[Elecraft] Settings for CM500 on K3?

[Lew Phelps K6LMP]

I recently acquired a very slightly used CM500 from a fellow ham who couldn't use it because the tight ear seals made his hearing aids squeal. 

I've found it to be a very comfortable headset to use (wore it for many hours during last weekend's VHF contest) and after setting up the mike as described by Jim, I got "outstanding audio" reports from friends with whom I conducted audio checks before the contest started, and who know my voice from face to face conversation as well as over the air. 

I have an MJF SWR/power meter that "sort of" shows peak readings by switching a capacitor into the circuit to capture the highest voltages, and the peaks, however imprecise on an absolute basis, are comparable on a relative basis to the peaks with two other mikes I have used (one a Heil, the other a studio type mike) with similar TXEQ settings. Only difference between what Jim recommends and my settings is that I knock the third octave down a few dB, because I have a relatively high pitched speaking voice (sang tenor in college choir). 

The Wikipedia entry on "Voice Frequency" states:  "The voiced speech of a typical adult male will have a fundamental frequency from 85 to 180 Hz, and that of a typical adult female from 165 to 255 Hz[1][2]. Thus, the fundamental frequency of most speech falls below the bottom of the 'voice frequency' band" (that is, the 300 Hz to 3400 Hz band used in telephony). "However, enough of the harmonic series will be present for the missing fundamental to create the impression of hearing the fundamental tone."

So how does this apply to the K3 TXEQ settings?

The K3 transmit equalizer has eight bands. Per the K3 manual, "The center frequencies of the 8 audio EQ bands are 50, 100, 200, 400, 800, 1600, 2400, and 3200 Hz."  Clearly, the lowest band is irrelevant for human speech and can be knocked down to -16 dB without losing any speech.  The second band, centered at 100 Hz, will partially cover the low end of the human male voice range, especially for males, but as stated above, you can knock out the primary frequency and still transmit intelligible speech because of the harmonics of the primary frequency. It might sound a little "tinny", but it will be fully intelligible. A female user of the K3 might want to knock the third equalizer band all the way down to -16 dB as well as the first two. These would be typical settings for SSB contesting where you want to maximize the modulated signal in the frequency band where it will have the most effect.  

If you're a fan of "broadcast quality" AM rag-chewing, you'd definitely want to use different settings, probably "flat" except for the lowest band for males and the lowest two bands for females.

But, as others have said, the human ear is the best way to discern proper TXEQ settings. You can do it yourself with a good noise-sealing headphone set and the rig in TEST XMIT mode, or over the air to someone who knows your voice well.

Lew K6LMP