Re: [Harp-L] Feedback?

[Rick Davis <bluesharpamps@xxxxxxxxx>]

Vern, good questions!

Someone has likely already pointed out that microphones do not have gain.
Like speakers, they are passive devices.  Your amp provides gain, and any
pedals you use may add gain.

Your mic and speaker certainly contribute to the overall amplitude of your
rig with their relative efficiency, but they are transducers that attempt to
faithfully reproduce the signal applied to them.  Some are hotter than
others, but that is not gain.

The amplitude of the mic may not be the most important element in feedback
but it is the best place to start.  When you hear your rig start to ring you
automatically reach for the mic volume knob and turn it down (you attenuate
the signal).  If you do not have a volume knob on your mic, order one of
Greg Heumann's excellent in-line volume controls from blowsmeaway.com.

Some microphones are more resistant to feedback because they have greater
rejection of off-axis sounds.  They have a stronger cardoid pattern.  Some
microphones have a greater proximity effect, reacting only to sounds from
very close an right in front of it.

All other things being equal, a less efficient mic (one with lower output)
will not cure feedback at all because you will just crank the gain of the
system elsewhere (amp, preamp, pedals) to achieve the same amplitude.  Low
output mics have the apparent ability to reduce feedback, but it is exactly
the same as if you had turned your mic down with the volume knob.

The microphone element in many popular bullet mics -- the Shure CM and CR
elements -- are pretty much omni-directional and are more prone to feedback
than some other mics.  However, they have great tone and desirability.
Players can overcome the feedback issue with these mics though playing
technique, particularly mic cupping, cheek blocking, etc.  The goal is to
acoustically isolate the  bullet mic as much as possible if it is feeding
back.

I've found that electronic solutions to feedback such as EQ, notch filters,
and anti-feedback pedals suck too much tone for my tastes.  Other players
like these devices.

Having said all this, here are the steps to curing feedback issues:

-Turn your mic down!  This cures a raft of tone problems, not just feedback.
-Turn your treble down and your bass up.
-Don't stand directly in front of your amp.
-Consider buying a harp-specific amp.
-Develop some volume discipline with your band.  Lower stage volume!

But... feedback is a demon that lives in the air.  Sometimes it will haunt
and harass you and other times it will vanish, even using the same gear in
the same room.

Best of luck.  It does indeed require some luck.

-- 
-Rick Davis
The Blues Harp Amps Blog
http://www.bluesharpamps.blogspot.com/


On Fri, Apr 29, 2011 at 9:28 PM, Vern <jevern@xxxxxxx> wrote:

> Every time I see a report on the feedback tendencies of a mic, I have the
> following questions.
>
> Q. Why is the gain of the mic more important than the gain of the entire
> system including the mic and the amp?
>
> It seems to me that the following things are important concerning feedback.
> - The amount of sound (at each frequency) from the speaker that enters the
> mic.
> - The phase of that sound with respect to the source and the speaker.
>
> Q. How can that involve the mic unless it is allowed to affect the overall
> system gain which would affect speaker loudness?
>
> Q. If the loudness at the speaker and the positions of the speaker and mic
> don't change, how can a different mic affect feedback?
>
> Q. If the responses of two mics are different at different frequencies,
> could not this be corrected by equalizer controls?
>
> Vern
>
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