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Re: Signal flow for live band vocals

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Jordan Wolf
Re: Signal flow for live band vocals
on Mar 16, 2010 at 8:04:22 am

First, if you can give us some specific gear models, that would help out a lot.

"The way we currently have the system set up is that all of our mics go straight into the mixer, then from the mixer we have four sub-outs going to four different EQs, then to amps for four monitors. We also have the Main Left and Right out, going into individual EQs, then to the amps for the Mains."

The way you're describing the "sub-outs", they sound like Auxiliary Sends. It may sound semantic, but some mixers ALSO have sub-outs (usually called Subgroup Outputs). Which one you are talking about will determine how correct the setup is.

"My question is, will it be best to run each of the vocal mics into an EQ first, then to the mixer and from the mixer, the outs going straight to the amps? I'm thinking this would be the best setup because right now if one mic has a specific frequency that is partial to feedback (let's just say 500Hz, for example), then when we notch that frequency out of the mains, it gets notched out for every mic."

Okay, well I see two separate situations here: (1) where the EQ is patched and (2) the desired function of the EQ.

For the first situation, you'll quickly find that the signal level will be extremely noisy and/or low, if present at all. This is because a microphone's electrical output is very small and needs to be boosted - the "gain" or "trim" knobs at the top of the mixer are in place to bring this low level up to a level that the rest of the components in the mixer (and further down the signal chain) can use.

Now for situation number 2: There are a number of ways to utilize the functions of an equalizer: feedback-fighting, tone-shaping, and system alignment. EQs used inline or inserted in the the monitor signal path will be primarily used to fight feedback. An EQ that is inline or inserted in the main speaker path will be primarily used for tone-shaping. System processors (usually located near the power amplifiers) use EQ to even out the frequency response of the system.

As for how you should use the EQs you have: if we assume they are graphic equalizers, then the resolution of each band may do more harm than good if inserted on any single channel. Most mixers/mixing consoles have EQs with knobs that (hopefully) allow control of at least one band of boost/cut and the center frequency desired. Some even allow for control over how wide/narrow the boost or cut is.

My recommendation is to "insert" the EQs over the Auxiliary Sends used for monitors and also "insert" them over the main outputs. Using them in this way, as compared to in-line (running a cable from the output of the mixer to the input of the EQ and then out to the amplifiers) will let you hear any changes you make on the EQs through headphones. That may help you learn frequencies and how cutting or boosting certain ones will affect a particular instrument/voice.

If you are interested in learning more about live sound reinforcement, I highly recommend checking out ProSoundWeb's Study Hall and forums, as it is focused much more on sound reinforcement. This forum is also a great place to ask questions but I have always felt it was more geared towards on-location audio recording and post-production.


Keep asking those questions.

Wolf
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