I'm having feedback issues with my guitar concert setups

Portable PA
1

Hi there

I've followed the Bose forum from time to time over the past 10 years since investing in my first two bose L1 Classical II models.  I now have a third.  I just PM'd ST and he said it would be of benefit to others to post publicly. So here's what seeking to know more about.

I'm having feedback issues with my guitar concert setups.

I have mutiple arrangements at our students concerts.  We use up to 4 microphones on stage for various purposes.

I own and use the following on stage:

OM7 Audix mic, OM2 Audix mic, Shure Beta SM58A, then I use one of two condensor mics - AKG LC or a AKG C1000s.

Our setups vary from kids strumming guitars in large groups (which we tend not to worry to much about with mics) then we have a small classical guitar ensemble, acoustic guitar ensemble, and 2 or 3 combo bands, along with a few soloists, duets, other bands ( 2 or 3).

Instruments used:  Classical Guitars, Acoustic guitars,Electric guitars (up to 3 in the bands), Vocals, Bass guitar.  I play drums for our concert and I actually use a wazinator instead of the kick drum as I like the tight sound it gives, the rest of the kit is unmiked.  

Here's some footage from our concerts.  I've learnt a few things about using the gate, compression, standing close to mics (eating the mic), keeping at least 8 feet in front of bose systems, keeping bose systems at 8 feet apart from each other, and that the more mics you have on stage the bigger chance for feedback, bringing back the trim.  I am a simple guitar teacher with not much intellectual capacity to get to get into technical knowledge, so I'm really looking for simple answers if you have any.

I guess I'm wondering if you recommend selling the condensors? They only reason I bought them was to give our instrumentalists a better chance of being heard, those who need to be miked.  Do I invest another type of mic that might not feedback as bad?  

I naturally favour the shure SM58A and Audix OM7 and OM2..... but it would be nice to be able to use the condensors for the classical guitar ensemble, kids playing in groups of five in a semi circle with one condensor mic in the middle.

 

We plug from left to right looking at the stage:

Into the first L1 Tower, Ch1 the kick and ch2 Audix OM2,

Then we use a T1 on the middle tower which has the following plugged into it: ch1 Bass guitar, ch2 Direct out to guitar amp, ch3 Audix OM7, ch4/5 acoustic guitar, then on the tower we plug in Ch1 the C1000s, and Ch2 electric guitar through a Boss ME-70. 

Then on the tower on the right we use: Ch1 nothing as it's faulty, ch2 Shure SM58A - wireless hand held mic, ch3 electric guitar via a Laney amp miked with a shure sm57 mic, and ch4/5 acoustic guitars, then on the tower itself we plug in the AKG girls mic.

This is what we are using so far for our concert on the 14th of December next week......Here's some footage from our last concert.

https://www.youtube.com/watch?v=Qg5o9vUtwOo

https://www.youtube.com/watch?v=tWz2wvFWnQk

Please be aware we use a Tascam DR-40 with two condensor mics hooked up to it which is hooked directly into our Canon 6D camera for sound and video to be recorded simuataneously.  A bit overcompressed, and we still haven't work out the best settings for video footage, or uploading to youtube for that matter, so the quality is quite lost.

In the venue we now use, which is a small theatre (170 seats).  The seats angle up like a picture theatre (perhaps 15 to 20 degrees in steepness).  Our sound mixer mixes at front of the stage due to using two T1 ToneMatch mixers. 

Anyway, I've rambled on to much already, but I'm hoping you might understand what I'm trying to achieve.  A couple pics of the condensor mics we use as they are older models now.

Hope to hear from you soon.

God bless,

Perrin Madsen

2

I've looked at both your videos and, it seems to me you are doing a very good job (both as a teacher and as a sound guy).

WRT to your miking issues, the feedback resistance of any mic is down to it's polar pattern*, which may be why the 'super cardioid' Audix and Shure Beta mics are better than the AKGs**.

The gain before feedback also depends on the ratio of direct sound and ambient sound/spill getting back to the mics from the FOH. L1's are exceptionally good at controlling feedback but your single mic in the middle of a small ensemble is always going to struggle (especially compared with a mic eating vocalist) simply 'cos of the distance from the, relatively quiet, classical guitars.

TBH, if you can't get the mics within a few inches of the instruments you are going to get a thin and weak sound anyway as your other mics are designed to be used within about 2" of the source. And you can't really boost the bass to compensate or you'll just excite feedback at lower frequencies. Where you are able to close mic the instruments the sound is pretty decent and, as you point out, its only the large ensembles you struggle to get out there. Basically you can't cheat the laws of physics.

HTH

* In a given situation, assuming correct placement, a narrower pattern will be less susceptible to feedback.

**Your C1000 has an option to add a baffle inside the basket to convert it's polar pattern to super-cardioid which would help but I have no knowledge of the LC. However the C1000 is not regarded as a particularly good mic though so I would not be over concerned about using it.

3

Hi Peza,

You have a lot going on and I doubt that I'm the person to teach you over the internet, but allow me to make just a couple observations and a suggestion or two.

Pickups on guitars are generally easier to control than mics, use them when available.

Shure SM 57  mics are tried and true for stage and studio. They can often be found on sale for less than $100. I would try to pick up 3 or 4 of those over time. Having the same types of mics will make the job easier for the sound man. Using a mixture of mics with various sensitivities and voices can create doubt in the mind of inexperienced sound personnel. 

My tendency is to not sell mics. The used market can be a great place to buy, but you generally take a beating when you sell. The mics you have listed all are good mics and will find a place in your ensembles sooner of later.

You can pick up good information just by searching How to mic a guitar. It might not all apply directly to you but you will pick up usable information.

I would utilize the mixers as much as possible for mic inputs. Usually easier to identify and control problems from the mixer, also easier to setup correctly to begin with.

Minimize the number of devices you run any particular signal through. The less knobs to turn the less chances for trouble.

A big part of playing live, amplified, is learning how to use the devices at hand. After you have found some good info on the net, send links to your students and encourage them to read and study too. It is important they understand not only how to best utilize a mic, but why. Best tone, best signal level, least chance for feedback all are related to mic position during use.

Hope you find something here that helps. I admire anyone who devotes time to musical instruction for kids.

O.. 

 

4

ok thank you for your reply Sam, that was good info your reinforcing in me.  There is only one song in the upcoming concert that I'm using one of the condensor mic's, and other times is mostly just 2, so I will be defaulting to the OM7 and the Shure SM58A.  

It's nice to know that I'm actually just up against physics .  

Thanks for taking the time out to reply.

God bless,

5

Thank you oldghm, helpful advice on how to combat it on other levels; ie: education, sm57 multiple use.  

The only reason I was putting the condensors on the towers and not through the T1's is because we use them the least, and I would have to control their volumes as the old 2 channel control on the older models doesn't reach right out the front, and takes a bit of confusion away from the mixer.  ps I drum in the concerts most of the time, so they reach me from all 3 towers.  Kind of handy if it really turns to custard and the mixer isn't quite on to it.

6

SM57 is a cardioid* mic and will not achieve the same gain before feedback than the Audix/Betas. All these mics really need to be within a few inches of the source to work as intended.

* This characteristic means they will work better for a 'mobile' vocalist who wanders off mic all the time, if the singer does that with a super cardioid he/she will drop in level significantly, a cardioid's wider pickup pattern is much more forgiving. (FWIW I never use super-cardioids when running open mic sessions for exactly that reason).

7

As Ogham rightly says, pickups on acoustic guitars are much less feedback prone than mics but I'd add that they usually don't sound as good as a well positioned mic. I'm a guitar player and have been looking for the perfect acoustic guitar pickup for over 50 years 

8

Hi Peza,

It's great you've had so much input from others.

Here's some information I found on the web about the AKG LC microphone.



and the AKG C1000S



mceclip1.png599×516 105 KB

More coming.

ST

9

Hi Perrin Madsen,

Thanks for all the background information. Please jump down to the highlighted portion below.

Peza posted:

Hi there

I've followed the Bose forum from time to time over the past 10 years since investing in my first two bose L1 Classical II models.  I now have a third.  I just PM'd ST and he said it would be of benefit to others to post publicly. So here's what seeking to know more about.

I'm having feedback issues with my guitar concert setups.

I have mutiple arrangements at our students concerts.  We use up to 4 microphones on stage for various purposes.

I own and use the following on stage:

OM7 Audix mic, OM2 Audix mic, Shure Beta SM58A, then I use one of two condensor mics - AKG LC or a AKG C1000s.

Our setups vary from kids strumming guitars in large groups (which we tend not to worry to much about with mics) then we have a small classical guitar ensemble, acoustic guitar ensemble, and 2 or 3 combo bands, along with a few soloists, duets, other bands ( 2 or 3).

Instruments used:  Classical Guitars, Acoustic guitars,Electric guitars (up to 3 in the bands), Vocals, Bass guitar.  I play drums for our concert and I actually use a wazinator instead of the kick drum as I like the tight sound it gives, the rest of the kit is unmiked.  

Here's some footage from our concerts.  I've learnt a few things about using the gate, compression, standing close to mics (eating the mic), keeping at least 8 feet in front of bose systems, keeping bose systems at 8 feet apart from each other, and that the more mics you have on stage the bigger chance for feedback, bringing back the trim.  I am a simple guitar teacher with not much intellectual capacity to get to get into technical knowledge, so I'm really looking for simple answers if you have any.

I guess I'm wondering if you recommend selling the condensors? They only reason I bought them was to give our instrumentalists a better chance of being heard, those who need to be miked.  Do I invest another type of mic that might not feedback as bad?  

I naturally favour the shure SM58A and Audix OM7 and OM2..... but it would be nice to be able to use the condensors for the classical guitar ensemble,kids playing in groups of five in a semi circle with one condensor mic in the middle.

This is going to be extremely difficult to do. In your live sound reinforcement application, you the microphone is in the same sound field as the L1 systems. To make this work (one microphone for five performers) the sound sources (guitars), must be louder at the microphone than the L1 systems. You probably can't do that if the guitarists are in a semi-circle around a single microphone.

If the microphone can hear the L1 as loud or louder than the guitars, you will have feedback.

You've got a few choices (not all are practical)

  • Get a microphone for each guitarist and position it as close as possible to each guitar. That is likely no more than 6-12 inches from the guitar, aimed at the point where the neck meets the body.
    Unless you have time to experiment with mic positioning (which is unlikely for a live show), the safest place to point your mic is the area where the guitar's neck and body meet.
    See: Mixing Acoustic Guitars Live
  • Get pickups for the guitars that don't have them.
  • Move the L1 systems to the front of the stage between the microphone and the audience. I'm not recommending this. I only mention it because it may solve the feedback issue, but at the sacrifice to the way you are used to doing things.



We plug from left to right looking at the stage:

Into the first L1 Tower, Ch1 the kick and ch2 Audix OM2,

Then we use a T1 on the middle tower which has the following plugged into it: ch1 Bass guitar, ch2 Direct out to guitar amp, ch3 Audix OM7, ch4/5 acoustic guitar, then on the tower we plug in Ch1 the C1000s, and Ch2 electric guitar through a Boss ME-70. 

Then on the tower on the right we use: Ch1 nothing as it's faulty, ch2 Shure SM58A - wireless hand held mic, ch3 electric guitar via a Laney amp miked with a shure sm57 mic, and ch4/5 acoustic guitars, then on the tower itself we plug in the AKG girls mic.

This is what we are using so far for our concert on the 14th of December next week......Here's some footage from our last concert.

https://www.youtube.com/watch?v=Qg5o9vUtwOo

https://www.youtube.com/watch?v=tWz2wvFWnQk

Please be aware we use a Tascam DR-40 with two condensor mics hooked up to it which is hooked directly into our Canon 6D camera for sound and video to be recorded simuataneously.  A bit overcompressed, and we still haven't work out the best settings for video footage, or uploading to youtube for that matter, so the quality is quite lost.

In the venue we now use, which is a small theatre (170 seats).  The seats angle up like a picture theatre (perhaps 15 to 20 degrees in steepness).  Our sound mixer mixes at front of the stage due to using two T1 ToneMatch mixers. 

Anyway, I've rambled on to much already, but I'm hoping you might understand what I'm trying to achieve.  A couple pics of the condensor mics we use as they are older models now.

Hope to hear from you soon.

God bless,

Perrin Madsen

10

Hi Peza,

I most always find mic conversations interesting. Long time users usually have a favorite, those new to use will tend to go with a name they have previously heard or what a friend uses. Some will shop by price, low and high, and many choices are made without understanding why or where one mic performs better than an other.

Here, we often recommend super or hyper cardioid mics for use with L1 systems for vocalists. It is often stated they are less prone to feedback, and they are, in some situations. With the primary sound source behind a vocalist, hyper and super cardioid work great, but if you place a floor monitor in front of the vocalist, then that becomes another issue to deal with, because those same mics will pick up sound from the back side, more so than the simple cardioid.

Hyper and super cardioid mics will teach good habits to a new user because they have to be on axis to be heard. Of course that's assuming the new user gets over the fear of being heard.

Young people in a learning environment need to be exposed to the "why", when told to sing directly into the mic. Good habits, understood and practiced in the beginning will solve many issues later if they chose to stay on the stage as they mature.

Most of us have heard, or know from experience, that to get the best sound from an acoustic guitar we don't mic the sound hole, and not too close, but, .... that's for the studio when recording. On stage it is not usually feasible to utilize two mics at a distance of a foot or more, so we compromise. With a stationary guitarist, especially one who is sitting, we can place a single mic reasonably close to the instrument, and expect that the player and the guitar will shield the mic from the L1. If we place the mic, and EQ in a manner that does not allow low omni directional frequencies to excite and cause a runaway sustain of resonant frequencies in the guitar, we can get pretty good sound. As a guitarist improves and gains confidence they can move in a manner that allows the mic to enhance dynamics. Done correctly with intention a pro can remove the sound man from the equation.

So, .... while a seasoned user might substitute a SM 57 in as a vocal mic and some guitarist might utilize an OM 7 as an instrument mic, generally speaking, they actually work better when used as intended, SM 57 for instrument, OM 7 for vocal.

Then we have to remember the old saying, rules are meant to be broken. Sometime the unconventional is what works in a particular situation. Learning to adapt, roll with the flow, can keep the show moving and everyone in a good state of mind, and that's more important than the equipment.

I might add, I have two AKG C1000's. I used these quite a bit a few years back for solo performances on both guitar and vocal. I found them to be natural and warm sounding, even with the presence boost adapter on my vocal mic. I have not used them as much since fitting all of my stage guitars with pickups and the L1 being my primary sound system, but I could use them if I chose to. 

O..

 PS, If you haven't already, please click on the blue links in my previous post. 

11

Hi guys, thank you for the replies, they are much appreciated and are sharpening up again.  We only do concerts every six months with the students so I get rusty with the knows and hows of things.  Sounds like ST saved me going down a tricky path with 5 students in a semi circle with the C1000s.  Out of interest, and excuse my lack of expertise..... but would a Rode NT1-A condensor work better.  

I 'could' use this instead of the c1000s in the semi circle, I'm assuming a similar response from C1000s but I'll ask anyway.  Or I also own a AKG C2000B.  Maybe these wide of the outer L1 towers?.  We would probably be able to get them about 12 to 15 feet away from the L1 towers....

The dilemma then is that I would have to use the C1000s and the AKG LC as recording mics to record the concert through the tascam DR-40...... 

Any thoughts around this idea?

 

12

No, put simply one mic will not get you much level before feedback becomes a problem. To understand why you need to understand a little about how sound propagates. The fundamental rule is the inverse square law, if you move a mic twice as far from a source it will receive 6dB less level, that applies when you move from lips on the basket (or from, say 1cm from the capsule) to 1cm away to moving a guitar mic from 6" to 12" from the guitar. If you now consider that a strong voice is significantly louder than a finger style classical guitar you'll see you have vastly different levels reaching the various mics. The max gain you can apply before feedback, in a single mic system, is dependant purely on the amount of signal from the speakers is reaching the mic, when the ambient sound comes out of the speakers and is louder at the mic than than the unamplified ambient sound it will build into the characteristic 'howl round' we know and hate......

So, whatever mic you use if you turn it up enough it will feedback, if you can't turn it up enough to make the guitars heard before this happens you are, basically, stuffed...... As Scottie would have said "Ye canna change the laws of physics Cap'n"

13

You need the ensemble SR mics MUCH closer to the ensemble than to the PA speakers. This is one situation where a conventional FOH plus monitors system would work better than the L1s beind the performers. Or, as has been suggested, get all the guitars fitted with pickups, I have just ordered 5 piezo UST pickups from China for under £10, they are easy enough to fit or for a non invasive solution for steel strung guitars Artec do a mag pickup for around £20. Beware of contact pickups that attach with bluetack, I have yet to hear one that sounded good (not even the mega expensive Schertler).

14

Ok, thank you again.  Looks like I'm going to save myself a few dead ends, I appreciate the knowledge in here.  

Cheers & God bless .

15

It's a tough call, my pet hate, as a sound engineer, was choirs........ They expect you to stick a couple of mics up on the front of the stage and get them as loud as a full on rock band.........

You seem to be doing a decent job given the restrictions placed upon you. 

Just a thought, if you put two of the L1 systems in the conventional FOH position either side of the stage and use the third at the back for additional reinforcement and foldback you'd be able to not send he ensemble mic to the rear L1. That would probably gain you a few dB out front.

16

Thank you Sam .  

17

I don't think this has been linked yet. Another article, this one on feedback and how to avoid, or control it.

O..

18

Thank you will give that a read over, and pass on to my sound mixer

 

19

Hi again,

I'm just wondering if there's a recommended volume to have on the Bose L1 model II Base for the Master input going between the L1 Bose to the ToneMatch 4 channel I use.....

I've normally had them between 3 and 4 but have been experimenting between 6 and 7....... 

What do you recommend.  Obviously it's louder, but I kind of need it as the OM7 needs a lot to get up with the other mics.......

Hope I've explained it well enough.

20

Hi, Perrin Madsen.

Peza posted:

Hi again,

I'm just wondering if there's a recommended volume to have on the Bose L1 model II Base for the Master input going between the L1 Bose to the ToneMatch 4 channel I use.....

If you are talking about the L1 Model II Power Stand Analog Input Trim control, it should be off.  Assuming you are using the ToneMatch cable

EtherconMale.jpg

to connect the T4S to the L1 Model II Power Stand, you aren't using the analog signal path, and the Analog Input Trim does not affect the volume.  We turn it off to avoid any RF noise at the venue.

         

I've normally had them between 3 and 4 but have been experimenting between 6 and 7....... 

What do you recommend.  Obviously it's louder, but I kind of need it as the OM7 needs a lot to get up with the other mics.......

Set the gain staging with the trim controls for the OM7, on the T4S.

Start with the initial gain staging like this.

Repeat the process shown above for each microphone in its respective channel.  The trim control will probably be much higher for the OM7 than the other microphones.



Hope I've explained it well enough.

ST