Anyone experienced with PA systems for live band performances?

Deathmetalconga

Platinum Member
Yeah, here at Disneyland I've seen the big Meyer audio powered speaker arrays and other big powered speaker thingy's, and it's insane. However, on this side of the huge spectrum, powered speakers means not having to haul around super huge racks filled with power amps, which is just as troublesome when you're talking moving 30-40 amps at a time. Thank god for fork lifts! In fact, sometimes it's better if you had a crane!

So when I get home to deal with my paltry personal band set-up, I'm all about light!
Don't amped speakers just require one cord, which carries both power and audio signals? I find that I have to carry a fair number of audio extension cords and power strips when I set up my two EON 15s. Again, probably not a problem for gigs that just need a two to four speakers, but when you start needing more and more, it could just be a mess.
 
M

mediocrefunkybeat

Guest
DMC - whilst sharing one lead might seem a good idea, unless they are heavily shielded, you're better off with separate leads for audio and power. Always. Electrical interference can be bad enough with split leads, especially in a crammed pit, but sharing leads? Big no no!

I've only ever found weight a serious issue with subs and centre clusters. If a speaker is to be ceiling rigged, I'd rather it were passive - just for safety's sake.
 

Bo Eder

Platinum Member
Don't amped speakers just require one cord, which carries both power and audio signals? I find that I have to carry a fair number of audio extension cords and power strips when I set up my two EON 15s. Again, probably not a problem for gigs that just need a two to four speakers, but when you start needing more and more, it could just be a mess.
I'm sure someone in this industry has probably successfully created a proprietary cable that can carry both audio and power, but for the most part, as you know with your EONs, the power is separate from the audio signal. Usually this is a general rule because power and audio cables mixing together is a sort of no-no since it will induce a hum.
 

Aeolian

Platinum Member
Hosa, Straight Wire and others have cables where the power cord and an XLR signal cord are bundled in one jacket.

On EON's, there is apparently a difference in the distance between the connectors on the speaker as some cable folks make special ones for EON's with longer pigtails.

One problem is that with an Edison plug on one end, and an IEC on the other, you can't daisy chain these cables for longer runs the way you can with XLR or conventional Edison extention cords.

I have a 25' and a 50'. Sometimes the 50' is way too long, and other times I just have to use conventional cabling to get over there.

The pro guys keep after QSC to use Neutrik PowerCon connectors instead of the IEC's like Meyer and other pro powered speakers do. PowerCon's don't directly daisy chain but you can get a barrel adapter to do it in a pinch.

At 32 lbs, the QSC's are reasonable. I wouldn't use a powered 15" system without those Ultimate Support lift stands where you twist the clutch and you can raise or lower it gently.
 

Deathmetalconga

Platinum Member
Hosa, Straight Wire and others have cables where the power cord and an XLR signal cord are bundled in one jacket.

On EON's, there is apparently a difference in the distance between the connectors on the speaker as some cable folks make special ones for EON's with longer pigtails.

One problem is that with an Edison plug on one end, and an IEC on the other, you can't daisy chain these cables for longer runs the way you can with XLR or conventional Edison extention cords.

I have a 25' and a 50'. Sometimes the 50' is way too long, and other times I just have to use conventional cabling to get over there.

The pro guys keep after QSC to use Neutrik PowerCon connectors instead of the IEC's like Meyer and other pro powered speakers do. PowerCon's don't directly daisy chain but you can get a barrel adapter to do it in a pinch.

At 32 lbs, the QSC's are reasonable. I wouldn't use a powered 15" system without those Ultimate Support lift stands where you twist the clutch and you can raise or lower it gently.
One thing I like about powered speakers is that you can usually find a power plug near them, so you don't necessarily have to run a power cord to where the mixer is.

If you're not supposed to mix power and audio signals, then home come home stereos get away with having a single cable or power and signal? Is it because they are low-powered?
 

Deathmetalconga

Platinum Member
One problem is that with an Edison plug on one end, and an IEC on the other, you can't daisy chain these cables for longer runs the way you can with XLR or conventional Edison extention cords.
I find no problem with this as I chain together as many standard Edison extension cords as I need, then finally hook them to the IEC power cable going into the speaker. I also have one 50-foot IEC cable. It is not often that the mixer is midway between the speakers. Usually is is to one side so the cable setups are asymmetrical.
 

Aeolian

Platinum Member
One thing I like about powered speakers is that you can usually find a power plug near them, so you don't necessarily have to run a power cord to where the mixer is.
This is an invitation to ground loops. Pro practice is to always have a common ground point. Either a proper power distro, or what is called a Poor Man's Distro where you plug into multiple AC outlets in the venue, they all go to one box where the grounds are all tied together (only the grounds, never the neutrals, per NEC. If you don't understand this don't mess with it, call ProStage & Power or a licensed electrician to build one for you.) and then all the stringers are plugged into the poorman's box. This creates what is called a star ground.

When you have a keyboard plugged into one outlet, and then plugged into a mixer on another circuit, and then the mixer is plugged into an amp or powered speaker on yet another circuit, you will have current flow on the grounds because of different resistance paths. This will create noise in your system.

Thus you want the AC ground to be the same as the signal ground at the source. This means plugging your powered speakers into a common ground point as the mixer. Thus the bundled cables reducing the things you have to wind up at the end of the night. And the issue of extending them if the far side is further away than your longest cable.

If you're not supposed to mix power and audio signals, then home come home stereos get away with having a single cable or power and signal? Is it because they are low-powered?
I'm sorry. I've never heard of a home stereo that mixes power and audio on the same cable. There are such things as 70v distributed sound in commercial buildings where the audio is superimposed on a 70v carrier (something like a phone line) so that you can run lots of speakers all over the place, but the levels are limited and sound quality not all that great. There is also such a thing as phantom power, like you mixer sends to a condensor mic, but the current in that is also very limited. You couldn't run a powered speaker off of that. There may be some small bookshelf systems that use some proprietary multi conductor cable to feed low level audio and power to a self powered speaker or sub. When I worked as an engineer for Dolby there were a lot of interesting units down in the licensing department where manufacturers sent in samples to get permission to put the logo onto. But I never saw anything running an amp off of phantom power.

Do you have examples of home units running power and signal though the same cable? I'd like to check them out and see what they are doing.
 

Skitch

Pioneer Member
I'm looking to buy a PA system including speakers, but I don't know where to start. I'd include a budget, but I'm not familiar enough with what would be a fair price range if I don't know what I'm talking about!

I'm in a 3 piece band and we're going to be playing shows in bars around Chicago, does anyone have experience with live sound and perhaps recommendations for PA systems? General knowledge about the subject is very very welcomed as well, I'm eager to learn.
Low gain, High fader. The gain turns up the mic in both, the mains and the monitors and this why some many bands sound amateurish is due to the feedback caused by using too much gain. Singer needs more monitor, do it off the monitor send or the aux channel, not the gain knob. Run the EQ knobs straight up at 12 o'clock on about everything but the drums otherwise you are begging for feedback. Tell your singer to never point the mic at any monitor or speaker or feedback.

Have someone play your drums one at a time while you adjust the mix from out front, not the stage. Eventually, you will want to invest in Compressor/limiter to help control feedback and spice up your drums' sound.

A not-so-sexy but worth every penny rack unit is a power conditioner because you may end up pluging your PA into a dimmer circut (found in most in hotel ballrooms) and dimmer circuts, by nature, are just big power spikes. You don't want to blow up your PA on the secong gig!

You can add outboard effects such Graphic EQ later, but you just need the basics to get started.

Mike

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Deathmetalconga

Platinum Member
Do you have examples of home units running power and signal though the same cable? I'd like to check them out and see what they are doing.
Every home stereo system I have ever owned uses standard speaker cable coming out of the amplifier (which usually has a radio receiver built-in) to send audio signals to the speakers. Apparently this audio signal is enough to power the speakers, even big 15-inch home stereo speakers. Only subwoofers appear to have their own power supply (plugging into the wall).
 

Aeolian

Platinum Member
Every home stereo system I have ever owned uses standard speaker cable coming out of the amplifier (which usually has a radio receiver built-in) to send audio signals to the speakers. Apparently this audio signal is enough to power the speakers, even big 15-inch home stereo speakers. Only subwoofers appear to have their own power supply (plugging into the wall).
Okay. There are basically 4 kinds of things running though the wires. 3 are audio signals. You can think of it as very low level; like a microphone, low level; like what comes out of a mixer and goes into a power amplifier, and high or speaker level; the level of signal capable of driving a speaker to desired audible levels (commonly called volume). To get from any level to a higher level requires amplification. To have amplification, you need additional power from somewhere. Thus the 4th signal. e.g. the AC power coming from your wall.

Ever notice that the British refer to the things we call electron tubes as "valves"? Because in reality, that's exactly what they do. Think of the water pressure in your house as the AC coming from the wall. You provide a "signal" by turning on the valve on your faucet. That very low force (hopefully you don't have stuck faucet handles) of turning the valve on allows the much larger force to be released in proportion to how much you turn the handle. Imagine your hand to be a microphone picking up the sound of your kick drum. The louder the drum, the further you turn the handle and the more water (energy) is allowed out.

An amplifier does the same thing. Takes the raw energy from the wall and doles it out according to the signal coming into it. The signal coming into it gets attenuated or reduced by another valve upstream from the amplifier (the level or volume control) on devices that have one. e.g a stereo which has all the levels of amplification needed to take the ouput of a CD player or a turntable and raise it to the level required to drive a speaker, usually has a level control on it. Otherwise you would be listening to everything full blast. Some basic power amplifiers, like you find in high end stereos, only amplify from low level to speaker level. And may not have level controls. All the level control for the system is further upstream in the "preamplifier" which raises the very low level from a turntable to low level (commonly called line level) needed to drive the basic power amplifier.

In your example of a home stereo, the AV receiver takes the line level signals from DVD players, cable boxes and the like, along with internally generated signals like the radio (which has tons of amplification stages to take the very weak level from the antenna, convert it to audio and raise it to the standard line level so it can be treated like any other signal) and then provides switching between different sources, additional processing like level controls, tone controls and surround decoding, and then feeds it to a power amplifier section to raise the signal enough to drive speakers. The exception is the LFE output which is line level. Most home subwoofers have their own internal power amps that raise the line level LFE signal enough to drive the speaker in the box. Note that the sub also needs to be plugged into a raw power source like the wall (or a wall wart for a small computer system) to provide the power for it's internal amplifier.

In a typical PA you have the very low microphone level signal going into a mixer. Which amplifies it to line level along with all the other microphones while allowing you to independently control each level (mixing). Along with adding tone controls (eq) sometimes signal processing (either built in or though external loops running at line level) and an additional master control section that allows you to vary the entire mix of all the individual controls. This then goes though global signal processing like a global equalizer, a speaker processor or crossover that divides the signal into separate frequencies to drive subs, midrange drivers, or high frequency horns (in a larger multi amp system). Then the signal ,still at line level, goes into power amplifiers which provide the increase to push the electro-mechanical speakers to the levels desired.

All these functions can be split or bundled in different ways. In a "top box" PA head, the mixer and one or more power amplifiers are bundled in the same box. You plug your mics in the front, and jacks on the back provide a speaker level signal that runs your speaker cabinets. In a powered speaker, there is both a basic power amplifier (line level to speaker level) and the actual speaker, in the same cabinet. Similar to the powered subwoofer. Now you don't need the mixer bundled with a power amplifier (or racks with separate power amplifiers in them) because that function is in the speaker. But you now have to get both the line level signal to it, and get raw power to the internal amplifier section. Now you need two cables. Or the kind of bundled dual cables I mentioned earlier. You can run a long cord back to your mixer and run the power cord to the nearest outlet, but you run the risk of there being resistance between the ground pin of the outlet that you plugged the powered speaker into, and the ground pin of the outlet that you plugged the mixer into. Since there is also a ground connection in the line level signal cable coupling the mixer to the ampifier section of the powered speaker, that difference in the outlets will try to resolve itself though the signal cable. This is a ground loop and it creates noise in the system. That is why the preferred scheme is to run the signal and AC power back to a central place at the mixer. Or in the case of varsity systems, a central place at the stage where the signals to and from the mixer are run down a long snake along with AC that originates on stage at a power distribution box that everything else is plugged directly into.

Whew!
 

Aeolian

Platinum Member
Eventually, you will want to invest in Compressor/limiter to help control feedback and spice up your drums' sound.
Actually, a compressor will make feedback worse. A compressor reduces the gain on high level signals, turning it back up as the signal level goes back down. Meaning that if you set the sound at the same level in the mix as you had without a compressor, when the compressor "releases" (stops reducing the gain), the effect is that the level of the open mic is turned up more than it was before. Ergo, more feedback prone.

Compressors can fatten up a drum sound and are very common in recording. They can also fatten up the FOH sound and make the levels a bit more consistent at the top end. Which makes it easier to mix since the levels aren't jumping up and down as much. By squeezing down the initial attack and then allowing the gain to come back up as the sound decays, they increase the apparent sustain of the drum.

Using compressors is a high end trick though. You have to put them individually on each drum. Otherwise, every time you hit one drum hard enough to cause the compressor to go into action, it will cause the sound of the other drums to drop. Listen to an over compressed radio station and you can hear the background of the music pumping in and out with every hit of the kick. Now you see that you need a lot of compressors. Unless you have a decent digital board like a Yamaha LS9, that's a lot of expensive outboard gear to haul out and hook up every gig.

When you put something on one channel only, it is called an "insert". You insert it into the signal path of that one channel of the mixer. Now comes the next problem. As mentioned before, a compressor tends to increase feedback. So you don't want the monitor feed compressed (except in very high end situations where they really know what they are doing and have total control on a very big stage). The other thing with compressing a monitor feed is that you don't have any sense of your dynamics. You can't tell if you're hitting harder or softer. This can cause you to start bashing harder trying to get it to sound louder. Bash harder and harder and it doesn't get any louder, only now you're swinging so hard your technique and the song suffers. It's really deadly for singers who can throw their voice out screaming into a mic that doesn't get any louder and they can't tell what they are doing.
High end mixing boards allow you to switch the insert point after the tap for the monitor sends for when you are using compressors. But your typical band Mackie mixer won't do this. Even my Allen & Heath mixer requires some surgery and jumpers to do this.

Bottom line, compressors on drums are a varsity thing. You can insert a gate without much trouble. In fact I like putting gates on kicks, even in the monitor mix, it actually helps feedback by switching off the mic before the monitor starts making the kick drum rumble by itself. But leave the compressors to the big league venues and recordings.
 

Bo Eder

Platinum Member
Regarding the compression, if you get a console like the Yamaha O1v 96, you get a compressor for every channel. That board for me is the ultimate swiss army knife for audio projects.
 

Deathmetalconga

Platinum Member
Okay. There are basically 4 kinds of things running though the wires ...
Wow, thanks for your knowledge! Very informative posts.

So, if I plug all my gear - mixers and powered speakers - into the same outlet, I should be fine and not have to worry about a ground loop?
 
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