Feedback with PA + standalone amps??

[ImpaledRound]

Hi,

 

We played a gig today in school using the PA system for the vocalist and a myriad assortment of guitar and bass amps for the others. The vocal mic was placed behind the main PA speakers and yet we still experienced very low signal gain before feedback.

 

The mic was an electret condenser, the AKG C1000S, with a hypercardioid pattern converter slipped onto the capsule. I assumed because of the smallish pickup pattern feedback would not be a problem, but it was actually worse than any other gig we've done before with cheapo wireless mics.

 

Do the guitar and bass amps need to be in front of the vocal mic also? Do the PA speakers need to be placed even further away in front? Would a uni-directional dynamic mic help?

 

Sorry if these are noobish questions but we're repeating the gig next week so it would be awesome if we didn't have the same awful feed.

 

Many thanks for any suggestions,

 

Elis

[tlbonehead]

Set up in time to check things out and dial in. Were the speakers pointed mostly forward at the crowd? You shouldn't have much trouble with feedback thru the mains if all is well in the immediate world. Did you try other mics? Did you punch different mics in/out to isolate that it was indeed the vocal mic causing the problems? How was the mic tone. Was it nice, full, and balanced or was it harsh, thin, piercing, bright. Tone that would suggest an EQing issue. Did you mess with the main graphic EQ and the channel strip? What area frequencywise was the feedback coming from?

[alcohol]

The AKG C1000 is a condenser mic and I'm guessing that because it's a condenser it's generally more sensitive to sounds further away than standard dynamic PA mics. I think your problem was choosing the wrong mic for your application.

[ImpaledRound]

The speakers were all pointing directly towards the crowd. Unfortunately, being the shoddy school that I go to, that was the only mic available (i.e. my own, that I use for home recording). The tone was fine and the mic was used on a lot of solo instrumentalists and singers before it came to us playing in the band. Then there were just a lot of amps behind the mic (does this cause problems?) and probably the mic was turned up more because of the increased sound from the band.

 

As for the frequency of the feed, I'm afraid I've no idea!

 

I just wanted to make certain that having separate amps behind the mic shouldn't cause problems.... unless the mic is picking up the sound of the amps, then picking up the sound of the guitars through the speakers....?

 

And yes, I do need to get hold of some uni dynamic mics.

[alcohol]

I'm guessing this is the situation. amplifying singers or acoustic instruments withe C1000 is doable before feedback.

 

Bands are so much louder that you probably had to bring the volume up to the point where the system fed back.

 

It wasn't that you had separate amps, it was probably because you were so much louder than prior situations in which the mic was used.

[agedhorse]

One problem with loud back line amps is that you will get a lot of bleed into the vocal mic(s) to the point in some cases of bringing the volume of the vocal mic up also increases the band volume to the point that you can never get the vocal loud enough. It's sometimes made worse by the hyper-cardiod pattern because as you move your head, there is a big lobe that then picks up the back line, maybe a bit more than a regular cardiod mic would. Condenser mics tend to be bigger offenders as well.

 

The only solution in this situation is to lower the volume of the band so that the vocal can keep up.

[ImpaledRound]

And presumably move the amps further forward so that there is less bleed into the mic.

 

Would you be able to recommend a budget dynamic mic that I might be able to persuade the school to buy a set of if they were pretty inexpensive? Or is it hard to go wrong - they're all pretty rubbish below a certain price?

 

Thanks all for your replies,

 

Elis