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Question about feedback via singers mic - am I imagining it?


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Hi I all – I’m a bit puzzled and looking for advice….

My question is …. can a singer’s mic going through the pa,  feedback through my bass?

 

I play in a big band (double bass through lifeline pickup into fishman platinum pro and my own amp). I’ve noticed on a couple of occasions that whilst we can be loud, feedback is under control when playing with the band – but when the singer joins in – it all gets a bit frisky…I’m sort of on the edge of feedback – slow and gradual build up not Hendrix screeching.

 

Last time I noticed that it happened even when muting the bass strings with my hand….and only stopped when I muted the preamp.

So it is possible the body of  my bass is picking up the vocals and feeding back through the vocal mic/pa ?

 

I've got a notch filter on the preamp but not had tome to fiddle with it to see if that cures the problem.

 

All advice gratefully received.

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1 hour ago, haruki said:

only stopped when I muted the preamp.

So it is possible the body of  my bass is picking up the vocals and feeding back through the vocal mic/pa ?

 

I reckon it's the body of your bass picking up the vocals and then feeding back through your own bass amp.  Sweep your notch filter frequency until (hopefully) the feedback stops.

 

Also try your variable high pass filter (on the Fishman, they call it 'low cut').  N.B. the knob controls the cut-off frequency, not the amount of cut.  Turn the knob up until (hopefully) the feedback stops - even up to the max if needed.  I sometimes HPF at 160Hz, which is the Fishman's max frequency.  If your instrument now doesn't sound as full, you can still increase the 'bass' knob.

 

Some people have had results by blocking their f-holes with foam.  That might be worth a try, although for me this didn't make a difference.

 

Is your bass positioned right in front of your amp?  Can you try moving things about so that you're further from your amp, or at least slightly to the side of it; or elevate your amp considerably so that it's firing over the top of the body of your bass rather than straight into it?

 

As well as your amp, is your bass also going through the PA?  If not, is that something you can consider doing - this might allow you have a lower stage volume on your amp.

 

A larger change to consider is the setup of your bass and playing style/technique.  If you were to play unplugged, are you getting much acoustic volume?  Or are you tickling the strings and relying on the amp to be heard?  The higher the volume is on your amp, the more chance of feedback. It's going to vary for each player/instrument, but for me, a slightly higher string height and more robust (but not heavy-handed) pizz technique resulted in better tone and more volume, which meant lower volume needed on the amp.

 

 

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If you have a phase switch on the preamp, that's worth a go in these edge of feedback situations too. I find there's usually one position of the switch that reaches the feedback point slightly later than the other, but it's not the same one in every situation.

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10 minutes ago, jrixn1 said:

 

I reckon it's the body of your bass picking up the vocals and then feeding back through your own bass amp.  Sweep your notch filter frequency until (hopefully) the feedback stops.

 

 

 

 

 

thanks ...thats what I was thinking.  I don't usually put the bass through the pa - just go through my amp positioned  in front of me to the right with bass on the left.  I use the high pass filter a lot to control feedback - and usually its ok.  Its just when singer starts I seem to lose control.

 

Wil try the notch filter next time.

 

And thanks Beer of Bass =- I haven't tried the phase switch - easy enough to test. 

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Is the singer using a stage monitor? If so, try asking them to angle it away from you so that your’e not picking up the vibrations from this directly. 

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It's also possible that the singer's mic is picking up the bass and sending it through the PA, then the body of the bass resonates with the PA output, that comes out of your amp and back into the singer's mic, and you have a feedback loop. You could ask the sound engineer to roll off the bass on the vocal mic - you could probably wipe off everything below 150hz without it doing much harm for a female vocalist.

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Thanks for the advice....we don't have  an engineer - we just kind a mix on the fly with little of no monitoring.  The horns/brass players tend to be a doubtful about using the pa at all - and most of the time they don't need it. But faced with 5 saxes 4 trumpets and 4 trombones I certainly need some assistance - cant imagine how they did it on the old days without amplifying the bass

 

I guess i need to experiment a bit more in rehearsal - I can ask the singer to adjust her mic to see if that stops it.  I'll check to see if they use a low  cut on the mixer too.

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If the desk has a low cut button (<50hz) on

each channel, which they often do, you could do worse than just hitting that on every channel.

I find that for double bass the real action is up around 100 to 200hz, and you can roll everything below this right back on your own amp (or with a low cut pedal).

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46 minutes ago, NickA said:

phase switch will sort it ..but it sounds a bit weird to the player as the amp cancels out the bass itself.

 

 

 

 I have been given to understand that the phase switch is used when you have two forms of input, such as a microphone and a piezo, and you want to adjust the phase between the two signals. What effect does it have on a single input?

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48 minutes ago, pete.young said:

 

 I have been given to understand that the phase switch is used when you have two forms of input, such as a microphone and a piezo, and you want to adjust the phase between the two signals. What effect does it have on a single input?

 

it inverts the absolute polarity of that single input.  Makes very little difference at mid and high frequencies.  But at low frequencies where the wavelength is very long, inverting the waveform can alter the speaker to instrument feedback path quite significantly.  Might make it less feedback prone, but also might make it worse. Definitely worth a shot.

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We used to have big issues with vocal mics howling at mid/high frequencies.  It never occurred to me that my bass might be involved.  But after taking advice from you guys on Bass Chat, I did all the bass feedback prevention measures: LPF, f-hole blockers, amp off the floor, etc.  And as soon as I damped my instrument down, all the vocal mic feedback disappeared.

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On 06/04/2024 at 00:04, Paddy Morris said:

 

it inverts the absolute polarity of that single input.  Makes very little difference at mid and high frequencies.  But at low frequencies where the wavelength is very long, inverting the waveform can alter the speaker to instrument feedback path quite significantly.  Might make it less feedback prone, but also might make it worse. Definitely worth a shot.

Thank you @Paddy Morris for a great explanation, I'll give it a try next time i encounter problems (which with the current band will be sooner rather than later, alas).

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On 06/04/2024 at 00:04, Paddy Morris said:

 

it inverts the absolute polarity of that single input.  Makes very little difference at mid and high frequencies.  But at low frequencies where the wavelength is very long, inverting the waveform can alter the speaker to instrument feedback path quite significantly.  Might make it less feedback prone, but also might make it worse. Definitely worth a shot.

 

Yep, I find it varies a lot with the size and shape of the room and the relative position of bass and speakers, but typically I find that there's one position of the phase switch where feedback starts later and at a different frequency to the other, and because of all the variables it's nigh-on impossible to anticipate which position will work better at a given gig.

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My phase switch only has two positions ... On & Off.  IE reverse and not reverse.  Hard to have a partial reverse.

 

I guess you're talking about some kind of digital phase shift thing?

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My EDB-1 preamp has a phase reversal switch, which reverses the phase of Channel 2. Since I've been using my piezo through Channel 1, this might explain why it doesn't seem to do a lot! At least thanks to this thread I have now RTFM, so I will swap over and see what happens.

 

My iAmp Doubler has a phase control knob:  "Phase Control: The Doubler features an innovative 180 degree sweep able phase control to adjust the phase between Channel 1 and Channel 2. This control only works when BOTH Channel 1 and Channel 2 inputs are being used"

 

The moral of the story seems to be  that not all phase switches or controls are the same.

 

 

 

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On 03/04/2024 at 05:17, JoeEvans said:

It's also possible that the singer's mic is picking up the bass and sending it through the PA, then the body of the bass resonates with the PA output, that comes out of your amp and back into the singer's mic, and you have a feedback loop. You could ask the sound engineer to roll off the bass on the vocal mic - you could probably wipe off everything below 150hz without it doing much harm for a female vocalist.

Except it didn't stop with muting the strings. It could still be the singer's monitor and mic but it's vocal frequencies doing it because it stops when she stops. Must be a right Shirley.

 

HPF aka low cut her mic and see how it goes. Get away from the vocal monitor and any amount less of crankage will help.

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