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



Man there's a lot of B.S. floating around on this subject. Some truths too, but a lot of misinformation. Here's my two cents.

Feedback comes from, in order of priority:

1) Gain of the mic: Although engineers would like the mic's relationship of input signal to output signal to be linear, it isn't - some mics go from low output to full output with far less input signal than others. The Audix Fireball has the highest "headroom" of any mic I've ever tried - meaning it can tolerate extremely high input levels before it reaches its output peak, which isn't very high in any case (see #2). This is why it is so feedback resistant. (That doesn't mean it is the right mic for you - I personally care MUCH more about a mic's tonal characteristics than its feedback characteristics.) Every once in a while I get a Shure CM that seems to be very gainy compared to the average. These are feedback monsters, but they are the exception among these otherwise great elements.

2) The output level of the mic: For a given sound level, some mics produce more output than others. This will in turn make the amp louder at the same volume setting. All other things being equal, two identical mics with different output levels, adjusting the amp for the same volume between the two of them will result in the same feedback level - assuming the amp's volume control provides linear increase in gain.

3) The frequency response of the mic: Most mics, especially performance (as opposed to studio) mics have non-linear frequency response. If there is a bump, say, at 2500Hz, and the amp happens to also have a bump there, feedback is more likely.

4) The directionality of the mic: If the mic picks up sound from all directions ("omni-directional") it is more likely to "see" the amplifier's output - which is of course how feedback happens. SM57's are very directional - effectively blocking sounds coming at them from the sides and in front of you. An SM58 with its ball has a wider pickup pattern and will feedback before the SM57 does - especially in regards to floor monitors at the front of the stage. Anytime you hand hold a mic you totally change its directionality anyway, so if you hand hold a mic all bets are off.

Note that impedance itself does NOT have an effect on feedback OR tone. Sometimes converting a low-Z mic to high-Z or vice versa, whether with a dual-impedance internal transformer like the 545, or an external impedance matching transformer, will produce MORE output and sometimes it will produce LESS. Depends on the mic and the transformer. But equalize the volume at your amp between the two configurations and the feedback level will be THE SAME because the frequency response and directionality of the mic does not change.

When it is all said and done, the GAIN OF THE AMP is the biggest variable by far. Gainy amps will be feedback monsters, which is why harp-specific amps and recommended mods to stock guitar amps always involve reducing the gain from where guitar players like it. Pick a mic for tone. Dial in your amp to manage feedback. Need more volume before feedback? Employ anti-feedback electronics, EQ the offending frequency range down, or... Get a bigger amp with more speakers. (Multiple speakers tend to disperse the sound better so the energy level where you're standing compared to the total energy in the room is better than with a single speaker amp of the same power.)


/Greg


http://www.blowsmeaway.com
http://www.bluestateband.net






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