[CQ-Contest] Mics for SSB Contesting

[Jim Brown]

On Sat,12/5/2015 6:25 PM, donovanf at starpower.net wrote:
> Has anyone else tried the Antlion ModMic 4.0 uni-directional (noise cancelling) microphone?

There's something quite fishy about the description. First, a couple of 
definitions.

An omni-directional mic picks up sound more or less uniformly from all 
directions.

A uni-directional mic favors a single direction; it's pattern is pretty 
broad, and for all practical purposes is a half-space mic. Most have a 
cardioid pattern.

Both of these mics use a single capsule. The omni-directional mic has a 
single opening for the capsule.

Uni-directional (cardioid) mics have two openings, one facing to the 
front (the favored direction) and the other facing to the rear. The 
directional pattern is formed by cancellation between the two openings.

Both of these mics reject noise by virtue of the relative distance 
between our mouth and the noise source. The signal to noise ratio is 
determined by inverse square law and room reverberation.

The uni-directional mic provides additional noise rejection two ways. 
First, because it's a half-space pattern, it hears half as much wild 
sound from the room. Second, cardioid mics have bass boost for close 
sound sources (like our mouth), so we must reduce the bass response for 
voices to sound natural. BUT -- there is no bass boost for distant 
sounds, so the bass rolloff provides additional rejection of low 
frequency noise (below about 300 Hz).

NEITHER OF THESE MIC TYPES IS NOISE CANCELLING.  A noise cancelling mic 
has two omni-directional capsules wired out of polarity with each other, 
one of which is much closer to the mouth than the other. Cancellation of 
noise occurs for sounds that are approximately equi-distant from the two 
capsules. The voice, which is much closer to one capsule than the other, 
doesn't cancel much.

True noise-cancelling mics sound varying degrees of awful (they tend to 
sound "spitty"). They are primarily used in applications like aircraft 
cockpits where the noise is really severe. Years ago, I evaluated an 
attempt by Shure at a performer's noise cancelling mic. It sounded 
pretty bad, and they never marketed it.

Bottom line: We do NOT want noise cancelling mics for ham radio. 
Uni-directional (cardioid) mics can be good for us IF, AND ONLY IF, the 
mic points to our mouth, we don't work it too close (I suggest no closer 
than about 2 inches to avoid breath pops), and we roll off the lows 
severely to get rid of the bass boost.

A FAR better solution is to use an omni-directional mic, work it fairly 
close (about 2 inches diagonally above and to the side of the mouth), 
and NOT TURN IT UP TOO HIGH. The vast majority of noise I hear on the 
air is the result of the mic gain being turned up too high, combined 
with excessive processing.

A good rule is to 1) roll off the low end severely below about 400 Hz; 
and 2) after setting that rolloff, adjust mic gain and compression for 
indicated 10 dB of compression on voice peaks.

Another good move is to add acoustic absorption (thick fiberglass, heavy 
drapes, etc.) to the operating environment to reduce reverberation. 
EVERY SSB multi-op needs this absorption. It's an effective and 
inexpensive low-tech solution. Fan noise can be reduced my setting the 
power amp chassis that has the fan on a thick soft pad to minimize 
coupling to the desk, and by putting sound absorbing "fuzz" on wall 
surfaces behind and alongside the amp. Similar panels can be used to 
baffle the sound between operating positions. In this context, the 
panels can be something as simple as thick (6-inches or more) fiberglass 
insulation mounted to a piece of plywood. For adjacent operating 
positions, mount the panel vertically with that "fuzz" on both sides.

If you've heard me on SSB in the past 6-8 years, you've been listening 
to a Yamaha CM500 driving a K3 with lots of bass rolloff. My power amps 
have fairly noisy fans, and are on the operating desk only about 3 ft 
from the mic. My shack has a modest amount of absorption and diffusion, 
mostly in the form of a lot of bookcases, most of which are on a side 
wall, and a fairly thin carpet on the floor.

73, Jim K9YC