Question, Graphic EQ's

studiorat

Ok here's one.
Does anybody have any suggestions for good practices when setting up Graphic EQ's for a live show? Normally I'll just leave it alone unless it's obviously way off, mostly I'm arriving in to a PA already set up.

Should I use a CD? A vocal mic and my own voice? Is there a way I can say set up with a mic in the room and use a feedback threshold of some sort?

And what exactly am I looking for anyway? Sounding good or able to get the thing loud without feedback? A mixture of both I'd guess.

madtheory

An analyser and a measurement mic, coupled with a CD is one way to do it. I like to position all the mics first, then use the graphic to get plenty of gain before feedback, while keeping the sound of the system as flat as possible.

The only problem is that this can take quite a bit of time, and often there are other things more pressing that need sorting.

Believe it or not, the Behringer feedback destroyers are actually brilliant for this, you'll have all of the above done in 5 mins. IMO 99% of analogue graphics mess up the sound even when they're set at 0, so a Behringer converter is more preferable. YMMV.

If only there was an easy way to bring bass traps to gigs...

studiorat

madtheory wrote: »

An analyser and a measurement mic, coupled with a CD is one way to do it. I like to position all the mics first, then use the graphic to get plenty of gain before feedback, while keeping the sound of the system as flat as possible.

So position the mics and start turning up the gain until something feeds back and pull that frequency out? Obviously having a rough idea of the gain needed for each mic already...

PaulBrewer

studiorat wrote: »

So position the mics and start turning up the gain until something feeds back and pull that frequency out? Obviously having a rough idea of the gain needed for each mic already...

Too many variables for my liking ...

Savman

Hmmm...graphic EQ's. Often used, even more often misunderstood. The 'ringing out' process is really for wedge mixes if you have the time, you can cut the most severe offending frequencies. But alas, when there's 50 or 100 bodies in the room later, and the band stand in front of the mics, everything changes. Personally I think its a good idea to try zap feedback at source, so get out and physically move that mic, monitor, amp, whatever. Take into account ceiling and wall reflections or, god forbid, the dreaded wall mirrors.

In a general FOH mix, I'm not sure why/where you'd even begin with a graphic unless you had a specific outcome in mind. As Paul says, there are literally dozens of variables to consider. What's the frequency response of the PA speakers like? Do they have a 'spike' at 8khz? If so, cut to taste.

As the saying goes: A Professional "cuts" - an amateur "boosts"

In other words, you won't see any 6dB boosts on any properly run touring system. Whereas your weekend warrior DJ has been known to whack up everything below 500Hz "to make the bass louder man"....

So....I dunno really.

studiorat

PaulBrewer wrote: »

Too many variables for my liking ...

Would tend to agree.

The outcome in mind would be clarity and evenness of frequency response in the room I suppose. So any EQ applied on the console would be for musical purposes in terms of balance etc. and not to make up for problems in the PA and the room.

With this in mind I'd ask the lads with a bit of experience, how do you do it? What do you look out for?

madtheory

studiorat, in the "turn up the gain til it feeds" approach I described earlier, I mean that you bring up the master fader til the system feeds; the channel gains should be already set from soundcheck.

As for this thread- thinking about it, this is a big question IMO. A few glib remarks don't really help.

First thing to do is make sure the backline is sounding good, then add to it with the PA, vocals first. Make sure the musicians can hear themselves- have their amps pointing at their ears, not their feet. This avoids excessive level coming off stage. In most venues, you only need vocal and a bit of low end reinforcement coming through the PA; the backline and kit have plenty of welly.

Position the mics with the priority being to reject the FOH and monitor speakers; either have an analyzer running all the time or know the ISO frequencies by ear. Problem with that is, you'll have to subject the punters to feedback before you deal with it. That's not a good idea! IMO it's better to use a feedback destroyer in auto on the monitors and manual on FOH.

Give yourself enough time to soundcheck; for example, get the mic positioning and line check done before the talent arrives. Get up on stage to hear the monitor mix rather than relying completely on what the talent asks for. You're more likely to spot quick and easy solutions by putting yourself in their shoes.

Only do the channel eq if you have time, it's not as important as making sure there's no feedback or rumbles, etc.

Yes, when the bodies are in the sound changes and that's the main reason why there's no point in spending a lot of time on eq in sound check. But the major room modes don't change that much, those will still need pulling out on the graphic. When the room is empty don't cut on the graphic too much.

Yes, there are many variables, and that's what you use your instinct and experience to judge.

studiorat

Well I've always spent a good bit of time up on the stage listening to monitor mixes. I suppose that's the studio training, good monitor mixes would be a priority for me since if the musicians aren't playing well nothing is going to make that sound good.

Though I always thought of tuning the PA as something you would do before the sound check. I've often tweeked it a little once the band are up and running. Usually where the bit of boost comes in. But I suppose I was asking about options to check the rig before the sound check.

Most of my gigs these days are acoustic gigs and I do like to use condensers when they are available. Monitors aren't a big deal really, as "ringing" them is usually the only way since there's only one of me. So I'll push the gain on the graphic and adjust from there if they do end up sounding terrible at that stage well I'll go back and re-adjust. There's also the fact that acoustically musicians don't seem to need as much as full electric bands in terms of level.

madtheory

I agree 100%. However, I've always been frustrated with efforts to flatten the PA using a graphic. The sound changes depending on where you are in the room. Now that I've learned a bit about acoustics, I know why! I would aim to do some "correction" with the graphic and get an average quality sound over as wide an area as possible, but not try to perfect it, since that's physically impossible. I've found that taking the reinforcement approach is best, i.e. try to get the backline to do most of the work.

Acoustic gigs tend to expose all the flaws in the room/ PA combination. I find that turning the bass amps down a lot is a quick and easy way to clean up the sound. So if someone can come up with bass traps that would fit in the car boot, that would solve that problem- and defy the laws of physics! Goodnight...

ogy

i would always ring out the PA in the usual way, cutting the frequencies most prone to feedback, so that you can set the channel gain and mix at reasonable levels, so i guess this would be using the graphic to make up for problems with room modes etc. Also would try and take any "honk" out of the vocal sound, or any other undesirable frequency ranges, as i presume thats a room characteristic that will effect all the instruments. I do understand the concerns with doing this, i.e. messing up phase, colouring your sound, but i figured this was a neccesary evil in doing live sound. definitely would never boost anything though, except for looking for problem frequencies obviously. agree the behringer feedback destroyers for monitor mixes are great, especially if something goes off in the middle of a gig!

looking forward to hearing other ideas on this from more experienced folk!

madtheory

The problem with using a graphic to combat room modes is that this will only be effective for one point in the room. If the room is big and sounds nice, it's less of a problem. Rooms that have floating floors and stud partitions tend to sound muddy because the room is actually ringing. This happens a lot with stages too, especially when the subs are installed right up against it, in some cases the subs are actually part of the stage, that's disastrous.

Ringing out the PA is a necessary compromise. Yes you will improve gain before feedback, but you still have the room modes causing problems.

In soundcheck you have to eq the PA a little on the bright side to allow for the HF absorption of the bodies. I've never seen any guidelines on the absorption spectrum of a crowd of people, I wonder if that would be useful info, it might make the setup more scientific. Certainly better than some half deaf dude going one two into a 58.

Although the Behringer FBD is effective, their analogue graphics have many phase shifts and cause problems if you have lots of cuts, you end up trying to fix bubbles in wallpaper. A good analogue graphic is quite expensive.

ogy

The problem with using a graphic to combat room modes is that this will only be effective for one point in the room.

of course, but the microphones will pretty much be at the same points as will the speakers for the gig. given the lead singer might run around a bit but in general all the other vocal and instrument mics aren't gonna budge so fixing the offending frequencies for those points will be effective right?

Although the Behringer FBD is effective, their analogue graphics have many phase shifts and cause problems if you have lots of cuts, you end up trying to fix bubbles in wallpaper. A good analogue graphic is quite expensive.

yeh i would only use them for monitor mixes, not FOH. i think they are acceptable if definitely on the budget side. aside from vocals, the on stage sound will be a balance between backline and monitors anyway. i think the first thing average audience members with no interest in sound engineering would remember and judge the sound on is feedback!

PaulBrewer

madtheory wrote: »

T I've never seen any guidelines on the absorption spectrum of a crowd of people, I wonder if that would be useful info, it might make the setup more scientific.

There's a formula! I'll get it and post it.

madtheory

ogy wrote: »

vocal and instrument mics aren't gonna budge so fixing the offending frequencies for those points will be effective right?

Yes, so, as I said, you will get improved gain before feedback, but you're not going to fix the other room mode issues; sound will vary through out the room.

PaulBrewer wrote: »

There's a formula! I'll get it and post it.

O cool, thanks.

studiorat

Absorption with people in the room works mostly for high and mid frequencies. And again it matters if they are closely packed or further apart. Further apart they actually have more absorption different again if they are seated or standing.

Persons have a coefficient of between 2.0 and 5.0.

http://www.engineeringtoolbox.com/accoustic-sound-absorption-d_68.html

PaulBrewer

studiorat wrote: »

Absorption with people in the room works mostly for high and mid frequencies. And again it matters if they are closely packed or further apart. Further apart they actually have more absorption different again if they are seated or standing.

Persons have a coefficient of between 2.0 and 5.0.

http://www.engineeringtoolbox.com/accoustic-sound-absorption-d_68.html

I'd say I'm a 5.0 ...:cool:

madtheory

studiorat wrote: »

Absorption with people in the room works mostly for high and mid frequencies.

Has anyone ever measured the actual frequency response of that absorption though?