Feedback

[since 1982]

Can any one explain to me the reason why if say on a small stage and space to put main pa speakers, if you were to place ( due to lack of room) the bands stage montors just slightly in front of the F.O.H pa feedback is generated i know it happens as i found out the hard way but i would like to know why it happens.

Thanks

R

[Tim Halligan]

Are the main PA stacks actually on the stage?

Is the stage hollow or solid?

I suspect mechanical transmission.

Cheers,
Tim

[Jason Phair]

Wild guess?

The musicians move to the wedges. That puts them, and their microphones, in front of the rig.

Or you've any of a wide variety of reflections causing additive interference.


Or maybe the night you did that, the humidity was different.


In other words?


Impossible to tell with that amount of information.

[Spock]

Yea, like others said, I'm not getting exactly what you are saying. I need to see a picture.

I've many times had wedges that were out further than the mains, but the mics always stayed behind the mains.

[since 1982]

Small venue solid stage.
main pa placed on the floor on stands front of stage .

http://jblpro.com/products/portablesound/prx/prx535.html

everything hunched close together due to lack of space prob with mics behind main pa (but only just say one meter)with monitors slightly more forward than main pa placed off the floor.

The musicians move to the wedges. That puts them, and their microphones, in front of the rig.

Or you've any of a wide variety of reflections causing additive interference.


This is prob the cause.

[lebouche]

I'd like to know a little about feedback. I did my second live gig tonight. Was a club with a low ceiling, grand piano and vox & vocalist walking around the place. I played the piano till I found a few problem notes and pulled the offending bits out. The desk only gave me three eq options so I could only really choose one freq to pull out and then I had a low cut and high cut to choose from with no crossover option.
I couldn't get the portable mic that loud without feeding back.
Is that always going to be a problem? Is there always a maximum volume for a venue or if I had several eq's would I always be able to tame it? also would buying a portable feedback destroyer be a waste o time and would compression on Vox help reduce feedback?

Thanks

Sorry for the hijack Since1982
P.s. no work on studio till tile samples come back from testing lab in-case of asbestos.

[Spock]

Back when I was young and just starting to do stuff for bands, all we had was very basic stuff.

I would have killed for a real 31 band EQ.

Anyway, the way you kept feedback out of the system was placement of the mics and the mains.

We only got feedback in highly reflective rooms, or when we tried to push things super stupid loud.

[since 1982]

also when asked to mic up an acoustic instrument without a pickup, i often recieve nasty feedback when raising gain stage to high as often the source level is to low, i have to get in real close to the source (often directing the mic to pick up the signal from the sound hole then rolling off some low freq ) causing restrictive play by the musician, i generally use a dynamic for such a job as they are hardwaring, inexpensive and less prone to feedback in a live scenario ( so ive been told) would a small condenser be a good help and investment or should i just tell any one without a pick up to get lost or play louder. lol.

Thanks.

[Jasco]

Is there always a maximum volume for a venue or if I had several eq's would I always be able to tame it?



The nature of this question leads to my opinion of feedback problems in small venue settings: Just turn it down a little. One doesn't always need to strive for 'maximum volume.'

I play small venues all the time. No eq. No problems. And yes, I play loud at times. But I don't worry about being as loud as I possibly can.

[Jasco]

also when asked to mic up an acoustic instrument without a pickup, i often recieve nasty feedback when raising gain stage to high as often the source level is to low, i have to get in real close to the source (often directing the mic to pick up the signal from the sound hole then rolling off some low freq ) causing restrictive play by the musician, i generally use a dynamic for such a job as they are hardwaring, inexpensive and less prone to feedback in a live scenario ( so ive been told) would a small condenser be a good help and investment or should i just tell any one without a pick up to get lost or play louder. lol.

Thanks.


Getting acoustic instruments mic'd loud in a small venue with meager gear is tough to do without feedback.

Especially if they have to compete with electric instruments.

Half of the solution lies with the players. Other players in the group must be aware and sensitive enough not to stomp on the acoustic player(s). If that doesn't happen you're fighting an uphill battle.

A pickup might solve the volume problem, but it's often at the expense of good tone.

[AxeSlash]

I'd like to know a little about feedback. I did my second live gig tonight. Was a club with a low ceiling, grand piano and vox & vocalist walking around the place. I played the piano till I found a few problem notes and pulled the offending bits out. The desk only gave me three eq options so I could only really choose one freq to pull out and then I had a low cut and high cut to choose from with no crossover option.
I couldn't get the portable mic that loud without feeding back.
Is that always going to be a problem? Is there always a maximum volume for a venue or if I had several eq's would I always be able to tame it? also would buying a portable feedback destroyer be a waste o time and would compression on Vox help reduce feedback?

Thanks

Sorry for the hijack Since1982
P.s. no work on studio till tile samples come back from testing lab in-case of asbestos.

Judging from your post you didn't have a graphic EQ across the PA and/or any mons you were running.

A graphic is usually the first port of call for feedback elimination if moving stuff around doesn't help.

But to some extent you can be limited by unfortunate combinations of mic, player's style and venue. I.e. if you're miccing up a quiet instrument with an SDC (or worse, a clip on mic) in a small, reflective room, with a crap PA...you're gonna have some fun. In that scenario we often carry something like a KT DN410 (dual 5 band parametric) to chop out any offending shit.

As for feedback eliminators...a lot of people here will more than likely tell you that if you need a feedback eliminator you don't know how to use a graphic properly. That said, they do have their advantages in some scenarios. Personally I don't like them.

Compression on your vocal mic(s)...more than likely will make feedback worse. Coz in the gaps in between where the guy/gal is speaking/singing, the gain is effectively HIGHER. If anything, you want the opposite, which is why in some extreme examples (like, guy stood in front of a large PA with a crap mic) I've seen people GATE the vocal mic(s).

Think about the null points in the pickup pattern of the mics you're using as well. If you're pointing a mic directly at a loudspeaker, you can guess the consequences; I try and get the null point pointing at the boxes if I can (not always possible).

Another thing that may or may not help (depending on the situation) is running the subs off an auxilliary. Sub is (to an extent...here's a can of worms) omnidirectional, and thus you can find yourself especially prone to low end feedback on big rigs with lots of sub; thus if you run them off an aux, you can only send e.g. bass and kick to them, minimising the possibility of low end feedback in general from any other mics.

On a slightly related note, if you're dealing with a groundstacked line array, be aware that there will be a hefty lobe of low mid coming out of the BACK of that thing (assuming it's actually a proper line source box and that it's curved), and you may need to adjust PA/mic positioning as appropriate. We had an unfortunate incident of an Adamson Spectrix rig's rear lobe pointing directly into a pair of lectern mics a few years back...it was not a pleasant experience.

There are other tricks you can play as well, like delaying the boxes slightly (delaying the mains back to the drum kit can sometimes HELP eliminate feedback), or even polarity reversing the boxes can sometimes help.

And if the front and back walls aren't draped or have something else absorbant on them, see if you can do something about it, it can help immeasurably. The Jools Holland guys drape out almost the entire stage as a matter of course, and I'm yet to hear a squeak out of their monitor rig.

[lebouche]

Judging from your post you didn't have a graphic EQ across the PA and/or any mons you were running.

A graphic is usually the first port of call for feedback elimination if moving stuff around doesn't help.

But to some extent you can be limited by unfortunate combinations of mic, player's style and venue. I.e. if you're miccing up a quiet instrument with an SDC (or worse, a clip on mic) in a small, reflective room, with a crap PA...you're gonna have some fun. In that scenario we often carry something like a KT DN410 (dual 5 band parametric) to chop out any offending shit.

As for feedback eliminators...a lot of people here will more than likely tell you that if you need a feedback eliminator you don't know how to use a graphic properly. That said, they do have their advantages in some scenarios. Personally I don't like them.

Compression on your vocal mic(s)...more than likely will make feedback worse. Coz in the gaps in between where the guy/gal is speaking/singing, the gain is effectively HIGHER. If anything, you want the opposite, which is why in some extreme examples (like, guy stood in front of a large PA with a crap mic) I've seen people GATE the vocal mic(s).

Think about the null points in the pickup pattern of the mics you're using as well. If you're pointing a mic directly at a loudspeaker, you can guess the consequences; I try and get the null point pointing at the boxes if I can (not always possible).

Another thing that may or may not help (depending on the situation) is running the subs off an auxilliary. Sub is (to an extent...here's a can of worms) omnidirectional, and thus you can find yourself especially prone to low end feedback on big rigs with lots of sub; thus if you run them off an aux, you can only send e.g. bass and kick to them, minimising the possibility of low end feedback in general from any other mics.

On a slightly related note, if you're dealing with a groundstacked line array, be aware that there will be a hefty lobe of low mid coming out of the BACK of that thing (assuming it's actually a proper line source box and that it's curved), and you may need to adjust PA/mic positioning as appropriate. We had an unfortunate incident of an Adamson Spectrix rig's rear lobe pointing directly into a pair of lectern mics a few years back...it was not a pleasant experience.

There are other tricks you can play as well, like delaying the boxes slightly (delaying the mains back to the drum kit can sometimes HELP eliminate feedback), or even polarity reversing the boxes can sometimes help.

And if the front and back walls aren't draped or have something else absorbant on them, see if you can do something about it, it can help immeasurably. The Jools Holland guys drape out almost the entire stage as a matter of course, and I'm yet to hear a squeak out of their monitor rig.

Thanks Axe,
Lots of interesting Info...
the bit from "groundstacked line array" to "not a pleasent experience" is in a foreign language I don't comprehend. Nothing some googling won't fix.:Wink:
Cheers

[ggunn]

also when asked to mic up an acoustic instrument without a pickup, i often recieve nasty feedback when raising gain stage to high as often the source level is to low, i have to get in real close to the source (often directing the mic to pick up the signal from the sound hole then rolling off some low freq ) causing restrictive play by the musician, i generally use a dynamic for such a job as they are hardwaring, inexpensive and less prone to feedback in a live scenario ( so ive been told) would a small condenser be a good help and investment or should i just tell any one without a pick up to get lost or play louder. lol.

Thanks.

A condenser mic will most likely make it worse.

[ggunn]

If your guys are on a hollow bare wooden stage and your PA has a lot of low end and/or the low freq cabs are on the stage as well, one source of low end feedback is up through the bases of the mic stands. A square of carpet under each stand will help this.

[AxeSlash]

If your guys are on a hollow bare wooden stage and your PA has a lot of low end and/or the low freq cabs are on the stage as well, one source of low end feedback is up through the bases of the mic stands. A square of carpet under each stand will help this.

Ah yes, resonant stages are one thing I forgot to mention.

We had one recently that was constructed mostly of tubing that had a lovely ring in it at about 400Hz. Was really fucking weird to stamp your foot on stage and hear a "OOOoooooo" come back at ya. It didn't ACTUALLY make owt feed back, but it sure as hell sounded like it.

As for the mic stand thing...decent mic stands normally help. Make sure that the main upright of the stand isn't resting on the floor - the only points of contact should be the (soft) rubber feet. Plastic feet and/or no feet at all are always a recipe for Weird Shit to happen.

[AxeSlash]

Thanks Axe,
Lots of interesting Info...
the bit from "groundstacked line array" to "not a pleasent experience" is in a foreign language I don't comprehend. Nothing some googling won't fix.:Wink:
Cheers

If you google "line array", you could very well spend YEARS reading the results.

http://www.gtaust.com/filter/06/08.shtml might give you a semi-decent overview of what line arrays (line SOURCEs, even) are all about. It doesn't mention the lobe that's coming off the arse end of the rig though.

If you're gonna get serious about live sound for a living, I'd suggest you do do some serious reading about line arrays; they're a large trend (for all the wrong reasons) at the moment - people love them. Even if they're the wrong box for the job (as is so often the case).

I'm of the opinion that line arrays should be saved for big open fields and/or venues with a VERY reflective back wall. Other than that, they're probably the wrong box.

F1, anyone?

[since 1982]

Well put Jasco

[since 1982]

Thanks for all the advice guys i've got lots of ammunition now for venue owners who have low standard acoustic treatment and expect miracles.

R

[AxeSlash]

...venue owners who have low standard acoustic treatment and expect miracles.

R

Welcome to the busiess :grin:

[Tim Halligan]

If you're gonna get serious about live sound for a living, I'd suggest you do do some serious reading about line arrays; they're a large trend (for all the wrong reasons) at the moment - people love them. Even if they're the wrong box for the job (as is so often the case).

I'm of the opinion that line arrays should be saved for big open fields and/or venues with a VERY reflective back wall. Other than that, they're probably the wrong box.


Line Arrays....the PA equivalent of "Valve gear".

I'm so glad I'm not the only one who feels this way.


Cheers,
Tim

[AxeSlash]

Line Arrays....the PA equivalent of "Valve gear".

I'm so glad I'm not the only one who feels this way.


Cheers,
Tim

Tell me about it. The problem is that they're too damn convenient. Take away the low weight/need less gear thing and they'd be nowhere near as popular. I still reckon that a large portion of them sound like cock and balls anyway (with a few exceptions).

[Jasco]

If your guys are on a hollow bare wooden stage and your PA has a lot of low end and/or the low freq cabs are on the stage as well, one source of low end feedback is up through the bases of the mic stands. A square of carpet under each stand will help this.

As a side note to this, a previous band of mine played a club for quite a while that had no stage. The owner started having a lot of success with live music and decided to build a stage. For some reason he asked us about advice for the acoustic properties of the stage. Not being acoustical engineers, we jokingly told him to fill the stage with sand.

And to our complete suprise, he actually did it. It was a lot of sand, and had to be loaded in by wheel-barrel down the elevator (club wasn't on ground floor.) :grin:

The stage didn't have any boomy low end resonances.

I'm just glad we didn't tell him something like "fill it with BB's".

[ggunn]

If you google "line array", you could very well spend YEARS reading the results.

http://www.gtaust.com/filter/06/08.shtml might give you a semi-decent overview of what line arrays (line SOURCEs, even) are all about. It doesn't mention the lobe that's coming off the arse end of the rig though.

If you're gonna get serious about live sound for a living, I'd suggest you do do some serious reading about line arrays; they're a large trend (for all the wrong reasons) at the moment - people love them. Even if they're the wrong box for the job (as is so often the case).

I'm of the opinion that line arrays should be saved for big open fields and/or venues with a VERY reflective back wall. Other than that, they're probably the wrong box.

F1, anyone?

The first LA I heard was at a mid sized outdoor show, and it was pretty impressive. It was exceptionally clear and the volume at the back was nearly the same as the volume up front.

[AxeSlash]

The first LA I heard was at a mid sized outdoor show, and it was pretty impressive. It was exceptionally clear and the volume at the back was nearly the same as the volume up front.

That's where line arrays shine.

Put em in a square room though with insufficent trim height and they can be way outmatched by some more conventional cabinets that won't bounce off the walls.

That said, the newer L Acoustics thing (KUDO I think it's called?) might solve that horizontal problem...just interested whether it would stay line source when you've got variable horiz. dispersion happening down the array...

I appear to have hijacked the thread somewhat. Sorry guys :P

[Jason Phair]

That said, the newer L Acoustics thing (KUDO I think it's called?) might solve that horizontal problem...just interested whether it would stay line source when you've got variable horiz. dispersion happening down the array...

I appear to have hijacked the thread somewhat. Sorry guys :P


Downside: It weighs 4,000lbs/box.


Good shit all around. I'd just like to add that if you're going to be putting drape up on a stage, make ABSOLUTELY DEAD SURE THAT THEY'RE FLAME-RETARDANT.

[since 1982]

http://www.l-acoustics.com/anglais/press047.htm

Interesting variable directivity aspects.

[Tim Halligan]

Downside: It weighs 4,000lbs/box.


If I've told you once, I've told you one hundred million billion thousand times - don't exaggerate!

:D

It actually weighs 87kg/191.4lbs per box...


...if you can believe the manual.

Cheers,
Tim

[Jason Phair]

The Q1 weighs 40.


And sounds really fucking good.



I'll take it.

[Tim Halligan]

The Q1 weighs 40.


And sounds really fucking good.



I'll take it.

Fair enough.

:D


Cheers,
Tim

[AxeSlash]

I'd just like to add that if you're going to be putting drape up on a stage, make ABSOLUTELY DEAD SURE THAT THEY'RE FLAME-RETARDANT.

That sounds like you've just had one hell of a barrel of laughs...

[Jason Phair]

Oh trust me, it's not from experience.


Just a good general precaution.


Think of that hair metal band named after the shark.


What was their name again? Hammerhead? Tiger?


Something like that.

[ggunn]

If I've told you once, I've told you one hundred million billion thousand times - don't exaggerate!


Never in a billion years would I use hyperbole to make a point!

[omikl]

Acoustic treatments? The dives I play in you're lucky to get power :)

[AxeSlash]

Acoustic treatments? The dives I play in you're lucky to get power :)

"Where's our power?"

*dude points to a lonely single plastic 13A socket with a leak immediately above it*

"Riiiiiiight..."





Been there, done that, didn't enjoy it.

Some people are so clueless.

[ggunn]

"Where's our power?"

*dude points to a lonely single plastic 13A socket with a leak immediately above it*

"Riiiiiiight..."





Been there, done that, didn't enjoy it.

Some people are so clueless.

The band I was FOH for many moons ago showed up to play an outdoor gig; the "stage" was a 20' X 20' slab and the "power" was a single ungrounded outlet. I drove an unpainted tire iron deep into the ground right by the outlet and poured a couple of gallons of water around it, plugged our power box into the outlet through a ground lift, and tied off the ring of the ground lift to the tire iron with some heavy copper wire. I made sure that everyone's gear had a short run to that ground pin. It was the quietest stage I ever ran and nobody got shocked.