[Elecraft] CM-500 Response (was: Heil HC-4, HC-5)

[Jim Brown]

On Thu, 1 Apr 2010 19:06:14 -0400, Joe Subich, W4TV wrote:

>In order to have reasonable articulation, the CM-500 
>needs at least 3dB (closer to 6dB) per octave of boost 
>above 800 Hz and requires 6dB per octave of cut below 
>400 Hz in order to avoid being "boomy" or "muddy."  

You and I must be listening to very different CM500s. Many 
members of our contest club bought them and have them on the 
air, and I own two. Every CM500 I've heard sounds great with 
only the two low octaves at full cut, and no other EQ. 

How do you listen to evaluate a transmitted signal?  My 
standard method is with my K3 set for at least 2.7 kHz 
bandwidth (and wider is better, so that I'm not fooled by what 
the RX filtering is doing, and so that I don't miss 
distortion). Indeed, you can make any signal on the band sound 
very muddy or very thin and bright by using a narrow filter and 
shifting it high or low with respect to the signal. 

>It should never be necessary to use that much EQ to make 
>a microphone "sound good" and is a symptom of a poorly 
>designed capsule (or preamp). 

No, it's the sound of a mic with different EQ. Go to the Shure 
website and study the frequency response of their 
communications mics, like the 444. They have limited low end, 
and a BIG peak (about 8dB) around 3kHz. The reason for that 
peak is the rolloff built into the skirts of SSB TX filters -- 
it compensates for that rolloff!  Heil mics do the same thing 
(but not very nicely, to my ear). Compare those communications 
mics with the Shure SM81, which is flat as a pancake up to 15 
kHz. 

I own a lot of pro dynamic and condenser mics that are flat 
from 50 Hz to 12 kHz, and I've used a few of the dynamics with 
my ham gear when I didn't have a ham mic handy. RE16, RE20, 
RE27 are examples -- I've done a LOT of contesting with them, 
and I can easily make them sound very competitive, but also 
very clean. If I plugged them in with no TXEQ, they would sound 
VERY muddy. They need a LOT of low cut (full cut on at least 
the three lowest bands of the K3 equalizer) and that big peak 
around 3kHz. There's NOTHING wrong with the design of those 
mics or the preamp. They are simply designed for a different 
purpose -- high quality recording and broadcast of speech and 
music. 

73,

Jim Brown K9YC