[CQ-Contest] Mics for SSB Contesting

David Aslin G3WGN david at aslinvc.com
Sun Dec 6 17:58:51 EST 2015

Thanks for the clarification Jim.
I probably should have included in my review:
- I have the unidirectional version of ModMic.  I was under no illusion that it was noise cancelling - I just wanted to try a mic with the QC15s and the omni was not available at the time.
- K3 audio settings already followed the K9YC recommendations for the Yamaha CM500s, so the bass roll-off is set as Jim describes.
- It's worth experimenting with mic placement relative to your mouth.  Not hard to do, but a few minutes with that and gain/comp settings will give decent quality output.
73, David G3WGN  M6O

-----Original Message-----
From: Jim Brown [mailto:k9yc at audiosystemsgroup.com] 
Sent: 06 December 2015 19:51
To: cq-contest at contesting.com
Subject: [CQ-Contest] Mics for SSB Contesting

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

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