PA question... powered mixer vs unpowered mixer + power amp?

[Matt42]

Re: PA question... powered mixer vs unpowered mixer + power amp?

Another board I'm considering. A question about something on that board as well, why are the last 4 xlr inputs listed with 2 channels each?

[Dr. Vegetable]

Re: PA question... powered mixer vs unpowered mixer + power amp?

Another board I'm considering. A question about something on that board as well, why are the last 4 xlr inputs listed with 2 channels each?

I have this exact board, and I love it. (I can truly say that Yamaha has *never* let me down with any piece of equipment or instrument.)

To answer your question, the two channels per strip is a common trick that you will see on these compact boards for fitting more mixer channels into a smaller space. The rightmost four mixer strips (in this case) can be used to mix either mono or stereo signals. So you can plug a Left and Right cable into these channels, and you will get slightly different controls than you would for a mono signal. For example, a mono signal has a Pan knob to place it in the Left-Right sound field; in a stereo track this will act as a Balance control that adjusts the relative volume of the Left and Right signals. The slider on those channels adjusts both L+R levels together. You would usually use the stereo channels to mix a keyboard, drum machine, or output from a stereo guitar processor.

You cannot easily use stereo mixer channels independently, so it is best to think of this board as only able to mix 16 different sources, even though it has 20 audio channels in the main mixer section. Stereo strips are convenient for stereo sources, as you don't need to move two volume sliders together at the same time to affect the instrument level. You can also use one half of a stereo strip as if it was a mono section, but it is not so easy to run two different sources through the L+R sides of a stereo strip.

Things I like about this particular mixing board are: The onboard compression - very handy for vocal mics and even Bass. The EQ is very good on this board as well. And it is nice to have a 20-channel mixer in a rack-mount space. Decent pre-amps, too.

The only thing I don't like about this mixer is that the input jacks along the rear/top of the board do not line up with the mixer tracks below. (A side-effect of trying to cram all those strips into one rack width.) This can be confusing, because I am used to finding the right strip by following the cable downward. Just yesterday I was looking at this board and deciding I need to add some slanted guide lines to visually reinforce which inputs go to which strips.

As far as mixing for monitor feeds, you want to be aware of the number of mixing busses at your disposal. Mixers are often described using a string of three numbers to describe the number of parallel audio paths at each stage. The Yamaha board you are looking at is a 20 x 4 x 2 mixer, for example. This means that it can take in 20 audio signals and mix them into 4 independent "Aux" signals that can then be mixed down onto your 2 main stereo out signals. (You can also mix each of the 20 inputs to the Main outputs directly.) You can use the four "Aux" knobs in each mixer strip to set the level of each instrument independently in each of the four Aux mixes. These are commonly used to create monitor mixes, so you could have four different monitor mixes on stage without impacting your ability to set the house mix. Aux busses add size and cost to a board, so best to figure out how many you can live with - 2 or 4 Aux busses is common on boards this size.

One other thing to keep in mind is that when you are recording you will usually mix in stereo, but when playing live, you will probably run a mono bi-amped setup. You want people in the live audience to hear the same thing no matter where they are sitting, so usually your Left and Right speakers will be playing the same audio. Because you still have L+R Main outputs, many bands will EQ these differently to run one side to the regular speakers and the other to either your horns or your subs. This lets you send bass and kick drum mostly to one set of speakers to avoid saturating the amp that is also carrying vocals and melodic instruments. The point being, you will probably mix differently when live vs. recording, but the same equipment should handle both situations.

Not to beat the Yamaha drum too much, but I recommend you read the Sound Reinforcement Handbook. (You can download a free PDF file if you don't want to spring for the actual book.) There is a ton of great information in there about every facet of running a sound system. I refer to this book often.

[SlyFoxx]

Re: PA question... powered mixer vs unpowered mixer + power amp?

Another question, regarding wattage with this stuff. When you say 500 watts of real power, are we talking about one 500 watt amp? Since the Eon's are 250w, would 250x2 equal 500 in this case? Would we then need another power amp (or a larger one) to run the monitors off of, plus more for the sub (if and when we get one)? Sorry for the noobish questions, I'm just horribly uniformed about sound equipment. I know my guitar stuff fairly well, but have never really looked at live sound equipment.

About watts. Some amps will claim to be..say 500 watts per side but that rating will be for a 4 ohm load or sometimes even a 2 ohm load. (sometimes you'll even see a huge rating for bridged power. Bridged is when the two channels are linked together. It's a nice feature but don't get fooled.) The standard speakers you'll encounter will be 8 ohm so you want to be sure what the amp is rated to achieve driving an 8 ohm load. But it's nice to look at how low of an impedance the amp can handle in case you need to drive two 8 ohm boxes on each side of the stage. (Say in a outdoor setting so you can spread the sound around more.)

For the mains, 500 a side watts should provide enough power for small to medium crowds. In fact you'll probably find in most cases you're no driving the amp(s) too hard. That's a good thing. A cool running amp lasts longer. For stage monitors 200-300 watts is usually plenty save for a big speaker for the drummer who likes to feel the kick drum then 500 would be better. Low bass takes more power to achieve a certain volume than mid and high frequencies. But if you have a few extra hundred to spend just get the amp with the higher power. Better to have it and not need it.

So lets tally up. For amps you'll probably want a 500 watt per channel amp for your top speakers, a 700 watt amp per channel for sub woofers and a 250-300 watt amp for the two monitor mixes as each mix will use one side of the amp. You also need a crossover. I can't recommend running kick drum through only a 15 or 12 inch speaker like the Eons. They just can't reproduce the kick well and the speaker will get working too hard so the midrange can really suffer. In many cases you can also get away with running only one sub so that could be something to think about. In fact I've done plenty of small bar gigs with a band running just one top and one sub. (If you really think you won't need so much volume you could cut those wattage figures in half but I wouldn't want to roll that way.)

As for Mackie. I can not recommend their stuff for live use. I've just seen too many of their boards fail..three in my old band. I do use one in my acoustic rig but even it has given me fits of the years though it be the most reliable Mackie I've used. For about the same money as the mackie you could get a 16 channel version of the board I linked to and I promise you you'll be much better off.

Plus one on the Yamaha Sound Reinforcement Handbook. It's 20 -25 bucks well spent. Consume the basics of that book and you'll be well on your way to understanding all this stuff. Get your mates to read it too. It's nice to not be the only one who knows who to plug all this stuff in!

[Bludave]

Re: PA question... powered mixer vs unpowered mixer + power amp?

you cannot have too much power.

This is so true. If you don't have enough power you will constantly be raising the volume and the power amp will distort. Go with more then what you really need and you should be OK. I also have used the Carvin power amps & Crown(I really like the Crown stuff) As far as speakers I have monitor that I cant remember who made it. I had bought a Mackie, brand new at guitar center. Took it out of the box at the GIg & it didn't work at all. I replaced it with some other brand(can't remember as it is still in the box) but it worked really well. I would also go with at least 12 channels, but this could be more depending on how you want to run the PA. I like the idea of having everything miked and running what you need into the monitors. For me its always a matter of being able to hear what everyone else is doing. I like having all the rhythm instruments running into the monitos with enough volume so I can hear well.

[Matt42]

Re: PA question... powered mixer vs unpowered mixer + power amp?

I think we will be going with either that Yamaha mixer I linked, or an Allen & Heath if we can find a good deal on one. It seems like most of the A&H's are going to be a bit out of our price range at the moment.

And thanks for the recommendation of that book. I downloaded the PDF and it seems like it will be really informative. I'll have to convert it to an e-book at put in on my Kindle.