In your original post for this thread, also wanted to know what it was about
bullets that made them so prone to feed-back. I want to answer this but I
know I have my facts out of whack a little on this and I invite others
correct me where I'm wrong. I'm sure I'm wrong on some (or maybe all) of
these points so I'd like to be set straight - and I do think that I have
some of it right.
The bullets are prone to feedback because they are High Impedance
microphones whereas microphones like the 57, 58, Audix Fireball - any modern
vocal microphone really - are low impedance microphones. I'm not sure what
impedance means in the context of this topic but someone explained it to me
once like this: An electric guitar pick-up sends a signal to a tube amp
that's around 7 watts and what ever you can say about the frequency range of
that signal, the fact is that the pick-up that produces it is really only
sensitive to the strings directly in front of it to make signals to send to
the amp. So the sound that comes out of the amp is not likely to reach the
guitar pick-up that produced it and "feed back" into the sound mix. If the
amp is loud enough and the guitar is close enough (a la Jimmy Hendrix) this
can happen as some of the harmonics produced by the guitar resonate with the
strings and make them vibrate at strange and undesired frequencies. Then
you get feed-back.
A bullet microphone sends a signal to the amp that's anywhere from 16 to 20
watts and it is a very FAT signal, having a very broad frequency range with
a wide range of harmonics. So there are two problems at this point. The
bullet sends this fat signal at higher wattage AND it remains sensitive to
ANY sound that reaches it, not just the ones produced close to it (like form
your harmonica). Since the Harmonica produces a rather complex sound, full
of harmonica overtones, there is now a wide range of vibrations available to
resonate with the primary signal (your harp). The result is that most
bullets feed back these tones over and over, cycling through certain
frequencies that resonate well with the original harp signal, producing that
squeal that we all know.
The Kinder Box works by measuring the harmonics that are cycling the most and then canceling those signals out. Since there is such a wide range of these harmonics we don't miss them and the resulting sound contains only harmonics that are too far away in frequency from the source frequency to resonate and then start the whole feed-back cycle up again.
Modern, low impedance microphones don't have this problem so much (but they
can to if the conditions are right, i.e. your loud enough, close enough)
because they produce a signal of lower wattage and only produce a signal
from sounds in a very close rage, like a couple of inches. Some of those
microphones pick up sound in an area that's like a sphere of air directly in
front or just around the sides of the microphone (cardioid) and some from
only directly in front of it (unidirectional).
So why do people (me, for one) still fool with the bullets? My
understanding is that the signal is so fat and of such high wattage that
this is what produces the distortions that we lovingly call "crunch", or
"brown sound" and other names. And all the money and creativity that goes
into producing modern harp amps (Sony Jr., Meteor, Harp Gear, etc.) is about
producing an amp that will reproduce the harmonica's wide range of tones,
along with the microphone's distortion, without reproducing the segments
that will feed-back.
I know this is riddled with errors and I'd appreciate being corrected. But
I, for one, am pretty much a bullet man all the way. I have three good ones
and I love their sound.
Sam Blancato, Pittsburgh
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