Re: [Harp-L] Which harp mic is most feedback resistant?

[Richard Hunter <turtlehill@xxxxxxxxxxxxx>]

"sam blancato" wrote:
<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. 

This doesn't explain why Bullets feed back so much more than a 57/58/Fireball equipped with a lo-z to hi-z transformer, which effectively converts the mic to hi-z.

<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. 

Bullet mics actually put out a very restricted frequency range compared to a vocal like a Shure SM58.  The SM58 picks up frequencies from about 40 hZ to about 15 kHz.  The Bullet tops out at about 6 kHz, with very minimal response above that.  In fact, a harmonica puts out a lot of energy in the frequencies above 6 kHz that a Bullet mic doesn't reproduce.  So that's not the problem either.

The reasons bullets feed back through guitar amps is that the bullet tends to emphasize the very same frequencies that a guitar amp emphasizes.  (Most guitar amps put out most of their energy below 6 kHz too.)  Too much energy in a particular frequency range = feedback.  

What the various anti-feedback devices do, in general, is remove energy from the signal at the frequencies that are overloaded, thus reducing feedback. That's one solution, and when it's done well, e.g. the Kinder AFB, the damage to the tone is minimal.  Another solution is to switch mics, which of course changes the sound noticeably in many cases.  It probably changes the sound more for players who haven't developed a tone that sounds strong when they're not using an amp.  I've seen Charlie Musselwhite using a number of diferent mics over the years, and while he always sounded very much like himself, some of those mics produced a lot of feedback.  I particularly remember how much feedback he got from a Shure Sphereodyne omniderectional dynamic mic at one show in the early 1970s. Wow, that thing howled every time he turned around. 

Regards, Richard Hunter

author, "Jazz Harp"
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