ideal, but you can make it work if things are not too demanding.

Do not forget to budget for cable (Power as well as audio), and all the usual ******** trimmings (DI Boxes, Mic stands, Mic clips, stand adaptors, the list is endless).

New venues should generally shop PA second hand (It looses about half its value as soon as it leaves that showroom). Good pro gear is usually fine on the second hand market, and makes your money go much further. Find someone who knows the game (and your local market) to assist you as you are clearly out of your league if you think amp power is the be all and end all and DSP is scary.

DSP (either in the desk or the amps or both) is a big win.

 

[JonSnell Electronic]

House PA systems likely have more amplifiers than a single left/right one. Usually we use a separate amp for subwoofers. I certainly would have separate amps for monitors. MAny subwoofers are powered speakers, in which case a line out feed from the mixer into the self-powered sub. But passive subs with separate power amp is certainly not rare.


Rather than look through Sweetwater, CALL them and talk to a sales engineer. He will know all the equipment, and will be able to ask you things to determine your needs. Don't shop by eliminating any amp with DSP, just because you don't know DSP. Geez, I know nothing about automotive computers, but I sure don't want a car without one. DSP means many things, but if your amp has say an anti-clipping feature in DSP, you really don't need to know anything to turn it on.

Correct, the amplifiers are on stage or within the loud speakers if active speakers otherwise the stereo feed sends audio to the amplifiers that drive the speakers.
There is only ever a stereo feed to the stage and there they feed the electronic crossovers and in turn they feed the amplifiers as described.
Here is a link to the manufacturer we like to use; https://www.nexo-sa.com/wp-content/uploads/nexo_alpha_brochure.pdf

 

[Dolmetscher007]

The left and right are for front of house or the main PA. The chosen mixer must have at least four groups or monitor channels. These groups can produce, at your selectable level, a mix of what the drummer needs, so say his monitor is group 1, group 2 and three can have different outputs programmed.
Most drummers want kick drum, lead vocal and a general mix in the back ground yet a lead guitarist will want backing vocals, snare drum for rhythm and some lead vocals.
The variation is endless when you use groups or monitor outputs.
In professional systems a 'snake' or multi-way cable from the desk is the most efficient way to send signals to the stage.
Hope that helps.

I think it is helpful to use a mixer as an example. Here is a very large image of the, Mackie 1604VLZ4 16-Channel. In the bottom right, there are four faders that I imagine what you are talking about above, @JonSnell. I know that you can send channels to those faders so that you can send "a mix" to the drummer's monitor, and a different mix to the guitar player, and one to the singer, etc.

However, if you look at, the back panel of the Mackie mixer... I see under, "MAIN OUT Bal/UnBal". Those two outs go to the two ins on the power amp. Likewise, the two outs on the Power Amp, drive the two, L & R, main speakers. On down the panel, I see: Sub-Group Outs, Aux Sends, and Direct Outs. If those are the outs you are referring to, @JonSnell, none of those outputs have any power behind them to drive on-stage monitors, and the Power Amp's only two ins/outs are being used for the main speakers.

Am I missing something?

 

[indianajo]

Small venues often use a powered mixer to power the monitors, ~ 100 watts/ch, and a main amp on stage to power the mains. If separate midrange & top, two main amps. Subwoofer single channel usually. Even basic mixers like my unity 12 have different balances for the monitor send and the main send.
If theft can be a problem you don't want 12 or 10 ga cables running from amps at the sound booth to the stage speakers. you want a twisted pair snake as stated above, or more modern, Cat 5 or 6 cable (cheap, no resale value) with cat 5 or 6 converters at booth & stage. Fireproof cat 5 or 6 can be buried in walls or ceiling, snake needs a trench in the floor. Then the power amps can be on the stage with short heavy gage speaker runs. Powered speakers can be good, but watch various threads under PA for brands to stay away from because the switcher supplies blow up so often.
Upscale bands want a different mix for the singer, the main band, the drummer. These are usually handled by an upscale mixer with 3 or more sends & radio links to the various in ear monitors. Very common these days, on stage monitors can damage hearing and are being phased out. If done without radio you need 6 or 8 sends in the snake, fairly rare.
See this thread for some opinions on modern power amps: Who makes half decent power amps these days?
reliability etc. Note the inexpensive behringers have copyrighted schematics and can only be repaired usually by authorized repair stations.
Whatever you do, don't use 1/4 phone plugs for speaker connections. Slightly pulled out they can short and blow up any amp. Use speakons, or at the very minumum, dual banana jacks & plugs.

 

[conanski]

Am I missing something?

Yes, you need a separate amplifier channel for each speaker box you want to power, so for 2 mains, 3 monitors and a sub that is 6 channels or 3 separate amplifiers minimum. Another way to do this would be to buy active(powered) speakers to use as monitors assuming the venue doesn't already have passive speakers for this and then rack amplifiers to power the mains .



A couple more points.


NO WAY is 1 sub enough for the types of events you describe, a pair of double 18's would be the bare minimum and you could double that for the DJ/hip-hop events.


This is gonna cost a bunch of money because cheap amplifiers won't last in this environment and neither will the speakers without so very good DSP protection.


By the sound of it you are just not qualified for this task, but don't take that the wrong way. I'm trying to offer sound advice based on history of having been around this block more than a few times already. What you need to do is find somebody locally with solid experience in this field, a sound and lighting provider that has experience doing the type of events you want to do. You need to see what it takes to do this and what reliable equipment looks like and costs. Yes you could put a bunch of cheap Ebay gear in there but you will be replacing it regularly when it fails mid gig, that will end up costing more in the long run and it will hurt the venues reputation which means this is a well worn path to failure.

In a nut shell this type of thing has to be done right from the start or you're wasting a lot of time and money, you don't have to buy high end gear but you do have to get stuff that is good enough, but even that is certainly going to inflict sticker shock. You need a $10k budget here.

 

[Dolmetscher007]

By the sound of it you are just not qualified for this task, but don't take that the wrong way.

Could not agree with you more! LOL

 

[David Morison]

However, if you look at the back panel of the Mackie mixer... I see under, "MAIN OUT Bal/UnBal". Those two outs go to the two ins on the power amp. Likewise, the two outs on the Power Amp, drive the two, L & R, main speakers. On down the panel, I see: Sub-Group Outs, Aux Sends, and Direct Outs. If those are the outs you are referring to, @JonSnell, none of those outputs have any power behind them to drive on-stage monitors, and the Power Amp's only two ins/outs are being used for the main speakers.

Am I missing something?

Generally, monitor sends come from the aux sends on the desk, so you're on the right track so far.

Every speaker that is getting its own mix needs a channel* of amplification.
So, if you want L&R front of house, you need 2 channels of amp, ie one conventional amplifier.
If you want 2 channels of monitors (perhaps one for lead vox and one for everyone else), then you buy a second amp to get those extra channels of power. If you want 4 channels of monitors, you're buying 2 extra amps etc.
If you want subwoofers, that's another amp.

In other words, a PA system with Main speakers, Subwoofers and Monitors does not just run off one amp - several are used.

* or channels if the speaker does not have an internal crossover.

Note there are a couple of exceptions to what I've written above - as others have mentioned, many PA speakers, subwoofers and monitors these days come with the amplification built in, so you don't have to worry about all this if that kind of rig is chosen. I'm guessing from the way you phrased the OP that the speaker system may already have been decided on though.

The other is that some models of amp come with more than 2 channels, so you could run for example L&R Mains and 2 subwoofers off one 4 channel amp, and 4 monitor mixes off another.
That does take up less space in the amprack, but is sort of an "all your eggs in one basket" situation in that a failure of one amp can take out a greater proportion of your PA than with conventional 2 channel models.

 

[MAAC0]

I've seen many concerts where there is a large mixer on stage and another mixer far away in front of the stage for monitoring and mixing the main sound. I believe the mixer on stage is responsible for the monitors and the musicians headphones. Oh and there are Kilograms of amps on each side of the stage powering the line arrays and subs in front of the stage daisy-chained. For U2, Coldplay we are talking about 50-100KW sound power for a stadium...

 

[Enzo]

MAACO is correct, large acts will have a dedicated monitor mixer on stage, and a separate mixer system for house. Big tome monitor mixers are often laid out in a matrix, as in each mic channel will have a number of sends, and each send bus will have its own master fader. That way the vocalists can have their mon mix, the horn section theirs, the instruments get theirs, and so on. In fact mixers made for monitor mixing often have inputs that include a splitter. In other words you plug all teh mics into the monotor mixer, and then more cables jump the split outs over to the mic inputs of the main house mixer.

On your typical club mixer, you will see the MAIN L and R, which do feed to the main L and R amps, but the mixer will ALSO have extra outputs. SOme might be called MON - as in monitor - and others will just call them all AUX, for auxilliary In any case you choose either a monitor or aux bus to be your stage monitors, then take THAT output to run to a separate power amp for the monitor speakers.

You COULD use the sub groups as monitor mixes, but that is not really how it is done. If your mixer has four subs say, a typical use might be the assign all teh vocal channels to sub 1, maybe the drum channels to sub2, the instruments to sub 3, or whatever. That way I have the ability to turn ALL the vocals up and down together without changing the mix between them.

 

[chris661]

What they said, but a bit more:

It's important that the Aux sends are pre-fader sends when running from the FOH desk. ie, the level out the monitor will be constant, no matter what you do with the FOH mix.

The stage monitors are pointing directly at the mics, and at rock shows are often being operated just below the feedback threshold. If you're using post-fade sends and push the FOH faders, the monitor levels will go up and you'll get feedback.
Having the monitor mix constantly shifting will also be very distracting to the performers.


I'd also like to echo the advice about getting a professional to select the equipment and install it for you. Hand them a list of requirements and tell them roughly what your budget is, and let them come up with options for you.


My suggestion for you would be that, unless the venue has all the passive cabinets already, go for active speakers. They're much more user friendly.

Chris

 

[Enzo]

Good point. If your mixer has sends labelled MONITOR, they will be pre-fader. AUX sends can be either, often some pre-fader, and some post.

 

[turk 182]

and then there's whether or not the monitor or aux's are pre or post EQ (which messes with the theory of the monitors being constant no matter what you do with the main mix) ...and we have not broached the subject of "aux fed subs"



bi-amped monitors, anyone?

 

[Sublimacon]

Many good recommendations already!

What I would recommend is - try to get a few gear tours of local clubs who host similar bands/acts your venue anticipates!

It will be enlightening for you to comprehend the amount of gear required to reliably produce war-volume gigs night after night! For Dubstep/EDM, to entertain the hardcore fans 2-4X the rock club subs!!!

 

[nigelwright7557]

Its not just number of amps/speakers, the mains power has to be managed well too.
You can use many kilowatts.

 

[Sublimacon]

If your venue is a 40x80Ft bar that hosts weekend gigs, than a good set of powered mains + 4 powered subs + monitors/amp + snake + mix board + dsp PA management unit. The Harman Group gear has integrated setup parameters for JBL/Crown/DBX/Etc. The "auto" cfg with only a few calibration mic locations makes install/set-up much easier to obtain good results!