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Feedback in FOH subs, adjusting gain,

JamesDC

JamesDC

Guest
Sep 26, 2013
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18
#1
Hi. I'm a sound guys nightmare,Shure 57 mic sunk in bow of sousaphone picks up everything on stage, and any time there are subs I have such a wallop that I'm feeding back easily. Experienced sound guys often figure it out quickly and I feel the subss but can play mid range and do tuba stuff with not too much clipping, but mostly I get guys who go from crazy sub hell to nothing but my 2x10.

It's been suggested that I put the mic in a rubber sole shoe
I've thought about a foam barrier on the bell - which will stuff the sound a bit too,
One guy solved it by not running subs through an aux channel.

I run through a mixer, pedals, amp. And another issue I run into is figuring out how to adjust gain, I generally keep the gain on my genz 6.2 at a little less than half with volume around the same, compression is always on with input generally set a bit higher than output, On the board, I end up turning gain up and volume down a little. I tend to get better sound with the pad off when my amp is alone, and on when I'm running to a board,

Clearly, I have no idea what I'm doing, any suggestions on how to prioritize which gain/volume I adjust first ap(preamp/amp) and how to put compression on it (input vs output) appreciated,

And, any standard advice or settings help on my end to offer a sound guy who has an all or none approache to subs?
 
#3
yikes...where to begin?

mic: get a high gain before feedback mic (audix, Shure beta series) and pull the mic out to the flare of the bell - not in the throat. You can use a percussion or drum clip to get the mic located properly.

IMG_7470-1.jpg


feed to FOH desk: where in your signal chain is your feed being sent from? You should be sending a split off your signal chain that only includes the elements of your sound that are essential (after your effects stomps, for example) which is BEFORE (PRE) any treatments or EQ adjustments that accommodate your stage rig. You have a 2x10 cabinet, which likely sounds nothing like a typical PA system with respect to frequency range and EQ. If you send the FOH desk a feed AFTER (POST) all your stage EQ treatments, then you're handcuffing the FOH mixer with adjustments that may be totally in appropriate for the PA. I can imagine you may be pushing extra low end to get the 2x10 cab to pump a little. This would be deadly if this POST treated signal were sent to the FOH.

do you get sound checks?

What effects/stomps/processors are you using?

If you aren't well versed in setting up compression, avoid pre-treating your signal with a comp. If you need compression to protect your stage rig, address it so that the compression only impacts your stage rig. Improper comp settings can lead to early onset feedback.

Just some immediate thoughts/questions...
 
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#4
Get a good parametric EQ , with bandwidth control , set it for your sousaphone only.

You got an iPhone ?
Get that App :http://www.faberacoustical.com/ios_apps/signalscope/
Check the frequency of the feedback and cut it with the Para EQ , start with narrowest bandwidth and give it some Width ONLY if needed.

As for the leak of the mike , it's normal , any mike on any stage will pick up other stuff.
IME/IMHO low frequency stuff is critical due to phase cancellation.
But you don't have a choice , sadly , to use a mike. Until Roland makes a V-Tuba :)

As for the gain structure it depends if you work on an analogic or digital board.
- Analogic : set the master to 0 , the input fader to 0 and adjust the gain until to the right volume.
- Digital ; set the gain as hot as possible before clipping , or until it reaches -6dbfs at the loudest , Fader to 0 , then use the attenuation to lower it to the disired level.
 
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#5
Thanks y'all. All of these answers are helpful. One thing, jim fist, the mic in the horn isn't going to change. The clip,on mic is a totally differnent sound than what I'm going for,

For boxes. Fuzz, filter, freeze, compression, hot hand and will maybe be adding a bit crusher as well as an octave up box.

I have to re read all of this to make sure I'm understanding,,thanks y'all.
 
#7
JamesDC said:
Hi. I'm a sound guys nightmare,Shure 57 mic sunk in bow of sousaphone picks up everything on stage, and any time there are subs I have such a wallop that I'm feeding back easily. Experienced sound guys often figure it out quickly and I feel the subss but can play mid range and do tuba stuff with not too much clipping, but mostly I get guys who go from crazy sub hell to nothing but my 2x10.
Click to expand...

We are micing a tuba in similar way. Our experience is to put the mic down the bell a bit as this helps isolate the mic from other stage sounds. You have to play around a bit for the right location of the mic. We are using a either a Shure SM 98 or Beta 98 clip-on mic taped to the inside of the bell. The clip is taped to the inside of the horn and the mic element is centered in the bell and pointed straight down the bore. This give you maximum rejection from sounds outside the horn. The front facing bell on a sousaphone, as opposed to the straight up bell of a tuba, may complicate things. You may find a mic mounted on the bell aimed down the throat works better as one of the other posters mentioned...or not. We prefer to be down in the horn just below where the bell flairs. We feel this gives us more fundamental and less of the overtones generated by the bell. Our intent is to sound more like a bass guitar.

The only feedback problems we are getting comes from the amp. In my opinion the amp is way to loud, but I am not the tuba player. Anyway the feedback becomes more a problem when the tuba uses distortion type effects. Why? Distortion tends to add some degree of compression to the signal which limits how loud the amp plays, but when you stop feeding signal into the pedal, the gain increases and feedback occurs. We controlled this problem by using a noise gate and also switched to a distortion pedal with less compression. If this sounds like your problem, my recommendation would be to get an ISP Decimator II G string noise gate. http://www.isptechnologies.com/portfolio/decimator-ii-g-string-pedal/

Before you buy a noise gate, you should read up on the Decimator II as it is not cheap and it must be connected in two places to work properly. First it is connected at the beginning of the signal chain. This part of the Decimator samples the pre-effect signal and sends it out of the pedal without changing it. The gate part of the pedal is connected after your distortion effects and any compressor you may be using, but before any time-based effect such as reverb or digital delay. The sample generated in the first stage is used to key the gate part of the pedal. By keying of an unprocessed signal the gating tracks better. The manual says to run the Decimator in your amps effect loop, but this is not necessary.

Check out a recording here

Recorded with Zoom

good luck:bassist:
 
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#9
Www.blackmasala.bandcamp.com. Is the group I tend to have FOH sound issues with.The purple record is a straight studio recording, the orange one (which is the one being featured now) is a remix album, so my percussion and Sousa sound good- but it's not generally a sound I get on stage. I am aiming for a bass guitar prescence - hence compression and a hot enough signal to articulate 8th notes easily without worrying about the air column, a lot,of the sound in the studio was a little overdriven- which I like, but don't try on stage for fear of causing problems.

And yeah, I sink a beta57a down in the bell. I'll make sure I am sending the signal pre effects and I'll check the board during sound check to make sure I understand where the settings should be.

The problem has been a lot less noticeable as of late, but these are good suggestions for what I can do to eliminate it completely.

Thanks for the tip on decimator.

Thanks again,
 
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#10

Never got an answer to my question:
WayneP said:
If I understand, you’re using a bass guitar amp with your Sousaphone? Is the 57 connected to your “mixer, pedals, amp?”
Click to expand...
Regardless, the feedback problem might simply be your choice of mic. The SM57 is a vocal mic. Below is a frequency response graph published by Shure, and basically it is not a good choice for a low-frequency instrument. As you can see that mic rolls out about 5 dB/octave below 200 Hz. I suspect that your feedback problem is likely happening because you might be adjusting your stage amp to compensate for the 57’s inadequacies, like perhaps boosting the overall volume or EQ to compensate for the lows the 57 isn’t delivering.

Bottom line, I’d suggest switching to a mic with better low frequency extension, such as the SM 98 that Wasnex mentioned.


Shure_SM57_freqResp.gif


Regards,
Wayne A. Pflughaupt


Administrator, Pedulla Club #45
Administrator, Tobias Club
Fretless Club #943
Big Cabs Club #23
Pedulla Club #45

 
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#12
WayneP said:
Regardless, the feedback problem might simply be your choice of mic. The SM57 is a vocal mic. Below is a frequency response graph published by Shure, and basically it is not a good choice for a low-frequency instrument. As you can see that mic rolls out about 5 dB/octave below 200 Hz. I suspect that your feedback problem is likely happening because you might be adjusting your stage amp to compensate for the 57’s inadequacies, like perhaps boosting the overall volume or EQ to compensate for the lows the 57 isn’t delivering.

Bottom line, I’d suggest switching to a mic with better low frequency extension, such as the SM 98 that Wasnex mentioned.


Shure_SM57_freqResp.gif
​
Click to expand...
Very true. I thought the same thing but couldn't find a frequency graph to post in support of my assertion.

FYI, any feedback we have experienced has been in about the 200-400 hz range and resulted from interaction with the amp rather than the PA. We run a pair of double 18 D&B Tech subs on a regular basis without problems. On a recent gig they doubled the amount of subs, and still no problem.
 

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